A simple assay for direct visual and colorimetric sensing application of cysteamine using Au@Ag core-shell nanoparticles

The present study elucidates the preparation of colorimetric Au@Ag core-shell nanoparticles (Au@Ag core-shell NPs) probe for sensitive, label-free and rapid sensing of trace levels of cysteamine (CSH). The Au@Ag core-shell NPs were prepared by a simple chemical reduction method. The physico-chemical properties of the Au@Ag coreshell NPs were extensively characterized by various spectroscopic and microscopic techniques. Upon the successive addition of increasing concentrations of CSH to Au@Ag core-shell NPs, the absorption intensity showed a decrease with the formation of a new peak at 652 nm. In the presence of CSH, the negatively charged citrate ions that are adsorbed on the surface of Au@Ag core-shell NPs readily get replaced by the CSH and result in the aggregation of NPs. The observed absorption spectral evolution is proportional with the addition of increasing concentrations of CSH. The Au@Ag core-shell NPs showed high selectivity towards the selectivedetermination of CSH even in the presence of other interfering biomolecules. The proposed sensing strategy can selectively detect CSH in the concentrations range of 1.00 x 10(-7) mol dm(-3) to 8.00 x 10(-7) mol dm(-3) with a limit of detection as low as 0.33 nM. The practical applicability of the sensing probe is further demonstrated by performing the detection of CSH in serum and urine samples with high accuracy.