A traffic light-type sensitive visual detection of mercury by golden nanoclusters mixed with fluorescein

A novel colorimetric sensor based on red-emitting bovine serum albumin‑golden nanoclusters (BSA-AuNCs) and green-colored fluorescein that exhibited traffic light-type color change was developed for ratiometric and visual detection of mercury (Hg). In the presence of Hg2+, the red fluorescence from BSA-AuNCs was quenched while the green fluorescein was inert thus as a reference. And it presented traffic light-type (red, yellow and green) color in the low, middle and high concentration of Hg2+. A potential mechanism was investigated by Energy Dispersive Spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS). The selective quenching mechanism may be due to the formation of gold amalgam bonds between BSA-AuNCs and Hg2+. A linear correlation was constructed for Hg2+ in the concentration range of 10–500 μg L−1. A limit of detection (LOD) of 7.4 μg L−1 and a relative standard deviation (RSD, n = 7) of 0.4% were obtained, which can be used to monitor the concentration of Hg2+. In visual detection, as low as 0.1 μg mL−1 of Hg2+ can be easily discriminated from the blank with the naked eye. The proposed method was validated by analysis of certified environment and food samples with satisfactory results.