Fluorescent Phloroglucinol–Boric Acid Carbon Dots for the Detection of Metanil Yellow: Investigation of Inner Filter Effect–Induced Quenching

ABSTRACT

A solvent‐free solid‐state method was employed to synthesize phloroglucinol–boric acid carbon dots (PBCDs) using phloroglucinol and boric acid as precursors. The PBCDs exhibited bright cyan fluorescence with an emission maximum at 472 nm under excitation at 375 nm, together with good aqueous dispersibility and photostability. Their fluorescence response toward Metanil Yellow (MY), a banned food colorant, was investigated for quantitative detection. Strong spectral overlap between MY absorption and the excitation/emission bands of PBCDs indicated a major contribution from primary and secondary inner filter effects (IFE) to the observed fluorescence attenuation. Time‐resolved fluorescence measurements showed only a marginal change in average lifetime from 5.12 to 5.10 ns upon MY addition, supporting an IFE‐dominated attenuation process while not excluding minor ground‐state interactions. The method exhibited a detection limit of 4.34 µM and a practical quantification range of 14.5–150.7 µM. A preferential response toward MY was observed in the presence of investigated interferents, with recoveries of 90–110% and relative standard deviations below 5% in turmeric powder and coloured beverage samples. The results demonstrate the potential of the PBCD platform for simple, solvent‐free preliminary screening of appreciable MY adulteration in food samples.