Study On Photoelectronchemical Response And Application For L-cysteine And Coenzyme Aat CdSe/ZnO Electrode

L-Cysteine(L-Cys),a natural amino acid,it has been widely used in medicine,food additives and cosmetics.L-Cys can alleviate and repair the radiation damage to body,and has the general effect in the detoxification.Among the amino acids that compose the protein,L-Cys is the only amino acid with reducing activity and has a high reactivity,and plays a very important role in the structure and function of the protein.Coenzyme A is a kind of coenzyme containing pantothenic acid,which is synthesized by pantothenic acid,L-Cys and adenosine triphosphate in the cell.It can promote the metabolism of substances and the energy supply in the body.Both L-Cys and Coenzyme A are compounds containing mercapto(-SH),which can be used as electron donor to produce the electron transfer reaction,and can restrain the recombination of photogenerated electron-hole pairs of photosensitive semiconductor nanomaterials,resulting in photoelectric effect.In this paper,nano-CdSe/ZnO electrode was prepared,make it with L-Cys or Coenzyme A to form photoelectrochemical(PEC)system by utilizing its photosensitivity and property as electron acceptor,developing the PEC method for the determination of L-Cys,Coenzyme A and Papain.The main work is as follows:1.The ZnO nanorods were prepared on the surface of ITO electrode by using electrodeposition.The CdSe QDs were prepared by hydrothermal method.CdSe QDs were modified onto the surface of ZnO nanorods by layer self-assembly technique,to fabricate CdSe/ZnO electrode on the basis of optimized preparation conditions.The modification process and result of the electrode were characterized by scanning electron microscopy(SEM),transmission electron microscopy(TEM),electrochemical impedance spectroscopy(EIS)and X-ray diffraction(XRD).2.To CdSe/ZnO electrode as the photoelectronchemically sensitive interface,the quantitative analysis of L-Cys was achieved through detecting the photocurrent based on PEC response of L-Cys at the electrode.In the paper,the response mechanism of PEC sensitive interface with L-Cys was discussed.The effects of p H and bias on detecting L-Cys were investigated,and experimental conditions were optimized.The reproducibility,stability and anti-interference of the method were investigated.Under the optimized experimental conditions,the photocurrent intensity increases with the increase of the concentration of the matrix,and is proportional to the concentration of L-Cys in the concentration range of 0.01 ~ 20.0 ?mol/L.The linear equation is?I(n A)= 72.66 + 65.32C(?mol/L)with the correlation coefficient of 0.998.The detection limit was estimated to be 0.5 nmol/L(S/N = 3),and the detection sensitivity was 65.3 n A/(?mol?L-1).The method was applied to the determination of acetyl L-Cysteine,the relative standard deviation(RSD)and the recovery were 2.32% and99.3%~104%respectively,and other amino acids did not interfere with the determination.3.Using the PEC system composed of CdSe/ZnO electrode and the electron donor Coenzyme A,The detection of Coenzyme A was achieved through detecting the photocurrent generated by PEC reaction between the CdSe/ZnO electrode and Coenzyme A.Under the optimized conditions of bias voltage 0 V,electrolyte p H of9.5,the photocurrent intensity has a good logarithmic response to Coenzyme A in the concentration range of 0.01 ~ 50.0 ?mol/L,The correlation coefficient was 0.992 and the detection limit was estimated to be 1.0 nmol/L(S/N = 3).The results for the determination of Coenzyme A injection showed that RSD and the recovery were2.13% and 99.1% ~ 105% respectively,and other coenzymes did not interfere with the determination.4.Based on the property of Papain as thiol protease and CdSe/ZnO electrode-L-Cys PEC reaction system,the PEC analysis of Papain was established through the direct electron transfer between Papain and CdSe/ZnO electrode by utilizing the sodium alginate to transfer charge.After optimizing the concentration of sodium alginate and the electrolyte p H,the photocurrent intensity is logarithmically proportional to the concentration of Papain in the range of 120 ~ 2400U/m L,with correlation coefficient of 0.993,and detection limit was estimated to be 24 U/m L.