| can detect the ion concentration and the parameters change of biochemical process by measuring the photoactive currents and voltage. Semiconductor nanoparticles have attracted much attention, due to the unique size- and shape-dependent optic and electronic properties as well as easy aqueous processing potential for large-scale fabrication. The major contents of the thesis are as follows:1. A label-free photoelectrochemical cytosensor for highly sensitive and specific detection of Ramos cell was developed based on photoactive films. The films were fabricated by a layer-by-layer （LBL） assembly of positively charged poly（dimethyl- diallylammonium chloride） （PDDA） and negatively charged CdSe semiconductor nanoparticles （NPs） capped with mercaptoacetic acid. The resulting modified electrodes were tested as sensors for Ramos cell through the recognition of DNA aptamer which was covalently bound to the electrode using the classic coupling reactions between -COOH groups on the surfaces of CdSe NPs and -NH2 groups of the aptamer. The newly developed cytosensor exhibited excellent sensitivity and selectivity. The linear range was from 160 to 1600 cells/mL with the equation of ?I = 6.0663 + 0.2198C and the detection limit was 84 cells/mL.2. Graphene, as a novel 2D carbon material, was used in photoelectrochemical biosensor. The photoactive films were fabricated by a LBL assembly of PAA-functionalized graphene and positively charged CdSe NPs. The significantly improved photoresponses with a very fast response time confirmed that graphene is a good candidate for the collection and transport of photogenerated charges, which could enhance the sensitivity of the biosensor. As a potential application, an aptamer was modified successfully on the layered nanofilm, and a label-free photoelectrochemical aptasensor for highly sensitive and specific detection of thrombin was developed based on graphene/CdSe NPs multilayer films. The decrease of photocurrent intensity was linearly related to the concentration of thrombin in the range from 1.0×10-12 to 1.0×10*-11 M. The regression equation was ?I （nA）= 8.6215 + 19.4720Cthrombin （10-12 M）. A detection limit of 4.5×10-13 M can be estimated using 3σ. In addition, the good selectivity and the ability to detect the analyte in complex matrices demonstrated the potentialities of aptamer based sensing for potential medical investigations. |
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