Development Of PEC Biosensor Based On G-C₃N₄/TiO₂ NTs And Their Application

Photoelectrochemical?PEC? measurement a newly emerging analytical technique which is based on the photocatalytic reduction or oxidation of molecules to carry out photogenerated electron transfer between the target analyte and the electrode surface under light irradiation, leading to the amplification of the analytical signal. Benefiting from the complete separation of excitation source?light? and detection signal?photocurrent?, the undesired background signals can be significantly reduced in the PEC detection. So PEC sensor has the advantage of high sensitivity, short response time, and low background signals. This thesis focuses on the developing of PEC biosensor based on g-C3N4/TiO2 and their application in biological analysis. Details are listed below: 1. Sensitive detection of ascorbic acid and alkaline phosphatase activityby double-channel photoelectrochemical detection design based on g-C3N4/TiO2 nanotubes hybrid film.This work developed a simple double-channel detection approach to improve the stability and credibility in photoelectrochemical?PEC? sensors. The working principle is based on differential signal between the measuring and reference PEC cells. This measurement approach offers the advantage over established single-channel PEC mode in that the effect of the drift in the intensity of excitation source is diminished owing to the differentiating nature of the system, leading to better signal-to-noise ratio and hence higher measurement sensitivity. Additionally, the differential measurement scheme reduced the interference from matrix effect. Sensitive detection of ascorbic acid and alkaline phosphatase activity by the differential PEC mode based on g-C3N4/TiO2 nanotube array hybrid film was demonstrated. The as-prepared PEC sensor offers signal-enhancement response to ascorbic acid?AA? in a concentration variation from 1 nM to10 ?M with a detection limit of 0.3 nM. The activity of alkaline phosphatase?ALP? was determined indirectly according to the concentration of AA, generated in the hydrolysis reaction of L-ascorbic acid 2-phosphate sesquimagnesium in the presence of ALP as a catalyst, The quantification range is 0.3 mU/L–1 U/L with a detection limit of 0.1 mU/L. The as-proposed PEC method was applied in the determination the concentration of AA and the activity of ALP in serum samples 2. Sensitive detection of hydrogen peroxide based on TiO2 NTs modified by Cu₃?BTC?₂ with catalytic effectIn this chapter two PEC sensors were prepared to detect H2O2 and AA which was modified with Cu₃?BTC?₂ or ZIF-8. The responses of the PEC sensor to AA and H2O2 was compared. After modified by ZIF-8, the sensitivity to H2O2 is not affected distinctly but the response to AA was suppressed. The reason is that H2O2 is smaller than the pore apertures of ZIF-8, it can pass through the ZIF-8 pores and is oxidized by the photogenerated holes on the surface of photoelectrode. On the contrary, the molecule size of AA is larger than the pore aperture of ZIF-8, reducing the possiblity to react at electrode surface. Thus, the molecular sieve of ZIF-8 film improve the selectivity to small molecule like H2O2. Because Cu₃?BTC?₂ can be used as a catalysis to facilitate the radical generation and electron-transfer processes on its surface, Cu₃?BTC?₂/C3N4/CNT/TNTs PEC sensor shows higher detection sensitivity than C3N4/CNT/TNTs PEC sensor. The molecular sieve in Cu₃?BTC?₂ reduce the PEC response to larger molecule like AA. Hence, the Cu₃?BTC?₂ film can improve both the sensitivity and selectivity to H2O2 due to its molecule size selectivity and catalytic effect.