Role of a mild reducing agent in designing a copper nanocluster-based tunable dual-metal sensor for the selective and sensitive detection of Ag+ and Fe2+

Abstract

Protein-protected metal nanoclusters emerged as a promising class of biofriendly nano-materials due to their interdisciplinary applications, namely as efficient metal sensors. Here we have successfully designed a photoluminescent protein (lysozyme) scaffolded copper nanocluster (Lys-Cu NC) (λex= 365 nm, λem= 437 nm) that can be used as a cost-effective dual metal sensor for the sensitive and selective detection of silver (Ag+) and ferrous (Fe2+) ions through two independent photoluminescence turn off mechanisms. The nanocluster when synthesized in the presence of a mild reducing agent, hydrazine (N2H4), can selectively detect Ag+ (LOD = 4 nM) through a size-induced photoluminescence quenching method involving both static and dynamic mechanisms. By removing the excess N2H4 from the medium, the selectivity can be tuned towards Fe2+, which can quench the photoluminescence intensity through a static charge transfer process. However, the selectivity towards Ag+ can be recovered by externally adding N2H4 again to the medium. Thus, the selectivity of the nanocluster can be switched back and forth between Ag+ and Fe2+ by simply controlling the redox properties of the medium. This simple method of designing a dual-metal sensor reported in this study is unique and can be further extended to design multi-metal sensors for specific biologically and environmentally relevant metal ions in the future.