Study On The Photoelectrochemical Bioanalysis

Photoelectrochemical (PEC) bioanalysis is a newly emerged and rapidly developing analysis technique, its sensing principle depends on the fact that the electrical signal change could be brought about by the biological interactions between various recognition elements and their corresponding target analytes. Because of its superior merits and desirable potential in future biosensing, increasing research attention has been drawn for its advancement among the analytical community and substantial progress has been obtained in their analytical performance and biosensing applications. Despite the great opportunities clearly manifested in these pioneering works, indeed, the investigation on PEC bioanalysis is still in its infancy. Especially, its biosensing format and signaling mechanism are highly limited as compared to its electrochemical or optical counterparts. Hence, it is very necessary to develop new methods in PEC bioanalysis, the successes of them could present novel and general routes for future PEC bioanalysis. In this thesis, through the design and fabrication of innovative PEC system and the exploitation of ingenious signaling mechanism, we have established some advanced methods of PEC bioanalysis which might benefit the broad PEC bioanalysis and biosensor design and development.In the first chapter of introduction, from the perspective of the biological specificity-conferring mechanism, we summarized the recent advances in the state-of-the-art research activities of PEC biosensing and classified the related works in terms of the corresponding analysis approaches. Specifically, the first section of this review briefly presented the basic principle, classification, and biosensing mechanism of PEC biosensors; recent bioanalytical applications in PEC DNA analysis, immunosensing and enzyme biosensing were then discussed according to the signaling strategy in the second section; the future prospects in this area were also evaluated and discussed in the final section.In the second chapter about PEC DNA analysis, we firstly proposed an energy transfer-based mechanism in PEC system and exploited its PEC DNA analysis application. Specifically, with DNA as a rigid spacer, noble metal (Au and Ag) nanoparticles (NPs) were bridged to CdS quantum dots (QDs) for the stimulation of exciton-plasmon interactions (EPI) in a PEC system. It was found that the EPI resonant nature enabled manipulating photoresponse of the QDs via tuning interparticle distances, and the photocurrent of the QDs could be greatly attenuated and even be completely damped by the generated EPI. This phenomenon underlied a novel DNA analysis, and in this work the DNA could be detected down to the level of10-15M. The work opened a different horizon for EPI investigation through an engineered PEC nanosystem, and provided a viable mechanism for new and general DNA sensing protocol.In the third chapter about PEC enzymatic biosensing, we successfully developed two PEC enzyme analysis protocols using horseradish peroxidase (HRP) and glucose oxidase (GOx), respectively. Firstly, homogeneous TiO2film was formed on ITO glass via the method of liquid phase deposition (LPD), followed by the sequential immobilization of CdS particles and HRP onto the TiO2matrix. HRP could accelerate the oxidation of4-chloro-1-naphthol (4-CN) by H2O2to yield the insoluble and insulating product benzo-4-chlorohexadienone on the photoelectrode surface, retarding the interfacial electron transfer and hence influencing the photocurrent generation. Based on this mechanism, the PEC detection of H2O2could be realized with a linear range from1.0×10-9to2.0×10-5M and detection limit of5.0×10-10M. Secondly, localized surface plasmon resonance-based photoelectrochemistry and nanoparticle size effect was exploited for novel concept of plasmonic PEC biosensing. This methodology capitalized on the size-dependent LSPR property and the plasmonic photoelectrochemistry of the Au NPs, hence it was different from both the traditional dielectric properties-based LSPR biosensing and semiconductor-based PEC biosensing. As a model system, the H2O2-mediated enlargement of Au NPs on a nanoporous TiO2substrate was used to transduce the GOx catalytic events for glucose determination and the glucose could be detected at3.0×10-6M.It has been demonstrated that the stimulation of BCP could alter the interfacial electron-transfer feature greatly in the PEC enzymatic biosensing. In the forth chapter concerning PEC immunoassay, we then demonstrated the protocol of a BCP-based sandwich PEC HRP-linked immunoassay on the basis of their synergy effect for the ultrasensitive detection of mouse IgG as a model protein. As compared to the conventional label-free immunoassays with enhanced steric hindrances as the exclusive cause for signal variation, this new biosensing strategy exhibited higher sensitivity by means of multi amplification via HRP-labeled secondary antibodies (Ab2), not only enhancing the effect of steric hindrance greatly but also introducing the HRP competitive absorption and the BCP amplification route into the system that altered the light-absorption feature of the electrode. As a result of the multisignal amplification, the immunoassay possessed excellent analytical performance. The mouse IgG could be detected from0.5pg/mL to5.0ng/mL with a detection limit of0.5pg/mL. To further strengthen this HRP catalyzed BCP-based PEC immunoassay, immunogold labeling was introduced into the system for improved PEC immunoassay of prostate-specific antigen (PSA), an important tumor marker for prostate cancer (CaP). Due to the high HRP loading on Au NPs, the PSA could be detected at levels down to0.06pg/mL. The work provided a feasible alternative technique for PSA screening to facilitate the early CaP diagnosis.In the fifth chapter of cell-related PEC analysis, a robust and facile PEC approach for cell capture and quantification was achieved firstly based on carboxylic-group-containing free-base-porphyrin bridged3-aminophenylboronic acid and TiO2biosensing interface. The corresponding linear range was from1.0×102to1.0×106cells/mL and the detection limit was experimentally found to be1.0×102cells/mL. Using sialidase, an extension of the work made possible a new PEC platform for living cell surface carbohydrates evaluation. This novel PEC cell capture and analysis could find applications in cell biology, pharmacology and toxicity monitoring, while PEC cell surface carbohydrates evaluation may benefit for related cancer researches and clinical diagnostics.