Point-of-care Testing Based On MnO₂ Nanosheets

Point-of-care testing(POCT)is an analytical testing method that is performed at the sampling site and uses portable instruments to quickly obtain test results.With the advantages of rapid,simple,portable and low cost,it has been widely used in various fields such as food,environment and medical.Compared with the traditional testing method of laboratory precision instruments,POCT is not restricted by time,place and professional operators,and can obtain accurate experimental results quickly in the field.Therefore,it greatly meets the practical testing needs of clinical treatment,home monitoring,and health management,and is especially suitable for environments with limited resources.Two-dimensional(2D)nanomaterials have attracted widespread attention from researchers for their excellent physicochemical properties and broad application prospects,and have a wide range of applications in catalysis,energy,sensing,bioimaging,antibacterial,and therapeutic fields.Among them,two-dimensional nanoenzyme materials often have layered nanostructures with higher chemical and thermal stability than natural enzymes,and thus are more suitable for the construction of new POCT methods with excellent sensing properties,which have potential utilization in the fields of environmental analysis,food safety,and medical diagnosis.Therefore,in this thesis,a POCT sensing strategy based on simple signal readout such as pressure,color and temperature was designed as a starting point for constructing simple signal readout and successfully applied to the sensing analysis of disease-related biological enzymes.This thesis is divided into four parts as follows.The first chapter mainly introduces the concept,characteristics,classification and development trend of POCT.The introduction and properties of 2D nanomaterials and POCT sensing strategies based on 2D nanomaterials are reviewed in detail.The second chapter started with the construction of simple,economical and sensitive signal readout,an effective integration of the two redox reaction process was proposed to construct a manometric sensing platform for acetylcholinesterase(ACh E)activity detection,only using a common pressure meter as the reader.The sensing mechanism is based on the two redox reaction processes,one is the MnO₂nanosheets-catalyzed H₂C₂O₄to CO₂generation along with a significant pressure increase,and another is the thiocholine(TCh)-mediated decomposition of MnO₂nanosheets that accompanied by the inhibition on the increased pressure change of the reaction system in a closed vessel.In this reaction system,TCh was in-situ produced through a specific hydrolysis of acetylcholine(ATCh)by the target ACh E.Based on this,we successfully constructed a gas pressure serve as the powerful signal readout assay for ACh E activity with the limit of detection(LOD)of 0.478 m U/m L.It therefore as a simple,low cost and user friendliness POCT analysis method,will open a new horizon for pressure readout based biosensor in future.The third chapter started with the oxidase-like activity of MnO₂nanosheets,a novel colorimetric and photothermal sensing platform was successfully constructed for detection of?-galactosidase(?-gal)activity.MnO₂nanosheets can directly catalyze the oxidation of the colorless substrate 3,3',5,5'-tetramethylbenzidine(TMB)into oxidized TMB(TMBox),In the presence of?-gal,the substrate p-aminophenyl?-D-galactopyranoside(PAPD)is hydrolyzed to produce p-aminophenol(PAP).Reduction of TMBox by PAP generates colorless TMB.Therefore,with the unique color change of TMBox and the system temperature change caused by photothermal effect as signal readout,the colorimetric method based on color signal readout and the analysis method based on temperature signal readout of photothermal sensing target?-gal can be developed.Among them,the detection limit of?-gal by colorimetric method is 0.16 U/L;the detection limit of photothermal method is 0.07 U/L.In addition,this study uses the thermometer commonly used in daily life as the signal readout device,which not only solves the problem of low color resolution of the colorimetric sensor,but also is more suitable for real-time detection in clinical diagnosis.Chapter four summarized the advantages of POCT sensing strategies based on simple signal readout such as pressure,color and temperature,and the prospect of the construction and development of POCT sensing strategy based on two-dimensional nanomaterials as sensing substrates in the future is presented.