Photoelectrochemistry for Biosensors
Authors: Zhu Jun-Jie , Fan Gao-Chao , Zhang Jian-Rong 
Published: February 2020

Photoelectrochemical biosensing is a new kind of sensor technique, which is developed on the combination of photoelectrochemical process and electrochemical analysis technology. As an ideal sensor technique, photoelectrochemical biosensing has attracted considerable research interests. Herein, we have fabricated the photoelectrochemical biosensors for the detection of biomarker and DNA sequence, respectively. First, we fabricated a photoelectrochemical immunosensing platform for sensitive detection of biomarkers. The immunoassay for matrix metalloproteinase-2 detection was established on the basis of CdS:Mn/CdTe co-sensitized TiO2 nanotubes and signal amplification of SiO2@Ab2 conjugates. The TiO2-NTs/CdS:Mn/CdTe co-sensitized structure could significantly enhance the photocurrent due to its excellent properties of adequate absorption of light energy, ultrafast electron transfer, and effective inhibition of charge recombination. As signal amplification elements, SiO2@Ab2 conjugates could significantly reduce the photocurrent because of it obvious steric hindrance effect. Based on superior photoelectrochemical property of the TiO2-NTs/CdS:Mn/CdTe co-sensitized structure and signal amplification of the SiO2@Ab2 conjugates, the immunoassay exhibited an low detection limit for MMP-2 detection. We also developed a technique for the determination of carcinoembryonic antigen (CEA, Ag). Here, TiO2 modified electrode was assembled with CdSeTe alloyed quantum dots (AQDs) via electrostatic adsorption, and then further deposited with CdS:Mn shells on the surface of CdSeTe AQDs via successive ionic layer adsorption and reaction strategy, forming TiO2/CdSeTe@CdS:Mn sensitization structure as the photoelectrochemical matrix to immobilize capture CEA antibodies (Ab1), signal CEA antibodies (Ab2) were labeled with CuS nanocrystals (NCs) to form Ab2-CuS conjugates, which were employed as signal amplification elements when speciﬁc immunoreaction occurred. Before detection of target Ag, the TiO2/CdSeTe@CdS:Mn sensitization structure could adequately harvest the exciting light with different bands, evidently expedite the electron transfer, and effectively depress the charge recombination, resulting in noticeably increased photocurrent. When target Ag existed, the Ab2−CuS conjugates could dramatically decrease the photocurrent due to competitive absorption of exciting light and consumption of electron donor for CuS NCs coupled with steric hindrance of Ab2 molecules. Second, enhanced photoelectrochemical strategy for ultrasensitive DNA detection was developed based on two different sizes of CdTe quantum dots co-sensitized TiO2/CdS:Mn hybrid structure. Multilabeling of hairpin DNA probe with different size CdTe QDs was adopted to achieve a co-sensitization effect to significantly amplify the photocurrent signal. Conformation change of hairpin DNA probe after hybridization with target DNA promoted the disappearance of the co-sensitization effect to sensitively decrease the photocurrent signal. Due to excellent photoelectrochemical performance of this co-sensitization effect, the well-designed DNA assay could offer an ultralow detection limit for specific DNA detection.

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