Controlled side-by-side assembly of gold nanorods: A strategy for lead detection

A label-free and aggregation-based gold nanorods (AuNRs) probe has been developed for the detection of Pb2+ in aqueous solution, based on the fact that Pb2+ ions induce assembly mediated signal enhancement of cysteine-functionalized AuNRs. Cysteine (Cys) molecules are conjugated on AuNR surfaces to form cysteine-modified AuNRs (Cys-AuNRs), acting as nanoprobes in the detection of Pb2+. Transmission electron microscopy (TEM) and UV–vis absorption spectroscopy data reveal the formation of controlled side-by-side assembly of the AuNRs in the presence of Pb2+. The formation of aggregation of AuNRs significantly enhances detection signals, leading to dramatic decrease in the longitudinal surface plasmon resonance (SPR) absorption. The experiment conditions, including AuNRs aspect ratio, reaction time, pH value and salt concentration, are optimized. The Cys-AuNRs probe is highly sensitive (LOD = 0.1 nM) and selective toward Pb2+ ions, with a liner detection range from 0.1 nM to 1.0 nM. This system only becomes less sensitive when other metal ion is present at a very high concentration (i.e., >0.5 μM). The cost-effective nanoprobes allow rapid and simple determination of the concentration of Pb2+ ions in city tap water samples, with results showing its practicality for the detection of lead in real samples.