Ultrasensitive sensing of Hg(2+) and CH(3)Hg(+) based on the fluorescence quenching of lysozyme type VI-stabilized gold nanoclusters.

This study presents a one-step approach to prepare lysozyme type VI-stabilized gold nanoclusters (Lys VI-AuNCs) for the ultrasensitive detection of Hg(2+) and CH(3)Hg(+) based on fluorescence quenching. The optical properties and size of Lys VI-AuNCs are highly dependent on the concentration of Lys VI, which acts as both a reducing and a stabilizing agent. With an increase in the concentration of Lys VI, we observed a systematic blue shift in the fluorescence maxima, an increase in the quantum yields, and a reduction in the particle size. When using 25 mg/mL Lys VI as a reducing agent, the formed Lys VI-AuNCs (denoted as Au-631) were found to be highly stable in a high-concentration glutathione or NaCl. Additionally, the Au-631 were capable of sensing Hg(2+) and CH(3)Hg(+) through the interaction between Hg(2+)/CH(3)Hg(+) and Au(+) on the Au surface; the limits of detection (LODs) for Hg(2+) and CH(3)Hg(+) were 3 pM and 4 nM, respectively. The selectivity of this probe is more than 500-fold for Hg(2+) over any metal ions. As compared to bovine serum albumin-stabilized AuNCs, Au-631 provided an approximately 330-fold improvement in the detection of Hg(2+). To the best of our knowledge, Au-631 not only provide the first example for detecting CH(3)Hg(+) but also have the lowest LOD value for Hg(2+) when compared to other AuNC-based Hg(2+) sensors. Importantly, this probe was successfully applied to the determination of Hg(2+) and CH(3)Hg(+) in seawater.