Synthesis and Characterization of Red-Emitting Bimetallic BSA-Capped Cu–Mn Nanoclusters for the Turn-Off Cys/Hcy Detection

Apart from monometallic NCs, bimetallic nanoclusters have drawn more attention because of their spatial atomic arrangement and synergistic effects that result from combining two different metal elements. In this study, we report the facile synthesis of intense red fluorescent bimetallic copper–manganese nanoclusters (CuMnNCs) in a straightforward one-step method employing bovine serum albumin (BSA) as a stabilizing agent (BSA-CuMnNCs; λex = 380 nm, λem = 642 nm). The as-synthesized BSA-CuMnNCs were thoroughly characterized using FTIR, XPS, DLS, HR-TEM, UV–vis absorption, and fluorescence emission, confirming the successful formation of ultrasmall, stable, red-emitting bimetallic nanoclusters. The red fluorescence of BSA-CuMnNCs was efficiently quenched upon interaction with Cys and Hcy via strong interaction between thiol groups, and the metal center in nanoclusters leads to partial displacement of the BSA shell from BSA-CuMnNCs, enabling a sensitive detection platform. The BSA-CuMnNCs exhibited a linear response in the concentration range of 4.98–55 μM, with detection limits calculated as 2.15 × 10–7 M for Cys and 4.51 × 10–7 M for Hcy. The BSA-CuMnNCs demonstrated excellent accuracy with recovery values of Cys and Hcy ranging from 94.67 to 101.26% in urine samples and from 96.13% to 103.14% in serum samples, with RSDs below 3.21%. These findings suggest that BSA-CuMnNCs hold great promise as a biocompatible and efficient fluorescent platform for thiol sensing in clinical diagnostics and bioanalytical applications.