Surface molecularly imprinted polymers fabricated by differential UV–vis spectra and reverse prediction method for the enrichment and determination of sterigmatocystin

Highlights

• The differential UV–vis spectra is combined with the reverse prediction technique.

• A novel magnetic molecular imprinted polymers (MMIPs) was successfully prepared.

• MSPE-HPLC method was established.

• The method was successfully prepared to determine of STG in wheat for the first time.

• This method can provide reference for the specific monitoring of biotoxins in grain.

Abstract

A novel magnetic molecularly imprinted polymers (MMIPs) with a new functional monomer Triallyl isocyanurate was synthesized successfully to enrich and detect sterigmatocystin (STG) in wheat samples. The differential UV–vis spectra and the reverse prediction method were selected to achieve the optimal synthesis conditions of the MMIPs, which were characterized well. The adsorption experiment showed that MMIPs have high selectivity and sensitivity. A magnetic solid phase extraction combined with high performance liquid chromatography (MSPE-HPLC) method based on the MMIPs was successfully established with the optimal extraction condition. The linear range and RSD were 1.8–25 ng·g⁻¹ and 2.6–4.1%, respectively. The recovery of this method was 87.6–96.9% and the limit of detection (LOD) was 0.63 ng·g⁻¹. The excellent sensitivity and selectivity of this method were confirmed by experiment of the extraction and detection of STG in wheat extracts. This work extends the use of molecular imprinting in mycotoxins applications.

Introduction

Sterigmatocystin (STG) is one of fungal secondary metabolites, which can be converted to aflatoxins by Aspergillus parasiticus, Aspergillus flavus and so on (Holmes et al., 2019, Iranifam, 2016, Yuan et al., 2015). As a biochemical precursor of aflatoxins, multiple studies have shown that STG can cause mammalian hepatocarcinomas and animal toxicities (Amoli-Diva, Sadighi-Bonabi, Pourghazi, & Hadilou, 2018), therefore it is classified in group 2B by IARC (Liu, Shi, Liu, & Peng, 2010). When the environment is humid, Aspergillus flavus is easy to breed on grains, food products and other mildew organic matter (Guo et al., 2018, Habib et al., 2011). In addition, food processing can not completely remove STG, so if people eat foods containing STG (such as grains and grain-based products) (Chung et al., 2013, Jiang et al., 2011), it will cause great harm to the human body, for example gastriccarcinoma and liver cancer.

Currently, manyl analytical methods for detecting STG in food have been established including chromatographic methods (Morar et al., 2009, Speltini et al., 2017), ELISA immunoassays (Yao, Zhao, Liu, Fang, & Wang, 2020) and chemical sensors (Fernández et al., 2017). However, due to the interference of complex matrix in grain samples and the low content of mycotoxins, these methods are difficult to directly detect STG (Liu et al., 2010). The simple pretreatment techniques not only affect the results but also don't damage the analytical instruments. Therefore, developing an appropriate preparation method that can eliminate this interference is very important.

As a promising solid phase extraction technique, molecular imprinting has the ability to enrich and separate the targets selectively from complex samples matrixes by molecularly imprinted polymers (MIPs) (Batzias et al., 2005, Luo et al., 2014, Wang et al., 2019). The main reason for the selectivity of MIPs is the interaction between functional monomers and template molecules (Zhang et al., 2019). Therefore, the focus of this method is to find suitable monomers providing functional groups that can form the pre-polymer with the templates (Wang & Yu, 2007). Triallyl isocyanurate (TAIC) is a multifunctional olefin monomer containing aromatic heterocycles. The three lactam bonds in the molecule can provide more chemical sites to interact with templates. At present, differential UV–vis spectra is an effective method to select suitable monomers, which has achieved the screening of monomers by analyzing the changes of UV–vis spectra of target analytes caused by changes in the concentration of functional monomers (Cho et al., 2005, Guo et al., 2015). Therefore, this method was selected to screen several common functional monomers and TAIC to obtain the most suitable monomer.

The success of the imprinting process is not only relied on an adequate selection of template molecules and functional monomers, but also on other chemical parameters such as the type and amount of cross-linker and the reaction solvent, which will have a significant impact on the performance of MIPs (Hatamluyi et al., 2020, Zhong et al., 2018). The mechanism of reverse prediction method is that selects the best performing MIPs by studying the performance of Non-molecularly imprinted polymers (NIPs), which can obtain the optimal synthesis conditions of MIPs. This method can make it easier for the cumbersome process of optimizing a MIPs formulation (Bragazzi et al., 2015). However, the complicated synthesis process of material is not only a waste of resources but also increase the difficulty of the experiment. Therefore, the combination of different UV–vis spectra and reverse prediction method can shorten the cycle, simplify the steps and establish the detection method more quickly.

Magnetic MIPs (MMIPs) usually use magnetic nanoparticles as the core covered by MIPs shell (Pereira, Matos, Gratieri, Cunha-Filho, & Gelfuso, 2018). Due to the magnetism of magnetic nanoparticles, the MMIPs can be separated with solvent by external magnetic field (Batzias, Delis, & Koutsoviti-Papadopoulou, 2004). n addition, magnetic nanoparticles also have the advantages of low toxicity. Because of these characteristics, MMIPs have been applied to many fields of separation and purification (Medina, Sartori, Moraes, Cardoso, & Jacob, 2019).

In this work, the differential UV–vis spectra was used to screen the optimal functional monomers and reverse prediction technique was selected to obtain appropriated porogen and cross-linker, which can obtain the optimal synthesis conditions of MMIPs. Under these conditions, the prepared material has the advantage of high selectivity. It is the first report to select TAIC as a functional monomer to synthesize MIPs.