Red to brown to green colorimetric detection of Ag+ based on the formation of Au-Ag core-shell NPs stabilized by a multi-sulfhydryl functionalized hyperbranched polymer

The hyperbranched polyethylenimine (HPEI) derivative with thiol (SH) terminals was synthesized and used as multidentate ligand to stabilize AuNPs/analyte composites. A facile and rapid colorimetric method for the sensitive and selective detection of Ag+ based on the formation of Au-Ag core-shell NPs with three color changes (red through brown to green) was developed. Successive multiple color changes can greatly improve the specificity and selectivity of this colorimetric sensor owing to the lower possibility of false positive results. Other environmentally relevant metal ions did not interfere with the determination of Ag+ The response (i.e., the absorbance at 600 nm, A(600 nm)) was linearly proportional to the Ag+ concentration in a range from 8.76 x 10(-9) to 1.27 x 10(-4) M with a detection limit of 8.76 x 10(-8) M by the naked eyes and 8.76 x 10(-9) M by the UV-vis spectra. For the first time, this novel colorimetric sensor based on multiple color changes was developed and successfully applied to detect Ag+ in real samples. (C) 2016 Elsevier B.V. All rights reserved.