Impedance Characteristics Of Photoelectrochemical Sensors In Two-electrode Systems And Differential Measurement

The photoelectrochemical?PEC?methods have the advantages of simple equipment,high sensitivity and fast analysis speed.However,the PEC process is related to redox reaction,lowering the selectivity of PEC detection method compared with other sensors.Hence,it is commonly used as a detection platform and is combined with other recognition membranes such as enzymes,proteins,nucleic acids,nanomaterials,etc.In this thesis,the measurement method for PEC sensors is improved.Based on a simple two-electrode system,a double-channel photocurrent measurement model is designed to perform differential PEC detection,improving the anti-interference ability of the analytical methods.The response characteristics of the PEC photocell with two photoelectrodes are investigated.The main contents are outlined below.1.Differential photoelectrochemical dopamine sensor based on molecularly imprintpolymerTiO₂ nanotube array?NTs?is an excellent semiconductor photosensitive material.After the graphene quantum dots?GODs?,the PEC performance of the as-prepared GODs/TiO₂NTs photoelectrode is improved.Using pyrrole as the monomer and dopamine as the template molecule,the molecularly imprinted polymer?MIP?film with selective recognition of dopamine was prepared by electropolymerization.MIP/GODs/TiO₂ NTs was used for the sensitive detection of dopamine.However,the imprint factor of the MIP for dopamine is only4.59.In order to improve the selectivity,a PEC differential sensing platform based on the difference in MIP and no-imprinted polymer?NIP?was established,by using MIP/GODs/TiO₂ NTs and NIP/GODs/TiO₂ NTs as the sensing and reference photoelectrodes,respectively.The differential photocurrent signal offers good anti-interference ability,improving the selectivity in the determination of dopamine and eliminating the baseline drift of PEC sensor.The proposed differential PEC sensor is used for the detection of dopamine in actual serum samples in thea linear range of 0.5 to 12.5?M,and detection limit of 0.018?M.2.Differential photoelectrochemical glucose sensor based on nanomimetic enzymesRecently,much attention has been paid to the study of nanomimetic enzymes.Lots of nanomaterials are demonstrated to have the similar catalytic activity of peroxidase.But there are few reports about the nanomimetic enzymes of glucose oxidase.In this work,it is shown that ZIF-67 is also a kind of mimetic of peroxidase.After alkali treatment,the nanomimetic enzyme of glucose oxidase was obtained.The nanomatrials with double mimetic enzyme of both peroxidase and glucose oxidase offers the convenience for the development of enzyme-free glucose sensor.Under the catalysis of the mimics of the glucose oxidase,glucose reacts with dissolved oxygen to generate hydrogen peroxide,which in turn improves the PEC efficiency of TiO₂ NTs photoelectrode under the catalysis of the mimics peroxidase.Based on the difference of catalytic activity of the ZIF-67 with and without alkali treatmentand to glucose,a differential PEC method for glucose determination was established based on TiO₂ NTs.The molecular sieve effect of ZIF-67 can reduce the interference of molecules larger than its pore size,and the differential strategy can reduce the interference of PEC reaction and small molecules on the surface.Hence,the selectivity for glucose determination is much improved.Under the conditions used,the detection limit is 0.03mM,which can be used for glucose determination in the concentration range of 0.1mM–1 mM.3.A measurement method for the internal resistance of the PEC sensor with doublephotoelectrodesThe photocurrent in a photoelectrochemical sensor is usually measured by a three-electrode system consisting of the photoelectrode,counter electrode and reference electrode to measure its photocurrent for sensing detection.When a photoelectrodes with opposite p-n polar semiconductor material is used instead of the counter electrode,the PEC response will be enhanced,especially the two-electrode detection system.By using the PEC sensing system with double photoelectrodes of g-C3N4/TiO2 NTs and CuO@Cu as the model,the method to measure the photovoltage,photocurrent and internal resistance of the phtocell was established.It is shown that the photocurrent of the PEC system with double photoelectrodes is greater than the sum of photocurrents in the two independent PEC systems,which is helpful to improving the sensitivity of PEC method.The enhancement in photocurrent is due to the increase in photovoltage and the decrease in electrode internal resistance.The PEC sensor with double photosensitive electrodes is used to determine ascorbic acid as well as the activity of and alkaline phosphatase.