Rapid, selective, and ultrasensitive fluorescence ratiometric detection of sulfide ions using dual-emitting BSA–erbium(iii)-modulated gold–silver bimetallic nanoclusters

Abstract

Dual-emitting bovine serum albumin–erbium(III) complex-modulated gold–silver bimetallic nanoclusters (BSA–Er/Au/Ag-NCs) have been synthesized for the first time by a simple one-pot synthesis route. The BSA–Er/Au/Ag-NCs show unique and well-resolved dual emission bands at 400 nm corresponding to the emission of the BSA–Er complex and 585 nm related to the emission of Au/Ag-NCs under a single wavelength excitation at 340 nm, respectively. Interestingly, with the addition of sulfide (S²⁻) ions, the emission intensity at 400 nm (I₄₀₀) increases, while the emission intensity at 585 nm (I₅₈₅) decreases, which could be due to the formation of an Ag₂S layer on Au/Ag-NCs. The Ag₂S layer not only quenches the fluorescence of Au/Ag-NCs due to the surface capping phenomenon, but also separates the BSA–Er complex and Au/Ag-NCs. The enlarging distance blocks the fluorescence energy transfer (ET) from the BSA–Er complex to Au/Ag-NCs, leading to an enhancement of the photoluminescence intensity at 400 nm. The opposite effect makes the ratio of the two emission intensities (I₄₀₀/I₅₈₅) ultrasensitive to detect the existence of S²⁻ ions. Accordingly, a ratiometric fluorescent nanosensor for the determination of S²⁻ ions was established. Under optimum conditions, the fluorescence intensity ratio (I₄₀₀/I₅₈₅) of the nanosensor against the concentration of S²⁻ ions shows a good linear range from 0.02 μM to 180 μM with a lower detection limit of 6.0 nM and excellent anti-interference performance.