Fabrication And Application Of Photoelectrochemical Sensors Based On Quantum Dot And Enzyme Nanocomposites

Photoelectrochemical sensors which is based on the photoelectric effect, exhibit some unique advantages over other sensors. For example, its sensitivity is high because it uses a visible light as excitation source and a potentiostat as transducer, which can delete some undesired background signals.In this thesis, a simple procedure for constructing the photoelectrochemical biosensor based on TiO₂/CdSe@CdS QD nanocomposite modified electrode was developed. The TiO₂/CdSe@CdS QD nanocomposite modified electrode was obtained by alternately depositing water-soluble CdSe@CdS QD and a mixture of [cobalt(o-phen)3]^2+/3+ and poly(ethyleneimine) (PEI) over mesoscopic TiO₂ films. The obtained TiO₂/CdSe@CdS QD nanocomposite modified electrode exhibits much higher and stable photocurrent intensity than that of the photoelectrochemical biosensors reported so far. We deposited glucose oxidase or cholinesterase on the surface of TiO₂/CdSe@CdS QD nanocomposite film according to need of detection, such as detecting glucose, detecting parathion.After the TiO₂/CdSe@CdS QD nanocomposite modified electrode was coated with glucose oxidase, the photocurrent intensity was enhanced towards the addition of glucose. Thus, a photoelectochemical biosensor for the detection of glucose was developed by monitoring the changes in the photocurrent intensity. Moreover, the proposed biosensor possessed good reproducibility and storage stability.Then the acetylcholinesterase enzyme (AChE) was deposited on the top of the TiO₂/CdSe@CdS QD nanocomposite modified electrode, resulting in a highly sensitive optical biosensor for detection of organophosphorus pesticide (OP) based on enzyme inhibition mechanism. AChE catalyzed hydrolysis of acetylthiocholine to acetate and thiocholine. The latter product acts as donor for the holes generated in the valence band upon excitation of CdSe@CdS QD, yielding a stable photocurrent. When parathion is introduced in solution, it can interact with the active centre of AChE and decrease the enzyme activity. This leads to the decrease in the thiocholine production and then the photocurrent. By means of measuring the photocurrent before and after an incubation step with the pesticide, one can calculate the concentration of OPs.