One-pot synthesis of dual-emitting BSA-Pt-Au bimetallic nanoclusters for fluorescence ratiometric detection of mercury ions and cysteine

Water-soluble and dual-emitting bovine serum albumin-templated bimetallic platinum-gold fluorescent nanoclusters (BSA-Pt-Au NCs) have been synthesized for the first time by a simple and rapid one-pot synthesis strategy at a vital molar ratio of Pt/Au precursors under basic conditions. The BSA-Pt-Au NCs show unique and well-resolved dual-emission bands at 405 nm and 640 nm corresponding to the emission of the BSA-metal complex and Au NCs under the excitation at 340 nm, respectively. Interestingly, with the addition of mercury(II) (Hg2+) ions, the emission intensity at 405 nm (F-405) has a negligible influence, while the emission intensity at 640 nm (F-640) decreases dramatically, which is due to the specific and strong d(10)-d(10) interactions between Hg2+ ions and Au atoms/ions on the surface of the BSA-Pt-Au NCs. Meanwhile, cysteine (Cys) could effectively block Hg2+ ions to quench the fluorescence of BSA-Pt-Au NCs, which is based on the strong interaction between Hg2+ ions and the thiol functional group. These allowed the analysis of Hg2+ ions and Cys with the ratio of two emission intensities (F-405/F-640) in ultra-sensitivity and selectivity with high accuracy. The limit of detection (LOD) was 0.3 nM for Hg2+ ions and 0.04 mM for Cys (S/N - 3), respectively. This work indicates that the fluorescent sensor possesses potential applications for biological detection.