A double-emission molecularly imprinted ratiometric fluorescent sensor based on carbon quantum dots and fluorescein isothiocyanate for visual detection of p-nitroaniline

A novel molecularly imprinted ratiometric fluorescent sensor CQDs@MIP/FITC@SiO 2 for the detection of p-nitroaniline (p-NA) was constructed through the mixture of CQDs@MIP and FITC@SiO 2 in the ratio of 1:1 ( V CQDs@MIP : V FITC@SiO₂ ). The polymers of CQDs@MIP and FITC@SiO 2 were prepared by sol-gel method and reversed-phase microemulsion method, respectively. CQDs@MIP was used as the auxiliary response signal and FITC@SiO 2 was used as the reference enhancement signal. The signal was measured at excitation/emission wavelengths of 365/438, 512 nm. The sensor showed good linearity in the concentration range 0.14–40.00 µM ( R 2  = 0.998) with a detection limit of 0.042 µM for p-NA. The color change of “blue-cyan-green” could be observed by the naked eye under 365 nm UV light, thus realizing the visual detection of p-NA. The sensor presented comparable results compared with high-performance liquid chromatography (HPLC) method for the detection of p-NA in hair dye paste and aqueous samples with recoveries of 96.8–103.7% and 95.8–104.4%, respectively. It was demonstrated that the constructed sensor possesses the advantages of simplicity, excellent selectivity, superior sensitivity, and outstanding stability. Graphical Abstract