Ultra-stable copper nanoclusters modulated by chitosan and the application to serum cholesterol detection

Ultra-stable copper nanoclusters were fabricated for the sensitive determination of cholesterol based on fluorescence turn-off. Red-emitting copper nanoclusters capped with cysteine were first synthesized with a short storage time (15 d). Then, the addition of chitosan and the adjustment of media pH were applied to modulate the unstable clusters into exceptionally stable aggregates with cyan-green emission possessing a long lifetime over 180 days. The aggregation-induced emission (AIE) of chitosan-modified copper nanoclusters (Cys-CuNCs) can be significantly quenched by cholesterol due to the interaction between cholesterol and chitosan. The fluorescence response of Cys-CuNCs to cholesterol exhibits a rapid equilibrium (1 min), high sensitivity with a detection limit of 19.63 μmol·L⁻¹ (3σ, n = 3), and a wide linear concentration range of 25.0 ~ 1000.0 μmol·L⁻¹. The proposed method has good stability and can be employed for cholesterol determination in biofluids.