Colorimetric detection of Ag+ based on CAg+C binding as a bridge between gold nanoparticles

We have developed aptamer-functionalized gold nanoparticles (AuNPs) for the rapid, selective, and sensitive detection of Ag+ in aqueous solution. Two DNA strands are designed to functionalized on the surface of AuNPs through AuS bond. In the presence of Ag+, aptamer1 hybridizes with the partially complementary aptamer2 with the aid of CAg+C bindings, which could lead to different degrees of AuNP aggregation. This process is accompanied by a color change from red to bluish-purple as observed by naked eyes. This colorimetric sensor is shown to detect the presence of as low as a 0.236 nM concentration of Ag+. Importantly, it could be applied to complex samples without complicated sample pretreatment and sophisticated instruments.