Rapid, Selective, and Ultrasensitive Fluorimetric Analysis of Mercury and Copper Levels in Blood Using Bimetallic Gold–Silver Nanoclusters with “Silver Effect”-Enhanced Red Fluorescence

Bimetallic alloying gold–silver nanoclusters (Au-AgNCs) have been synthesized by a one-pot biomineralization synthesis route at a vital molar ratio of Au/Ag precursors in the protein matrix. Unexpectedly, the prepared Au-AgNCs could exhibit dramatically enhanced red fluorescence, which is about 6.5-fold and 4.7-fold higher than that of common AuNCs and core–shell Au@AgNCs, respectively. A rapid, selective, and ultrasensitive fluorimetric method has thereby been developed using Au-AgNCs as fluorescent probes toward the separate detections of Hg²⁺ and Cu²⁺ ions in blood. The interactions of Au-AgNCs with Hg²⁺ and Cu²⁺ ions were systematically characterized by microscopy imaging, UV–vis, and fluorescence measurements. It is demonstrated that the “silver effect” gives the Au-AgNCs probes not only greatly enhanced red fluorescence but also the strong capacity to specifically sense Cu²⁺ ions in addition to improved response to Hg²⁺ ions. Moreover, aided by a Cu²⁺ chelating agent, exclusive detection of Hg²⁺ ions could also be expected with the coexistence of a high level of Cu²⁺ ions, as well as reversible Cu²⁺ analysis by restoring the fluorescence of Au-AgNCs. Additionally, Au-AgNCs with strong red fluorescence could facilitate fluorimetric analysis with minimal interference from blood backgrounds. Such an Au-AgNCs-based fluorimetric method can allow for the selective analysis of Hg²⁺ and Cu²⁺ ions down to 0.30 nM and 0.60 nM in blood, respectively, promising a novel detection method to be applied in the clinical laboratory.