The Construction And Application Of Colorimetric Sensors System Based On Nanozyme

Colorimetric sensing has a widely practical application due to its low cost,practicality and simplicity.It dose not require expensive or complex instruments because the color changes can be readout by naked eyes.It can be used in field analysis and point-of-care diagnosis.The key challenge for colorimetric biosensing is transforming the detection events into apparent color changes.To set up a colorimetric sensing system,enzyme catalytic chromogenic substrate is a sensible choice due to its simple reaction conditions and high catalysis efficiency.However,a most of nature enzyme are protein,the structure is easy to change and loss the catalytic activity under the harsh conditions(heated,alkali,acid,etc.).In addition,low levels of natural enzyme exist in biological organism,which result in difficult extraction and purification,high cost,and complicated operation.Thesefore,the practical application of colorimetric sensing system based on natural enzyme was restricted.In order to improve the stability of the natural emzyme and reduce the cost,in recent years,researchers have been trying to fabricate various colorimetric sensor systems with nanomaterials-based natural enzyme mimetics.Compared to natural enzyme,nanozymes have several advantages,such as low cost,east of preparation and purification,good stability.However,material types and applications of developed nanozymes are still limited.Therefore,to develop more nanozymes with high catalysis activity and application to colorimetric sensing is still significant.In this thesis,we design and prepare several nanozymes with oxidase and/or horseradish peroxidase mimetics activity.Meanwhile,we construct nanozymes-based colorimetric sensor systems and use for detection of small molecular species.The main contents are as follows:1.MnO2,which was prepared using a simple redox reaction,was demonstrated that it exhibits intrinsic oxidase-like activity.The MnO2 nanorods can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine(TMB)into a blue colored cation radical without the requirement for additional oxidizing agents.Glutathione(GSH)could successfully hinder the cation radical production and restore them to colourless TMB molecules.Hg2+ had a strong affinity to thiolated compounds.If GSH and Hg2+ were pre-incubated,the solution would be recovered to blue colored solution in the presence of MnO2 nanorods.Based on this phenomenon,a simple and rapid colorimetric path for the sensing of Hg2+ was developed.A good linear relationship could be obtained from 0.1 to 8.0 ?mol/L(R2=0.996).The limit of detection was estimated to be 0.08 ?mol/L.2.CoS,which was prepared using a facile solvothermal method,was demonstrated for the first time to exhibit intrinsic peroxidase-like activity.CoS catalyzed the oxidation of the peroxidase substrate TMB in the presence of H2O2 rendering the reaction solution blue,which is the principle used for H2O2 sensing.The mechanism of the CoS catalysis was also investigated.Under optimal conditions,the linearity of H2O2 detection ranged from 0.05 to 0.8 mmol/L(R2=0.9965).More importantly,using the reducibility of glutathione(GSH)and the strong affinity to thiol compounds exhibited by mercury ions(Hg22),a novel "off-on"colorimetric sensor for Hg2+ determination was designed using CoS as a peroxidase mimics.The analytical platform for ri2+determination was developed,ranging from 0.25 to 3 mmol/L(R2=0.9965).The limit of detection was 0.1 mmol/L.3.A simple hydrothermal method was proposed for the preparation of CeVO4.The as-synthesized CeVO4 was,for the first time,demonstrated to exhibit both peroxidase-like and oxidase-like activity.Moreover,the mechanism of its dual-enzyme activity was investigated in detail.Interestingly,hydroquinone(H2Q),dihydroxybenzene isomer,undergoes reduction accompanying the oxidation of TMB by the CeV04 oxidase mimic along with a visible color change,while the other two dihydroxybenzene isomers,i.e.,resorcinol(RC)and catechol(CC),do not.Based on these findings,a colorimetric platform was developed to discriminate H2Q from RC and CC.Under optimal conditions,a linear relationship between the H2Q concentration and absorbance was observed from 0.05 to 8 umol/L,and a limit of detection of 0.04 pmol/L was achieved.Moreover,this colorimetric platform can selectively reveal H2Q concentrations in the presence of other dihydroxybenzene isomers.4.Bimetallic metal-organic framework MOF(Co/2Fe),which was successfully synthesized using a simple hydrothermal method,has been demonstrated to exhibit peroxidase-like activity and oxidase-like activity for the first time.With dual enzyme mimetic activities,MOF(Co/2Fe)not only has the advantages of low cost,good stabilization,and ease of preparation,but also maintains Michaelis-Menten behavior.In addition,the catalytic mechanisms and catalytic kinetics of the dual enzyme activities were studied in detail.A simple colorimetric method for H2O2 determination was developed based on the peroxidase-like activity of MOF(Co/2Fe).Under the optimal conditions,a good linear relationship was obtained from 10 to 100 ?mol/L H2O2 with a limit of detection of 5 ?mol/L.