An efficiently ratiometric fluorescent probe based on bis-dihydroxyboron fluorescein complexes for detection of pyrethroid residues in fruit juices

Abstract

Among boron-containing fluorescent probes, fluorescein modified by dihydroxyboron is rarely reported as a probe for detecting contaminants. For the first time, a non-covalent ratiometric fluorophore (NRF) was synthesized based on the interactive reaction between 4,5-bis-dihydroxyboron fluorescein and dibenzofuran. The optimized synthetic conditions for NRF were 1 mmol% Ni(dppp)Cl2 as a catalyst, 5 mmol% PPh3 as an additive, room-temperature reaction, and 72-h stirring, and in such cases, the yield reached as high as 91%. At the 290-nm excitation wavelength, the NRF molecules produced dual-emitting phenomenon at 315 and 560 nm. When fenpropathrin as a representative species of pyrethroid pesticides (Pys) was added, the 315-nm fluorescence intensities (FIs) were dramatically decreased, whereas the 560-nm FIs were slightly changed. Therefore, the ratios (I560/I315) of 560-nm FIs to 315-nm FIs could be utilized as an appropriate ratiometric indicator for sensitive Pys detection. Optimized conditions for the ratiometric probe were 60-min incubation and neutral solution pH; under such circumstances, the linear range, limit of detection and fortified recoveries for Pys were 5–150 μg·L−1, 1.5 μg·L−1 and 97.55–105.90%, respectively, which are comparable or even better than those of previously reported methods. As verified by certified reference material in apple juice (QC-198B-1), the NRF probe yielded a highly relative recovery up to 98.25% for fenpropathrin. Common salts and other pesticides had little effect on the ratiometric indicator of NRF, evidencing good selectivity and specificity for Pys. Collectively, this ratiometric probe shows great prospects in application for trace-level Pys detection in daily food monitoring.