Gold nanostar as an ultrasensitive colorimetric probe for picomolar detection of lead ion

The sensitivity for analytes of interest is vital for environment protection and food safety. Here, we propose an extremely sensitive assay toward Pb2+ by using gold nanostars (GNSs) as probes based on the catalytic activity of Pb on etching gold atoms after being reduced in the presence of 2-mercaptoethanol (2-ME) and sodium thiosulfate. GNSs were prepared by using 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid as both the reducing and capping agents, enabling high stability and sensitivity for quantitation of Pb2+. Upon increasing Pb2+ concentration over the range of 0–10 μM, GNS solution color changed from greenish-blue to blue to purple to red, and eventually to colorless. The color change can be distinguished by naked eye at the Pb2+ concentration as low as 200 pM. Through monitoring longitudinal localized surface plasmon of GNSs, Pb2+ could be detected with a limit of detection of 1.5 pM, and the working range is 2 pM-1 μM. The ultra-high sensitivity of our assay stems from the high catalysis of Pb on etching gold on tips and branches in the presence of 2-ME and sodium thiosulfate, leading to the shape deformation to spherical gold nanoparticle and the corresponding significant changes in their optical properties. The assay provides high selectivity of Pb2+ over the tested interfering metal ions like Cu2+. With high sensitivity and selectivity, the assay was efficiently validated by analyzing water samples and monitoring the migration of Pb2+ from the tested container to water. An ultrasensitive colorimetric assay for picomolar detection of lead ion by using gold nanostars is proposed. [Display omitted] •Gold nanostars (GNSs) with unique optical properties show great potentials as probes for sensitively detecting analytes.•An ultrasensitive assay for detecting picomolar Pb2+ is proposed by using GNSs.•The assay is based on the catalyst of Pb on etching GNSs by 2-mercaptoethanol and Na2S2O3.•The sensitive assay is valuable to investigate lead migration from food packages to waters.