Rapid determination of aflatoxin B1 by an automated immunomagnetic bead purification sample pretreatment method combined with high-performance liquid chromatography

Characterization of a Trametes versicolor aflatoxin B1-degrading enzyme (TV-AFB1D) and its application in the AFB1 degradation of contaminated rice in situ

Aflatoxin B₁ (AFB₁) contaminates rice during harvest or storage and causes a considerable risk to human and animal health. In this study, Trametes versicolor AFB₁–degrading enzyme (TV–AFB₁D) gene recombinantly expressed in engineered E. coli BL21 (DE3) and Saccharomyces cerevisiae. The TV–AFB₁D enzymatic characteristics and AFB₁ degradation efficiency in contaminated rice were investigated. Results showed that the size of recombinant TV-AFB₁D expressing in E. coli BL21 (DE3) and S. cerevisiae was appropriately 77 KDa. The kinetic equation of TV-AFB₁D was y = 0.01671x + 1.80756 (R² = 0.994, K_m = 9.24 mM, and V_max = 553.23 mM/min). The Kcat and Kcat/K_m values of TV-AFB₁D were 0.07392 (s⁻¹) and 8 M⁻¹ s⁻¹, respectively. The AFB₁ concentration of contaminated rice decreased from 100 μg/ml to 32.6 μg/ml after treatment at 32°C for 5 h under the catabolism of TV-AFB₁D. S. cerevisiae engineered strains carrying aldehyde oxidase 1 (AOX1) and Cauliflower mosaic virus 35 S (CaMV 35 S) promoters caused the residual AFB₁ contents, respectively, decreased to 3.4 and 2.9 μg/g from the initial AFB₁ content of 7.4 μg/g after 24 h of fermentation using AFB₁-contaminated rice as substrate. The AFB₁ degradation rates of S. cerevisiae engineered strains carrying AOX1 and CaMV promoters were 54 and 61%, respectively. Engineered S. cerevisiae strains integrated with TV-AFB₁D expression cassettes were developed to simultaneously degrade AFB₁ and produce ethanol using AFB₁-contaminated rice as substrate. Thus, TV-AFB₁D has significant application potential in the AFB₁ decomposition from contaminated agricultural products.

Rapid determination of 2,4-diaminopyrimidine residues through sample pretreatment using immunomagnetic bead purification along with HPLC-UV

To reduce matrix interference and realize simultaneous detection of multiple homologous compounds (trimethoprim (TMP), diaveridine (DVD), ormetoprim (OMP), baquiloprim (BQP), and aditoprim (ADP) in pig, cattle, chicken, and fish muscles), an immunomagnetic bead (IMB)-based sample purification pretreatment with HPLC-UV was developed. A broad-spectrum monoclonal antibody (mAb, named 14C6) was prepared and conjugated with carboxylic-acid-functionalized magnetic nanoparticles using the active ester method to obtain IMBs for sample purification. The extraction solvent was optimized based on the extraction efficiency. Good linearity was observed for all the five analytes (10-200 μg/kg) with the LOD and LOQ of 5 and 10 μg/kg, respectively. The mean recoveries ranged from 62.5% to 76.9%, while the coefficient of variation was <12.2%. The IMB method afforded greater sample purification and enrichment than those achieved with the SPE column-based conventional method. Hence, the IMB-based sample purification is a useful tool to determine 2,4-diaminopyrimidine residues in edible animal tissues.

Gold nanoparticle-based colorimetric aptasensor for rapid detection of multiple mycotoxins in rice

A novel, simple and rapid colorimetric aptasensor for multiple mycotoxins (ochratoxin A (OTA) and aflatoxin B₁ (AFB₁)) detection was developed using unmodified gold nanoparticles (AuNPs). In the work, the high affinities of OTA and AFB₁ aptamers were employed as the recognition elements for the colorimetric determination of OTA and AFB₁. In the absence of mycotoxins, the sulfhydryl-modified aptamers were directly adsorbed to the AuNP surface through Au-S bonds, further prohibiting the aggregation induced by a high concentration of salt, and the solutions remain red. In the presence of mycotoxins, the corresponding aptamer-target complexes were formed and the corresponding aptamers were detached from the surface of AuNPs, leading to the aggregation of AuNPs under the optimal salt solution and a color change. By spectroscopic quantitative analysis and visual analysis, the LODs of OTA and AFB₁ were down to 0.005 ng mL^-1 and 0.07 ng mL^-1, respectively. Furthermore, the colorimetric aptasensor showed a high specificity in the presence of other interfering mycotoxins and metal ions. Finally, the developed aptasensor was applicable to detect OTA and AFB₁ in rice samples with satisfactory performance. Our strategy has great potential for the rapid and sensitive detection of OTA and AFB₁ for on-site analysis.

Establishment of a Chemiluminescence Immunoassay Combined with Immunomagnetic Beads for Rapid Analysis Of Ochratoxin A

BACKGROUND

Ochratoxins A (OTA), as the harmful mycotoxins, are toxic secondary metabolite produced by several species of Aspergillus and Penicillium. Hence, it is of vital important to establish a sensitive method to detect OTA in various grains.

OBJECTIVE

Herein a novel highly sensitive chemiluminescence immunoassay was developed to determination of ochratoxin A in wheat, corn, and poultry feed.

METHODS

The immunomagnetic beads were used as solid phase carrier and separator in the competitive chemiluminescence method, the monoclonal antibodies anti-OTA coated on immunomagnetic beads were applied as the capturing antibody, in which OTA would compete with Ochratoxin A-alkaline phosphatase (OTA-ALP) in binding with OTA antibodies.

RESULTS

The proposed method exhibited good linearity (R2 ≥ 0.999), adequate OTA recovery rate (83.60% to 102.50%), and good repeatability. The sensitivity of the proposed method was 2.05 pg/mL. In addition, the method was highly selective, it did not have cross-reaction with other mycotoxin (e.g., AFB1, DON, ZEN). Furthermore, the developed method was applied in the analysis of wheat, corn and two animal feeds successfully, the results obtained by the chemiluminescence method showed the high correlation with those obtained by HPLC method (correlation coefficient 0.9958) when testing each extract by both methods.

CONCLUSIONS

This strategy shows great potential application for other toxic and harmful mycotoxin detection.

HIGHLIGHTS

A novel highly rapid and sensitive chemiluminescence immunoassay was established to quantitation for ochratoxin A.

Label-Free Amperometric Immunosensor Based on Versatile Carbon Nanofibers Network Coupled with Au Nanoparticles for Aflatoxin B1 Detection

Facile detection methods for mycotoxins with high sensitivity are of great significance to prevent potential harm to humans. Herein, a label-free amperometric immunosensor based on a 3-D interconnected carbon nanofibers (CNFs) network coupled with well-dispersed Au nanoparticles (AuNPs) is proposed for the quantitative determination of aflatoxin B₁ (AFB₁) in wheat samples. In comparison to common carbon nanotubes (CNTs), the CNFs network derived from bacterial cellulose biomass possesses a unique hierarchically porous structure for fast electrolyte diffusion and a larger electrochemical active area, which increases the peak current of differential pulse voltammetry curves for an immunosensor. Combined with AuNPs that are incorporated into CNFs by using linear polyethyleneimine (PEI) as a soft template, the developed Au@PEI@CNFs-based immunosensor showed a good linear response to AFB₁ concentrations in a wide range from 0.05 to 25 ng mL^-1. The limit of detection was 0.027 ng mL^-1 (S/N = 3), more than three-fold lower than that of an Au@PEI@CNTs-based sensor. The reproducibility, storage stability and selectivity of the immunosensor were proved to be satisfactory. The developed immunosensor with appropriate sensitivity and reliable accuracy can be used for the analysis of wheat samples.