| The photoelectrochemical(PEC) process mainly refers to the conversion of photonto-electricity. The principle of the photocurrent generation is that a photoactive material(usually organic or inorganic semiconductors) absorbs energy upon illumination and forms electron-hole pairs at the interface with the process of the electron from ground state to excited state, which generates the photocurrent. Electron separation and transfer would generate photocurrent. Such a photo-driven principle has long been applied to photosynthesis, photocatalysis and photovoltaics. In recent years, some researchers have incorporated the photoelectrochemical process into bioanalysis, which opens up a new field of photoelectrochemical bioanalysis.In the introduction charter, we elaborated the PEC biosensor from the working principle to the application of the photoelectrochemistry. Subsequently, we classified the PEC biosensor by sensor strategies and summaried the different sensor models. Finally, the development potential of the PEC biosensor in this field was expounded.In the second chapter, we fabricated the PEC biosensor combining exciton energy transfer(EET) effect with site-specific cleavage of restriction endonuclease(HpaII) for the DNA methyltransferase(MTase) activity and inhibitor screening. The probe DNA hybrided with the target DNA(tDNA) to form a DNA duplex, which carried a special region for cleavage. HpaII cleaved the specific site of the DNA duplex with the release of Au NPs, which destroyed the EET and generated the recovering of photocurrent signal. Hence, the amount of the restored photocurrent was proportional to the MTase activity. In other words, the restored photocurrent was inversely proportional to the MTase activity. In addition, the assay could be used for the screening of the inhibitors of MTase. A prospective platform for assaying the activity and inhibition effect of MTase is provided by the PEC biosensor.In the third chapter, we developed a PEC biosensor for sensitive detection of HTLV-II DNA,which combined the enzymatic amplification with TdT-mediated extension strategy. In this paper, GR-CdS:Mn nanocomposites was choosed as the photoelectric conversaion materials to construct the highly sensitive biosensor with dual signal amplification. First, GR-CdS:Mn nanocomposites film was deposited on the working electrode. Then, ZnS as the inactivation layer of GR-CdS:Mn nanocomposites was modified. When the double DNA chains crossed on the electrode, we used TdT to mediate the extension of biotin labeled DNA chain. Then, by the affinity interaction of biotin and avidin, the ALP enzyme was modified on the DNA chain. At the same time, ALP catalyzed AAP to produce of AA(electron donor), which could capture the holes and impede the recombination of the electron-hole pairs, which not only enhanced the signal of photocurrent, but also increased the detection sensitivity. The detection limit for the HTLV-II DNA detection was 0.043 fM, which provide a new method for the assay of DNA at trace level.In the fourth chapter about a PEC biosensor was based on energy transfer and duplex-speci?c nuclease(DSN) cleave strategy. In this work, we utilized TiO2 and CdSe QDs to fabricate a supersensitive PEC biosensor for assaying miRNA. At first, we deposited TiO2 thin film on the electrode. After calcined at 450 ℃ for 30 min, we modified CdSe QDs via layer by layer assembling. Subsequently, we incubated the electrode with the GR-Au NPs labled probe DNA(pDNA). Finally, we dropped the buffer containing miRNA and DSN on the modified electrode to incubating. At the time, DSN cleaves the pDNA in the DNA/miRNA duplex. The cleavage of the pDNA allowed the miRNA to be released and hybridize with another pDNA, which initiated a next round of cleavage, releasing and hybridization. This cyclic reaction generated a great ampli?cation of photocurrent signal. The detection limit of the PEC biosensor was 0.015 fM for miRNA, which supply new platform for miRNA at trace level. |
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