Fabrication Of Photoelectrochemical Biosen-Sors Based On Quantum Dots And Their Na-Nocomposites

The photoelectrochemical biosensor based on quantum dots and their nanocompo-sites, which combine the advantages of photoelectrochemical detection technology and nanomaterials with the various properties of nanomaterials, have been considered to be a promising analytical method. Nowadays, the photoelectrochemical detection method has been extensively applied in molecular measurement, environmental anal-ysis, food security, development of new drugs and medical research fields, due to the merits of high sensitivity, simple equipment, easy miniaturization, etc. This thesis fo-cuses on the fabrication of photoelectrochemical and its application in biosensing platform based on CdTe quantum dots and their nanocomposites.1. Visible light induced photoelectrochemical biosensing based on oxygen-sensitive quantum dotsA visible light induced photoelectrochemical biosensing platform based on oxy-gen-sensitive near-infrared quantum dots (NIR QDs) was developed for detection of glucose. The NIR QDs were synthesized in an aqueous solution, and characterized with scanning electron microscopy and X-ray photoelectron spectroscopy. The as-prepared NIR QDs were employed to construct oxygen-sensitive photoelectro-chemical biosensor on a fluorine-doped tin oxide (FTO) electrode. The oxygen de-pendency of the photocurrent was investigated at as-prepared electrode, which dem-onstrated the signal of photocurrent is suppressed with the decreasing of oxygen. Coupling with the consumption of oxygen during enzymatic reaction, a photoelectro-chemical strategy was proposed for the detection of substrate. Using glucose oxidase (GOx) as a model enzyme, that is, GOx was covalently attached to the surface of CdTe QDs, the resulting biosensor showed the sensitive response to glucose. Under the irradiation of visible light of a wavelength at505nm, the proposed photoelectro-chemical method could detect glucose ranging from0.1mM to11mM with a detec-tion limit of0.04mM. The photoelectrochemical biosensor showed a good perfor-mance with high upper detection limit, acceptable stability and accuracy, providing an alternative method for monitoring biomolecules and extending the application of near-infrared QDs.2. Photoelectrochemical biosensing of DNA based on quantum-dot-functionalized porous ZnO nanoplatesThis work reports the preparation of visible-light absorbing CdTe quantum dots (QDs) functionalized porous ZnO nanoplates as a photoelectrode and their photoelec-trochemical application for DNA detection. The novel nanohybrid was synthesized through a facile, two-step method, that is the CdTe QDs was covalently bound to the porous ZnO nanoplates through a linker molecule, and characterized with morpho-logical, spectroscopic and photoelectrochemical techniques. Because of the porous structure and appropriate band alignment between CdTe QDs and ZnO, which signif-icantly promoted the electron transfer and reduced the recombination of photogene-rated electrons and holes, the CdTe/ZnO electrode showed much higher photoelec-trochemical activities than pure CdTe QDs and ZnO nanoplates. The as-prepared na-nohybrid was further applied to immobilize with the biotin labeled capture probe. Combining with "Y" junction structure and restriction endonuclease-aided target re-cycling strategy, a sensitive photoelectrochemical DNA biosensor was obtained. By investigation of the photocurrent dependency on hydrogen peroxide, the signal of photocurrent is suppressed with the consumption of hydrogen peroxide. The higher concentration of the target probe, the more hydrogen peroxide left. Therefore, a sig-nal-on strategy was achieved. The newly designed nanohybrids are promising for applications in solar cells and determination of different sequences of target DNA.