Green synthesis of highly fluorescent Au(i)@Ag2/Ag3-thiolate core–shell particles for selective detection of cysteine and Pb(ii)

Abstract

Giant Au(I)@Ag₂/Ag₃-thiolate clusters with strong fluorescence (λ_ex 400 nm, λ_em 564 nm, and quantum yield 8.3%) have been prepared in aqueous medium from glutathione and corresponding precursor salts at neutral pH under sunlight. An intriguing synergism between Au(I)_core and Ag(0)_shell imparts long-term stability to the fluorescent giant clusters (synthesized with a chemically green method) due to drifting of electron density towards core from shell. The strong fluorescence is selectively damped by cysteine (Cys) leaving aside all other essential amino acids (“Turn Off”). This quenched fluorescence is restored again on introducing Pb(II) ions in the system (“Turn On”). No other metal ion can cause such a recovery of the lost fluorescence. Such “Turn Off” and “Turn On” fluorescence helps in the design of a selective Cys as well as Pb(II) sensor in one pot. Detection of Cys and Pb(II) down to 5 × 10⁻⁸ M and 15 × 10⁻⁸ M, respectively, is possible following the present strategy.