Fluorescent microsphere immunochromatographic sensor for ultrasensitive monitoring deoxynivalenol in agricultural products

Rapid and simultaneous detection of five mycotoxins and their analogs with a gold nanoparticle-based multiplex immuno-strip sensor

Mycotoxins, as secondary metabolites produced by fungi, have been the focus of researchers in various countries and are considered to be one of the major risk factors in agricultural products. There is an urgent need for a rapid, simple and high-performance method to detect residues of harmful mycotoxins in agricultural foods. We have developed a gold nanoparticle-based multiplexed immunochromatographic strip biosensor that can simultaneously detect fifteen mycotoxins in cereal samples. With this optimized procedure, five representative mycotoxins, deoxynivalenol (DON), zearalenone (ZEN), T-2 toxin (T-2), tenuazonic acid (TEA) and alternariol (AOH) were detected in the range of 0.91-4.77, 0.04-0.56, 0.11-0.68, 0.12-1.02 and 0.09-0.75 ng/mL, respectively. The accuracy and stability of these measurements were demonstrated by analysis of spiked samples with recoveries of 91.8%-115.3% and coefficients of variation <8.7%. In addition, commercially available samples of real cereals were tested using the strips and showed good agreement with the results verified by LC-MS/MS. Therefore, Our assembled ICA strips can be used for the simultaneous detection of 5 mycotoxins and their analogs (15 mycotoxins in total) in grain samples, and the results were consistent between different types of cereal foods, this multiplexed immunochromatographic strip biosensor can be used as an effective tool for the primary screening of mycotoxin residues in agricultural products.

Development of alkaline phosphatase-linked single-chain variable fragment fusion proteins for one-step immunodetection of deoxynivalenol in cereals

Deoxynivalenol (DON) is a mycotoxin that widely distributes in various foods and seriously threatens food safety. To minimize the consumers' dietary exposure to DON, there is an urgent demand for developing rapid and sensitive detection methods for DON in food. In this study, a bifunctional single-chain variable fragment (scFv) linked alkaline phosphatase (ALP) fusion protein was developed for rapid and sensitive detection of deoxynivalenol (DON). The scFv gene was chemically synthesized and cloned into the expression vector pET25b containing the ALP gene by homologous recombination. The prokaryotic expression, purification, and activity analysis of fusion proteins (scFv-ALP and ALP-scFv) were well characterized and performed. The interactions between scFv and DON were investigated by computer-assisted simulation, which included hydrogen bonds, hydrophobic interactions, and van der Waals forces. The scFv-ALP which showed better bifunctional activity was selected for developing a direct competitive enzyme-linked immunosorbent assay (dc-ELISA) for DON in cereals. The dc-ELISA takes 90 min for one test and exhibits a half inhibitory concentration (IC50) of 11.72 ng/mL, of which the IC50 was 3.08-fold lower than that of the scFv-based dc-ELISA. The developed method showed high selectivity for DON, and good accuracy was obtained from the spike experiments. Furthermore, the detection results of actual cereal samples analyzed by the method correlated well with that determined by high-performance liquid chromatography (R2=0.97165). These results indicated that the scFv-ALP is a promising bifunctional probe for developing the one-step colorimetric immunoassay, providing a new strategy for rapid and sensitive detection of DON in cereals.

Development of an immunochromatographic assay for the rapid screening of torasemide in health food

Torasemide is a new loop diuretic agent added illegally to health foods for weight loss, which can result in serious health risks for consumers. A rapid and sensitive immunochromatographic assay for detection of torasemide (ICA) based on a new monoclonal antibody (mAb) was developed. The mAb IC50 for torasemide was 0.93 ng/mL, and the mAb did not cross-react with other analogues. In PBS, the cut-off value and limit of detection were 1 ng/mL and 0.11 ng/mL, respectively, with a linear range between 0.61 and 6.13 ng/mL. In slimming tablet and capsule samples, the cut-off value was 5 ng/g. Recoveries were 101.1% ± 1.7%-106.1% ± 1.3% in tablet samples and 101.2% ± 2.2%-109.1% ± 3.9% in capsule samples, with coefficients of variation 2.1%-3.1% and 1.8%-3.6%, respectively, consistent with existing LC-MS/MS methods. Therefore, the ICA is suitable for use in slimming tablet and capsule samples.

Paper-based visualization of auramine O in food and drug samples with carbon dots-incorporated fluorescent microspheres as sensing element

A paper-based assay for visualization of auramine O (AO) was for the first time established by using CFMs as a ratiometric fluorescent probe (RFP). The CFMs were melamine formaldehyde microspheres (MFMs) incorporated with carbon dots (CDs), where the CDs species as sensing units and MFMs as a signal amplification carrier. The proposed RFP can quantitatively measure AO content from 0.0 to 10.0 μM and exhibited an ultralow limit of detection (LOD, 15.7 nM). In particular, obvious luminescence color change of CFMs from blue to green was perceived with naked-eyes and therefore, a solution-based and a paper-based visualization platform were respectively proposed for on-site visual detection of AO with LODs of 1.15 μM and 0.83 μM, separately. Finally, those fluorescence methods were adopted in sensitively quantitative measurement of AO within various food and drug samples, providing new prospects for analysts and technical support in food quality monitoring.

Current Trends in Mycotoxin Detection with Various Types of Biosensors

One of the most important tasks in food safety is to properly manage the investigation of mycotoxin contamination in agricultural products and foods made from them, as well as to prevent its occurrence. Monitoring requires a wide range of analytical methods, from expensive analytical procedures with high-tech instrumentation to significantly cheaper biosensor developments or even single-use assays suitable for on-site monitoring. This review provides a summary of the development directions over approximately a decade and a half, grouped according to the biologically sensitive components used. We provide an overview of the use of antibodies, molecularly imprinted polymers, and aptamers, as well as the diversity of biosensors and their applications within the food industry. We also mention the possibility of determining multiple toxins side by side, which would significantly reduce the time required for the analyses.

Strategy of functional nucleic acids-mediated isothermal amplification for detection of foodborne microbial contaminants: A review

Foodborne microbial contamination (FMC) is the leading cause of food poisoning and foodborne illness. The foodborne microbial detection methods based on isothermal amplification have high sensitivity and short detection time, and functional nucleic acids (FNAs) could extend the detectable object of isothermal amplification to mycotoxins. Therefore, the strategy of FNAs-mediated isothermal amplification has been emergingly applied in biosensors for foodborne microbial contaminants detection, making biosensors more sensitive with lower cost and less dependent on nanomaterials for signal output. Here, the mechanism of six isothermal amplification technologies and their application in detecting FMC is firstly introduced. Then the strategy of FNAs-mediated isothermal amplification is systematically discussed from perspectives of FNAs' versatility including recognition elements (Aptamer, DNAzyme), programming tools (DNA tweezer, DNA walker and CRISPR-Cas) and signal units (G-quadruplex, FNAs-based nanomaterials). Finally, challenges and prospects are presented in terms of addressing the issue of nonspecific amplification reaction, developing better FNAs-based sensing elements and eliminating food matrix effects.

Enhanced Competitive Immunomagnetic Beads Assay Assisted with PAMAM-Gold Nanoparticles Multi-Enzyme Probes for Detection of Deoxynivalenol

Contamination of deoxynivalenol (DON) in grains has attracted widespread concern. It is urgently needed to develop a highly sensitive and robust assay for DON high-throughput screening. Antibody against DON was assembled on the surface of immunomagnetic beads orientationally by the aid of Protein G. AuNPs were obtained under the scaffolding of poly(amidoamine) dendrimer (PAMAM). DON-horseradish peroxidase (HRP) was combined on the periphery of AuNPs/PAMAM by a covalent link to develop DON-HRP/AuNPs/PAMAM. Magnetic immunoassay based on DON-HRP/AuNPs/PAMAM was optimized and that based on DON-HRP/AuNPs and DON-HRP was adopted as comparison. The limits of detection (LODs) were 0.447 ng/mL, 0.127 ng/mL and 0.035 ng/mL for magnetic immunoassays based on DON-HRP, DON-HRP/Au and DON-HRP/Au/PAMAM, respectively. Magnetic immunoassay based on DON-HRP/AuNPs/PAMAM displayed higher specificity towards DON and was utilized to analyze grain samples. The recovery for the spiked DON in grain samples was 90.8-116.2% and the method presented a good correlation with UPLC/MS. It was found that the concentration of DON was in the range of ND-3.76 ng/mL. This method allows the integration of dendrimer-inorganic NPs with signal amplification properties for applications in food safety analysis.

The Simultaneous Determination of Chlorpyrifos-Ethyl and -Methyl with a New Format of Fluorescence-Based Immunochromatographic Assay

The improper and excessive use in agriculture of chlorpyrifos-methyl (CPSM) and chlorpyrifos-ethyl (CPSE) may affect the health of human beings. Herein, a fluorescence-based immunochromatographic assay (FICA) was developed for the simultaneous determination of CPSM and CPSE. A monoclonal antibody (mAb) with equal recognition of CPSM and CPSE was generated by the careful designing of haptens and screening of hybridoma cells. Instead of labeling fluorescence with mAb, the probe was labeled with goat-anti-mouse IgG (GAM-IgG) and pre-incubated with mAb in the sample. The complex could compete with CPS by coating antigen in the test line. The new format of FICA used goat-anti-rabbit IgG (GAR-IgG) conjugated with rabbit IgG labeled with fluorescence microspheres as an independent quality control line (C line). The novel strategy significantly reduced nonspecific reactions and increased assay sensitivity. Under the optimal conditions, the proposed FICA showed a linear range of 0.015-64 mg/L and limit of detection (LOD) of 0.015 mg/L for both CPSE and CPSM. The average recoveries of CPS from spiked food samples by FICA were 82.0-110.0%. The accuracy was similar to the gas chromatography-tandem mass spectrometry (GC-MS/MS) results. The developed FICA was an ideal on-site tool for rapid screening of CPS residues in foods.

Surface Plasmon Resonance (SPR) biosensor for detection of mycotoxins: A review

Mycotoxin is one of the most important natural pollutants, which poses a global threat to food safety. However, the pollution of mold in food production is inevitable. The detection technology of mycotoxins in food production is an important means to prevent the damage of mycotoxins, so rapid detection and screening to avoid pollution diffusion is essential. The focus of this review is to update the literature on the detection of mycotoxins by surface plasmon resonance (SPR) technology, rather than just traditional chromatographic methods. As a relatively novel and simple analytical method, SPR has been proved to be fast, sensitive and label-free, and has been widely used in real-time qualitative and quantitative analysis of various pollutants. This paper aims to give a broad overview of the sensors for detection and analysis of several common mycotoxins.

Preparation of Monoclonal Antibody against Deoxynivalenol and Development of Immunoassays

Fusarium toxins are the largest group of mycotoxins, which contain more than 140 known secondary metabolites of fungi. Deoxynivalenol (DON) is one of the most important compounds of this class due to its high toxicity and its potential to harm mankind and animals and a widespread contaminant of agricultural commodities, such as wheat, corn, barley, oats, bread, and biscuits. Herein, a hybridoma cell 8G2 secreting mAb against DON was produced by fusing the splenocytes with a tumor cell line Sp2/0. The obtained mAb had a high affinity (2.39 × 10⁹ L/mol) to DON. An indirect competitive Enzyme-Linked Immunosorbent Assay (ic-ELISA) showed that the linear range for DON detection was 3.125–25 μg/mL, and the minimum inhibitory concentration (IC₅₀) was 18.125 μg/mL with a limit of detection (LOD) of 7.875 μg/mL. A colloidal gold nanoparticle (AuNP) with 20 nm in diameter was synthesized for on-site detection of DON within 10 min with vLOD of 20 μg/mL. To improve the limit of detection, the gold nanoflower (AuNF) with a larger size (75 nm) was used to develop the AuNF-based strip with vLOD of 6.67 μg/mL. Compared to the vLOD of a convectional AuNP-based strip, the AuNF-based strip was three times lower. Herein, three immunoassay methods (ic-ELISA and AuNP/AuNF-based strips) were successfully developed, and these methods could be applied for the DON detection in agricultural products.

Rapid, on-site quantitative determination of higenamine in functional food using a time-resolved fluorescence microsphere test strip

Higenamine (HIG), a benzyltetrahydroisoquinoline alkaloid found naturally in plants, is classified as an S3 Prohibited Substance in the 2020 World Anti-Doping Agency (WADA) report. To avoid problems such as doping violations in competitive events, it is necessary to develop rapid and sensitive detection methods. In this study, a highly-sensitive anti-HIG monoclonal antibody (mAb) was prepared and a time-resolved fluorescent microsphere immunochromatographic test strip (TRFM-ICTS) was established for the rapid quantitative detection of HIG in functional foods. Under optimized conditions, the TRFM-ICTS was compared with colloidal gold immunochromatographic test strip (CG-ICTS), and the half-maximal inhibitory concentration (IC₅₀) of TRFM-ICTS was 1.37 ng/mL. The spiked recoveries ranged from 86.4% to 105.3%, which was consistent with the results of liquid chromatography-tandem mass spectrometry (LC-MS/MS) in the detection of real functional food. Therefore, TRFM-ICTS can be a candidate method for doping monitoring in functional foods and a powerful tool for HIG quantification.

Immunoassay technology: Research progress in microcystin-LR detection in water samples

Increasing global warming and eutrophication have led to frequent outbreaks of cyanobacteria blooms in freshwater. Cyanobacteria blooms cause the death of aquatic and terrestrial organisms and have attracted considerable attention since the 19th century. Microcystin-LR (MC-LR) is one of the most typical cyanobacterial toxins. Therefore, the fast, sensitive, and accurate determination of MC-LR plays an important role in the health of humans and animals. Immunoassay refers to a method that uses the principle of immunology to determine the content of the tested substance in a sample using the tested substance as an antigen or antibody. In analytical applications, the immunoassay technology could use the specific recognition of antibodies for MC-LR detection. In this review, we firstly highlight the immunoassay detection of MC-LR over the past two decades, including classical enzyme-link immunosorbent assay (ELISA), modern immunoassay with optical signal, and modern immunoassay with electrical signal. Among these detection methods, the water environment was used as the main detection system. The advantages and disadvantages of the different detection methods were compared and analyzed, and the principles and applications of immunoassays in water samples were elaborated. Furthermore, the current challenges and developmental trends in immunoassay were systematically introduced to enhance MC-LR detection performance, and some critical points were given to deal with current challenges. This review provides novel insight into MC-LR detection based on immunoassay method.

Immunochromatographic assays for ultrasensitive and high specific determination of enrofloxacin in milk, eggs, honey, and chicken meat

Enrofloxacin, a veterinary antibiotic that persists in food, poses a risk to human health. Here, a monoclonal antibody against enrofloxacin, 1H12, was prepared based on the hapten ENR-1, and showed excellent sensitivity with a 50% inhibitory concentration (IC₅₀) of 0.03 ng/mL. Using this antibody, 2 lateral-flow immunochromatographic assays were developed for determination of enrofloxacin in egg, milk, honey, and chicken meat samples. The detection ranges (IC₂₀-IC₈₀) were 0.16-0.82 ng/g, 0.24-1.8 ng/g, 0.25-3.6 ng/g, and 0.61-3.9 ng/g by colloidal gold-immunochromatographic sensor (CG-ICS) analysis, and 0.022-0.42 ng/g, 0.054-0.42 ng/g, 0.069-1.4 ng/g, and 0.19-2.2 ng/g by Eu-fluorescence-immunochromatographic sensor (EF-ICS) analysis. The intraassay and interassay recovery rates were 88.9 to 108.5% with coefficients of variation of 1.3 to 7.0% by CG-ICS analysis, and 88.6 to 113.6% with coefficients of variation of 1.3 to 8.1% by EF-ICS analysis. Thus, our newly developed ICS are sensitive and reliable, providing an option for rapid quantitative detection of enrofloxacin in food samples.

A fluorescent paper biosensor for the rapid and ultrasensitive detection of zearalenone in corn and wheat

Zearalenone (ZEN) is a kind of estrogen-like mycotoxin which contaminates primary crops and their products under natural conditions and becomes a serious hazard to human health. In this study, we prepared a sensitive and specific anti-ZEN monoclonal antibody (mAb) belonging to the IgG2b subclass, with a 50%-inhibitory concentration of 0.034 ng mL^-1. A lateral flow fluorescence microsphere immunochromatographic test strip (FM-ICTS) for the rapid and ultrasensitive detection of zearalenone in corn and wheat samples was developed based on this mAb. After optimizing experimental parameters, the visual limit of detection (LOD) of the strip assay in both corn and wheat samples was 2.5 ng mL^-1, and the cut-off value was 25 ng mL^-1. The LOD was calculated to be 0.68 ng mL^-1 in corn samples and 0.48 ng mL^-1 in wheat samples. Recovery experiments showed that the test results of the strip were consistent with those of ic-ELISA. As a result, this FM-ICTS assay is reliable, simple and sensitive, and can be used for rapid detection of ZEN in corn and wheat.