Nanomaterials with enzyme-like characteristics (nanozymes)_ next-generation artificial enzymes

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Nanomaterials with enzyme-like characteristics (nanozymes):next-generation artificial enzymes ?

Hui Wei*z and Erkang Wang*

Over the past few decades,researchers have established artificial enzymes as highly stable and low-cost

alternatives to natural enzymes in a wide range of applications.A variety of materials including cyclodextrins,metal complexes,porphyrins,polymers,dendrimers and biomolecules have been extensively explored to mimic the structures and functions of naturally occurring enzymes.Recently,some nanomaterials have been found to exhibit unexpected enzyme-like activities,and great advances have been made in this area due to the tremendous progress in nano-research and the unique characteristics of nanomaterials.To highlight the progress in the field of nanomaterial-based artificial enzymes (nanozymes),this review discusses various nanomaterials that have been explored to mimic di?erent kinds of enzymes.We cover their kinetics,mechanisms and applications in numerous fields,from

biosensing and immunoassays,to stem cell growth and pollutant removal.We also summarize several approaches to tune the activities of nanozymes.Finally,we make comparisons between nanozymes and other catalytic materials (other artificial enzymes,natural enzymes,organic catalysts and nanomaterial-based catalysts)and address the current challenges and future directions (302references).

1.Introduction

Artificial enzymes,the term coined by Ronald Breslow for enzyme mimics,1is a very important and exciting branch of biomimetic chemistry which is inspired by nature and aims to imitate the essential and general principles of natural enzymes using alter-native materials.2,3Over the past few decades,researchers have established artificial enzymes as highly stable and low-cost alter-natives to natural enzymes in a wide range of applications.Cyclodextrins,metal complexes,porphyrins,polymers,supra-molecules and biomolecules (such as nucleic acids,catalytic antibodies and proteins)have been extensively explored to mimic the structures and functions of natural enzymes through various approaches.1–17To date,remarkable progress has been made in the field of artificial enzymes (Fig.1),and several monographs and numerous excellent reviews have been published.2–4,18–34

Recently,some nanomaterials,such as fullerene derivatives,gold nanoparticles,rare earth nanoparticles and ferromagnetic nanoparticles,have been found to exhibit unexpected enzyme-like

activity.35–48Since then,considerable advances have been made in this area due to the tremendous progress in nano-research and the unique characteristics of nanomaterials.49–53These nanomaterial-based artificial enzymes (nanozymes)have already found wide applications in numerous fields,including biosensing,immunoassays,cancer diagnostics and therapy,neuroprotection,stem cell growth,and pollutant removal.The term ‘‘nanozymes’’was initially coined by Scrimin,Pasquato and co-workers to describe their thiol monolayer protected gold clusters with outstanding ribonuclease-like activity.39Here,we adopt the term and extend it to nanomaterials with enzyme-like activities.Although the progress and achievements of classic artificial enzymes have been thoroughly reviewed in the litera-ture,no comprehensive review has been devoted to nano-zymes.51–63To highlight the significant progress of nanozyme research,this review discusses various nanomaterials that mimic natural enzymes and their mechanisms,kinetics and numerous applications.Different approaches to tune the activities of nano-zymes are summarized.We also compare nanozymes to other catalytic materials (such as other artificial enzymes,natural enzymes,organic catalysts and nanomaterial-based catalysts).Finally,we discuss the current challenges facing nanozyme technologies and future directions to realize their great potential.Note:although nanozymes include artificial hydrolytic enzymes and others,the current review mainly focuses on redox-based nanozymes,the intrinsic enzyme-like activities of which are from

State Key Laboratory of Electroanalytical Chemistry,Changchun Institute of Applied Chemistry,Chinese Academy of Sciences,Changchun,Jilin 130022,China.E-mail:weihui@https://www.doczj.com/doc/be17707786.html,,ekwang@https://www.doczj.com/doc/be17707786.html,

?Electronic supplementary information (ESI)available:See DOI:10.1039/c3cs35486e

?Current address:Department of Biomedical Engineering,College of Engineer-ing and Applied Sciences,Nanjing University,Nanjing,Jiangsu,210093,China.

Received 28th November 2012DOI:10.1039/c3cs35486e

https://www.doczj.com/doc/be17707786.html,/csr

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the nanomaterials cores instead of the functional groups present on the protecting shells.

Readers are referred to the monographs and reviews for more comprehensive information regarding other artificial enzymes rather than nanozymes (note:due to the space limit,only a small number of references are cited).2–4,17–32,64–67

2.Nanomaterials as nanozymes to mimic natural enzymes

At first glance,it seems counterintuitive to imitate natural enzymes with nanomaterials since they are so di?erent in many ways.For example,most natural enzymes,which are

proteins,

Fig.1A brief timeline for the development of artificial enzymes (natural enzymes are also listed for comparison)(see Table S1,ESI?for related

references).

Hui Wei

Hui Wei is a Professor in College of Engineering and Applied Sciences at Nanjing University.He joined Nanjing University after postdoctoral training with Professors Yi Lu and Shuming Nie,respectively.He received his BS degree from Nanjing University in 2003,where he carried out undergraduate research with Professor Xinghua Xia.In the same year he joined Professor Erkang Wang’s group at Changchun Institute of Applied

Chemistry,Chinese Academy of Sciences,and received his PhD degree in 2008.He has published over 30papers in peer-reviewed international journals.His work has been cited more than 1500times with an H-index of 24.His research interests are focused on functional nanomaterials and new methodology for analytical and biomedical

applications.

Erkang Wang

Erkang Wang is a Professor of Chemistry at Changchun Institute of Applied Chemistry,Chinese Academy of Sciences.He is Academicians of the Chinese Academy of Sciences and the Third World Academy of Sciences.He obtained his BS degree from University of Shanghai in 1952and his PhD degree from Czechoslovak Academy of Sciences in 1959under the direction of Professor J.Heyrovsky (Nobel Laureate).He

has published over 690papers in peer-reviewed journals.His work has been cited more than 15000times with an H-index of 62.His research interests lie in the fields of nanomaterials/nanotechnology,biosensors,electrochemistry and electrochemiluminescence.

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have exact amino acid sequences and thus well-defined tertiary structures.On the other hand,most nanomaterials are not atomically uniform due to size and shape variations.68Proteins are also considered as soft materials while nanomaterials can be hard with crystalline cores.68However,they share certain similarities,such as overall size,shape and surface charge,which enable nanomaterials to mimic natural enzymes.68In this section,we will survey various nanomaterials that can mimic natural enzymes.2.1

Cerium oxide-based nanomaterials

Cerium oxide (ceria)is well known for its highly catalytic performance in various applications due to the presence of mixed valence states of Ce 3+and Ce 4+,and the presence of oxygen vacancies.51,53,69Oxygen vacancies compensate the reduction of positive charge by Ce 3+and thus stabilize the chemically active Ce 3+oxidation state.The redox couple can switch between each state in a CeO 22CeO 2àx +x /2O 2(Ce 4+2Ce 3+)recycle process,which is the key to the catalytic activity.51,53Moreover,nanoceria has dominant Ce 3+and oxygen vacancies on its surface due to a large surface-to-volume ratio.Early studies have shown that cerium complexes have many biological applications.For example,cerium(III )nitrate decreased superoxide content and thus promoted the germination of aged rice seed.70Thus,it was reasonable to investigate the superoxide oxidase (SOD)mimetic activity of nanoceria for catalytic removal of superoxide radicals.The seminal study by Seal et al.showed that vacancy-engineered nanoceria indeed protected normal cells but not tumor cells from radiation-induced damage (Fig.2).41The protective role of the nanoceria was attributed to the elimination of radiation-induced free radicals,which were hypothesized to occur through catalyza-tion via a Ce 3+-Ce 4+-Ce 3+regeneration process.The di?er-ential protecting capabilities in normal cells vs .tumor cells might be due to the fact that chromatin in tumors was more loosely packed and thus exposed more bases for free-radical attack.41Following this early work,numerous studies have confirmed the enzyme (including SOD,catalase,oxidase,etc.)mimetic properties

of nanoceria and have shown promising biomedical applications for scavenging radicals both in vitro and in vivo .43,51,53,71–108Here,we discuss the enzyme mimetic properties of nanoceria and their applications.

2.1.1Nanoceria as SOD mimics.SOD catalyzes the dismuta-tion of superoxide anions into hydrogen peroxide and molecular oxygen (Scheme 1).Superoxide anion,one of the reactive oxygen species,has been known to cause tissue injury and associated inflammation.Previous research has revealed that SOD play protective roles in the removal of superoxide anions.Due to the limits of native SOD (such as short term stability and high cost),significant e?orts have been made to develop SOD mimics.23,59,64For example,a manganese-containing biscyclo-hexylpyridine complex,M40403,has been developed for this purpose.64Inspired by the work from Seal and co-workers,recent studies have showed that nanoceria exhibits interesting and promising SOD activity.43,71,73,76,80,88,91,102

No direct evidence was presented to support the redox regeneration mechanism in the early study.41In a later study,Seal et al.performed a competitive assay against cytochrome c ,which indicated the SOD mimicking activity of the nanoceria.73The superoxide anion elimination capability of the nanoceria was also confirmed by electron paramagnetic resonance (EPR)measurements.76The results showed that nanoceria with a higher ratio of Ce 3+/Ce 4+has better activity.73They also observed the formation of hydrogen peroxide,which is one of the products of the SOD catalyzing reaction.The kinetics measure-ment showed that the nanoceria with a size of 3–5nm was more efficient as a SOD mimic than a native CuZn SOD (with rate constants of 3.6?109M –1s –1and (1.3–2.8)?109M –1s –1,respectively).A dismutation mechanism similar to Fe-and Mn-SOD was proposed (Fig.3a).73An alternative mechanism was also proposed as shown in Fig.3b.53None of them clearly involved the auto-regeneration process of Ce 3+on nanoceria,though the second mechanism indicated that nanoceria with a higher ratio of Ce 3+/Ce 4+should have higher activity.If an auto-regeneration process indeed occurred,the ratio of H 2O 2to O 2would be larger than 1.This could be tested and verified experimentally in the https://www.doczj.com/doc/be17707786.html,putational studies would also help to clarify the detailed mechanism when combined with further experimental results.Though initial studies suggested that nanoceria could also eliminate hydroxyl radicals,43,72later EPR measurements demon-strated that nanoceria does not have such hydroxyl radical elim-ination capability.76This also suggested that nanoceria has some specificity towards superoxide radicals dismutation.

Applications.SOD mimics play important roles in many redox-active processes,such as scavenging reactive oxygen species,acting as anti-inflammatory and anti-oxidation agents,and promoting stem cell growth.Below,several selected examples are discussed to show the wide and promising applications of nanoceria based SOD

mimics.

Fig.2Nanoceria with SOD mimicking activity could prevent normal human breast cell line (CRL8798)but not a human breast tumor cell line (MCF-7)from radiation induced damage.Reprinted with permission from ref.41.Copyright (2005)American Chemical

Society.

Scheme 1The reaction catalyzed by SOD.

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(a)Anti-inflammatory e?ects.Similar to native SOD,nano-ceria-based nanozymes exhibit anti-inflammatory e?ects due to the presence of mixed valence and oxygen defects,rendering them as highly e?cient catalysts.Hirst and co-workers reported the anti-inflammatory properties of nanoceria.84Using J774A.1murine macrophage cells as a model,they demonstrated that the nanoceria were benign and were internalized by the cells.Chemiluminescent and fluorescent measurements demon-strated that the nanoceria was able to decrease ROS production in J774A.1cells.They further showed that nanoceria inhibited the production of the free radical nitric oxide,a critical med-iator of inflammation when over-expressed.They also claimed that the nanoparticles did not cause any in vivo lesions in mice when di?erent doses were administered intravenously,but did not further investigate the in vivo activity of the nanozymes.(b)Antioxidants.Nanoceria-based SOD mimics have also been investigated as antioxidants.The antioxidant e?ects and the biological antioxidant mechanisms of nanoceria were examined by gradual doping of Sm 3+.91Since the doping decreased the Ce 3+concentration without a?ecting oxygen vacancies,the study confirmed that the Ce 3+/Ce 4+redox reactions were responsible for the nanozymes’outstanding biological activ-ities.91When encapsulated within a ferritin cage,Liu et al.showed that the ROS-scavenging activity of 4.5nm nanoceria was enhanced.99The presence of a ferritin shell also facilitated cellular uptake and improved their biocompatibility.A recent study showed that nanoceria was able to protect cardiac progenitor cells (CPCs),a promising cell source for cardiac regeneration,from hydrogen peroxide-induced cytotoxicity for one week.100The observed protective e?ects was attributed to the nanozyme’s self-regenerating antioxidant mechanism involving the Ce 3+/Ce 4+redox cycles.

(c)Promotion of stem cell growth.Polymeric biomaterials have been extensively used in tissue engineering (such as in directing the growth of stem cells)because of their unique properties.Hybrid materials formed by incorporating inorganic materials into a polymeric matrix have even more promising advantages,such as novel functionalities,enhanced biocom-patibility and improved mechanical and chemical properties.In their interesting study,Mandoli and co-workers showed that when nanoceria was fabricated together with PLGA sca?olds,the as-prepared hybrids exhibited enhanced mechanical prop-erties.87They further cast the hybrids onto pre-patterned molds and demonstrated that the composite sca?old could align murine-derived cardiac and mesenchymal stem cells growth with enhanced bioactivity and better adhesion (Fig.4).They then elucidated the potential mechanism by comparing the nanoceria composites to PLGA films without nanoceria and PLGA films with nanostructured TiO 2.Though nanostructured TiO 2also induced directional cell growth,the cell proliferative activity was lower than the activity observed for nanoceria-loaded PLGA.Since the Ce 3+/Ce 4+redox pair of nanoceria is recyclable while the Ti 3+/Ti 4+redox pair of TiO 2is not,the improved performance of the nanoceria hybrids was attributed to the nanoceria’s anti-oxidation properties.

(d)Neuroprotection.Nanoceria as a SOD mimic also exhibited neuroprotective activity.43,72,92In Chen and co-workers’semi-nal study,they showed that the pretreatment of cultured retinal neuron cells with nanoceria eliminated the accumulation of hydrogen peroxide-induced reactive oxygen intermediates.43More importantly,their animal studies have firmly demon-strated that the nanozymes protected rat retina photoreceptor cells from light-induced degeneration after intravitreal injection (Fig.5).Surprisingly,the nanozymes still exhibited protective activity towards photoreceptor cells even when administrated after the light exposure.Again,the reactive oxygen intermediate-scavenging activity was attributed to the switchable feature of the Ce 3+/Ce 4+redox https://www.doczj.com/doc/be17707786.html,ter studies showed that the nanozymes’neuroprotective activity could be realized in other systems,

such

Fig.3Proposed mechanisms of nanoceria based SOD mimic:(a)reprinted with permission from ref.73;copyright (2007)Royal Society of Chemistry;(b)reprinted with permission from ref.53;copyright (2011)Royal Society of

Chemistry.

Fig.4Stem cell aligned growth induced by nanoceria in PLGA sca?olds.Reprinted with permission from ref.87.Copyright (2010)John Wiley and Sons.

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as adult rat spinal cord neuron and other diseases of the central nervous system.72

(e)Other applications.Nanoceria-based SOD nanozymes have been studied for other interesting applications as well.As mentioned above,vacancy engineered nanoceria were able to protect normal human breast cells (but not breast tumor cells)from radiation-induced cell death,suggesting a new application in radiation oncology.41Using diabetic rats as a model system,a recent study also showed that the combination of nanoceria and sodium selenite was more e?ective than either alone in reducing diabetes-induced oxidative stress.109

2.1.2Nanoceria as catalase mimics.Catalase catalyzes the decomposition of hydrogen peroxide into molecular oxygen and water (Scheme 2).Hydrogen peroxide,as the stable end product of superoxide radicals’dismutation (Scheme 1),plays a dual role in biological systems.It can be either a signaling molecule or a non-radical reactive oxygen species.51Though hydrogen peroxide itself is stable and less active,it can be converted into highly active and detrimental hydroxyl radical through Fenton chemistry.In nature,catalase is employed as the most e?cient enzyme for the conversion of hydrogen peroxide to less active oxygen.Researchers have found that numerous metal oxide (such as nanoceria),as well as metal,nanomaterials exhibit intrinsic catalase activity.88,95,110,111

Inspired by the fact that some SOD mimics,such as manganese porphyrins,can also convert hydrogen peroxide into oxygen and water as catalase mimics,Self and co-workers performed a careful study to explore the catalase-like property of nanoceria.88The results established that catalase-like activity was dominant for nanoceria with a low Ce 3+/Ce 4+ratio while SOD-like activity was dominant for nanoceria with a high Ce 3+/Ce 4+ratio.In a later review from Ghibelli et al.,a possible molecular mechanism was proposed (Fig.6).53

So far,there have been no studies reporting the application of a nanomaterial-based catalase mimic.

2.1.3Nanoceria as oxidase mimics.For reactions catalyzed by oxidase,a substrate is oxidized by molecular oxygen,which can be converted into either water or hydrogen peroxide (or even superoxide radical in some cases)(Scheme 3).For certain substrates,oxidation can result in a color change,which makes them ideal agents for detection purposes.Recent studies have shown that certain nanomaterials can imitate the catalytic activity of oxidase.40,42,81,90,102,111–119

As discussed above,nanoceria acts as an e?cient anti-oxidant since it can be either a SOD mimic or a catalase mimic,depending on the Ce 3+/Ce 4+ratio.88Studies by Perez and co-workers have revealed that nanoceria can have additional functionality,reporting nanoceria with oxidase-like activity.81,90The oxidase mimetic activity of the biocompatible dextran-coated nanoceria towards several colorimetric substrates (ABTS,DOPA and TMB)was studied at acidic pH (Fig.7).81The activity of oxidase instead of peroxidase was confirmed since no H 2O 2

was

Fig.5Intravitreal injection of nanoceria protected rat retina photoreceptor cells from light-induced degeneration.Reprinted with permission from ref.43.Copyright (2006)Nature Publishing

Group.

Scheme 2The reaction catalyzed by

catalase.

Fig.6Proposed mechanism of nanoceria based catalase mimic.Reprinted with permission from ref.53.Copyright (2011)Royal Society of Chemistry.

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added.This activity was found to be highly dependent on pH,size,and the coating of the nanoceria.The kinetics studies agreed well with the pH-,size-,and coating thickness-dependent activities (i.e.,lower pH,smaller size,and thinner coatings on the nano-zymes led to higher activities).Based on measured values,the nanozymes had a faster rate constant (1–7?10à7M –1s –1of the nanozyme vs .1?10à8M –1s –1of HRP).

Applications

(a)Immunoassays.Similar to traditional enzyme-linked immunosorbent assays (ELISA),several immunoassays using oxidase nanozyme mimics were developed for the detection of important targets,such as tumor cells.81,90Perez and co-workers reported an assay for the determination of tumor cells with poly(acrylic acid)-coated nanoceria as an oxidase mimic.When the nanoparticles were conjugated with folic acid,they could specifically recognize tumor cells,such as A-549lung cancer cells,due to the elevated-expression of folate receptors on the cell surface.The targeting e?ect was based on the evidence that folate receptors are present in various tumors but absent in most normal tissue except choroid plexus,lung,thyroid and kidney.120The presence of the nanoparticles could then oxidize a colorless substrate to a colored product without H 2O 2.They also evaluated the selectivity using H9c2cardiac myocytes as a control,showing good results.81Several advantages of the nanozyme-based assay were discussed,such as:(a)the nanozyme is more stable and robust,and is less expensive than HRP;(b)the nanozyme oxidizes the substrate without H 2O 2,eliminating the potential stability issue of H 2O 2;and (c)folic acid is used instead of an antibody,eliminating the potential stability issue of antibodies.Note that folate receptor is limited to cancer cells,and cannot di?erentiate the di?erent cancer cell types.The a?nity of folic acid to folate receptor is also lower than that of an antibody to the receptor.In a subsequent study,they showed that for the substrate ampliflu,the oxidase-like activity of the nanoceria could be fine

tuned by changing the reaction pH (Fig.8).90Di?erent from HRP/H 2O 2at pH 4–7and nanoceria at or below pH 5.0,nanoceria at pH 7mediated mild and controlled oxidation of amplifu to a fluorescent product (resorufin)instead of the further oxidized nonfluorescent product (resazurin).This unique phenomenon was able to provide an assay format for long ELISA readout at neutral pH without the use of H 2O 2.The assay format was then successfully used to detect tumors by employing the nanozyme with protein G and specific anti-bodies (i.e.,folate receptor antibody for A549cells and EpCAM antibody for MCF-7cells).2.2

Iron oxide-based nanomaterials

Iron oxide nanomaterials,especially magnetic iron oxide nano-materials,have found broad use in many areas,such as the separation and capture of analytes,sensing and imaging.57,121–132They are usually considered chemically and biologically inert,so metal catalysts,enzymes,or antibodies are often conjugated for further functionalization.When magnetite nanoparticles were coated with small peptides,for example,they were shown to have specific tumor targeting activity for magnetic resonance imaging.133They have also been used for (bio)analysis,(bio)electro-catalysis,drug delivery,bacteria inactivation,etc .122–126,128,130–132Unexpectedly,Yan and co-workers have recently discovered that Fe 3O 4magnetic nanoparticles (MNPs)actually exhibit an intrinsic peroxidase-like activity.44,134Since the pioneering study reported by Yan et al.,44a significant amount of research has been focused on imitating peroxidase activity with various nanomaterials and exploring the potential applications.45–47,98,102,110–112,119,135–264Here,we discuss the enzyme mimetic properties of iron oxide nano-materials and their applications.

2.2.1Iron oxide as peroxidase mimics.In nature,perox-idase,consisting of a large family of enzymes,catalyzes the oxidation of its substrate with peroxide (hydrogen peroxide in most cases)(Scheme 4).Through this catalysis,peroxidases play many critical roles in biological systems,such as detoxify-ing reactive oxygen species (e.g.glutathione peroxidase)and defending against pathogens (e.g.myeloperoxidase).In addition,peroxidase (especially HRP)has been widely used in bioanalytical and clinical chemistry,where it is usually employed as a conjugate to an antibody for enzymatically catalyzing colorimetric substrates for signaling or imaging.Recent studies from Yan’s and others’groups have shown that certain nanomaterials can imitate perox-idase catalytic activity.44–47,98,102,110–112,119,135–264

In Yan’s work,Fe 3O 4MNPs with three di?erent sizes (30,50and 300nm)all oxidized TMB to the blue-colored product in the presence of H 2O 2(Fig.9).44The other two substrates tested (DAB and OPD)were also oxidized to their corresponding products,mimicking the activity of HRP.The catalytic activity of the nano-zyme was size dependent,with smaller sized particles exhibiting higher activity.Like native HRP,the nanozyme performance varies with pH and temperature.However,compared with HRP,the Fe 3O 4MNPs are much more robust as they remain stable and retain their catalytic activity after incubation at a range of tem-peratures (4–901C)and pH (0–12).The robustness of

the

Scheme 3The reactions catalyzed by

oxidase.

Fig.7Nanoceria as nanozyme to mimic oxidase.The oxidase mimetic property of the nanoceria was demonstrated by oxidizing colorimetric substrates (TMB,ABTS and DOPA)to form colored products at pH 4.0.Reprinted with permission from ref.81.Copyright (2009)John Wiley and Sons.

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nanozyme,as well as its low cost,makes it suitable for a wide range of applications.44

In the study from Yan’s group,it was suggested that the Fe 3O 4MNP-based peroxidase activity is the result of a ping-pong mechanism (i.e.,no tertiary intermediate of an enzyme

and its two substrates forms since one substrate is converted to the product and dissociates before the other one binds).44Their steady state kinetic measurements showed that the substrate concentration dependent Lineweaver–Burk (double-reciprocal)plots were parallel,characteristic of the ping-pong mechanism (Fig.10).Native HRP also has a ping-pong catalytic mechanism.The Michaelis–Menten constants (Km ,measuring the substrate’s binding affinity)from the Lineweaver–Burk plots showed that the nanozyme had less affinity to hydrogen peroxide compared with HRP (154mM for the nanozyme vs .3.70mM for HRP),

but

Fig.8Schematic showing the HRP/H 2O 2and nanoceria mediated oxidation of ampliflu.(a)In the pH range 4–7,HRP/H 2O 2oxidizes ampliflu to a nonfluorescent final product (resazurin).(b)In contrast,nanoceria oxidizes ampliflu to the intermediate oxidation fluorescent product (resorufin)at pH 7,(c)while at or below pH 5.0,nanoceria yields the terminal oxidized nonfluorescent product resazurin.(d,e)The ability of nanoceria to oxidize ampliflu to a stable fluorescent product in the pH range 6–8will facilitate its use in ELISA without the use of H 2O 2.Reprinted with permission from ref.90.Copyright (2011)American Chemical

Society.

Scheme 4The reaction catalyzed by peroxidase.

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had higher affinity to TMB compared with HRP (0.098mM for the nanozyme vs .0.434mM for HRP).The calculated rate

constant K cat (measuring the overall catalytic rate)indicated that the Fe 3O 4MNPs mimics reacted faster than native HRP towards both TMB and H 2O 2.

Soon after Yan’s report,Wei and Wang developed novel sensing platforms for both H 2O 2and glucose detection with Fe 3O 4MNPs as peroxidase mimics.45The results of these initial studies stimulated rapidly expanding interests in the use of iron oxide nanomaterials as a peroxidase mimic.Among them,Fe 3O 4(magnetite)nanomaterials have been the mostly exten-sively studied.In most cases,a substrate (such as ABTS or TMB)was used to examine the nanomaterials’peroxidase mimetic properties through the convenient colorimetric reaction in the presence of H 2O 2.160–162,166,171,175,178,181,182,248A previous study has suggested that TMB could be a better choice in certain cases since ABTS could be oxidized in the absence of peroxidase using H 2O 2alone.149The nanomaterials’activity was also compared with HRP in some reports.143,155Wu et al.performed a detailed study to investigate the effects of aqueous–organic solvents on the activities of HRP and an Fe 3O 4-based nanozyme.143,155They showed that the relative catalytic activities of the nanozyme under given conditions were generally better than that of

HRP.

Fig.9Fe 3O 4MNPs as nanozyme to mimic peroxidase.(a)TEM image of Fe 3O 4MNPs with di?erent sizes investigated.(b)The substrates,TMB,DAB and OPD,were catalytically oxidized to form colorimetric products with Fe 3O 4MNPs.(c)The reaction catalyzed by Fe 3O 4MNPs.Reprinted with permission from ref.44.Copyright (2007)Nature Publishing

Group.

Fig.10Steady-state kinetic assay and catalytic mechanism of Fe 3O 4MNPs as peroxidase mimic.Reprinted with permission from ref.44.Copyright (2007)Nature Publishing Group.

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Several studies have also been devoted to Fe 2O 3(hematite)nanomaterials.47,154,177,233,239Very recently,magnetoferritin (Fe 2O 3in ferritin)nanoparticles have been employed for target-ing and visualizing tumor tissues.47The natural inorganic core of ferritin is hydrated iron oxide ferrihydrite,which has very low peroxidase mimic activity.To combat this lowered activity,the magnetic core was post-constructed by in situ oxidation of iron ions inside of the apo-ferritin,resulting in magnetoferritin nanoparticles with excellent peroxidase-like activity.In a recent comparison study of nanoparticles with similar size,Fe 3O 4showed higher peroxidase mimetic activity than Fe 2O 3.110Though naturally-occurring hydrated iron oxide ferrihydrite has little activity,peroxidase mimetic activities have been found in certain iron oxide containing organelles,such as magneto-somes and ferruginous bodies.210,235,241

Doped ferrites,such as MFeO 3(M =Bi,Eu)and MFe 2O 4(M =Co,Mn,Zn),were also explored as peroxidase mimics.180,197,212,216,223,231,257,264For example,CoFe 2O 4MNPs were used as a peroxidase mimic for the detection of H 2O 2and glucose through chemiluminescence.231The performance was further improved by chitosan coating,which provided more monodispersed MNPs and a positive surface charge for a?nity to luminol.180

The molecular level mechanisms responsible for iron oxide as peroxidase mimics have not been completely determined.They may adopt a Fenton and/or Haber–Weiss reaction mecha-nism though a mechanism similar to an authentic enzyme cannot be excluded.151,228,265In Tang and co-workers’study,they employed EPR measurements and a radical inhibition assay to elucidate the possible mechanism for catalytic degra-dation of organic pollutant by Fe 3O 4MNPs-based nanozyme.151HO àand O 2 à/HO 2 were detected using EPR,and the sub-sequent radical inhibition assay showed that O 2 à/HO 2 was https://www.doczj.com/doc/be17707786.html,bining with the fact that MNPs,rather than the leached ions,had catalytic activity,they proposed a mechanism as shown in Fig.11.151Whether the proposed mechanism can be applied to other substrates should be studied in the future.Since there is concern about whether the nanozymes’activity is from the nanomaterials or leached active species (such as iron ions for iron oxide-based nanozymes),it is important to investi-gate the activity of the leached ions.44,45,144,220,257Several studies confirmed that the nanozymes’activities originate from the intact nanomaterials and not the leachate.44,45,220,257For Fe 3O 4MNP-based nanozymes,atomic absorption spectroscopy measurements indicated that small amounts of iron could be released from the Fe 3O 4MNPs.44,45However,the number of leached ions was too low to explain the catalytic activity,further confirming that the observed activity was from intact MNPs rather than the leached ions.In Gao’s work,however,they argued that the Fe 3O 4MNPs catalyzed the polymerization of aniline via Fe ions.144This discrepancy may be due to the instability of the MNPs used and the pH of the reaction solution tested.

Applications

(a)H 2O 2detection.H 2O 2detection is of significant impor-tance in many fields such as biology,medicine,environmental

protection and the food industry.Since H 2O 2is involved in the catalytic reaction of peroxidase and its mimics (Scheme 4),it is straightforward to measure H 2O 2concentration through the color change of certain colorimetric substrates.In Wei and Wang’s seminal report,a colorimetric platform for H 2O 2deter-mination was developed using ABTS as the substrate and Fe 3O 4MNPs as the nanozyme.45The H 2O 2mediated oxidation of ABTS produced a green colored product,which facilitated its colorimetric detection even by the naked eye.Via the proposed method,concentrations as low as 3m M H 2O 2were detected with a linear range from 5m M to 100m https://www.doczj.com/doc/be17707786.html,ter,H 2O 2detection was demonstrated as a model in many follow-up studies (see Table 1).Besides ABTS,many other colorimetric substrates have been used,including 4-AAP-phenol,DPD,OPD and TMB.Tang et al.reported that their system for H 2O 2detection showed good selectivity over several ions,ascorbic acid,glucose,etc.203They further determined H 2O 2concentrations in rain-water,honey and milk samples.

If the substrate oxidation is associated with a fluorescent signaling change,a fluorometric approach to the determination of H 2O 2can be used.156,158,212When fluorescent rhodamine B is oxidized by H 2O 2,it leads to fluorescence quenching.Based on this phenomenon,a selective sensor for H 2O 2was developed.158The fluorescence of CdTe quantum dots is quenched upon oxidation as well,and can also be used for H 2O 2determina-tion.156A signal-on sensor was developed when non-fluorescent substrate BA was converted to its fluorescent product.212When luminol was employed as the substrate,its oxidation could result in chemiluminescence.A few studies based on chemiluminescent detection of H 2O 2have been reported.180,208,231

Electrochemistry provides a convenient way for H 2O 2detection with either natural HRP or its mimics.138,141,159,161,167,174,183,199,201,204,206,219,220,238,239,249,266–268Dong and co-workers fabricated the first electrochemical sen-sor for H 2O 2detection using layer-by-layer assembly of Fe 3O 4MNPs and poly(diallyldimethylammonium chloride)(PDDA)through electrostatic interactions on a tin-doped indium oxide (ITO)electrode.138The sensor had good sensitivity with a detection limit of 1.4m M and was selective for H 2O 2over ascorbic acid and uric https://www.doczj.com/doc/be17707786.html,pared with HRP,the nanozyme system showed several advantages,such as low cost,increased stability,

sustainable

Fig.11A mechanism for the activation of H 2O 2on the peroxidase-like Fe 3O 4MNPs catalyst in the degradation of organic pollutants.Reprinted with permission from ref.151.Copyright (2010)Elsevier.

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electrocatalytic activity,and robustness to harsh environments.138Given the good selectivity of the sensors developed,the determina-tion of H 2O 2in real samples (such as toothpaste,Walgreens

antiseptic/oral debriding agent,Crest whitening mouthwash solution,Diet coke and Gatorade)has been reported in several studies.167,199

Table 1

H 2O 2detection with peroxidase mimics a

Nanozyme Method Linear range LOD Comments Ref.Fe 3O 4MNPs Color.5–100m M 3m M Substrate:ABTS 45Fe 3O 4MNPs Color.0.5–150.0m M 0.25m M

Substrate:DPD

203H 2O 2in rainwater,honey and milk was tested.

Fe 3O 4MNPs

Color.1–100m M 0.5m M Substrate:TMB

160Fe 3O 4was encapsulated in mesoporous silica.

Fe 3O 4graphene oxide composites Color.1–50m M 0.32m M Substrate:TMB 178Fe-substituted SBA-15microparticles Color.0.4–15m M 0.2m M Substrate:TMB 163Iron phosphate microflowers

Color.10–50m M 10nM Substrate:TMB 189[FeIII(biuret-amide)]on mesoporous silica Color.0.1–5mM 10m M Substrate:TMB 252FeTe nanorods

Color.0.1–5m M 55nM Substrate:ABTS 254Fe(III )-based coordination polymer Color.1–50m M 0.4m M Substrate:TMB 258CuO NPs Color.0.01–1mM N/A Substrate:4-AAP and phenol 236AuNPs

Color.18–1100m M 4m M Substrate:TMB

211Cysteamine was the ligand for AuNPs.

AuNC@BSA

Color.0.5–20m M 20nM Substrate:TMB 170Au@Pt core–shell nanorods Color.45–1000m M 45m M Substrate:OPD 119Graphene oxide

Color.0.05–100m M 50nM Substrate:TMB 213Hemin-graphene hybrid nanosheets Color.0.05–500m M 20nM Substrate:TMB 222Carbon nanodots Color.1–100m M 0.2m M Substrate:TMB 230Carbon nitride dots Color.1–100m M 0.4m M Substrate:TMB 225CoFe LDH nanoplates

Color.1–20m M 0.4m M Substrate:TMB 262Carboxyl functionalized mesoporous polymer Color.1–8m M

0.4m M Substrate:TMB 165Pt–DNA complexes Color.0.979–17.6mM 0.392mM Substrate:TMB

2373.92m M was detected with PVDF membrane.

Polyoxometalate Color.1–20m M 0.4m M Substrate:TMB 247Polyoxometalate Color.0.134–67m M 0.134m M Substrate:TMB 186Fe 3O 4MNPs Fluor.10–200nM 5.8nM Substrate:Rhodamine B

158Fluorescence of Rhodamine B was quenched.

BiFeO 3NPs

Fluor.20nM–20m M 4.5nM Substrate:BA

212Oxidation of BA gave fluorescence.H 2O 2in rainwater was tested.

Fe 3O 4MNPs Fluor.0.18–900m M 0.18m M Fluorescence of CdTe QD was quenched.156CoFe 2O 4NPs CL 0.1–4m M 0.02m M CoFe 2O 4NPs form complexes with beta-CD.208CoFe 2O 4NPs

CL 0.1–10m M 10nM H 2O 2in natural water was tested.231CoFe 2O 4NPs with chitosan coating CL 1nM–4m M 0.5nM CoFe 2O 4NPs was coated with chitosan.

180H 2O 2in natural water was tested.

Fe 3O 4MNPs

E-chem 4.2–800m M 1.4m M 138Fe 3O 4microspheres-AgNP hybrids E-chem 1.2–3500m M 1.2m M H 2O 2in disinfected FBS samples was tested.268Fe 3O 4MNPs E-chem 0–16nM 1.6nM Fe 3O 4was loaded on CNT.159Fe 3O 4

MNPs

E-chem

1–10mM

N/A Fe 3O 4was entrapped in mesoporous carbon

foam,and the composite was used to construct a carbon paste electrode.161

Not a linear response.

Fe 3O 4MNPs

E-chem 20–6250m M 2.5m M Fe 3O 4MNPs and PDDA-graphene formed

multilayer via layer-by-layer assembly.167H 2O 2in toothpaste was tested.

Fe 3O 4nanofilms on TiN substrate E-chem 1–700m M 1m M H 2O 2in Walgreens antiseptic/oral debriding agent,Crest whitening mouthwash solution,

Diet coke and Gatorade was tested.

199Fe 3O 4MNPs

E-chem 0.2–2mM 0.01mM 174Fe 3O 4MNPs E-chem 0.1–6mM 3.2m M Fe 3O 4was on reduced graphene oxide.201Fe 2O 3NPs E-chem 20–140m M 11m M 239Fe 2O 3NPs

E-chem 20–300m M 7m M Fe 2O 3was modified with Prussian blue.239Iron oxide NPs/CNT E-chem 0.099–6.54mM 53.6m M 141FeS nano-sheet E-chem 0.5–150m M 92nM 204FeS needles E-chem 5–140m M 4.3m M 238FeSe NPs E-chem 5–100m M 3.0m M 238FeS

E-chem 10–130m M 4.03m M 249Co 3O 4NPs

E-chem 0.05–25mM 0.01mM 183Hemin-graphene hybrid nanosheets E-chem 0.5–400m M 0.2m M 222Helical CNT E-chem 0.5–115m M 0.12m M 220LDH nanoflakes E-chem 12–254m M 2.3m M 206Calcined LDH E-chem 1–100m M 0.5m M 219CdS

E-chem

1–1900m M

0.28m M

251

a

Color.,Colorimetric;E-chem,electrochemical;Fluor.,fluorometric;LOD,limit of detection.

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Compared with colorimetric detection,fluorometric,chemi-luminescent and electrochemical methods could provide better sensitivity as shown in several reports.158,159,180,212

(b)Glucose detection.Glucose detection is of great impor-tance in clinical and food analysis and plays a critical role in the improvement of life quality.269Usually,glucose oxidase (GOx)is employed for glucose detection due to its high specificity and e?ciency.The catalytic oxidation of glucose with molecular oxygen in the presence of GOx produces H 2O 2,which can be further determined by many analytical methods (such as HRP catalyzed colorimetric and electrochemical methods).The use of peroxidase mimics for glucose detection would be advanta-geous based on their high stability,low cost,etc .

For the first time,Wei and Wang developed a sensitive and selective colorimetric approach towards glucose detection by combining the catalytic oxidation reaction of glucose with GOx and the catalytic reaction of ABTS with Fe 3O 4MNPs (Fig.12).45With the developed approach,glucose concentrations as low as 30m M were detected with a linear range from 50m M to 1mM.The system also showed excellent selectivity over other sugars such as fructose,lactose and maltose.

Similar to H 2O 2detection (vide supra ),numerous analytical approaches to glucose detection have been developed by varying the nanomaterials and substrates used (see Table 2).Several studies also reported novel methods for the determination of glucose concentration in real serum samples.For example,when PDDA-coated iron oxide nanoparticles (acting as nanozymes)were electrostatically assembled with GOx,the composites could be used for colorimetric sensing of glucose.153The sensing performance was validated by a commercial glucose meter.

Moreover,the glucose concentrations in serum samples could be accurately and selectively detected over several other sugars,such as galactose,lactose,mannose,maltose,arabinose,cello-biose,ra?nose and xylose.The glucose in urea was also deter-mined.178,257There are many advantages to using nanozymes instead of GOx,such as stability,robustness and recyclability,which are addressed in several studies.147,160

The analytical strategy described above is easily adapted for other oxidases as well,as shown in Fig.12b.Choline,choles-terol,galactose and xanthine have been successfully analyzed based on the above sensing strategy.119,160,162,170,173,181

(c)DNA detection.When double-stranded DNA’s shielding against MNPs’mimicking activity was combined with PCR,a label-free colorimetric platform for DNA sensing was developed (Fig.13).169The developed method was used for the selective detection of Chlamydia trachomatis pathogen using a human urine sample.One advantageous feature of the method is its simplicity,exemplified by achieving detection with the naked eye in 30min.

(d)Aptasensors.Aptamers are selected ssDNA or ssRNA that can specifically bind to a target,and can be considered as nucleic acid versions of an antibody.270Therefore,aptamers have been extensively studied for the construction of aptasen-sors.271–274When nanozymes are introduced as signaling elements,new aptasensing platforms can be developed.Zhang et al.con-structed a sandwich format for thrombin sensing using two anti-thrombin aptamers for capture and detection.155The detection aptamer was tagged with chitosan-modified Fe 3O 4MNPs,which converts TMB into a colored product for colorimetric https://www.doczj.com/doc/be17707786.html,ing this method,they were able to achieve a linear detection range from 1to 100nM and a detection limit of 1nM thrombin.In a study by Kong’s group,aptamers and Fe 3O 4MNPs were used to replace traditional small molecule electrochemical probes,resulting in a sensitive and reagentless electrochemical sensor for specific detection of thrombin (Fig.14).172The sensor exhibits good sensi-tivity,with a linear range of 1.0to 75nM and a detection limit of 1nM,and can also be regenerated.

(e)Immunoassay.Conjugating an antibody (or protein A)to a nanozyme,rather than a traditional enzyme like HRP,enables the use of nanozyme technology for a number of immunoassays (Table 3).44,111,135,154,192,216,229,232,264In Yan’s pioneering work,two immunoassay formats were developed (Fig.15a and b).44For the detection of hepatitis B virus surface antigen (preS1),the antigen was first adsorbed onto a plate.Anti-preS1anti-bodies were then added for specific target recognition,followed by protein A-Fe 3O 4MNP conjugates for signal development.This format was based on the traditional antigen-down immuno-assay.In the second case,a modified sandwich assay was developed for detection of the myocardial infarction biomarker troponin I (TnI).The antigen was magnetically captured and separated from a blood sample using the antibody–Fe 3O 4MNPs conjugate.This is different from a traditional sandwich assay,in which the antigen is captured by an antibody immobilized on a solid surface.The final sandwich format was formed between

the

Fig.12(a)Nanozyme as peroxidase mimic for colorimetric sensing of H 2O 2and glucose when combined with glucose oxidase.(b)The sensing format in (a)could be extended to other targets (substrate 1here)when combined with a appro-priate oxidase.Numerous transduction signals can be adopted for sensing (such as colorimetric,fluorometric and chemiluminescent signals when the corres-ponding substrates are used;and electrochemical signals when a nanozyme is immobilized on an electrode).

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Table 2

Targets detection combining oxidases and peroxidase mimics a

Nanozyme Method Linear range LOD Comments

Ref.Glucose Fe 3O 4MNPs

Color.50–1000m M 30m M Substrate:ABTS

45Selectivity against sugars:fructose,lactose and maltose.Fe 3O 4MNPs with PDDA coating

Color.

39–100m M

30m M

Substrate:ABTS

153

GOx was electrostatically assembled onto the Fe 3O 4@PDDA.Glucose in serum samples was https://www.doczj.com/doc/be17707786.html,pared with glucometer.

Selectivity against sugars:galactose,lactose,mannose,maltose,arabinose,cellobiose,ra?nose and xylose.Fe 3O 4MNPs Color.30–1000m M 3m M Substrate:TMB

160

Fe 3O 4was encapsulated in mesoporous silica with GOx.Showing the recycle capability.

Comparison between free MNPs vs .encapsulated MNPs.Fe 3O 4GO composites Color.2–200m M 0.74m M Substrate:TMB

178Glucose in urine was tested.Iron oxide NPs

Color.31.2–250m M 8.5m M Substrate:ABTS

147Iron oxide NPs was coated with glycine.

More robust than HRP towards NaN 3inhibition.Iron oxide NPs Color.31.2–250m M 15.8m M Substrate:ABTS

147Iron oxide NPs was coated with heparin.

More robust than HRP towards NaN 3inhibition.Iron oxide NPs Color.0.12–4m M 0.5m M Substrate:ABTS

168Iron oxide NPs was coated with APTES and MPTES.ZnFe 2O 4

Color.

1.25–18.75m M 0.3m M Substrate:TMB

257Glucose in urine was tested.[FeIII(biuret-amide)]on mesoporous silica

Color.20–300m M 10m M Substrate:TMB

252Glucose in mice blood plasma was tested.FeTe nanorods Color.1–100m M 0.38m M Substrate:ABTS

254Glucose in spiked blood was tested.Fe(III )-based coordination polymer Color.2–20m M 1m M Substrate:TMB

258Glucose in serum was tested.CuO NPs Color.0.1–8mM N/A Substrate:4-AAP and phenol 236AuNPs

Color. 2.0–200m M 0.5m M Substrate:TMB

211Cysteamine was the ligand for AuNPs.Au@Pt core–shell nanorods Color.45–400m M 45m M Substrate:OPD 119Graphene oxide

Color.

1–20m M 1m M Substrate:TMB

213Glucose in blood and fruit juice was tested.Hemin–graphene hybrid nanosheets Color.0.05–500m M 30nM Substrate:TMB 222Carbon nanodots Color.1–500m M 1m M Substrate:TMB

230Glucose in serum was tested.Carbon nitride dots Color.1–5m M 0.5m M Substrate:TMB 225CoFe LDH nanoplates Color.1–10mM 0.6m M Substrate:TMB

262Fe 3O 4MNPs

Fluor. 1.6–160m M 1.0m M Fluorescence of CdTe QD was quenched.156Glucose in serum was tested.

Fe 3O 4MNPs with PDDA coating

Fluor.

3–9m M

3m M

GOx was electrostatically assembled onto the Fe 3O 4@PDDA.162

Oxidation of AU gave fluorescence.Glucose in serum was tested.

Selectivity against sugars:arabinose,cellobiose,galactose,lactose,maltose,ra?nose and xylose.

BiFeO 3NPs Fluor.1–100m M 0.5m M Oxidation of BA gave fluorescence.212Glucose in serum was tested.CoFe 2O 4NPs

CL

0.1–10m M

0.024

m M

Other sugars

231CoFe 2O 4NPs

CL 0.05–10m M 10nM CoFe 2O 4NPs were coated with chitosan.180Glucose in serum was tested.Hemin-graphene hybrid nanosheets E-chem 0.5–400m M

0.3m M 222Fe 3O 4MNPs E-chem 6–2200m M 6m M Glucose in serum was tested.

145Compared with clinical analyzer.

Nafion for high selectivity against AA,UA,sucrose and lactose.

Fe 3O 4MNPs

E-chem 0.5–10mM

0.2mM Fe 3O 4was encapsulated in mesoporous carbon with GOx,and the

composite was used to construct a carbon paste electrode.161

Comparison between free MNPs vs .encapsulated MNPs.Choline Fe 3O 4

Fluor.20–100m M

20m M

Choline oxidase was electrostatically assembled onto the

Fe 3O 4@PDDA.

162MNPs with PDDA coating Oxidation of AU gave fluorescence.

Fe 3O 4MNPs

E-chem 1nM–10mM

(log)

0.1nM Fe 3O 4and choline oxidase were immobilized together on electrode.173

Selectivity against AA and UA.

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TnI/antibody-Fe 3O 4MNPs complex and another capture anti-body on a solid surface.The colorimetric signal was developed from the conversion of colorless TMB to its product.A slightly

different format was developed in a later study for the detection of carcinoembryonic antigen (CEA)(Fig.15c).135This format was very similar to a traditional sandwich assay,except that HRP was replaced with Fe 3O 4MNPs.

Based on the MNPs’intrinsic peroxidase activity and the interaction of folic acid and its receptor,polyacrylic-acid coated iron oxide MNPs were successfully used to di?erentiate carci-noma cells (A549cells)from non-carcinoma cells (H9c2).192The expression of the folic acid receptor in the A549cells rather than H9c2control cells was confirmed by flow cytometry,thus corroborating the nanozyme-based assay.192

(f)Immunostaining.Gu et al.demonstrated that ultra-small Fe 3O 4MNPs were able to replace expensive enzymes (such as HRP)for immunohistochemical staining.171When dimercaptosuccinic acid-coated ultra-small Fe 3O 4MNPs were conjugated with Nimo-tuzumab,a humanized monoclonal antibody for epidermal growth factor receptor (EGFR),the conjugates could specifically

Table 2

(continued )

Nanozyme Method Linear range LOD Comments

Ref.Cholesterol Fe 3O 4MNPs

Color.

10–250m M

5m M

Substrate:TMB

160

Fe 3O 4was encapsulated in mesoporous silica with cholesterol oxidase.

Showing the recycle capability.

Comparison between free MNPs vs .encapsulated MNPs.Au@Pt core–shell nanorods Color.30–300m M 30m M Substrate:OPD

119

Galactose Fe 3O 4MNPs

Color.

10–200mg L à15mg

L à1Substrate:ABTS 181Galactose in dried blood samples from normal people and patients was tested.

Plates were used for sensing.

Fe 3O 4MNPs with PDDA coating Fluor.

2–80m M

2m M

Galactose oxidase was electrostatically assembled onto the

Fe 3O 4@PDDA.

162Oxidation of AU gave fluorescence.

Xanthine AuNC@BSA

Color.1–200m M

0.5m M Substrate:TMB

170

Xanthine in serum and urine samples was tested.

a

Color.,Colorimetric;E-chem,electrochemical;Fluor.,fluorometric;LOD,limit of

detection.

Fig.13Schematic illustration of a label-free colorimetric platform for DNA sensing based on target-induced shielding of nanozyme’s activity.Reprinted with permission from ref.169.Copyright (2011)John Wiley and

Sons.

Fig.14An electrochemical aptasensor for reagentless protein detection.Reprinted with permission from ref.172.Copyright (2011)Elsevier.

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detect EGFR over-expression on the membrane of esophageal cancer cells.In a more recent study,Yan and Liang’s groups synthesized magnetoferritin nanoparticles (M-HFn)as novel reagents for targeting and visualizing tumor tissues (Fig.16).47The M-HFn was prepared by encapsulating iron oxide nano-particles inside the cavity of a recombinant human heavy-chain ferritin (HFn)protein cage.Since HFn binds directly to tumor cells via over-expressed transferrin receptor 1(TfR1)proteins,no further conjugation is needed for targeting.Another advantage is that no

additional contrast reagents are needed because the iron oxide nanoparticle cores act as peroxidase mimics and can catalyze the oxidation of peroxidase substrates to produce a colored product for the visualization of tumor tissues.They examined 474clinical specimens from patients (247clinical tumor tissue samples vs .227normal and lesion tissue control samples)with 9types of cancer and verified that the nanozyme technology could distinguish cancerous cells from normal cells with 98%sensitivity and 95%specificity.47

(g)Detection of other substances.Besides the above men-tioned targets,several other substances have been detected using peroxidase-like nanozymes.Reduced glutathione (GSH),an essential nutrient and an antioxidant,competitively inhibits ABTS catalytic oxidation by hydrogen peroxide and Fe 3O 4MNPs-based nanozymes.248Since the inhibiting e?ects are dependent on GSH concentration,a simple approach was developed for GSH determination.The method has a linear range from 3.0to 30.0m M.This method was robust,having good selectivity over several thiols and good recovery.The method was also applied to detect GSH in lung adenocarcinoma epithelial cell lines (A549).Based on a similar design,melamine in dairy product was tested,where melamine was the competing agent against the nanozyme’s substrate (ABTS).150

When Fe 3O 4MNPs were entrapped within mesoporous carbon,a conductive nanocomposite was obtained.The nano-composite was then used to construct highly e?cient electro-des for sensing several phenolic compounds,which showed great promise for environmental monitoring.161

(h)Promotion of stem cell growth.In Huang’s study,they investigated the e?ects of commercialized superparamagnetic iron oxide nanoparticles,Ferucarbotran (Resovist),on the pro-liferation of human mesenchymal stem cells (hMSCs).140Fer-ucarbotran was found to e?ciently label hMSCs,and dramatically induced hMSCs proliferation.Since Ferucarbotran

Table 3

Nanozyme as peroxidase mimics for immunoassay

Nanozyme

Target Format

Comments Ref.Fe 3O 4NPs with dextran coating

preS1Antigen-down immunoassay 44

TnI Capture-detection sandwich immunoassay

Fe 3O 4NPs with chitosan coating mouse IgG Antigen-down immunoassay 135

CEA Capture-detection sandwich immunoassay

CEA

Sandwich immunoassay Fe 2O 3NPs with Prussian blue coating IgG Antigen-down immunoassay 154Ferric nano-core residing in ferritin Avidin

Antigen-down immunoassay Avidin-biotin interaction

232

Nitrated human ceruloplasmin Sandwich immunoassay Fe 1àx Mn x Fe 2O 4NPs with PMIDA coating

Mouse IgG

Antigen-down immunoassay Both direct and indirect assay

216MnFe 2O 4NPs with citric acid coating Sticholysin II Antigen-down immunoassay 264Au@Pt nanorods with PSS coating Mouse IL-2Sandwich immunoassay 111

Graphene oxide

PSA

Sandwich immunoassay

Clinical samples were tested

229

Fig.15Fe 3O 4MNPs as nanozymes for immunoassay:(a)antigen-down immu-noassay format;(b)capture-detection sandwich immunoassay format;and (c)sandwich immunoassay format;(a)and (b)reprinted with permission from ref.44;copyright (2007)Nature Publishing Group;(c)reprinted with permission from ref.135;copyright (2008)American Chemical Society.

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exhibited in vitro and intracellular peroxidase-like activity,they proposed that the promotion of cell growth may be due to Ferucarbotran’s ability to eliminate intracellular H 2O 2through peroxidase mimetic activity (Fig.17).140The study also showed that after internalization,Ferucarbotran was degraded into free iron ions,which then accelerated the cell cycle progression.A later study further confirmed the promoting e?ects of MNPs on MSCs proliferation.195Compared with the control groups with phosphate-bu?ered saline alone and magnetized MSCs,the MSCs sheet created by a new magnetite tissue engineering technology had greater angiogenesis in ischemic tissues.The mechanism was again attributed to the MNPs’peroxidase-like activity.

(i)Pollutant removal.The development of highly e?cient,robust and low-cost catalysts for the removal of pollutants in wastewater is very important to our environment and health.The peroxidase-like activity of nanozymes has been explored for this purpose by several groups.137,149,151,157,176,196,249,275Model pollu-tants,such as phenol,rhodamine B,aniline,methylene blue and xylenol orange,have been tested.As high as 85%phenol removal was reported using ferromagnetic nanoparticles as the catalyst.137Using nanozymes as catalysts for pollutant removal has several distinct merits,such as low cost,easy preparation,high stability,low environmental impact,and recyclability.137

(j)Other applications.Dong et al.employed Fe 3O 4/Au nanocomposites to enhance the electricity generation from an electrogenic bacterium,Shewanella oneidensis MR-1(Fig.18).263The outer membrane c-type cytochromes act as molecular wires for electron transfer.When the Shewanella oneidensis MR-1

biofilm was co-immobilized onto a glassy carbon electrode with Fe 3O 4/Au nanocomposites,it exhibited a 22-fold increase in the current density compared with the biofilm without nanocom-posites.The boosted e?ciency was attributed to the unique properties of the nanocomposites.First,due to the peroxidase mimetic properties,the nanocomposites can participate in the electron transfer process;second,they lead to improved con-ductivity;third,the assembled nanocomposites provide a long-range pathway (instead of separated bacteria)for

electron

Fig.16Magnetoferritin nanoparticles as peroxidase mimic to target and visualize tumor tissues.Reprinted with permission from ref.47.Copyright (2012)Nature Publishing

Group.

Fig.17Superparamagnetic iron oxide (SPIO)nanoparticles can promote cell growth due to their ability to diminish intracellular H 2O 2through intrinsic peroxidase-like activity.Also,SPIO can accelerate cell cycle progression,which may be mediated by the free iron (Fe)released from lysosomal degradation.Reprinted with permission from ref.140.Copyright (2009)Elsevier.

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propagation;and finally,they provide a more favorable,bio-compatible environment for the proteinaceous electron transfer components needed for extracellular electron transfer.263

The peroxidase mimetic property was recently used for tracing ferrite nanoparticles in vivo .190By localizing MNPs within the main organs after intravenous injection,the biodis-tribution and organ clearance of MNPs were analyzed through MNP-mediated staining.

2.2.2Iron oxide as both peroxidase and catalase mimics.Interestingly,Gu et al.recently found that iron oxide nano-particles (both Fe 3O 4and g -Fe 2O 3)exhibited dual enzyme mimetic properties (i.e.,catalase and peroxidase mimics)(Fig.19).110The study showed that the enzymatic activities were pH dependent,with catalase activity dominant at neutral conditions (pH =7.4)while the peroxidase activity was dominant under acid conditions (pH =4.8).Since the two nanoparticles had similar size and surface charge,they also made a side-by-side comparison of their performance.Fe 3O 4MNPs alone (or with H 2O 2as peroxidase mimic)showed higher cell toxicity when compared with g -Fe 2O 3,which was attributed to Fe 3O 4MNPs’higher activity for both mimics.More,the EPR measurements confirmed that hydroxyl radical was formed at acidic conditions,suggesting a Fenton-like mechanism for the peroxidase mimicking activity (Fig.19a).No hydroxyl radical was detected at neutral conditions,suggesting a di?erent mechanism for the catalase mimicking activity (Fig.19b).They argued that at neutral or higher

pH,the formation of HO 2

was faster and it was then quickly ionized into O 2 à,further into O 2by reacting with hydroxyl radical.The cellular toxicity of the nanozymes was due to the entrapment of the nanoparticles into acidic lysosomes,where hydroxyl radical was produced.They also suggested a potential protective role of the nanozymes.When they are entrapped within the cytosol,they can convert H 2O 2into harmless products via catalase mimicking activity.Whether other peroxidase mimics have dual enzyme mimicking activities should be examined in the future to elucidate their mechanisms and explore the broad applications.

2.2.3Iron oxide as oxidase mimics.In addition to nanoceria,other nanomaterials have recently been studied for oxidase mimetic properties.Fe 2O 3nanowires were explored by Cao and Wang as a sensor for glucose detection using their oxidase-like activity.114The non-enzymatic glucose sensor was fabricated with a Fe 2O 3nanowire

array.114Because it mimicked GOx behavior,the nanozyme sensor behaved as an oxidase mimic,rather than a peroxidase mimic as claimed.The sensing system had a linear range of 0.015to 8mM,with a detection limit of 6m M towards glucose.More importantly,the system was able to detect glucose in serum samples with accurate performance.The system also showed good reproducibility and storage stability.2.3

Other metal oxide-based nanomaterials

Many other metal oxide-based nanomaterials have also been explored to mimic several enzymes.46,113,183,215,218,236,260

2.3.1Cobalt oxide as catalase and peroxidase mimics.Dual intrinsic enzyme mimicking activities (i.e.,catalase-and peroxidase-like activities)were observed for cubic Co 3O 4nanoparticles.183The peroxidase mimicking activity was confirmed by catalytic oxidation of TMB.Kinetics studies showed that the nanozyme had higher a?nity towards TMB but lower a?nity towards H 2O 2when compared with HRP.A further mechanism study suggested that the peroxidase-like activity was due to Co 3O 4nanoparticles’ability for electron transfer between the sub-strate and H 2O 2instead of hydroxyl radical.The catalase-like activity was also suggested based on the observation of increased oxygen generation in the presence of H 2O 2and the nanozyme (Scheme 2).No mechanism for catalase-like activity was proposed.Since the peroxidase-like activity was not inhibited at high con-centrations of H 2O 2,the cubic Co 3O 4nanoparticles may actually imitate horseradish peroxidase C (HRP-C)properties,which exhi-bits weak catalase activity in addition to its peroxidase activity.In another study,gillyflower-shaped Co 3O 4nanoparticles were synthesized via an L -arginine-assisted hydrothermal approach and their peroxidase-like activity was tested.260

When

Fig.18Fe 3O 4/Au nanocomposites mediated e?cient electron transfer between the electrogenic bacteria and electrode.Reprinted with permission from ref.263.Copyright (2010)Royal Society of

Chemistry.

Fig.19Dual enzyme-like activities (i.e.,catalase and peroxidase mimics)of iron oxide nanoparticles.The nanoparticles may decompose H 2O 2through catalase mimicking activity in neutral cytosol;however,they catalyzed H 2O 2to produce hydroxyl radicals through peroxidase mimicking activity when trapped in acidic lysosomes.Reprinted with permission from ref.110.Copyright (2012)American Chemical Society.

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compared with commercially-available nanoparticles,superior peroxidase mimicking activity was achieved due to the unique gillyflower structures with larger specific surface area.Di?erent from the above-mentioned cubic Co 3O 4nanoparticles,hydroxyl radicals were involved in the suggested mechanism.

2.3.2Copper oxide as oxidase mimics.Chen and co-workers found that commercially available 30nm CuO nanoparticles showed peroxidase mimicking activity.218Compared with HRP and some other nanozymes,the CuO nanoparticles had the highest a?nity to https://www.doczj.com/doc/be17707786.html,ter,they prepared water-soluble CuO nano-particles via a quick-precipitation approach.Since the nano-particles were smaller in size (6nm)and had higher a?nity towards H 2O 2,they showed higher peroxidase-like activity than the commercial ones.236A colorimetric assay for hydrogen peroxide and glucose was developed.

2.3.3Manganese dioxide as oxidase mimics.MnO 2nano-materials with di?erent morphologies (i.e.,nanosheets,nano-spheres,nanosticks,nanocomplexes and nanowires)have also been studied to determine their oxidase mimicking activity.113Among them,MnO 2nanowires had the highest and most stable activity,and were further used to label antibodies for an immunoassay of sulfate-reducing bacteria.A side-by-side study was carried out to compare the performance of the new nanozyme-based immunoassay to traditional HRP-based ELISA (Fig.20).113Using a sandwich assay for the detection of a pathogen as an example,they showed that both the MnO 2nanowire-ELISA and HRP-ELISA exhibited good sensitivity and high selectivity.However,the MnO 2nanowire-ELISA was advantageous in several aspects:first,compared with HRP,the nanozyme was more stable,more robust but less expensive;second,the nanozyme oxidized the substrate without H 2O 2,eliminating the potential stability issue of H 2O 2.

2.3.4Vanadium pentoxide as peroxidase mimics.V 2O 5nanowires had catalytic activity towards peroxidase substrates (such as ABTS and TMB)in the presence of H 2O 2as demonstrated in a study from Tremel’s group.215They also showed that V 2O 5nano-wires exhibited similar kinetics but higher a?nity towards both ABTS and H 2O 2when compared with natural vanadium-dependent haloperoxidase (V-HPO).Based on structure similarity between V 2O 5and V-HPO and EPR data,a reaction mechanism was proposed,in which a vanadium peroxo complex intermediate was involved (Fig.21).The V 2O 5based nanozymes could be re-used up to ten times and retained their activity in several organic solvents tested.The excellent activity of the V 2O 5-based nanozymes was further demonstrated in a subsequent study,in which Tremel and co-workers reported that the V-HPO-like V 2O 5nanowires prevented marine biofouling.46The long-term (60day)in situ studies demon-strated that V 2O 5nanowire-based nanozymes have excellent anti-biofouling capabilities (Fig.22).The mechanism studies indicated that the anti-biofouling originated from HOBr and 1O 2species.The as-prepared functional materials exerted a strong antibacterial activity against both Gram-negative and Gram-positive bacteria.Moreover,the nanozyme was even more inert than International Maritime Organization-approved antifouling products.2.4

Metal-based nanomaterials

Metal nanomaterials can also be potential candidates for enzyme mimics,as indicated by numerous recent reports.111,112,119,170,187,209,211,217,226,227,245

2.4.1Gold nanomaterials

2.4.1.1Gold nanomaterials as oxidase mimics.Citrate-coated gold nanoparticles have been extensively studied for a variety of applications,such as biomedical assays,due to the routine synthesis and functionalization methods that have

been

Fig.20MnO 2NP as nanozyme to mimic oxidase for immunoassay.Reprinted with permission from ref.113.Copyright (2012)Elsevier.

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developed.These nanomaterials have also been investigated for their catalytic activities.However,it was still surprising and remarkable when Rossi and co-workers showed that ‘‘naked’’citrate-coated gold nanoparticles catalyzed the aerobic oxida-tion of glucose with dissolved oxygen.40,42,276The reaction was very similar to the reaction catalyzed by GOx,and suggested

that gold nanoparticles could serve as a mimic for GOx (see Scheme 3a).Several other metal nanomaterials tested,such as Ag,Cu,Pd and Pt,did not show significant oxidase mimetic activity.Detailed mechanism studies were also carried out later by the same group.42,276Based on the experimental results,they proposed an Eley–Rideal mechanism for the catalysis.As sug-gested,glucose may first adsorb onto the gold nanoparticles;then an oxygen comes and reacts with the adsorbed glucose and forms the products (gluconic acids and H 2O 2).The gold nanozyme-based catalysis also followed Michaelis–Menten kinetics,and the results showed that native enzyme was 55times more active than the nanozyme.

Inspired by these initial results,Fan et al.reported an interesting self-catalyzed,self-limiting system for controllable growth of gold nanoparticles (Fig.23).115They further developed an innovative sensing strategy for DNA and microRNA detection based on the gold nanoparticles’intrinsic oxidase activity.115,118The di?erent a?nities of ssDNA and dsDNA towards gold nanoparticle seeds can be used to fine tune their growth,thus a?ecting their oxidase-like activity.Therefore,facilitated by the hybridization of the nucleic acids,nanozyme activity could be used to successfully detect target DNA or microRNA.118One appealing aspect of the strategy is that the final output signals are adaptable.When the system was coupled with HRP,colorimetric or chemiluminescent signals could be monitored.Without HRP,the plasmonic signals could be detected even at a single-nanoparticle level using dark field microscopy.The sensing system as a whole had single-base match di?erentiation capability.

2.4.1.2Gold nanomaterials as peroxidase mimics.Gold nano-particles with either positive or negative surface charges sur-prisingly showed peroxidase mimicking activity.211,226Chen and co-workers performed a systematic study to reveal the origin of the peroxidase-like activity seen from gold nanoparticles,confirming that the activity was indeed contributed by the gold nanoparticles.187The e?ects of surface modification on the activity were also examined,showing that the activities could be tuned by changing the a?nities between the nanozymes and substrates.BSA (bovine serum albumin)encapsulated fluorescent gold nanoclusters were also used to mimic peroxidase.

170

Fig.21The single layer structure of V 2O 5and the proposed mechanism for its peroxidase-mimicking activity.Reprinted with permission from ref.215.Copy-right (2011)John Wiley and

Sons.

Fig.22Long-term in situ investigation showed that V 2O 5nanowires based nanozymes had excellent anti-biofouling capability.Reprinted with permission from ref.46.Copyright (2012)Nature Publishing

Group.

Fig.23Gold nanoparticles as nanozyme to mimic glucose oxidase.When glucose was oxidized,it produced H 2O 2,which would further promote the growth of gold seeds by reducing HAuCl 4to Au 0.The system was self-limiting due to the presence of two negative feedback factors:size-dependent activity decrease of gold nanoparticles and product (gluconic acid)-induced surface passivation.Reprinted with permission from ref.115.Copyright (2010)the American Chemical Society.

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Mercury ions,which specifically enhance the peroxidase-like activity of gold nanoparticles compared with other metal ions,can also be detected using nanozyme technology.226Based on this phenomena,a colorimetric sensor for mercury ions was developed.

2.4.2Platinum nanomaterials

2.4.2.1Platinum nanomaterials as SOD mimics.Platinum nano-particles encapsulated within apo-ferritin (PtNP@apo-ferritin)were synthesized and tested for their ability to detoxify reactive oxygen species.277The PtNP@apo-ferritin exhibited good SOD-like in vitro activity and long-term stability.The PtNP@apo-ferritin were uptaken by cells via a ferritin-receptor-mediated process and increased cell viability under externally induced stress.277Compared with ceria nanoparticles,the SOD-like activity of PtNP@apo-ferritin was lower on a weight basis as suggested by another study.92

2.4.2.2Platinum nanomaterials as catalase and/or peroxidase mimics.1–2nm platinum nanoparticles within apo-ferritin (PtNP@apo-ferritin)were prepared and showed high stability.112Interestingly,the PtNP@apo-ferritin exhibited dual enzyme mimic behaviors (catalase and peroxidase),with both activities dependent on pH and temperature (Fig.24).The study from Nie’s research group indicated that the catalase-like activity were enhanced by increasing pH and temperature while the peroxidase-like activity had a maximum value at physiological temperature and slightly acidic conditions.112The catalytic activities were dependent on Pt content,with higher Pt content having better activities.Whether the PtNP@apo-ferritin from both reports also have triple enzyme mimicking activity should be investigated in the future.112,277

10nm Pt nanocubes stabilized by cetyltrimethylammonium bromide (CTAB)were synthesized and exhibited peroxidase mimicking capability.227An Eley–Rideal mechanism for the catalysis was proposed as shown in Fig.25.The catalytic activity was reduced when they formed aggregates,likely due to the decrease in surface area.227

2.4.3Bimetal and other metal nanomaterials

2.4.

3.1Au@M (M =Bi,Pd and Pt)nanostructures as enzyme mimics.Chang and co-workers demonstrated that bismuth–gold nanoparticles exhibited peroxidase-like activity (Fig.26).245They further developed a fluorescent signal-off assay for thrombin detection.The thrombin-induced signal decrease was due to the shielding of the peroxidase-like activity of bismuth–gold nano-particles by thrombin triggered fibrinogen assemblies.

Wu,Yin and co-workers extended the previous studies to bimetal nanoparticles,i.e.,Au@Pt nanorods.111,116,117,119The

Au@Pt nanorods showed multiple enzyme mimetic capabilities.The oxidase and peroxidase mimetic properties were confirmed by the oxidation of colorimetric substrates OPD and TMB in the absence and presence of hydrogen peroxide,respectively.111The catalase-like activity was confirmed by EPR spectroscopic studies.111An immunoassay for mouse interleukin 2was developed by exploring the Au@Pt nanorods’dual enzyme mimicking activity using a 96-well plate format (Fig.27).Further,they have shown that the Au@Pt nanorods also have ascorbate oxidase-like activities,which was used to eliminate the ascorbate interference towards glucose detection.119

2.4.

3.2AgM (M =Au,Pd and Pt)nanostructures as enzyme mimics.Another study from Wu,Yin and co-workers showed that a series of silver-based bimetallic alloy nanostructures,i.e.,AgM (M =Au,Pd and Pt),were able to oxidize colorimetric substrates to the corresponding products with H 2O 2,displaying peroxidase-like activity.209As expected,ascorbic acid was able to inhibit the oxidation of a substrate (OPD)in the presence of these silver nanozymes due to its natural antioxidant properties.Exploiting this phenomena,a method for determining ascorbic acid concentration was developed using these silver-based bimetallic nanozymes.The method has a linear range from 9to 45m M and a detection limit of 6.7m M.2.5

Carbon-based nanomaterials

Carbon-based nanomaterials,such as fullerene,carbon nano-tubes (CNTs)and graphene,are showing great promise in various applications.278They have also received considerable attention from the nanozyme community due to their ability to mimic the activity of natural enzymes.200,201,213,214,220–222,224,225,229,230,234

2.5.1Fullerene and derivatives as SOD mimics.Since its discovery,fullerene and its derivatives have attracted considerable attention in many research fields.279Early studies have shown that [60]fullerene (i.e.,C 60)could be considered as a radical sponge due to its unique chemical reactivity towards radicals.280However,fullerenes without any modifications are insoluble in water,which makes them unlikely to interact with biomolecules in aqueous solution.The ongoing e?orts in developing water-soluble fullerene derivatives via chemical modification strategies have led to several intriguing discoveries,such as their inter-actions with biomolecules and enzyme-like activities.

54,55,281,282

Fig.25Pt nanocubes as peroxidase mimics and the possible mechanism.Reprinted with permission from ref.227.Copyright (2011)

Elsevier.

Fig.24Pt nanoparticles encapsulated within ferritin as dual enzyme mimics.Reprinted with permission from ref.112.Copyright (2011)Elsevier.

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With的用法全解

With的用法全解 with结构是许多英语复合结构中最常用的一种。学好它对学好复合宾语结构、不定式复合结构、动名词复合结构和独立主格结构均能起很重要的作用。本文就此的构成、特点及用法等作一较全面阐述，以帮助同学们掌握这一重要的语法知识。 一、 with结构的构成 它是由介词with或without+复合结构构成，复合结构作介词with或without的复合宾语，复合宾语中第一部分宾语由名词或代词充当，第二部分补足语由形容词、副词、介词短语、动词不定式或分词充当，分词可以是现在分词，也可以是过去分词。With结构构成方式如下： 1. with或without-名词/代词+形容词； 2. with或without-名词/代词+副词； 3. with或without-名词/代词+介词短语； 4. with或without-名词/代词 +动词不定式； 5. with或without-名词/代词 +分词。 下面分别举例： 1、 She came into the room，with her nose red because of cold.（with+名词+形容词，作伴随状语）

2、 With the meal over ， we all went home.（with+名词+副词，作时间状语） 3、The master was walking up and down with the ruler under his arm。（with+名词+介词短语，作伴随状语。） The teacher entered the classroom with a book in his hand. 4、He lay in the dark empty house，with not a man ，woman or child to say he was kind to me.（with+名词+不定式，作伴随状语）He could not finish it without me to help him.（without+代词 +不定式，作条件状语） 5、She fell asleep with the light burning.（with+名词+现在分词，作伴随状语） Without anything left in the with结构是许多英 语复合结构中最常用的一种。学好它对学好复合宾语结构、不定式复合结构、动名词复合结构和独立主格结构均能起很重要的作用。本文就此的构成、特点及用法等作一较全面阐述，以帮助同学们掌握这一重要的语法知识。 二、with结构的用法 with是介词，其意义颇多，一时难掌握。为帮助大家理清头绪，以教材中的句子为例，进行分类，并配以简单的解释。在句子中with结构多数充当状语，表示行为方式，伴随情况、时间、原因或条件（详见上述例句）。 1.带着，牵着…… (表动作特征)。如： Run with the kite like this.

精神分裂症的病因及发病机理

精神分裂症的病因及发病机理 精神分裂症病因：尚未明，近百年来的研究结果也仅发现一些可能的致病因素。（一）生物学因素1．遗传遗传因素是精神分裂症最可能的一种素质因素。国内家系调查资料表明：精神分裂症患者亲属中的患病率比一般居民高6.2倍，血缘关系愈近，患病率也愈高。双生子研究表明：遗传信息几乎相同的单卵双生子的同病率远较遗传信息不完全相同 的双卵双生子为高，综合近年来11项研究资料：单卵双生子同病率（56.7%），是双卵双生子同病率（12.7%）的4.5倍，是一般人口患难与共病率的35-60倍。说明遗传因素在本病发生中具有重要作用，寄养子研究也证明遗传因素是本症发病的主要因素，而环境因素的重要性较小。以往的研究证明疾病并不按类型进行遗传，目前认为多基因遗传方式的可能性最大，也有人认为是常染色体单基因遗传或多源性遗传。Shields发现病情愈轻，病因愈复杂，愈属多源性遗传。高发家系的前瞻性研究与分子遗传的研究相结合，可能阐明一些问题。国内有报道用人类原癌基因Ha-ras-1为探针，对精神病患者基因组进行限止性片段长度多态性的分析，结果提示11号染色体上可能存在着精神分裂症与双相情感性精神病有关的DNA序列。2．性格特征：约40%患者的病前性格具有孤僻、冷淡、敏感、多疑、富于幻想等特征，即内向

型性格。3．其它：精神分裂症发病与年龄有一定关系，多发生于青壮年，约1/2患者于20～30岁发病。发病年龄与临床类型有关，偏执型发病较晚，有资料提示偏执型平均发病年龄为35岁，其它型为23岁。80年代国内12地区调查资料：女性总患病率（7.07%。）与时点患病率（5.91%。）明显高于男性（4.33%。与3.68%。）。Kretschmer在描述性格与精神分裂症关系时指出：61%患者为瘦长型和运动家型，12.8%为肥胖型，11.3%发育不良型。在躯体疾病或分娩之后发生精神分裂症是很常见的现象，可能是心理性生理性应激的非特异性影响。部分患者在脑外伤后或感染性疾病后发病；有报告在精神分裂症患者的脑脊液中发现病毒性物质；月经期内病情加重等躯体因素都可能是诱发因素，但在精神分裂症发病机理中的价值有待进一步证实。（二）心理社会因素1．环境因素①家庭中父母的性格，言行、举止和教育方式（如放纵、溺爱、过严）等都会影响子女的心身健康或导致个性偏离常态。②家庭成员间的关系及其精神交流的紊乱。③生活不安定、居住拥挤、职业不固定、人际关系不良、噪音干扰、环境污染等均对发病有一定作用。农村精神分裂症发病率明显低于城市。2．心理因素一般认为生活事件可发诱发精神分裂症。诸如失学、失恋、学习紧张、家庭纠纷、夫妻不和、意处事故等均对发病有一定影响，但这些事件的性质均无特殊性。因此，心理因素也仅属诱发因

with用法归纳

with用法归纳 （1）“用……”表示使用工具，手段等。例如： ①We can walk with our legs and feet. 我们用腿脚行走。 ②He writes with a pencil. 他用铅笔写。 （2）“和……在一起”，表示伴随。例如： ①Can you go to a movie with me? 你能和我一起去看电影'>电影吗？ ②He often goes to the library with Jenny. 他常和詹妮一起去图书馆。 （3）“与……”。例如： I’d like to have a talk with you. 我很想和你说句话。 （4）“关于，对于”，表示一种关系或适应范围。例如： What’s wrong with your watch? 你的手表怎么了？ （5）“带有，具有”。例如： ①He’s a tall kid with short hair. 他是个长着一头短发的高个子小孩。 ②They have no money with them. 他们没带钱。 （6）“在……方面”。例如： Kate helps me with my English. 凯特帮我学英语。 （7）“随着，与……同时”。例如： With these words, he left the room. 说完这些话，他离开了房间。 [解题过程] with结构也称为with复合结构。是由with+复合宾语组成。常在句中做状语，表示谓语动作发生的伴随情况、时间、原因、方式等。其构成有下列几种情形： 1.with+名词(或代词)+现在分词 此时，现在分词和前面的名词或代词是逻辑上的主谓关系。 例如:1)With prices going up so fast, we can't afford luxuries. 由于物价上涨很快，我们买不起高档商品。（原因状语） 2)With the crowds cheering, they drove to the palace. 在人群的欢呼声中，他们驱车来到皇宫。（伴随情况） 2.with+名词(或代词)+过去分词 此时，过去分词和前面的名词或代词是逻辑上的动宾关系。

独立主格with用法小全

独立主格篇 独立主格，首先它是一个“格”，而不是一个“句子”。在英语中任何一个句子都要有主谓结构，而在这个结构中，没有真正的主语和谓语动词，但又在逻辑上构成主谓或主表关系。独立主格结构主要用于描绘性文字中，其作用相当于一个状语从句，常用来表示时间、原因、条件、行为方式或伴随情况等。除名词/代词+名词、形容词、副词、非谓语动词及介词短语外，另有with或without短语可做独立主格，其中with可省略而without不可以。*注：独立主格结构一般放在句首，表示原因时还可放在句末；表伴随状况或补充说明时，相当于一个并列句，通常放于句末。 一、独立主格结构： 1. 名词/代词+形容词 He sat in the front row, his mouth half open. Close to the bank I saw deep pools, the water blue like the sky. 靠近岸时，我看见几汪深池塘，池水碧似蓝天。 2. 名词/代词+现在分词 Winter coming, it gets colder and colder. The rain having stopped, he went out for a walk.

The question having been settled, we wound up the meeting. 也可以The question settled, we wound up the meeting. 但含义稍有差异。前者强调了动作的先后。 We redoubled our efforts, each man working like two. 我们加倍努力，一个人干两个人的活。 3. 名词/代词+过去分词 The job finished, we went home. More time given, we should have done the job much better. *当表人体部位的词做逻辑主语时，不及物动词用现在分词，及物动词用过去分词。 He lay there, his teeth set, his hands clenched, his eyes looking straight up. 他躺在那儿，牙关紧闭，双拳紧握，两眼直视上方。 4. 名词/代词+不定式 We shall assemble at ten forty-five, the procession to start moving at precisely eleven. We divided the work, he to clean the windows and I to sweep the floor.

精神分裂症的发病原因是什么

精神分裂症的发病原因是什么 精神分裂症是一种精神病，对于我们的影响是很大的，如果不幸患上就要及时做好治疗，不然后果会很严重，无法进行正常的工作和生活，是一件很尴尬的事情。因此为了避免患上这样的疾病，我们就要做好预防，今天我们就请广州协佳的专家张可斌来介绍一下精神分裂症的发病原因。 精神分裂症是严重影响人们身体健康的一种疾病，这种疾病会让我们整体看起来不正常，会出现胡言乱语的情况，甚至还会出现幻想幻听，可见精神分裂症这种病的危害程度。 (1)精神刺激：人的心理与社会因素密切相关，个人与社会环境不相适应，就产生了精神刺激，精神刺激导致大脑功能紊乱，出现精神障碍。不管是令人愉快的良性刺激，还是使人痛苦的恶性刺激，超过一定的限度都会对人的心理造成影响。 (2)遗传因素：精神病中如精神分裂症、情感性精神障碍，家族中精神病的患病率明显高于一般普通人群，而且血缘关系愈近，发病机会愈高。此外，精神发育迟滞、癫痫性精神障碍的遗传性在发病因素中也占相当的比重。这也是精神病的病因之一。 (3)自身：在同样的环境中，承受同样的精神刺激，那些心理素质差、对精神刺激耐受力低的人易发病。通常情况下，性格内向、心胸狭窄、过分自尊的人，不与人交往、孤僻懒散的人受挫折后容易出现精神异常。 (4)躯体因素：感染、中毒、颅脑外伤、肿瘤、内分泌、代谢及营养障碍等均可导致精神障碍，。但应注意，精神障碍伴有的躯体因素，并不完全与精神症状直接相关，有些是由躯体因素直接引起的，有些则是以躯体因素只作为一种诱因而存在。 孕期感染。如果在怀孕期间，孕妇感染了某种病毒，病毒也传染给了胎儿的话，那么，胎儿出生长大后患上精神分裂症的可能性是极其的大。所以怀孕中的女性朋友要注意卫生，尽量不要接触病毒源。 上述就是关于精神分裂症的发病原因，想必大家都已经知道了吧。患上精神分裂症之后，大家也不必过于伤心，现在我国的医疗水平是足以让大家快速恢复过来的，所以说一定要保持良好的情绪。

with用法小结

with用法小结 一、with表拥有某物 Mary married a man with a lot of money . 马莉嫁给了一个有着很多钱的男人。 I often dream of a big house with a nice garden . 我经常梦想有一个带花园的大房子。 The old man lived with a little dog on the lonely island . 这个老人和一条小狗住在荒岛上。 二、with表用某种工具或手段 I cut the apple with a sharp knife . 我用一把锋利的刀削平果。 Tom drew the picture with a pencil . 汤母用铅笔画画。 三、with表人与人之间的协同关系 make friends with sb talk with sb quarrel with sb struggle with sb fight with sb play with sb work with sb cooperate with sb I have been friends with Tom for ten years since we worked with each other, and I have never quarreled with him . 自从我们一起工作以来，我和汤姆已经是十年的朋友了，我们从没有吵过架。 四、with 表原因或理由 John was in bed with high fever . 约翰因发烧卧床。 He jumped up with joy . 他因高兴跳起来。 Father is often excited with wine . 父亲常因白酒变的兴奋。 五、with 表“带来”，或“带有,具有”，在…身上，在…身边之意

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精神分裂症的病因是什么 精神分裂症是一种精神方面的疾病，青壮年发生的概率高，一般 在16～40岁间，没有正常器官的疾病出现，为一种功能性精神病。 精神分裂症大部分的患者是由于在日常的生活和工作当中受到的压力 过大，而患者没有一个良好的疏导的方式所导致。患者在出现该情况 不仅影响本人的正常社会生活，且对家庭和社会也造成很严重的影响。 精神分裂症常见的致病因素： 1、环境因素：工作环境比如经济水平低低收入人群、无职业的人群中，精神分裂症的患病率明显高于经济水平高的职业人群的患病率。还有实际的生活环境生活中的不如意不开心也会诱发该病。 2、心理因素：生活工作中的不开心不满意，导致情绪上的失控，心里长期受到压抑没有办法和没有正确的途径去发泄，如恋爱失败， 婚姻破裂，学习、工作中不愉快都会成为本病的原因。 3、遗传因素：家族中长辈或者亲属中曾经有过这样的病人，后代会出现精神分裂症的机会比正常人要高。 4、精神影响：人的心里与社会要各个方面都有着不可缺少的联系，对社会环境不适应，自己无法融入到社会中去，自己与社会环境不相

适应，精神和心情就会受到一定的影响，大脑控制着人的精神世界， 有可能促发精神分裂症。 5、身体方面：细菌感染、出现中毒情况、大脑外伤、肿瘤、身体的代谢及营养不良等均可能导致使精神分裂症，身体受到外界环境的 影响受到一定程度的伤害，心里受到打击，无法承受伤害造成的痛苦，可能会出现精神的问题。 对于精神分裂症一定要配合治疗，接受全面正确的治疗，最好的 疗法就是中医疗法加心理疗法。早发现并及时治疗并且科学合理的治疗，不要相信迷信，要去正规的医院接受合理的治疗，接受正确的治 疗按照医生的要求对症下药，配合医生和家人，给病人创造一个良好 的治疗环境，对于该病的康复和痊愈会起到意想不到的效果。

with的用法

with[wIT] prep.1.与…(在)一起，带着：Come with me. 跟我一起来吧。/ I went on holiday with my friend. 我跟我朋友一起去度假。/ Do you want to walk home with me? 你愿意和我一道走回家吗 2.(表带有或拥有)有…的，持有，随身带着：I have no money with me. 我没有带钱。/ He is a man with a hot temper. 他是一个脾气暴躁的人。/ We bought a house with a garden. 我们买了一座带花园的房子。/ China is a very large country with a long history. 中国是一个具有历史悠久的大国。3.(表方式、手段或工具)以，用：He caught the ball with his left hand. 他用左手接球。/ She wrote the letter with a pencil. 她用铅笔写那封信。4.(表材料或内容)以，用：Fill the glass with wine. 把杯子装满酒。/ The road is paved with stones. 这条路用石头铺砌。5.(表状态)在…的情况下，…地：He can read French with ease. 他能轻易地读法文。/ I finished my homework though with difficulty. 虽然有困难，我还是做完了功课。6.(表让步)尽管，虽然：With all his money, he is unhappy. 尽管他有钱，他并不快乐。/ With all his efforts, he lost the match. 虽然尽了全力，他还是输了那场比赛。7.(表条件)若是，如果：With your permission, I’ll go. 如蒙你同意我就去。8.(表原因或理由)因为，由于：He is tired with work. 他工作做累了。/ At the news we all jumped with joy. 听到这消息我们都高兴得跳了起来。9.(表时间)当…的时候，在…之后：With that remark, he left. 他说了那话就离开了。/ With daylight I hurried there to see what had happened. 天一亮我就去那儿看发生了什么事。10. (表同时或随同)与…一起，随着：The girl seemed to be growing prettier with each day. 那女孩好像长得一天比一天漂亮。11.(表伴随或附带情况)同时：I slept with the window open. 我开着窗户睡觉。/ Don’t speak with your mouth full. 不要满嘴巴食物说话。12.赞成，同意：I am with you there. 在那点上我同你意见一致。13.由…照看，交…管理，把…放在某处：I left a message for you with your secretary. 我给你留了个信儿交给你的秘书了。/ The keys are with reception. 钥匙放在接待处。14 (表连同或包含)连用，包含：The meal with wine came to ￡8 each. 那顿饭连酒每人8英镑。/ With preparation and marking a teacher works 12 hours a day. 一位老师连备课带批改作业每天工作12小时。15. (表对象或关系)对，关于，就…而言，对…来说：He is pleased with his new house. 他对他的新房子很满意。/ The teacher was very angry with him. 老师对他很生气。/ It’s the same with us students. 我们学生也是这样。16.(表对立或敌对)跟，以…为对手：The dog was fighting with the cat. 狗在同猫打架。/ He’s always arguing with his brother. 他老是跟他弟弟争论。17.(在祈使句中与副词连用)：Away with him! 带他走！/ Off with your clothes! 脱掉衣服！/ Down with your money! 交出钱来！ 【用法】1.表示方式、手段或工具等时(=以，用)，注意不要受汉语意思的影响而用错搭配，如“用英语”习惯上用in English，而不是with English。2.与某些抽象名词连用时，其作用相当于一个副词：with care=carefully 认真地/ with kindness=kindly 亲切地/ with joy=joyfully 高兴地/ with anger=angrily 生气地/ with sorrow=sorrowfully 悲伤地/ with ease=easily 容易地/ with delight=delightedly 高兴地/ with great fluency =very fluently 很流利地3.表示条件时，根据情况可与虚拟语气连用：With more money I would be able to buy it. 要是钱多一点，我就买得起了。/ With better equipment, we could have finished the job even sooner. 要是设备好些，我们完成这项工作还要快些。4.比较with 和as：两者均可表示“随着”，但前者是介词，后者是连词：He will improve as he grows older. 随着年龄的增长，他会进步的。/ People’s ideas change with the change of the times. 时代变了，人们的观念也会变化。5.介词with和to 均可表示“对”，但各自的搭配不同，注意不要受汉语意思的影响而用错，如在kind, polite, rude, good, married等形容词后通常不接介词with而接to。6.复合结构“with+宾语+宾语补足语”是一个很有用的结构，它在句中主要用作状语，表示伴随、原因、时间、条件、方式等；其中的宾语补足语可以是名词、形容词、副词、现在分词、过去分词、不定式、介词短语等：I went out with the windows open. 我外出时没有关窗户。/ He stood before his teacher with his head down. 他低着头站在老师面前。/ He was lying on the bed with all his clothes on. 他和衣躺在床上。/ He died with his daughter yet a schoolgirl. 他去世时，女儿还是个小学生。/ The old man sat there with a basket beside her. 老人坐在那儿，身边放着一个篮子。/ He fell asleep with the lamp burning. 他没熄灯就睡着了。/ He sat there with his eyes closed. 他闭目坐在那儿。/ I can’t go out with all these clothes to wash. 要洗这些衣服，我无法出去了。这类结构也常用于名词后作定语：The boy with nothing on is her son. 没穿衣服的这个男孩子是她儿子。 （摘自《英语常用词多用途词典》金盾出版社） - 1 -

精神分裂症应该怎么治疗

精神分裂症应该怎么治疗 1、坚持服药治疗 服药治疗是最有效的预防复发措施临床大量统计资料表明，大多数精神分裂症的复发与自行停药有关。坚持维持量服药的病人复发率为40%。而没坚持维持量服药者复发率高达80%。因此，病人和家属要高度重视维持治疗。 2、及时发现复发的先兆，及时处理 精神分裂症的复发是有先兆的，只要及时发现，及时调整药物和剂量，一般都能防止复发，常见的复发先兆为：病人无原因出现睡眠不好、懒散、不愿起床、发呆发愣、情绪不稳、无故发脾气、烦躁易怒、胡思乱想、说话离谱，或病中的想法又露头等。这时就应该及时就医，调整治疗病情波动时的及时处理可免于疾病的复发。 3、坚持定期门诊复查 一定要坚持定期到门诊复查，使医生连续地、动态地了解病情，使病人经常处于精神科医生的医疗监护之下，及时根据病情变化调整药量。通过复查也可使端正人及时得到咨询和心理治疗解除病人在生活、工作和药物治疗中的各种困惑，这对预防精神分裂症的复发也起着重要作用。 4、减少诱发因素 家属及周围人要充分认识到精神分裂症病人病后精神状态的薄弱性，帮助安排好日常的生活、工作、学习。经常与病人谈心，帮助病人正确对待疾病，正确对待现实生活，帮助病人提高心理承受能力，学会对待应激事件的方法，鼓励病人增强信心，指导病人充实生活，使病人在没有心理压力和精神困扰的环境中生活。 首先是性格上的改变，塬本活泼开朗爱玩的人，突然变得沉默寡言，独自发呆，不与人交往，爱干净的人也变的不注意卫生、生活

懒散、纪律松弛、做事注意力不集中，总是和患病之前的性格完全 相悖。 再者就是语言表达异常，在谈话中说一些无关的谈话内容，使人无法理解。连最简单的话语都无法准确称述，与之谈话完全感觉不 到重心。 第三个就是行为的异常，行为怪异让人无法理解，喜欢独处、不适意的追逐异性，不知廉耻，自语自笑、生活懒散、时常发呆、蒙 头大睡、四处乱跑，夜不归宿等。 还有情感上的变化，失去了以往的热情，开始变的冷淡、对亲人不关心、和友人疏远，对周围事情不感兴趣，一点消失都可大动干戈。 最后就是敏感多疑，对任何事情比较敏感，精神分裂症患者，总认为有人针对自己。甚至有时认为有人要害自己，从而不吃不喝。 但是也有的会出现难以入眠、容易被惊醒或睡眠不深，整晚做恶梦或者长睡不醒的现象。这些都有可能是患上了精神分裂症。 1.加强心理护理 心理护理是家庭护理中的重要方面，由于社会上普遍存在对精神病人的歧视和偏见，给病人造成很大的精神压力，常表现为自卑、 抑郁、绝望等，有的病人会因无法承受压力而自杀。家属应多给予 些爱心和理解，满足其心理需求，尽力消除病人的悲观情绪。病人 生活在家庭中，与亲人朝夕相处，接触密切，家属便于对病人的情感、行为进行细致的观察，病人的思想活动也易于向家属暴露。家 属应掌握适当的心理护理方法，随时对病人进行启发与帮助，启发 病人对病态的认识，帮助他们树立自信，以积极的心态好地回归社会。 2.重视服药的依从性 精神分裂症病人家庭护理的关键就在于要让病人按时按量吃药维持治疗。如果不按时服药，精神病尤其是精神分裂症的复发率很高。精神病人在医院经过一系统的治疗痊愈后，一般需要维持2~3年的

(完整版)with的复合结构用法及练习

with复合结构 一. with复合结构的常见形式 1.“with+名词/代词+介词短语”。 The man was walking on the street, with a book under his arm. 那人在街上走着，腋下夹着一本书。 2. “with+名词/代词+形容词”。 With the weather so close and stuffy, ten to one it’ll rain presently. 天气这么闷热，十之八九要下雨。 3. “with+名词/代词+副词”。 The square looks more beautiful than even with all the light on. 所有的灯亮起来，广场看起来更美。 4. “with+名词/代词+名词”。 He left home, with his wife a hopeless soul. 他走了，妻子十分伤心。 5. “with+名词/代词+done”。此结构过去分词和宾语是被动关系，表示动作已经完成。 With this problem solved, neomycin 1 is now in regular production. 随着这个问题的解决，新霉素一号现在已经正式产生。 6. “with+名词/代词+-ing分词”。此结构强调名词是-ing分词的动作的发出者或某动作、状态正在进行。 He felt more uneasy with the whole class staring at him. 全班同学看着他，他感到更不自然了。 7. “with+宾语+to do”。此结构中，不定式和宾语是被动关系，表示尚未发生的动作。 So in the afternoon, with nothing to do, I went on a round of the bookshops. 由于下午无事可做，我就去书店转了转。 二. with复合结构的句法功能 1. with 复合结构，在句中表状态或说明背景情况，常做伴随、方式、原因、条件等状语。With machinery to do all the work, they will soon have got in the crops. 由于所有的工作都是由机器进行，他们将很快收完庄稼。（原因状语） The boy always sleeps with his head on the arm. 这个孩子总是头枕着胳膊睡觉。（伴随状语）The soldier had him stand with his back to his father. 士兵要他背对着他父亲站着。（方式状语）With spring coming on, trees turn green. 春天到了，树变绿了。（时间状语） 2. with 复合结构可以作定语 Anyone with its eyes in his head can see it’s exactly like a rope. 任何一个头上长着眼睛的人都能看出它完全像一条绳子。 【高考链接】 1. ___two exams to worry about, I have to work really hard this weekend.（04北京） A. With B. Besides C. As for D. Because of 【解析】A。“with+宾语+不定式”作状语，表示原因。 2. It was a pity that the great writer died, ______his works unfinished. (04福建) A. for B. with C. from D.of 【解析】B。“with+宾语+过去分词”在句中作状语，表示状态。 3._____production up by 60%, the company has had another excellent year. (NMET) A. As B.For C. With D.Through 【解析】C。“with+宾语+副词”在句中作状语，表示程度。

精神分裂症患者在怎样的情况下会自杀

精神分裂症患者在怎样的情况下会自杀 精神分裂症是最常见的一种精神病。早期主要表现为性格改变，如不理采亲人、不讲卫生、对镜子独笑等。病情进一步发展，即表现为思维紊乱，病人的思考过程缺乏逻辑性和连贯性，言语零乱、词不达意。精神分裂症患者随时有可能出现危险行为，这主要是指伤人毁物、自伤自杀和忽然出走。这些危险行为是受特定的精神症状支配的.那么精神分裂症患者在什么情况下会自杀呢？ 被害妄想：这是所有精神病人最常见的症状之一，多数病人采取忍耐、逃避的态度，少数病人也会“先下手为强”，对他的“假想敌”主动攻击。对此，最重要的是弄清病人的妄想对象，即：病人以为是谁要害他。假如病人的妄想对象是某个家里人，则应尽量让这位家属阔别病人，至少不要让他与病人单独在一起。 抑郁情绪：精神分裂症病人在疾病的不同时期，可能出现情绪低落，甚至悲观厌世。特别需要留意的是，有相当一部分自杀成功的病人，是在疾病的恢复期实施自杀行为的。病人在精神病症状消除以后，因自己的病背上了沉重的思想包袱，不能正确对待升学、就业、婚姻等现实问题，感到走投无路，因此选择了轻生。对此，家属一定要防患于未然，要尽早发现病人的心理困扰，及时疏导。 对已经明确表示出自杀观念的病人，家属既不要惊慌失措，也不要躲躲闪闪，要主动与病人讨论自杀的利弊，帮助病人全面、客观地评估现实中碰到的各种困难，找出切实可行的解决办法。 另外，这种病人在自杀之前，是经过周密考虑，并且做了充分预备的，例如写遗书、收拾旧物、向家人离别、选择自杀时间、预备自杀工具等。这类病人的自杀方式也是比较温顺的，多数是服药自杀。因此，他需要一定的时间来积攒足足数目的药物，这时就能看出由家属保管药品的重要性了。只要家属密切观察病人的情绪变化，是不难早期发现病人的自杀企图的。 药源性焦虑：抗精神病药的副作用之一是可能引起病人莫名的焦躁不安、手足无措，并伴有心慌、出汗、恐惧等。这些表现多是发作性的，多数发生在下午到傍晚时分，也有的病人在打长效针以后的2?3天内出现上述表现。这种时间上的规律性，有助于家属判定病人的焦虑情绪是否由于药物所致。病人急于摆脱这种强烈的痛苦，会出现冲动伤人或自伤，这些行为只是为了发泄和解脱，并不以死为终极目的。家属可以在病人发作时，给他服用小剂量的安定类药物，或者在医生的指导下，调整抗精神病药的剂量或品种，这样就可以有效地控制病人的焦虑发作。 极度兴奋：病人的精神症状表现为严重的思维紊乱、言语杂乱无章、行为缺乏目的性，这类病人也可能出现自伤或伤人毁物。由于病人的兴奋躁动是持续性的，家属有充分的思想预备，一般比较轻易防范。家属要保管好家里的刀、剪、火、煤气等危险物品，但最根本的办法，是使用大剂量的、具有强烈镇静作用的药物来控制病人的兴奋。假如在家里护理病人确有困难，则可以强制病人住院治

我的精神分裂症形成和发展史

出生前背景 母亲是地道、淳朴、专一，文化程度不高的农村主妇，父亲是当地的混混，好色成性，道德观念淡薄，无责任感，为非作歹，攻击性强，专横，常聚众斗殴，浪荡无比。他的放荡从和母亲接姻前持续到今。从母亲断断断断续的回忆中我恍知我没呱呱落地前就已有不寻常的经历，失职的母亲怀着我和父亲怄气经常绝食威胁，奢望唤醒父亲的为父为夫的责任感。可怜的女人，痴痴的等待，身心俱损终换不来一时的真爱。他从不掩饰自己的劣迹，而是将其当作显示自己无限魅力和能耐的招牌加以渲染，毫无顾忌在当众谈论。 童年背景 除父母，还有两兄，我是幼女，相比较受宠爱。 爷爷 奶奶，传统的封建妇女，极重男轻女，从未给过我好脸色。爷爷、奶奶在家中居从属地位，对我没产生至关重要的影响。 儿时家里很穷，主要靠母亲支撑维系家族。她非常辛苦，在纺织厂，三班制。歇工还要步行到七八公里外的田地里劳作。很难照顾到我们的感受，她所能做的就是竭尽所能维系家庭的完整，让我们能生存下去。与此同时，她还要忍受父亲周而复始的背叛，虐待、暴打。生活不如意加之贫困无比，让她难免脾气暴躁，我是她时常爆发时的接纳对象。如此妇女，受封建思想灌输至深，永远铭记自己要恪守妇道，她始终如一的忠诚与父亲，永不离弃他，爱护他，疼爱他（她比父亲年长些，父亲相貌俊秀，而母亲姿色平平）。我可怜而鄙视她，丈夫如果某天一改往日作贱她的口吻，她会像孩子似的受宠若惊的心花怒放。 父亲霸道无比，家里人人惧怕他，他无比自恋。除了母亲，伤害最深的是大哥，每天无缘无故的遭受父亲的暴打。他性情多变，无法揣摩，吃饭时一家人欢声笑语，吃完饭看看大哥不顺眼他操起皮鞭就抽。看到大哥在皮鞭下嚎哭，新的皮鞭疤痕烙在旧疤痕上，我和二哥感到恐惧，怜悯大哥，然而我们是无助的，谁也不能阻挡皮鞭的落下。尽管如此，父亲当时在我心目中是高大的，令人崇拜的，对我产生的正负影响也是最强烈的。他多才多艺，知识渊博，开明，前卫，聪明，而母亲相比之下平庸很多，她每天只是起早贪黑的工作，思想保守，愚昧，无任何才华而言。 童年，虽说不是幸福的，但也算不上痛苦。 童年转青春期阶段 邻居是一个恶老太婆，和当时大多传统村妇一样，没知识、没修养也没教养。她确实很恶，不允许她看不顺眼的小孩从她家旁边的小巷经过，她不喜欢我。每次我冒险经过她都会如同恶狗样在我刚出现在她视野中就开始狂吠，连同我的老祖宗也一起骂，持续到我再次从原路返回，躲到家里，她的吠声还要延续十分钟。 被爱妄想出现在五年级，应该更早些。我喜欢上一个家境优越的的男生，尽管那时他已经有“女朋友”。从爱上他那刻起我就很明确他也是爱我的，他和同桌说话其实余光是在看我，尽管没有任何证实，我非常明确他就是偷偷看我的。即使在上课，即使他没有和同桌说话，我感觉他在狠狠的想着我。他回答老师的提问也暗示着对我的爱意。比如他的回答里有“她”，那就是暗示他说的是我。或是我读书看到书上的“他”字样，心便狂喜的乱跳，认为这是我暗恋对象给我的暗示，他一直在我身边！ 妄想形成初期就有泛化倾向，我似乎对自己相貌无限自信，觉得自己是最美的，一上街满街的男孩都为我的美貌所折服，他们都不由自主的盯着我看，我的一举一动都被他们密切关注着，一出门便有那么多双眼睛注视着我。

with用法

with结构是许多英语复合结构中最常用的一种。学好它对学好复合宾语结构、不定式复合结构、动名词复合结构和独立主格结构均能起很重要的作用。本文就此的构成、特点及用法等作一较全面阐述，以帮助同学们掌握这一重要的语法知识。 一、with结构的构成 它是由介词with或without+复合结构构成，复合结构作介词with或without的复合宾语，复合宾语中第一部分宾语由名词或代词充当，第二部分补足语由形容词、副词、介词短语、动词不定式或分词充当，分词可以是现在分词，也可以是过去分词。With结构构成方式如下： 1. with或without-名词/代词+形容词； 2. with或without-名词/代词+副词； 3. with或without-名词/代词+介词短语； 4. with或without-名词/代词+动词不定式； 5. with或without-名词/代词+分词。 下面分别举例： 1、She came into the room，with her nose red because of cold.（with+名词+形容词，作伴随状语） 2、With the meal over ，we all went home.（with+名词+副词，作时间状语） 3、The master was walking up and down with the ruler under his arm。（with+名词+介词短语，作伴随状语。）The teacher entered the classroom with a book in his hand. 4、He lay in the dark empty house，with not a man ，woman or child to say he was kind to me.（with+名词+不定式，作伴随状语）He could not finish it without me to help him.（without+代词+不定式，作条件状语） 5、She fell asleep with the light burning.（with+名词+现在分词，作伴随状语） 6、Without anything left in the cupboard，she went out to get something to eat.（without+代词+过去分词，作为原因状语） 二、with结构的用法 在句子中with结构多数充当状语，表示行为方式，伴随情况、时间、原因或条件（详见上述例句）。

引起精神分裂症的诱因有哪些

引起精神分裂症的诱因有哪些 精神分裂症作为一种高发疾病，给患者的健康带来了极大的危害，也让患者的家庭遭受着痛苦的折磨。精神分裂症虽然是一种精神类疾病，但是它给患者带来的创伤绝不亚于身体上的伤害。多了解一些有关精神分裂症疾病方面的知识，对于我们预防和治疗这种疾病，都有积极的意义。下面，请专家来为大家简单介绍一下，精神分裂症这种疾病发病诱因到底是什么： 精神分裂症诱因一：心理方面的因素。 人的心理方面的抵抗力如同自身的免疫系统，是一道天然的保护屏障。如果心理承受能力低下，当我们遭遇重大变故或者精神刺激的时候，就会发生严重的心理质变和扭曲，导致颓废、悲伤、痛苦，严重者就可能发生精神分裂症。 其实，影响心理承受能力的根本原因，还是在个人的性格方面。 精神分裂症诱因二：自身免疫系统的功能状况。 自身免疫系统就如同是一道坚固的堡垒，时刻抵御着外界的侵扰和威胁，保护着我们自身的身体健康。免疫力低下的人，很容易因外界环境因素的影响而发生器质性病变，比如有毒物质伤害神经递质，从而间接引发精神分裂症。因此，在生活和工作中，我们应当注意远离有毒物质和有污染的环境。 精神分裂症诱因三：社会因素。 人是一种社会性动物，在社会这个大的环境下生存和成长。因此，不可避免地影响着他人和被他人影响着。我们在成长中经历的各种重大事件，都会对自身的心理发生着潜移默化的影响。一个人若是长期处于悲观失望、极度痛苦的负面情绪中，就有可能在精神方面受到强烈的刺激，严重者就可能发生精神分裂症。 精神分裂症诱因四：遗传因素。 遗传因素也是导致精神分裂症的一个重要原因。有临床研究表明，精神分裂症患者中，有家族精神病史的患者占据着一个很大的比例。而且，精神分裂症的发病年龄段正在呈现逐渐年轻化的趋势。 总的来说，精神分裂症的发病原因非常复杂，这里仅仅例举了其中四个主要的原因。科学无止境，在精神分裂症的诱发原因方面，我们不了解的而还有很多，还有许多需要不断地去研究和探求的知识。但是，随着科学的而不断发展和进步，相信人类将来一定能克服这种精神疾病，迎来一个健康的精神面貌。

【初中英语】with的用法

【With的基本用法与独立主格】 with结构是许多英语复合结构中最常用的一种。学好它对学好复合宾语结构、不定式复合结构、动名词复合结构和独立主格结构均能起很重要的作用。 一、with结构的构成 它是由介词with或without+复合结构构成，复合结构作介词with或without的复合宾语，复合宾语中第一部分宾语由名词或代词充当，第二部分补足语由形容词、副词、介词短语、动词不定式或分词充当，分词可以是现在分词，也可以是过去分词。With结构构成方式如下： 1. with或without-名词/代词+形容词； 2. with或without-名词/代词+副词； 3. with或without-名词/代词+介词短语； 4. with或without-名词/代词+动词不定式； 5. with或without-名词/代词+分词。 下面分别举例： 1、She came into the room，with her nose red because of cold.（with+名词+形容词，作伴随状语） 2、With the meal over, we all went home.（with+名词+副词，作时间状语） 3、The master was walking up and down with the ruler under his arm。（with+名词+介词短语，作伴随状语。） 4、He could not finish it without me to help him.（without+代词+不定式，作条件状语） 5、She fell asleep with the light on.（with+名词+现在分词，作伴随状语） 二、with结构的用法 with是介词，其意义颇多，一时难掌握。为帮助大家理清头绪，以教材中的句子为例，进行分类，并配以简单的解释。在句子中with结构多数充当状语，表示行为方式，伴随情况、时间、原因或条件（详见上述例句）。 1. 带着，牵着……(表动作特征)。如： Run with the kite like this. 2. 附加、附带着……(表事物特征)。如： A glass of apple juice, two glasses of coke, two hamburgers with potato chips, rice and fish. 3. 和……(某人)一起。 a. 跟某人一起(居住、吃、喝、玩、交谈……) 。如： Now I am in China with my parents. Sometimes we go out to eat with our friends. He / She's talking with a friend. b. 跟go, come 连用，有"加入"到某方的意思。如： Do you want to come with me? 4. 和play一起构成短语动词play with 意为"玩耍……，玩弄……" 如： Two boys are playing with their yo-yos. 5. 与help 一起构成help...with...句式，意为"帮助(某人) 做(某事)"。如： On Monday and Wednesday, he helps his friends with their English. 6. 表示面部神情，有“含着……，带着……”如： "I'm late for school," said Sun Y ang, with tears in his eyes. 7. 表示"用……" 如：