Synthesis of BSA-stabilized copper nanoclusters and evaluation of their potential use as fluorescent sensors for folic acid

This study describes the synthesis and characterization of BSA-stabilized copper nanoclusters (BSA-CuNCs) for use as sensors for the B vitamin folic acid. Ascorbate served as a reducing agent while bovine serum albumin (BSA) served as a capping and stabilizing agent. The BSA-CuNCs had a golden-yellow appearance and perceivably have good dispersibility. Transmission electron microscopy indicated average diameters of the BSA-CuNCs as 2.47 ± 0.50 nm. With atomic force microscopy and dynamic light scattering, the diameters of the BSA-CuNCs were varied and larger than anticipated (64 ± 13 nm AFM; 11-608 nm DLS), since nanocluster sizes should be less than 2 nm. The BSA-CuNCs' UV–visible spectra did not show peaks in the 500–600 nm indicating the absence of the surface plasmon resonance (SPR) of larger nanoparticles. The BSA-CuNCs were excited at 320 nm and showed a fluorescence emission at 644 nm. The BSA-CuNCs were then evaluated as potential folic acid sensors. Fluorescence quenching was observed as folic acid was added incrementally. The quenching fitted well with the Stern-Volmer equation, with estimated limits for detection (LOD) and quantitation (LOQ) at 0.77 µg/mL and 2.35 µg/mL, respectively. Next, the folic acid content of some over-the-counter supplements was assessed. There was a range of 33.31% to 40.21% in the percent error between the claimed and experimental folic acid values, which were beyond the acceptable accuracy and precision errors of 5% and 10%, respectively. Nevertheless, current results may suggest potential that the BSA-CuNCs may be used to quantify folic acid. However, further research is required to improve sample preparations and analytical procedures.