| Flavin coenzyme including flavin mononucleotide(FMN),flavin adenine dinucleotide(FAD)and their precursor riboflavin(RF),is a cofactor of flavoprotein(mainly oxidoreductase),which can accept two protons and reduce to FMNH2 or FADH2,participate in a variety of redox reactions in vivo to promote sugar,amino acids,fat and protein metabolism.Therefore,the determination of flavin coenzyme and its related proteins is of important significance.If flavin coenzyme can play the role of electron donor to produce the photoelectrochemical(PEC)reaction with photosensitive nanomaterials,a PEC system can be fabricated.Thus,developing a new analytical method for the determination of flavin coenzyme is possible by means of this PEC platform.In this paper,the ZnO nanorod photoelectrode(ZnONRP)was as photosensitive interface and electron acceptor.After the flavin coenzyme was electrochemically reduced by using a four-electrode electrochemical system with two-channel,ZnONRP reacted with the reduced flavin coenzyme to produce PEC effect,achieving the direct determination for the flavin cofactor by measuring photocurrent.The main work in the paper is summarized as following three aspects:1.ZnONRP was prepared by electrochemical deposition method,and the preparation method was optimized.The modification results of the electrode were characterized by scanning electron microscopy(SEM)and X-ray diffraction(XRD).After RF was reduced to RFH2 with the second working electrode,the PEC reaction system was fabricated by ZnONRP and the reduced RF as electron donor.Based on PEC response of RFH2 on ZnONRP,the quantitative analysis of RF was achieved through detecting the photocurrent.The response mechanism of PEC sensitiveinterface to RF was discussed.The effects of bias voltage,electrolyte pH,light irradiation intensity and the distance between working electrode and reducing electrode are investigated on the PEC reaction and photocurrent.Under the optimized experimental conditions,the photocurrent intensity is proportional to the logarithm of RF concentration in the range of 1.00×10-11~1.00×10-6 mol/L with the correlation coefficient of 0.996.The sensitivity is 195.6 nA/logC(?mol/L)and the detection limit is estimated to be 6.0 ×10-12 mol/L(S/N = 3).The relative standard deviation(RSD)was less than 6.25% for detecting the actual sample,the recovery was 99.0% ~ 104%,and the common biochemical substance was not disturbed to the photocurrent response of RF.2.Using FMN and FAD instead of RF,PEC analysis of flavin coenzyme was developed by PEC reaction of flavin coenzyme on ZnONRP.Under the optimized experimental conditions,the photocurrent intensity is proportional to the logarithm of FMN or FAD concentration in the concentration range of 1.00×10-11 ~ 1.00×10-6mol/L.The linear correlation coefficients of regression equation were 0.996 and 0.998,respectively,and the detection limits were estimated to be 8.00 × 10-12 and 5.00 × 10-12mol/L(S/N = 3).3.Because FAD is coenzyme of glucose oxidase(GOD),and glucose is the substrate of GOD,the FAD in GOD can be reduced by glucose.Based on the direct electron transfer of GOD through using the chitosan as charge transport medium,a sensitive and simple method for the determination of glucose was developed by utilizing ZnONRP-FAD PEC system.After optimizing the concentration of chitosan,the amount of GOD and electrolyte pH,the photocurrent intensity was exponentially related to the glucose concentration in the range of 0.60 ~ 2.80 mmol/L with the correlation coefficient of 0.991,and the detection limit was estimated to be 0.20mmol/L.This method has been applied to detect the glucose content in human serum.The RSD and the recovery shown by the experimental results were 0.86% and 98.5% ~103.3%,respectively. |
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