An eco-friendly imprinted polymer based on graphene quantum dots for fluorescent detection of p-nitroaniline

Abstract

An eco-friendly fluorescent molecularly imprinted polymer anchored on the surface of graphene quantum dots (GQDs@MIP) was developed with an efficient sol-gel polymerization for highly sensitive and selective determination of p-nitroaniline (p-NA). The GQDs@MIP was characterized in detail by Fourier-transform infrared, fluorescence spectrometer, scanning electron microscope, transmission electron microscope and ultraviolet spectrophotometer. The results showed that the imprinted layer was successfully grafted on the surface of the GQDs. The fluorescence of the GQDs@MIP is efficiently quenched when p-NA recombines with the imprinting sites based on the photo-induced electron transfer fluorescence quenching mechanism. A good linear relationship was obtained between the fluorescence quenching efficiency of the GQDs@MIP and the concentration of p-NA in the range of 0-15.0 μM with a correlation coefficient of 0.99. The practicability of the proposed method in real samples was successfully evaluated through monitoring p-NA in water and fish samples with satisfactory recovery. The developed method provides a feasible and eco-friendly strategy to fabricate MIPs anchored on GQDs with good fluorescence properties for sensitive detection of organic pollutants in complex samples.

Fig. 1. Schematic illustration of the synthesis of the GQDs@MIP.

Fig. 2. Fluorescence intensity and fluorescence quenching capability of GQDs@MIP with different volume ratios of monomer to cross-linker.

Fig. 3. FT-IR spectra of the GQDs (A), GQDs@MIP (B) and GQDs@NIP (C).

Fig. 4. SEM image of the GQDs@MIP (A) and GQDs@MIP (B); TEM images of the GQDs (C) and GQDs@MIP (D); EDS image of the GQDs@MIP (E) and GQDs@NIP (F).

Fig. 5. Binding affinity of the GQDs@MIP and GQDs@NIP in solutions of different pHs.

Fig. 6. Response time of the GQDs@MIP (a) and GQDs@NIP (b) for p-NA.

Fig. 7. Fluorescence spectra of the GQDs@NIP (a) and the GQDs@MIP after (b) and before (c) removal of the template molecule.

Fig. 8. Fluorescence spectra of the GQDs@MIP (a) and GQDs@NIP (b) with different concentrations of p-NA; insets of Stern–Volmer equation for the GQDs@MIP (c) and GQDs@NIP (d) with p-NA.

Fig. 9. UV/vis spectrum of p-NA and fluorescence spectrum of the GQDs (A); UV/vis spectra of the GQDs, p-NA, and the mixture of GQDs and p-NA (B); Stern–Volmer plot of GQDs towards p-NA at 20 °C, 30 °C, and 40 °C (C).

Fig. 10. Fluorescence response of the GQDs@MIP and GQDs@NIP toward different analytes.