Electrostatically-driven self-assembly of copper nanoclusters and carbon dots for quantitative protamine and heparin determination

A novel nanosystem composed of red-emissive thiolate-capped copper nanoclusters (GSH-CuNCs) and blue-emissive polyethyleneimine-tailored carbon dots (B-CDs+) was utilized for the quantitative determination of protamine and heparin. Addition of B-CDs+ to a solution containing GSH-CuNCs resulted in a significant increase in the fluorescence emission of GSH-CuNCs due to their self-assembly through an electrostatic interaction. However, in the presence of protamine, a polycationic protein, the fluorescence emission of GSH-CuNCs at 590 nm was decreased as a result of adsorbing protamine on GSH-CuNCs surface instead of B-CDs+. This led to disassembling of GSH-CuNCs, while the fluorescence emission of B-CDs+ at 470 nm remained unchanged during the determination. In the presence of heparin, a negatively charged molecule, the fluorescence emission of GSH-CuNCs nanosystem was recovered due to strong electrostatic interaction between protamine and heparin. The displaced B-CDs+ aggregated the GSH-CuNCs, restoring its fluorescence emission. Under optimized conditions, the fluorescence responses were increased with the protamine and heparin concentrations in the range of 0.004–40 µg/mL and 0.01–28 µg/mL, with LODs (S/N = 3) of 0.001 µg/mL and 0.004 µg/mL, respectively. The nanosystem offers several merits, including an ultra-low LODs, wide dynamic linear range, good anti-interference, satisfactory detection reliability, and short response time. Importantly, this strategy was successfully devoted to estimate protamine and heparin in urine and serum samples, and the results were found to be acceptable.