Synthesis of Highly Fluorescent Copper Nanoclusters: Box-Behnken Design Based Statistical Modeling and Optimization

Copper nanoclusters (CuNCs) due to their fascinating physical and chemical properties and unique fluorescence characteristics have attracted great attention in the past decade. Compared to gold and silver NCs, CuNCs are relatively cheaper which makes them more attractive in development of sensing platforms. However, they still have limitations such as low quantum yield and susceptibility to oxidation. Herein, BSA as a scaffold, stabilizer, and protective agent has been used for CuNCs synthesis via a bottom-up approach. The effects of synthesis time, copper salt and BSA concentration in fluorescence intensities of the NCs were studied, modeled, and optimized in the form of Box-Behnken design. Finally, to validate the model, CuNCs were synthesized by the predicted optimal conditions and their optical properties were compared with the model predictions. The BSA/CuNCs synthesized in this work showed two fluorescence peaks at 400 nm and 670 nm relating to NCs with different sizes. The model proposed the optimal conditions for synthesis of 400nm emitting CuNCs as copper salt concentration of 10.05 mM, BSA concentration of 27.69 mg/ml and synthesis time of 3.3h. The optimal condition for production of 670nm emitting CuNCs was determined as copper salt concentration of 19.97mM, BSA concentration of 10.1 mg/ml and synthesis time of 3.61h. CuNCs were then synthesized for validation of the model, and their emission at 400 nm and 670 nm were 90.6% and 94.9% in agreement with the model predictions, respectively.