Turn-off chelation-enhanced fluorescence sensing of carbon dot-metallic deep eutectic solvent by imidazole-based small molecules

Abstract

Low accuracy, requirement of expensive instruments, derivatization and multi-step sample preparation, inconsistencies during the fabrication process, time-consuming procedures and utilization of eco-unfriendly chemicals are some limitations of various developed methods for detection of 4-methylimidazol (4-MeI). Herein, a rapid and miniaturized fluorescent probe based on the ultrasound‒assisted formation of carbon dots (CDs) in a metallic deep eutectic solvent (MDES) was developed and conveniently implemented to detect 4-MeI in commercial dark soft drinks. In-situ synthesis of CDs-chelated metals in the presence of the target analyte facilitates a kinetically fluorescence emission with no need to multi-step analysis. Simultaneous implementation of MDES as a green solvent and passivation agent also practically paves the way to minimize the hazardous chemicals consumption. Chelation of the divalent metal cations on the synthesized CDs and their strong interactions with the imidazole ring presumably provides a fluorescence quenching pathway induced by the model species. The formation kinetics of CDs in the presence of 4-MeI (as the model compound) and caffeine (as the significant interference) were also studied under the optimum conditions. Accordingly, the calibration plot covers 0.6−320 ng mL−1 concentration range. The limits of detection (LOD) and quantification (LOQ) are 0.18 and 0.6 ng mL−1, respectively. The relative standard deviations (RSDs) of the developed method are <11 % and the relative recoveries for eight real samples are in the range of 89–108 %.