Ratiometric fluorescence detection of Hg²⁺ and Fe³⁺ based on BSA-protected Au/Ag nanoclusters and His-stabilized Au nanoclusters

A ratiometric fluorescence method is designed and exploited for the sensitive detection of Hg²⁺ and Fe³⁺ ions, which is prepared by simply mixing bovine serum albumin-protected gold/silver nanoclusters (BSA-Au/Ag NCs) with histidine-stabilized gold nanoclusters (His-Au NCs). The as-prepared Au NCs/Au-Ag NCs solution emits pink fluorescence and exhibits two emission peaks around 485 and 660 nm excited by 370 nm. The fluorescence of the Au NCs/Au-Ag NCs system at 660 nm is obviously quenched in the presence of Hg²⁺, while the fluorescence at 485 nm is stable against Hg²⁺, thereby resulting in the decrease of fluorescence intensity ratio (I₆₆₀/I₄₈₅) of the system. The detection limit for Hg²⁺ is low as 1.56 nM. With the addition of Fe³⁺, the dual emission peaks of the Au NCs/Au-Ag NCs in the system show a substantial decline simultaneously with different rate, leading to the Fe³⁺ ions concentration-dependent variation of I₆₆₀/I₄₈₅ value. The linear detection range for Fe³⁺ is from 5 to 1000 μM. Furthermore, the developed fluorimetric strategy has been employed for separately analysis of different ions Hg²⁺ and Fe³⁺ in fish samples with satisfactory results.