Ultra-sensitive cholesterol sensor via a red emitting copper nanoclusters with large stokes shift and chemical stability

Abstract

Fluorescent copper nanoclusters (CuNCs) have attracted considerable attention due to their biocompatibility, substantial Stokes shift, heightened specific surface area, cost efficiency, and versatility in accommodating various additives. However, conventionally synthesized CuNCs often suffer from size variability and susceptibility to oxidation, posing challenges in achieving stable clusters through straightforward synthesis routes in metal cluster research. In this study, copper nitrate (CuNO3) was reduced by hydrazine hydrate (HYD) and subsequently coupled with bovine serum albumin (BSA) and 2-mercaptobenzothiazole (MBT) as protective agents. This meticulously designed approach resulted in the successful development of red-emitting CuNCs (BSA-CuNCs, λem = 613 nm) characterized by a substantial Stokes shift (253 nm) and remarkable stability. Experimental findings unequivocally demonstrated the fluorescence quenching of BSA-CuNCs orchestrated by the hydrophobic interaction with cholesterol (Chol), showing linear responsiveness in the concentration ranges of 0.01–0.82 μM and 0.82–10 μM. Furthermore, BSA-CuNCs exhibited a remarkably low detection limit of 4.6 nM and high selectivity for Chol in serum, underscoring their potential for facilitating early and precise diagnostic applications.