Magnetic molecular imprinting polymers based on three-dimensional (3D) graphene-carbon nanotube hybrid composites for analysis of melamine in milk powder

Current trends of functional monomers and cross linkers used to produce molecularly imprinted polymers for food analysis

Molecularly imprinted polymers (MIPs) as artificial synthetic receptors are in high demand for food analysis due to their inherent molecular recognition abilities. It is common practice to employ functional monomers with basic or acidic groups that can interact with analyte molecules via hydrogen bonds, covalent bonds, and other interactions (π-π, dipole-ion, hydrophobic, and Van der Waals). Therefore, selecting the appropriate functional monomer and cross-linker is crucial for determining how precisely they interact with the template and developing the polymeric network's three-dimensional structure. This study summarizes the advancements made in MIP's functional monomers and cross-linkers for food analysis from 2018 to 2023. The subsequent computational design of MIP has been thoroughly explained. The discussion has concluded with a look at the difficulties and prospects for MIP in food analysis.

Application of molecularly imprinted polymers as the sorbent for extraction of chemical contaminants from milk

Milk is one of the most consumed and balanced foods with a high nutritional value which could be contaminated with different chemicals such as antibiotics, melamine, and hormones. Because of the low concentration of these compounds and the complexity of milk samples, there is a need to use sample pre-treatment methods for purification and preconcentration of these compounds before instrumental techniques. Molecular imprinting polymers (MIPs) are synthetic materials with specific recognition sites complementary to the target molecule. MIPs have selectivity for a specific analyte or group of analytes, which could be used to extract and determine contaminants and remove the interfering compounds from complex samples. Compared to other techniques, sample preparation, high selectivity, excellent stability, and low cost are other advantages of using MIPs. The present article gives an overview of the synthesis of MIPs and their application for extracting antibiotics, hormones, and melamine in milk samples.

Nanomaterial-based magnetic surface molecularly imprinted polymers for specific extraction and efficient recognition of dibutyl phthalate

A rapid and selective sorbent for the enrichment of dibutyl phthalate (DBP) from water and Chinese Baijiu samples was established using magnetic surface molecularly imprinted polymers (MSMIPs) combined with gas chromatography-mass spectrometer (GC-MS). The MSMIPs were synthesized using a magnetic nanosphere material with silica layer, increasing the polymer surface area as a carrier. Compared with the traditional methods, the addition of magnetic microspheres simplified the process of food substrate purification and significantly shortened the pre-concentration time. The MSMIPs adsorption conforms to the Freundlich isotherm model as multilayer adsorption on an inhomogeneous surface and the pseudo-second-order model. The developed MSMIPs combined with GC-MS method showed good linearity in DBP concentration range of 0.02-1.0 mg L^-1 with low LOD (0.0054 mg L^-1) and LOQ (0.018 mg L^-1), and obtained good recoveries in real samples (95.2-97.2%) with RSD < 5.0% (n = 9), which were consistent with those from Chinese national standard method.

Application of molecular imprinting technology based on new nanomaterials in adsorption and detection of fluoroquinolones

Irrational use of fluoroquinolones (FQs) can lead to allergic reactions, adverse reactions to the heart and damage of the liver; thus, it is of great significance to establish rapid, sensitive and accurate detection methods for FQs. Molecularly imprinted polymers (MIPs) with specific structures synthesized by molecular imprinting technology (MIT) are widely used for the detection of FQs due to their high specificity, high sensitivity and stable performance. Recently, new functional nanomaterials with different morphologies and sizes, which can provide rich sites for surface chemical reactions, have attracted more and more attention of the researchers. Thus, the application status and development prospects of MIT based on new nanomaterials in the adsorption and detection of FQs were summarized in this study, providing a theoretical basis and technical guarantee for the development of new and efficient food safety analysis strategies based on MIPs.

Fabrication of a Molecularly-Imprinted-Polymer-Based Graphene Oxide Nanocomposite for Electrochemical Sensing of New Psychoactive Substances

As new psychoactive substances (commonly known as "the third generation drugs") have characteristics such as short-term emergence, rapid updating, and great social harmfulness, there is a large gap in the development of their detection methods. Herein, graphite oxide (GO) was first prepared and immobilized with a reversible addition-fragmentation chain transfer (RAFT) agent, then a new psychoactive substance (4-MEC) was chosen as a template, and then the surface RAFT polymerization of methacrylamide (MAAM) was carried out by using azobisisobutyronitrile (AIBN) as an initiator and divinylbenzene (DVB) as a cross-linker. After the removal of the embedded template, graphene oxide modified by molecularly imprinted polymers (GO-MIPs) was finally obtained. Owing to the specific imprinted cavities for 4-MEC, the satisfactory selectivity and stability of the GO-MIP nanocomposite have been demonstrated. The GO-MIP nanocomposite was then used to fabricate the electrochemical sensor, which displayed a high selectivity in detecting 4-MEC over a linear concentration range between 5 and 60 μg mL^-1 with a detection limit of 0.438 μg mL^-1. As a result, the GO-MIPs sensor developed an accurate, efficient, convenient, and sensitive method for public security departments to detect illicit drugs and new psychoactive substances.

Antioxidant analysis of ultra-fast selectively recovered 4-hydroxy benzoic acid from fruits and vegetable peel waste using graphene oxide based molecularly imprinted composite

Food processing industries generate 25-30% of fruit and vegetable peel (F&VP) waste of the total produce, which are rich in polyphenolic antioxidants (PA). Sustainable solution for the above waste can be its valorization for the recovery of PA, often used as natural preservative. Present work reports rationally designed graphene oxide-based molecularly imprinted composites (GOMIPs) using ionic liquid 1-allyl-3-octylimidazolium chloride (A) as a green functional monomer for selective recovery of PA 4-Hydroxy benzoic acid (4HA) from F&VP/pomegranate peel (PGP) waste. GOMIP-A and GOMIP-V were characterized using various techniques for its successful synthesis. GOMIP-A attained equilibrium within 10 min with adsorption capacity of 190.56 μmol g-1 for 4HA. Developed HPLC method depicted selective recovery of 77.23% and 62.83% 4HA from F&VP and PGP waste respectively by GOMIP-A. Subsequently, desorbed 4HA from GOMIP-A matrices exhibited the antioxidant potential of 33.53% (F&VP extract) and 47.97% (PGP extract) for DPPH radical.

Recent application of molecular imprinting technique in food safety

Due to the extensive use of chemical substances such as pesticides, antibiotics and food additives, food safety issues have gradually attracted people's attention. The extensive use of these chemicals seriously damages human health. In order to detect trace chemical residues in food, researchers have to find several simple, economical and effective tools for qualitative and quantitative analysis. As a kind of material that specifically and selectively recognize template molecules from real samples, molecular imprinting technique (MIT) has widely applied in food samples analysis. This article mainly reviews the application of molecularly imprinted polymer (MIP) in the detection of chemical residues from food in the past five years. Some recent and novel methods for fabrication of MIP are reviewed. Their application of sample pretreatment, sensors, etc. in food analysis is reviewed. The application of molecular imprinting in chromatographic stationary phase is referred. Additionally, the challenges faced by MIP are discussed.

In Situ Functionalization of Silver Nanoparticles by Gallic Acid as a Colorimetric Sensor for Simple Sensitive Determination of Melamine in Milk

A simple and green colorimetric sensing assay strategy for highly efficient determination of melamine has been fabricated, which is based on the redox reaction of gallic acid with Ag+. Monodispersed Ag nanoparticles (AgNPs) were obtained using gallic acid as a reducing and stabilizing agent. However, the aggregate behavior of AgNPs was observed, while the melamine was present in the reaction medium. As a result, the color of the solution changed from vivid yellow to brown, and the density of the color was quantitatively correlated with the melamine concentration. The aggregation of AgNPs could be attributable to the formation of hydrogen bonds between melamine and gallic acid. The designed sensor exhibited a good detection limit of 0.099 μM (0.012 ppm), which was much lower than the safety limit in China (1.0 ppm) and EU (2.0 ppm). Additionally, the sensing assay displayed good selectivity toward melamine over other coexisting substances. Consequently, the proposed colorimetric sensor was successfully used for the determination of melamine detection in raw milk samples.

Molecularly Imprinted Polymers for Dispersive (Micro)Solid Phase Extraction: A Review

The review describes the development of batch solid phase extraction procedures based on dispersive (micro)solid phase extraction with molecularly imprinted polymers (MIPs) and magnetic MIPs (MMIPs). Advantages and disadvantages of the various MIPs for dispersive solid phase extraction and dispersive (micro)solid phase extraction are discussed. In addition, an effort has also been made to condense the information regarding MMIPs since there are a great variety of supports (magnetite and magnetite composites with carbon nanotubes, graphene oxide, or organic metal framework) and magnetite surface functionalization mechanisms for enhancing MIP synthesis, including reversible addition-fragmentation chain-transfer (RAFT) polymerization. Finally, drawbacks and future prospects for improving molecularly imprinted (micro)solid phase extraction (MIMSPE) are also appraised.

Selective, sensitive, and miniaturized analytical method based on molecularly imprinted graphene oxide composites for the determination of naphthalene-derived plant growth regulators in apples

This paper reports a selective, sensitive, and miniaturized analytical method based on a molecularly imprinted graphene oxide (MIP-GO) composite as adsorbent for miniaturized tip solid-phase extraction (MTSPE) to determine naphthalene-derived plant growth regulators (PGRs) in apples. The proposed method combines the advantages of MIP-GOs (high selectivity), MTSPE (low consumption), and high-performance liquid chromatography-fluorescence detection (high sensitivity). Under optimized conditions, the method exhibited appreciable linearity (2.00-200 ng/g), low detection limits (0.21-0.53 ng/g), high accuracy (absolute recoveries: 87.6-99.5%), and high precision (relative standard deviations ≤ 3.0%), along with low consumption (0.5 mL sample solution and 2.0 mg adsorbent). In addition, the adsorption performance of the MIP-GO adsorbent did not decrease over ten months, highlighting the long storage and operational lifetime of the adsorbent. The proposed method was employed for the analysis of naphthalene-derived PGR residues in apples and exhibited promising potential for application in food safety analysis.

Functional Magnetic Graphene Composites for Biosensing

Magnetic graphene composites (MGCs), which are composed of magnetic nanoparticles with graphene or its derivatives, played an important role in sensors development. Due to the enhanced electronic properties and the synergistic effect of magnetic nanomaterials and graphene, MGCs could be used to realize more efficient sensors such as chemical, biological, and electronic sensors, compared to their single component alone. In this review, we first reviewed the various routes for MGCs preparation. Then, sensors based on MGCs were discussed in different groups, including optical sensors, electrochemical sensors, and others. At the end of the paper, the challenges and opportunities for MGCs in sensors implementation are also discussed.

Selective extraction and detection of β-agonists in swine urine for monitoring illegal use in livestock breeding

The illegal use of β-agonists often endangers animal-derived food safety. In this study, a selective detection method for β-agonists in swine urine was established via the combination of polymeric ionic liquid-molecularly imprinted graphene oxide-miniaturized pipette tip solid-phase extraction and high-performance liquid chromatography. It is worth noting that this method relied mainly on the designed adsorbent, which presented a rich adsorption mechanism, fast mass transfer rate, and high selectivity, and was successfully utilized in the selective extraction of β-agonists from swine urine samples. The proposed method has low LOD (0.20-0.56 ng/mL), high recovery (94.9-107.9%), and high reusability (4 times, 91.9-108.8%), which indicates its high potential as a selective, sensitive, accurate, and nonfatal method for monitoring the illegal use of β-agonists in the livestock breeding stage.

Theoretical design, preparation, and evaluation of Ginkgolide B molecularly imprinted polymers

Ginkgolide B is in great demand worldwide on account of its extensive and excellent pharmacological effects, however, it is difficult to separate and purify ginkgolide B. In this study, ginkgolide B molecularly imprinted polymers were prepared by combining software simulation and molecular imprinting technique, and its characterization and adsorption performed evaluation were performed to understand the adsorption behavior of the polymers. The adsorption equilibrium concentration of molecularly imprinted polymers was 0.70 mg/mL, and the adsorption equilibrium time was 4 h. Meanwhile, the adsorption isotherm of the polymers for ginkgolide B fitted well with the Langmuir model, and the adsorption kinetics was in line with the pseudo-second-order kinetics. In contrast, the adsorption capacity of molecularly imprinted polymers on ginkgolide B was higher than that of non-molecular imprinted polymers, with better selectivity and better adsorption after repeated use for six times. The application experiments showed that molecular imprinted polymers have a good adsorption effect in low purity samples. Therefore, the polymers reported herein can be expected to apply in the adsorption and separation of ginkgolide B samples.

Preparation of porous aromatic framework modified graphene oxide for pipette-tip solid-phase extraction of theophylline in tea

A new material called as porous aromatic frameworks modified graphene oxide (PAFs-GO) was synthesized, and it was used as an adsorbent in pipette-tip SPE for the effective purification and enrichment of theophylline in tea sample by HPLC. The properties of PAFs-GO were characterized by field emission SEM, FTIR, thermogravimetry analysis and Brunauer Emmett Teller N₂ adsorption-desorption analysis. The results of static adsorption and dynamic adsorption test showed PAFs-GO had higher adsorption ability (93.25 mg/g) than graphene oxide. The LOD and LOQ of the method were 0.0141 and 0.0471 µg/mL, respectively. The acceptable method reproducibility was found as intra- and inter-day precisions, yielding the RSDs <4.62%. By introducing PAFs as support skeleton, the specific surface area of GO was effectively increased, and the penetrability was improved. Studies showed that the proposed method had been successfully applied for purification and enrichment of theophylline in complex tea matrix.