Point-of-care Testing Of Ag⁺ And Cu²⁺ Ions Based On The Carbon-based Nanozymes

In these years,nanozymes have attracted extensive attention and exploration because of their good catalytic activity,low cost,high stability and easy modification.Nanozymes are widely used in the fields of biosensing,health care and environmental analysis because of their easy modification,high stability and multi-enzyme properties.In particular,in the field of analytical sensing,nano-enzymes can form sensing systems with different organic reagents and carry out sensor analysis by reading different signals of different target analytes,which provides a new opportunity for the development of convenient point-of-care testing（POCT）methods.POCT,according to the definition of POCT Equipment Technology Professional Committee of Chinese Medical Equipment Association,is a method of detection carried out at the sampling site and using portable analytical instruments and supporting reagents to quickly obtain test results.However,nanozymes still have low catalytic activity compared with natural enzymes,so it is necessary to modify and regulate nanozymes to improve their catalytic activity,so as to expand their application in POCT.In this paper,two POCT sensing platforms based on signal conversion strategy are designed and successfully applied to the analysis and sensing of heavy metals in the environment.This paper is divided into the following four parts:1.The definition,classification,material preparation and application of nano-enzymes are introduced,and the application of different signal readout methods in POCT field is summarized in detail.2.A nitrogen and sulfur-doped graphene quantum dots decorated platinum nanocluster（N,S-GQDs@Pt NCs）has been synthesized,and a POCT colorimetric sensing platform closed to silver ion（Ag⁺）signals has been developed based on its nanoenzyme properties.N,S-GQDs@Pt NCs was synthesized for the first time using AA as reducing agent N and S-GQDs as stabilizing agent and morphology guide agent.In the presence of H₂O₂,the color developing substrate 3,3’,5,5’-tetramethylbenzidine（TMB）was oxidized to the oxidation state TMB(_OXTMB),which turned the solution blue.In the presence of target Ag⁺,Ag⁺was reduced to Ag⁰ by capped N,S-GQDs and deposited on the surface of Pt NCs,thus significantly inhibiting the peroxidase activity of N,S-GQDs@Pt NCs.Ag-Pt interaction is more selective to Ag⁺than other ions.Ag+can interact with N,S-GQDs to promote electron transfer and speed up the reaction rate.The oxidation product of TMB has the maximum absorption peak at 652nm,which can be used as the detection signal.On this basis,a colorimetric vision Ag⁺sensor with detection range of 0.5-300 n M and detection limit of 0.2 n M was developed by using the colorimetric system of TMB and H₂O₂ catalyzed by N and S-GQDs@Pt NCs,which showed its potential application value in the Ag₊sensing analysis of actual water samples.3.A simple and fast nitrogen doped carbon point（N-CDs）photocatalytic sensor was developed for the visual detection of Cu²⁺.N-CDs can produce singlet oxygen（¹O₂）under ultraviolet light due to electron hole effect,and can oxidize TMB in the solution where TMB exists,making the solution turn blue.In the presence of Cu²⁺,the reduction reaction with N-CDs occurs and Cu²⁺adheres to the surface of N-CDs,thus inhibiting its photocatalytic activity.The solution will fade to varying degrees depending on the concentration of Cu²⁺.The Cu²⁺sensing platform can be effectively established through the change of solution color and the absorbance at 652 nm by ultraviolet spectrophotometer.It is calculated that the detection range is 0.5-300 n M and the detection limit of the sensor platform is 15 n M.This method not only has good selectivity,but also can complete the color change within 1 minute,which greatly reduces the reaction time,showing a good potential application for the POCT sensing of Cu²⁺in water environment.4.The advantages and practicability of POCT sensing platform for Ag⁺ion and Cu²⁺ ion detection based on nano-enzymes proposed in this paper are summarized,and the future POCT sensing of heavy metal ions by nano-enzymes is prospected.