Differential Interaction of Metal Ions with Gold Nanoclusters and Application in Detection of Cobalt and Cadmium.

Interest in biosensing platforms using protein fluorescent gold nanoclusters (FGNCs) has grown significantly in the past due to
the unique optical properties they offer. This study investigates the interaction of metal ions with FGNCs, and the structural
modifications brought about by the interaction resulting in fluorescence changes of the cluster and its successful application in the
detection of two heavy metals, cobalt and cadmium. The binding of cobalt and cadmium to FGNCs synthesized from BSA
significantly altered the secondary structure of the protein, causing a change in its hydrophobicity. It also resulted in a change in
fluorescence properties of FGNCs by intersystem crossing (ICT) and fluorescence resonance energy transfer (FRET). Cobalt and
cadmium could successfully be detected in the range of 5–165 ng/mL (R2 = 0.95) and 20–1000 ng/ mL (R2 = 0.91), respectively,
with appreciable sensitivity. The principle was also applied for the detection of Vitamin B12 in commercially available ampoules,
validating the proposed method.