From solvent-tailored carbon dots to a practical sensor array: fingerprint discrimination and quantification of azo dyes in beverages.

Azo dyes are widely used as synthetic food colorants, but non-compliant use poses health risks, necessitating rapid detection methods. Here, dual-emissive bromine-doped carbon dots (Br-CDs) were synthesized via solvent engineering by tuning the ethanol/water ratio, which precisely modulates their surface states and differential affinity toward azo dyes. Based on these Br-CDs, a dual-channel fluorescence sensor array was developed for discrimination and detection of azo dyes. This array achieves fingerprint-like discrimination of five common azo dyes (visual detection limit: 2 μM) and accurately resolves their complex mixtures regardless of composition ratios. Moreover, it enables simultaneous quantification of individual dyes in mixtures with high sensitivity (LODs: 0.028-0.072 μM). The array demonstrated 100% recognition accuracy for blind samples in various beverages and achieved satisfactory spike recoveries (90.4-113.6%). This work offers both a solvent-mediated strategy for tailoring carbon dots and a high-performance sensing platform for monitoring food-borne azo dyes.