Ultrasensitive detection of clenbuterol by a covalent imprinted polymer as a biomimetic antibody

Molecularly imprinted polymers for environmental adsorption applications

Molecular imprinting polymers (MIPs) are synthetic materials with pores or cavities to specifically retain a molecule of interest or analyte. Their synthesis consists of the generation of three-dimensional polymers with specific shapes, arrangements, orientations, and bonds to selectively retain a particular molecule called target. After target removal from the binding sites, it leaves empty cavities to be re-occupied by the analyte or a highly related compound. MIPs have been used in areas that require high selectivity (e.g., chromatographic methods, sensors, and contaminant removal). However, the most widely used application is their use as a highly selective extraction material because of its low cost, easy preparation, reversible adsorption and desorption, and thermal, mechanical, and chemical stability. Emerging pollutants are traces of substances recently found in wastewater, river waters, and drinking water samples that represent a special concern for human and ecological health. The low concentration in which these pollutants is found in the environment, and the complexity of their chemical structures makes the current wastewater treatment not efficient for complete degradation. Moreover, these substances are not yet regulated or controlled for their discharge into the environment. According to the literature, MIPs, as a highly selective adsorbent material, are a promising approach for the quantification and monitoring of emerging pollutants in complex matrices. Therefore, the main objective of this work was to give an overview of the actual state-of-art of applications of MIPs in the recovery and concentration of emerging pollutants.

Determination of Fumonisin B1 by Aptamer-Based Fluorescence Resonance Energy Transfer

Fumonisin FB is produced by Fusarium moniliforme Sheld, of which FB₁ is the most common and the most toxic. The establishment of a rapid detection method is an important means to prevent and control FB₁ pollution. A highly sensitive fluorescent sensor based on an aptamer for the rapid detection of fumonisin B₁ (FB₁) in corn was established. In this study, 5-carboxyfluorescein (FAM) was labeled on the aptamer of FB₁ (F10). F10 was adsorbed on the surface of graphene oxide (GO) by π-π stacking. The FAM fluorescence signal could be quenched by fluorescence resonance energy transfer between fluorescent molecules and graphene oxide (GO). In the presence of FB₁, the binding efficiency of the aptamer to GO was reduced. Therefore, the content of FB₁ in corn samples was determined by fluorescence measurements of mixed FAM-labeled F10, GO and corn samples. This method had a good linear relationship in an FB₁ concentration range of 0-3000 ng/mL. The equation was y = 0.2576x + 10.98, R² = 0.9936. The limit of detection was 14.42 ng/mL, and the limit of quantification was 43.70 ng/mL. The recovery of a spiked standard in the corn sample was 89.13-102.08%, and the time of detection was 30 min.

N-(2-Arylethyl)-2-methylprop-2-enamides as Versatile Reagents for Synthesis of Molecularly Imprinted Polymers

The paper describes the formation of six aromatic N-(2-arylethyl)-2-methylprop-2-enamides with various substituents in benzene ring, viz., 4-F, 4-Cl, 2,4-Cl₂, 4-Br, 4-OMe, and 3,4-(OMe)₂ from 2-arylethylamines and methacryloyl chloride in ethylene dichloride with high yields (46–94%). The structure of the compounds was confirmed by ¹H NMR, ¹³C NMR, IR, and HR-MS. Those compounds were obtained to serve as functionalized templates for the fabrication of molecularly imprinted polymers followed by the hydrolysis of an amide linkage. In an exemplary experiment, the imprinted polymer was produced from N-(2-(4-bromophenyl)ethyl)-2-methylprop-2-enamide and divinylbenzene, acting as cross-linker. The hydrolysis of 2-(4-bromophenyl)ethyl residue proceeded and the characterization of material including SEM, EDS, ¹³C CP MAS NMR, and BET on various steps of preparation was carried out. The adsorption studies proved that there was a high affinity towards the target biomolecules tyramine and L-norepinephrine, with imprinting factors equal to 2.47 and 2.50, respectively, when compared to non-imprinted polymer synthesized from methacrylic acid and divinylbenzene only.

Improving the Identification of Lysine-Acetylated Peptides Using a Molecularly Imprinted Monolith Prepared by a Deep Eutectic Solvent Monomer

To overcome the identification challenge of low-abundance lysine acetylation (Kac), a novel approach based on a molecularly imprinted polymer (MIP) was developed to improve the extraction capacity of Kac peptides in real samples. Green deep eutectic solvents (DESs) were introduced and used as one of the synergistic functional monomers with zinc acrylate (ZnA). Glycine-glycine-alanine-lysine(ac)-arginine (GGAKacR) was chosen as a template and N,N'-methylenbisacrylamide (MBAA) was used as a cross-linker. The obtained GGAKacR-MIP had excellent selectivity for the template with an imprinting factor (IF) of up to 21.4. The histone digest addition experiment demonstrated that GGAKacR-MIP could successfully extract GGAKacR from a complex sample. Finally, the application to the extraction of Kac peptides from mouse liver protein digestion was studied in detail. The number of Kac peptides and Kac proteins identified was 130 and 110, which were 3.71-fold and 3.93-fold higher than those of the untreated sample. In addition, the number of peptides and proteins identified after treatment increased from 5535 and 1092 to 17 149 and 4037 (3.10-fold and 3.70-fold, respectively). The results showed that the obtained MIP may provide an effective technical tool for the identification of Kac-modification and peptide fractionation, as well as a potential approach for simultaneously identifying post-translational-modified proteomic and proteomic information.

Fluorescent sensing platform based on green luminescence carbon dots and AuNPs for clenbuterol detection in pork liver

In this paper, water-soluble green fluorescent carbon dots (G-CDs) were prepared using p-phenylenediamine and glutathione (GSH) as the precursors. The G-CDs exhibit excellent optical properties, and the maximum emission wavelength is located at 522 nm (under 410 nm excitation), which greatly overlaps with the absorption spectrum of AuNPs. Consequently, an effective “off–on” fluorescent sensing platform involved in G-CDs and AuNPs for detection of clenbuterol (CLB) was constructed. The fluorescence of G-CDs was strongly quenched by AuNPs due to the inner filter effect (IFE). As CLB was introduced, the quenched fluorescence intensity was recovered due to the specific interaction between the AuNPs and CLB. The recovered fluorescence intensity is linear to CLB concentration in the range of 13–270 ng mL⁻¹ with a low detection limit of 3.75 ng mL⁻¹. The prepared sensor has been successfully applied for CLB detection in pork liver and could be utilized in food analysis.

Carbon dots (G-CDs) with bright green fluorescence are synthesized by hydrothermal treatment of p-phenylenediamine and glutathione. Employing the G-CDs and AuNPs as sensing platform, a simple fluorescence sensor to detect clenbuterol was established.

Application of Raman Spectroscopic Methods in Food Safety: A Review

Food detection technologies play a vital role in ensuring food safety in the supply chains. Conventional food detection methods for biological, chemical, and physical contaminants are labor-intensive, expensive, time-consuming, and often alter the food samples. These limitations drive the need of the food industry for developing more practical food detection tools that can detect contaminants of all three classes. Raman spectroscopy can offer widespread food safety assessment in a non-destructive, ease-to-operate, sensitive, and rapid manner. Recent advances of Raman spectroscopic methods further improve the detection capabilities of food contaminants, which largely boosts its applications in food safety. In this review, we introduce the basic principles of Raman spectroscopy, surface-enhanced Raman spectroscopy (SERS), and micro-Raman spectroscopy and imaging; summarize the recent progress to detect biological, chemical, and physical hazards in foods; and discuss the limitations and future perspectives of Raman spectroscopic methods for food safety surveillance. This review is aimed to emphasize potential opportunities for applying Raman spectroscopic methods as a promising technique for food safety detection.

Simultaneous Detection of Multiple β-Adrenergic Agonists with 2-Directional Lateral Flow Strip Platform

Clenbuterol (CL), salbutamol (SAL) and ractopamine (RAC) are the three common β-adrenergic agonists, which are the main hazards in food safety and affect human health through the food chain. A convenient and efficient method is urgently required to perform on-site detection of multiple β-adrenergic agonists to avoid frequent poisoning incidents. In this paper, a 2-directional lateral flow strip technique (2-directional LFS) is developed for rapid and simultaneous detection of CL, SAL and RAC with single sampling. Compared to the conventional lateral flow strip, this 2-directional LFS technique can realize simultaneous detection of three or more target analytes without any change of intrinsic simplicity of LFS. Furthermore, this 2-directional LFS can effectively avoid the potential intrinsic cross-reactivity among the reagents to analogues. Under the optimized conditions, CL, SAL and RAC were all successfully determined with satisfactory results in both buffer and urine samples with the detection limit as low as 0.5 ng/mL. This 2-directional LFS technique can revolutionize the commercial single-analyte LFS products and can effectively widen the applications of the classic LFS in various fields.

Development of Nanozyme-Labeled Biomimetic Immunoassay for Determination of Sulfadiazine Residue in Foods

The excessive use and ingestion of residues of sulfonamides harm the human body and the environment. To meet the requirements of the maximum residue limit specified by the Ministry of Agriculture of China, a rapid detection method urgently needs to be developed. In the present study, a molecularly imprinted polymer (MIP) that could selectively recognize sulfadiazine (SDZ) was prepared using SDZ as the template molecule and methacrylic acid as the functional monomer. Using MIP as biomimetic antibody and Au@Pt@SiO2 nanozyme as a marker, a new biomimetic immunoassay was developed to detect sulfadiazine. Under the optimal conditions, the limit of detection (IC15) and sensitivity (IC50) of this method were 0.09 and 6.1 mg/L, respectively. To determine the accuracy of this method, honey and milk samples spiked with sulfadiazine were analyzed, with recoveries in the range of 70.8%-90.2%. The method was also used for the quantitative analysis of sulfadiazine residues in milk powder and milk samples, producing results which correlated well with those obtained by high-performance liquid chromatography.

Fluorescence assay for three organophosphorus pesticides in agricultural products based on Magnetic-Assisted fluorescence labeling aptamer probe

There has been increasing recent concern about the agricultural use of organophosphorus pesticides. A rapid and sensitive fluorescence assay for the detection of three organophosphorus pesticides has therefore been developed using 6-carboxy-fluorescein labeling aptamer as the probe and functionalized magnetic nanoparticles as the separation carrier. The aptamer hybridized with complementary DNA conjugated on the surface of the magnetic nanoparticles to form a magnetic aptamer-complementary DNA complex. Upon introducing the target organophosphorus pesticide, the aptamer departed from the complementary DNA, resulting in the fluorescence signal. Under optimized conditions, the limits of detection (LODs, S/N = 3) for trichlorfon, glyphosate, and malathion were 72.20 ng L-1, 88.80 ng L-1, and 195.37 ng L-1, respectively. The method was applied for the detection of trichlorfon, glyphosate, and malathion in spiked lettuce and carrot samples. The recoveries were in the range of 79.4%-118.7%, which were in good agreement with those obtained by gas chromatography, and the relative standard deviations were also acceptable. The method therefore has high sensitivity, so provides a means for the detection of multiple organophosphorus pesticides.

A highly sensitive and accurate SERS/RRS dual-spectroscopic immunosensor for clenbuterol based on nitrogen/silver-codoped carbon dots catalytic amplification

Preparation of multifunctional codoped carbon dots, and their new analytical applications in surface-enhanced Raman scattering (SERS) quantitative analytical method are still challenge. To overcome these problems, the nitrogen/silver-codoped carbon dots (CD_N/Ag) with highly catalytic amplification are prepared by microwave method, and characterized by spectrophotometry and electron microscopy. The results show that CD_N/Ag can strongly catalyze trisodium citrate-HAuCl₄ reaction to generate red nanogold with resonance Rayleigh scattering (RRS) effect and SERS effect using Victoria blue B (VBB) as molecular probes. The CD_N/Ag catalytic amplification and specific immunoreaction of clenbuterol (Clen) are coupled with highly sensitive SERS and accurate RRS to fabricate a new dual-spectroscopic strategy with a detection limit of 0.68 pg mL^-1 Clen.

Recent advances of molecularly imprinted polymer-based sensors in the detection of food safety hazard factors

With increasing economic globalization, food safety is becoming the most serious concern in the food production and distribution system. Food safety hazard factors (FSHFs) can be categorized into chemical hazards, biological hazards and physical hazards, with the detection of the former two having fascinated interdisciplinary research areas spanning chemistry, material science and biological science. Molecularly imprinted polymer (MIP) -based sensors overcome many limitations of traditional detection methods and provide opportunities for efficient, sensitive and low-cost detection using smart miniaturized equipment. With highly specific molecular recognition capacity and high stability in harsh chemical and physical conditions, MIPs have been used in sensing platforms such as electrochemical, optical and mass-sensitive sensors as promising alternatives to bio-receptors for food analysis. In this systemic review, we summarize recent advances of MIPs and MIP-based sensors, such as popular monomers, usual polymerization strategies, fresh modification materials and advanced sensing mechanisms. The applications of MIP-based sensors in FSHF detection are discussed according to sensing mechanisms, including electrochemistry, optics and mass-sensitivity. Finally, future perspectives and challenges are discussed.

Fluorometric determination of ciprofloxacin using molecularly imprinted polymer and polystyrene microparticles doped with europium(III)(DBM)3phen

The authors describe a microparticle-based system for the detection of the fluoroquinolone antibiotic ciprofloxacin. The method is using the tris(dibenzoylmethane)(1,10-phenanthroline)europium(III) luminophore in polystyrene microparticles along with a molecularly imprinted polymer (MIP) for ciprofloxacin. If ciprofloxacin is captured by the MIP, it quenches the fluorescence of the luminophores. Fluorescence drops linearly in the 0.5-100 μg L^-1 ciprofloxacin concentration range, and the detection limit is 92 ng L^-1. The method was applied to the analysis of fish samples to assess the analytical performance of the probe. Recoveries ranged from 85.4 to 86.6%, and relative standard deviations between 2.1 and 3.9% (for n = 5). Graphical abstract Schematic presentation of a microparticle-based probe using the tris(dibenzoylmethane)(1,10-phenanthroline)europium(III) luminophore in polystyrene particles along with a molecularly imprinted polymer for ciprofloxacin. After removal of template, carboxylic groups left in the probe can bind to ciprofloxacin through hydrogen bonds.

A fluorometric clenbuterol immunoassay using sulfur and nitrogen doped carbon quantum dots

A fluorometric clenbuterol immunoassay is described that uses S- and N-co-doped carbon quantum dots as the fluorescent probe. Strongly fluorescent S/N-doped carbon quantum dots (S/N-CDs) were synthesized by hydrothermal method using fructose as the carbon precursor and L-cysteine as S/N sources. The S/N-CDs were characterized by transmission electron microscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy (FTIR). Under 350 nm photoexcitation, they display strong purple fluorescence with an emission peak at 405 nm. In pH 4.0 solution, the amino groups (confirmed by FTIR) on the carbon quantum dots were coupled to clenbuterol antibody (Ab) by amine-amine coupling reaction to quench the fluorescence. If clenbuterol (Clen) is added, it binds to the Ab to generate a stable Ab-Clen immunocomplex and free S/N-CD. This causes the fluorescence of nanoprobe to be restored. The fluorescence of the system increases linearly in the 0.07-1.7 ng·mL^-1 Clen concentration range. The probe of type S/N₄-CD displays the best sensitivity. The detection limit is 23 pg·mL^-1. Graphical abstract Schematic presentation of clenbuterol fluorometric immunoassay using sulfur and nitrogen doped carbon quantum dots.

A Novel Fluorescence and SPE Adsorption Nanomaterials of Molecularly Imprinted Polymers Based on Quantum Dot-Grafted Covalent Organic Frameworks for the High Selectivity and Sensitivity Detection of Ferulic Acid

A fluorescence and solid phase extraction (SPE) adsorption nanomaterials of molecularly imprinted polymers (MIPs) based on quantum dot-grafted covalent organic frameworks (QD-grafted COFs) was prepared by one-pot surface-imprinting synthesis method. Amino groups of silane reagent were at the surface of QDs to coordinate COFs efficiently by Schiff-base reactions, providing thermal and chemical stability to MIPs. It also reacted with the phenolic hydroxyl groups of ferulic acid (FA) through non-covalent interactions. The nanomaterials were used as fluorescence sensing and SPE adsorption toward determination of ferulic acid. The MIPs based on QD-grafted COFs had good fluorescence response ability, and quenching linearly at concentrations of ferulic acid from 0.03 to 60 mg kg^-1, with a detection limit of 5 µg kg^-1. At the same time, it exhibited a good SPE adsorption ability, and the FA extraction was from 1.63 to 3.11 mg kg^-1 in grain by-products by SPE coupled with high performance liquid chromatography/mass spectrometry (HPLC/MS). The fluorescence and SPE-HPLC/MS were used for the efficient detection of ferulic acid in real samples with recovery values of 88⁻114% and 90⁻97%, respectively. Furthermore, the nanomaterials of MIPs based on QD-grafted COFs were used for FA detection with high sensitivity and selectivity, and it also increased the recycling of waste resources.

Molecularly imprinted polymer nanoparticle-based assay (MINA): application for fumonisin B1 determination

The enzyme-linked immunosorbent assay (ELISA) has been used as a standard tool for monitoring food and animal feed contamination from the carcinogenic fumonisin B1 (FB1).