Nanomolar Hg²⁺ Detection Using β-Lactoglobulin-Stabilized Fluorescent Gold Nanoclusters in Beverage and Biological Media

Owing to diverse functionalities and metal binding abilities, proteins have been proven to be promising ligands in the synthesis of gold nanoclusters (Au NCs). In this work, we explored β-lactoglobulin (β-Lg), a protein byproduct generated during cheese processing, as a biotemplate for fabrication of Au NCs by a facile and green method for the first time. The as-prepared Au NCs are water soluble and highly fluorescent and exhibit high sensitivity and selectivity for Hg 2+ detection in aqueous solution. Interestingly, we found that the fluorescence of these Au NCs is stable either in a variety of complex matrixes or over a broad pH range (5.0–13.0) and therefore can be explored as a cell and animal imaging agent. More importantly, we demonstrated that the β-lactoglobulin-stabilized Au NCs (β-Lg–Au NCs) could serve as a sensor for the detection and quantification of Hg 2+ in beverages, urine, and serum with high sensitivity.