On-off-on switchable fluorescent chemosensor based on glutathione-protected gold nanoclusters for high-selective on-site Cr(VI) detection in complex biological samples

Given that Cr(VI) is highly carcinogenic and teratogenicity, its routine health monitoring is crucial to measuring Cr(VI)-induced health risk earlier. Despite being considered one of the most promising candidate tools for metal detection, the gold nanoclusters (AuNCs)-based fluorescent sensors have been widely applied due to their specialties (e.g., on-site conveniences, low toxicity, high stability, facile processability, and unique optical properties), while AuNCs are subjected to interference from the coexisted metals within complex mixtures, the specific detection of Cr(VI) remains a great challenge. A novel fluorescent "on -off -on" strategy (i.e., the switch of AuNCs, AuNCs-Cr(VI), and Cr(III)) is proposed for Cr(VI) measurement, based on core-shell structured Au(0)@Au(I)-SG NCs (2.5 nm) in the presence of L-glutathione (GSH, reductant of Cr(VI) to Cr(III)), providing enhanced Cr(VI)selective, stability, and biocompatibility. In this context, this approach enables specific detection of Cr(VI) in complex biological samples without interference from coexisting metals, exhibits high anti-interference ability, can be lowered up to 3.0 min and down to 75.0 nmol/L (well below regulatory limits). Compared with the conventionally-used flame atomic absorption spectroscopy (FAAS), our proposed approach is better for avoiding sample digestion, convenience, easy operation, and suitable monitoring at home. Herein, the proposed method has been successfully applied to Cr(VI) measurement in complex biological fluid samples and offers high sensitivity and selectivity for pre-diagnosis and post-treatment monitoring.