Ratiometric fluorescence detection of Cu²⁺ based on carbon dots/bovine serum albumin-Au nanoclusters

A ratiometric fluorescence sensor for Cu²⁺ detection was developed by employing carbon dots (CDs) as the reference fluorophore, and bovine serum albumin (BSA)-Au nanoclusters (AuNCs) both as specific recognition element and as response signal. The CDs were prepared by heating an acetic acid solution of chitosan at 180°C. The proposed nanoprobe was prepared by simply mixing the CDs and BSA-AuNCs. Here, the CDs were associated with BSA-AuNCs to form CDs/BSA-AuNCs nanoprobes based on electrostatic interaction and hydrogen bonds. In the hybrid fluorescent CDs/BSA-AuNCs nanoprobe, the emission of BSA-AuNCs at 640 nm was quenched by Cu²⁺, whereas the emission of CDs at 424 nm was maintained. The fluorescence changes of I₆₄₀/I₄₂₄ had good linearity with Cu²⁺ concentration in the range 1.5-600 nM, and the detection limit of the nanoprobe was 0.5 nM for Cu²⁺ detection, almost 4 × 10⁴ times lower than the maximum allowable amount of Cu²⁺ in drinking water. The proposed method for detecting Cu²⁺ also had high selectivity and feasibility.