Bi2O3-doped Au–Ag quantum dots with prominent peroxidase-mimic activity for multi-channel response to Hg2+ and Ag+

A kind of Bi2O3-doped Au–Ag quantum dots (Bi2O3-Ag-Au@FA QDs) was developed by one-pot homogeneous reduction in this work. By virtue of the synergistic effect among Bi, Au, Ag, and folic acid (FA), Bi2O3-Ag-Au@FA QDs expressed excellent peroxidase-like activity and inherent fluorescent performance, with a Km/Vmax of 0.14 mM/4.69 × 10−8 M s−1 to accelerate the oxidization of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) into blue oxTMB. Interestingly, the presence of Hg2+ could exclusively alter both the peroxidase-like and fluorescent activity of Bi2O3-Ag-Au@FA QDs, while Ag+ only weakened its fluorescent activity with an obvious time-resolved effect. Under the optimized conditions, Bi2O3-Ag-Au@FA QDs were applied for UV-vis/fluorescent/RGB monitoring of Hg2+ in real agricultural products, with detection limits of 3.74 × 10−9/6.97 × 10−10/6.63 × 10−9 mol l−1. And the one for time-resolved fluorescent differentiation of Ag+ was 1.87 × 10−9 mol l−1, which well met the requirements set by the World Health Organization. The probable catalytic recognition mechanisms for Bi2O3-Ag-Au@FA QDs toward Hg2+ and Ag+ were also proposed.