Molecularly imprinted polymers (MIPs) are synthetic receptor-like materials with specific recognition sites for template molecules[1]. The MIPs can rebind the template with high selectivity due to the complementarity of binding sites and template in shape, size and functionality[2]. Therefore, MIPs are used in many applications such as sensors[3–5], solid-phase extraction[6–8], simulated enzyme catalysis[9] and drugs delivery systems[10–12]. In particular, the fluorescent properties of fluorescent MIPs have been discovered and used for the detection of analytes, and their high sensitivity and selectivity make the detection of analytes more convenient. A simple method to prepare fluorescent MIPs is to add fluorescent monomers during the synthesis [13]. However, fluorescent monomers are often limited by the complexity of their synthesis and more suitable materials are needed to replace them. Quantum dots (QDs) are semiconductor nanocrystals that can provide narrow and tunable emission spectra[14]. Compared with organic dyes, quantum dots have attracted much attention due to their photochemical stability and good water dispersion. Due to these special properties, quantum dots can be combined with molecular blotting techniques into a composite system for efficient trace detection of target molecules.
At present, quantum dot-molecularly imprinted polymers (MIPs-QDs) have attracted much attention due to their unique properties such as their simplicity and efficiency in detecting target molecules[15–19]. Several protocols have been developed to construct the MIPs-based optical materials (QDs). For example, Zhang et al. have composed MIPs-capped CdTe QDs as a sensing material for cytochrome c and demonstrated that the MIPs anchored on the surface of the dBSA modified CdTe QDs could be used as selective materials for recognition of target protein [20]. Li et al. have reported that molecularly imprinted silica nanospheres embedded CdSe QDs could afford a highly selective and sensitive optosensing system for pyrethroids analysis [21]. Sun [22]et al. proposed a novel fluorescent MIP(SiO2@CdTe QDs@MIP), which could facilitate an efficient and convenient method for paraquat detection and adsorption. As a kind of trend, the ZnS QDs will have more important significance due to their environmental protection property. There have been several reports on MIPs-ZnS QDs for the detection of pesticides. Zhao[23] et al. successfully prepared composite QDs@MIP nanospheres via a facile and versatile ultrasonication-assisted encapsulation method, which were successfully applied to the fluorescence quantitative detection of diazinon in water. Ren[24] et al. prepared MIPs-capped ZnS:Mn QDs via a sol–gel process, which could be acted as a fluorescence probe and successfully applied to determine nicosulfuron in water samples. In addition, MIPs-QDs have been used for the detection and analysis of pesticide residues such as dimethoate[25], cypermethrin[26], methamidophos[27] and pentachlorophenol[28]. The novel dual-function MIPs- ZnS QDs have the advantages of high stability, rapid response, and high sensitivity.
Benzoylurea insecticides (BUs) are common and effective insecticides that poison insects by inhibiting the biosynthesis of chitin in their bodies. BUs have a number of attractive properties, such as high selectivity, good biological activity, rapid degradation in both soil and water, and low acute toxicity for animals[29]. They are widely used on vegetables, fruits and grains, providing a good guarantee of improved crop yields and harvests. However, the excessive use of BUs may lead to serious contamination of agricultural products and potential harm to human health. Therefore, it is great importance that the residues of BUs are effectively determined. Some analytical methods have previously been reported on the determination of BUs, such as high performance liquid chromatography (HPLC)[30–32], high performance liquid chromatography with ultraviolet detector [33, 34] and HPLC-mass spectrometry[35–37]. However, these methods encounter hindrances such as expensive equipment, tedious sample pre-treatment or need for highly skilled personnel. Therefore, it is necessary to develop a simple and effective method to recognize and analyze the BUs. To our knowledge, the use of MIPs-QDs to detect BUs residue has not been reported.
In this work, a novel quantum dots-molecularly imprinted polymers (MIPs-capped ZnS:Mn QDs) was prepared by sol-gel process using teflubenzuron (TBZ) as a template. The resulting polymers were characterized by Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), dynamic light scattering (DLS), and X-ray diffractometry (XRD) measurement. Most importantly, four structurally similar compounds were used for selectivity testing to verify the selectivity and recognition ability of MIPs-capped ZnS:Mn QDs. Moreover, the feasibility of MIPs-capped ZnS:Mn QDs materials for the detection of BUs from cabbage samples was examined. This work could provide a new idea for the detection of benzoylurea pesticides.