Study On Photoelectrochemical Analysis Based On Nile Blue/Graphene Photoelectrode

The photoelectrochemical(PEC) analysis is based on the energy transfer from light to electricity. It utilizesthe correlation between the tested substances with PEC reaction, and brings out photo-induced electron transfer between the substance and the electrode in light, to achieve the determinationof the substance concentrationthrough direct or indirect detection of photocurrent. This analytical method combines the advantages of two photochemical and electrochemical detection methods. It has become a hot spot in analytical chemistrybecause of its simple operation, high sensitivity, low background current and cost, etc., and has been applied to studies of life sciences in recent years.Key of PEC analysis is to fabricate a photoelectric chemistry system by using of photosensitive materials. In our study, Nile blue(Nb), a photosensitive compound was electropolymerized on the surface of ITO electrode modified by graphemeoxide (GOx), to preparea PNb-GOx nano-composite interface with photoelectricactivity and electron acceptor. The preparedinterfacecan occur to PEC reaction with nicotinamide adenine dinucleotide(NADH) as electron donor. Thus, enzymatic activity or substrate concentration could be indirectly monitored through detecting NADH, because NADH is coenzymeof dehydrogenase.Based on the preparation of PNb-GOx photoelectric interface, studies done in three aspects herein are listed below:1. A PEC sensor was fabricatedby using PNb-GOx/ITO photoelectrode as working electrode. The quantitative determination of NADH was achieved by monitoring photocurrent based on the PEC response of photoelectrode to NADH. The reaction mechanism between the photosensitive interface and NADH was studied in the paper. The influence of bias voltage, the solution pH, the light intensity on the PEC reaction and detection of NADH were investigated. Under the optimized conditions, the photocurrent is proportional to the logarithm of NADH concentration in the range of 0.01～80.0 μmol/L, and the detection limit was estimated to be 5 nmol/L (S/N=3). The regression equation is I(nA)=404.7+81.76 1gC(μmol/L) with correlation coefficient of 0.993. The relative standard deviation(RSD) is less than 2.75% for five parallel measurements of same sample.2. The catalyticreaction of lactate dehydrogenase(LDH) to lactic acidgenerates NADH in the presence of NAD+. The enzymatic activity of LDH wasdetected bymonitoring the photocurrentgenerated from the PEC reaction between PEC sensitive interface and NADH. The PEC reaction mechanism was studied and influence of bias voltage, pH value of electrolyte and NAD4 concentration on the catalytic activity of LDH were investigated. The feasibility of method was acknowledged through detecting the catalytic activity of LDH commodity, developing a PEC method for the determination of catalytic activity of protein.3. A novel PEC lactic acid biosensor was fabricatedby using chitosan and glutaraldehyde to covalently attach LDH on surface of photoelectrode. Due to coupling the catalyticand PEC reactionon the prepared biosensor, the determination of lactic acidcould be fulfilled based onthe detection of photocurrent. The preparation condition for the PEC biosensor, such as the amount of enzyme and coating fluid, the concentrations of CS and glutaraldehyde were optimized by experiment. The results shownfrom experiments, the photocurrent was proportional to the concentration of lactic acid with linear range from 1.00 to 100 μmol/L, and the detection limit was estimated to be 0.5 μmol/L (S/N=3). The regression equation is I(nA)=233.12+1.22 C(μmol/L) with a correlation coefficient of 0.992, and RSD is less than 2.26% for five parallel measurements of same sample.