Analytical Applications of Enzymatic Growth of Quantum Dots

We have developed an analytical assay to detect the enzymatic activity of acetylcholine esterase and alkaline phosphatase based on the generation of quantum dots by enzymatic products. Acetylcholine esterase converts acetylthiocholine into thiocholine. The latter enhances the rate of decomposition of sodium thiosulfate into H2S, which in the presence of cadmium sulfate yields CdS quantum dots showing a time dependent exponential growth, typical of autocatalytic processes. This assay was also applied to detect acetylcholine esterase inhibitors. Alkaline phosphatase hydrolyzes thiophosphate and yields H2S, which instantly reacts with Cd2+ to give CdS quantum clots. The formation of CdS quantum dots in both reactions was followed by fluorescence spectroscopy and showed dependence on the concentration of enzyme and substrate.