Fluorescent Switch-on Detection of Cadmium(II) Using Salicylaldehyde-Decorated Gold Nanoclusters

In this study, salicylaldehyde (SA) conjugated gold nanoclusters were synthesized, characterized, and applied for the fluorescent turn-on sensing of Cd²⁺. The trypsin-stabilized fluorescent gold nanocluster (Tryp-AuNCs, λ_em = 680 nm) was modified with SA to form the spherical-shaped SA_Tryp-AuNCs. After modification, the red-emitting Tryp-AuNCs turned to green-emitting SA_Tryp-AuNCs because of the formation of imine linkage between the -CHO group of SA with the -NH₂ group of functionalized trypsin. The modified SA_Tryp-AuNCs selectively interacted with Cd²⁺ and exhibited a fluorescence enhancement at 660 nm. The Cd²⁺ detection with SA_Tryp-AuNCs is simple and rapid with an estimated nanomolar detection limit of 98.1 nM. The practical utility of SA_Tryp-AuNCs was validated by quantifying Cd²⁺ in real environmental water samples.