Ligand-engineered copper nanoclusters combined with carbon dots as a ratiometric probe for brilliant blue detection...

Brilliant blue (BB) is a common food dye that can poses health risks at high intake, necessitating hypersensitive analysis. To this end, 6-Fluoro-2-mercaptobenzothiazole (6-F-MBT) was identified as the optimal ligand through comparative studies with its isomers and substituent-modified analogues. Then orange-emitting copper nanoclusters (6-F-MBT@PVP-CuNCs) were fabricated via an optimized hydrothermal route with 6-F-MBT and polyvinylpyrrolidone (PVP) as dual ligands, and later assembled with blue-emitting carbon dots (CDs) to yield a ratiometric fluorescent (RF) probe that could selectively monitor BB. The ratiometric detection relied on combined FRET and dynamic quenching, which together provided a limit of detection (LOD) of 33.5 nM and a linear range spanning 0.1 to 34.4 μM. It also supports solution-phase quantification via smartphone RGB analysis (1.4-44.8 μM) and on-site assay using paper-based strips (2.0-50.0 μM). Besides, the 6-F-MBT@PVP-CuNCs possess bright fluorescence and superior stability, holding promise for anti-tampering and finger mark recognition.