Colorimetric And Photothermal Sensing Based On Modulation Of Noble-based Nanozymes Catalytic Activity

Nanozymes are a type of nanomaterials with enzyme-like catalytic functions,which have attracted extensive attention in many fields,including biosensor,environmental monitoring,disease diagnosis,and so on,due to their low cost,good environmental stability,easy mass production,and tunable activity.However,the catalytic activity of most nanozymes is lower compared to the natural enzymes.It is therefore crucial for the construction of nanozymes with controllable activity through the design of a precise and simple regulation strategy.On the other hand,the signal readout in most nanozymes sensing assays ususally is limited due to by the color change,which greatly limits the accuracy of analysis results.Therefore,it is important to develop new modulation strategy of nanozymes activity,and effectively combine it with the novel signal readout to meet the current requirements and address the limitations of color signals.Focusing on this,we developed some strategies to modulate the nanozymes activity by using ions and small molecules-mediated process in this thesis,and established the corresponding colorimetric and photothermometric sensing methods for heavy metal ions and biological enzymes analysis.This thesis is divided into the following four parts:Chapter 1:Introduce the types of nanozymes,activity modulation strategies,and provide a detailed review of the applications of nanozymes in colorimetric and photothermometric sensing fields.Chapter 2:We have achieved the enhancement of chitosan-coated gold nanoparticles（CS@AuNPs）peroxidase-like（POX-like）activity by modulating the surface chemistry of CS@AuNPs by using Hg²⁺and therefore successfully applied it to the detection of Hg²⁺under the neutral conditions.It was based on the fact that CS@AuNPs had low POX-like activity under neutral conditions and could hardly oxidize the enzyme substrate3,3′,5,5′-tetramethylbenzidine（TMB）.But Hg²⁺could effectively activate the POX-like activity of CS@AuNPs under neutral conditions and significantly enhance the CS@AuNPs nanozyme’s activity.As a result,TMB could be oxidized to its oxidation product of TMBox with sensitive color change and good photothermal effect.Based on this principle,we constructed a simple and sensitive platform for colorimetric and photothermometric sensing Hg²⁺.This proposed strategy breaks the p H limitation of the catalytic activity of nanozyme and provides a useful exploration for the application of nanozyme in bioanalysis.Chapter 3:We develpoed a colorimetric and photothermometric method for the detection of acetylcholinesterase（AChE）by using the inhibition effect of catalytic activity of Au@PtNPs nanozymes.Au@PtNPs as a nanozyme with oxidase-like feature can directly oxidize TMB to TMBox with the participation of dissolved oxygen.And AChE can specifically hydrolyze acetylcholine（ATCh）to release TCh,the generated TCh can significantly induce the aggregation of Au@PtNPs nanozymes and resultantly inhibit their catalytic activity.As a result,an indirectly inhibition on the TMBox production could be observed.Based on this,a simple sensing method for the detection of AChE was constructed by using the color and temperature changes of TMBox as the signal readout.The detection limits for AChE by colorimetric and photothermal methods were 0.04m U/m L and 0.05 m U/m L,respectively.Chapter 4:The advantages and application progress of the noble metal nanozymes-based colorimetric and photothermal sensing based on the activity modulation strategy in this paper are summarized.The future perspective and fabrication of point-of-care testing（POCT）methods based on simple nanozymes and new signal readout are prospected.