Highly Selective Detection of Paraoxon in Food Based on the Platform of Cu Nanocluster/MnO2 Nanosheets

Abstract

Selective and sensitive identification of paraoxon residue in agricultural products is greatly significant for food safety but remains a challenging task. Herein, a detection platform was developed by integrating Cu nanoclusters (Cu NCs) with MnO₂ nanosheets, where the fluorescence of Cu NCs was effectively quenched. Upon introducing butyrylcholinesterase and butyrylcholine into the system, their hydrolysate, thiocholine, leads to the decomposition of the platform through a reaction between the MnO₂ nanosheets and thiol groups on thiocholine. The electron-rich groups on thiocholine can further promote the fluorescence intensity of Cu NCs through host-guest interactions. Adding paraoxon results in the failure of fluorescence recovery and further promotion, which could be utilized for the quantitative detection of paraoxon, and a limit of detection as low as 0.22 ng/mL can be achieved. The detection platform shows strong tolerance to common interference species, which endows its applications for the detection of paraoxon in vegetables and fruit. These presented results not only open a new door for the functionalization of metal nanoclusters but also offer an inspiring strategy for analytic techniques in nanomedicine and environmental science.

Keywords: MnO2 nanosheets; fluorescence quenching; fluorometry assay; metal nanoclusters; organophosphorus pesticides.

Figure 1

Schematic illustration for the detection of OPs based on the platform of Cu NCs/MnO₂ nanosheets.

Figure 2

Characterization of Cu NCs and MnO₂ nanosheets. (a) TEM, (b) high-resolution Cu 2p XPS spectrum, (c) fluorescence emission (blue solid line), excitation (blue dotted line), and UV-visible absorption spectra of Cu NCs. (d) High-resolution Mn 2p XPS spectrum of MnO₂ nanosheets.

Figure 3

(a) Fluorescence emission (blue line) of Cu NCs and UV-visible absorption spectra of MnO₂ nanosheets; (b) Fluorescence spectra of Cu NCs after adding different concentration of MnO₂ nanosheets; (c) Fluorescence decay curves of Cu NCs with (yellow line) and without (blue line) adding MnO₂ nanosheets; (d) Fluorescence spectra of the combination of Cu NCs (b), Cu NCs/MnO₂ nanosheets (d), Cu NCs/MnO₂ nanosheets + BChE (a), and Cu NCs/MnO₂ nanosheets + BChE + OPs (c); (e) Fluorescence spectra of the detection platform by adding different concentrations of OPs. All the emission spectra were collected under the excitation of 380 nm.

Figure 4

(a) Fluorescence emission spectra of the detection platform after adding different concentrations of paraoxon. Relationship between the ratio of fluorescence intensities and the concentrations of paraoxon showing as inset; (b) ratio of fluorescence intensities of the detection platform by adding different types of OPs; (c) evolution of the ratio of fluorescence intensities of the platform as a function of OPs concentrations; (d) selectivity test of the detection platform against different interference species, as presented on the frame. All the fluorescence intensities were recorded at 423 nm, under the excitation of 380 nm.