Determination of albumin using CdS/SiO₂ core/shell nanoparticles as fluorescence probes

CdS quantum dots (QD) were capped with SiO₂ via a microemulsion method for reducing the toxicity and imparting the biocompatibility of the CdS QD. The resulting CdS/SiO₂ core/shell nanoparticles (NP) showed an improved water-solubility and stability even in pH 4.0 acidic medium. Their fluorescence could be effectively enhanced in the presence of bovine serum albumin (BSA), due to the passivation effect of BSA on the surface of the NP. Furthermore, the concentration dependence of the fluorescence intensity obeys the Langmuir-type binding isotherm. Thus a novel fluorescence enhancement method for the determination of BSA has been developed using the less-toxic CdS/SiO₂ core/shell NP as probes. Under optimal conditions, the linear range of calibration curve is 0.6-30 μg•mL^-1, and the detection limit is 0.18 μg•mL^-1. Compared with the water-soluble CdS NP without SiO₂ shell, the CdS/SiO₂ core/shell NP exhibited slightly lower fluorescence response to BSA as well as other coexisting substances, such as heavy and transition metals, due to the inhibition of SiO₂ shell. The proposed method was applied to the quantification of BSA in synthetic and serum samples with satisfactory results.