Dongxia Nie

A reliable liquid chromatography–tandem mass spectrometry method for simultaneous determination of multiple mycotoxins in fresh fish and dried seafoods

A reliable liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for simultaneous determination of nine mycotoxins, i.e., aflatoxin B1 (AFB1), aflatoxin B2 (AFB2), aflatoxin G1 (AFG1), aflatoxin G2 (AFG2), ochratoxin A (OTA), zearalenone (ZEN), T-2 toxin, HT2 toxin and deoxynivalenol (DON), in fresh fish (muscle and entrails) as well as dried seafoods. Special focus was given to sample pretreatment which is crucial for an accurate and reliable analytical method. With regards to the high complexity of the matrices, extraction solvent, time, and temperature as well as clean-up cartridges were optimized to improve extraction efficiency and reduce matrix effects. The optimum procedure included ultrasound-assisted extraction with acetonitrile/water/acetic acid (79/20/1, v/v/v) at 40 °C for 30 min, defatting with n-hexane and purification by Oasis HLB cartridges. The method was further validated by determining the linearity (R(2) ≥ 0.9989), sensitivity (limit of detection ≤ 2 μg/kg, limit of quantitation ≤ 3 μg/kg), recovery (72.2-119.9%) and precision (≤ 18.3%) in muscle and entrails of fresh crucian carp (Carassius carassius) as well as dried fish products. The method was proven to be suitable for its intended purposes. Mycotoxins of OTA, ZEN and AFB2 have been found in fresh fish and dried seafoods for the first time.

A rabbit monoclonal antibody-based sensitive competitive indirect enzyme-linked immunoassay for rapid detection of chloramphenicol residue

A sensitive competitive indirect enzyme-linked immunoassay (ciELISA) based on a rabbit monoclonal antibody (RabMAb) against chloramphenicol (CAP) has been developed and validated in this study. After optimisation of several key physicochemical factors, such as Tween-20 percentage, pH value and ionic strength, the immunoassay showed excellent performance within the linear range of 0.18–6.37 ng mL−1, with the 50% inhibition concentration (IC50) of 1.06 ng mL−1 and the limit of detection (LOD) of 0.1 ng mL−1. In addition, the cross-reactivities of RabMAb towards chloramphenicol succinate, florfenicol and thiamphenicol were 2.09, 12.45 and 18.10%, respectively. Finally, the developed method was applied in spiked swine urine, milk and honey samples, with recoveries ranging from 71.03 to 109.62%. The result demonstrated that the developed immunoassay is a valuable method for screening and quantitation of CAP residues in real samples.

Multi-walled carbon nanotubes as solid-phase extraction sorbents for simultaneous determination of type A trichothecenes in maize, wheat and rice by ultra-high performance liquid chromatography-tandem mass spectrometry.

A solid-phase extraction (SPE) procedure using multi-walled carbon nanotubes (MWCNTs) as sorbents coupled with ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was developed for simultaneous determination of four type A trichothecenes in maize, wheat and rice for the first time. Several key parameters including the composition of sample loading solutions, washing and elution solvents were thoroughly investigated to achieve optimal SPE recoveries and efficiency. Performance of the MWCNTs materials was significantly affected by pH, and after optimization, n-hexane and 5% methanol aqueous solution as the washing solutions and methanol containing 1% formic acid as the elution solvent presented an excellent purification efficiency for the four targets in the different matrices. The method was validated by determining the linearity (R(2)≥0.992), recovery (73.4-113.7%), precision (1.2-17.1%) and sensitivity (limit of quantification in the range of 0.02-0.10μg/kg), and was further applied for simultaneous determination of type A trichothecenes in 30 samples. Although low contamination levels of type A trichothecenes in wheat, maize and rice were observed revealing mitigated risks to consumers in Shanghai, China, the developed method has proven to be a valuable tool for type A trichothecenes monitoring in complex crop matrices.

Analysis of amicarbazone and its two metabolites in grains and soybeans by liquid chromatography with tandem mass spectrometry.

A sensitive, simple and reliable analytical method based on a modified quick, easy, cheap, effective, rugged, safe sample preparation and liquid chromatography with tandem mass spectrometry detection was developed for the simultaneous determination of amicarbazone and its two major metabolites desamino amicarbazone and isopropyl-2-hydroxy-desamino amicarbazone residues in grains (rice, wheat, corn, buckwheat) and soybean. Several parameters, including liquid chromatography and tandem mass spectrometry conditions, extraction approaches and the adsorbents for clean-up, which might influence the accuracy of the method, were extensively investigated. The established method was further validated by determining the linearity (R(2) > 0.99), fortified recovery (79-118%), precision (1-12%) and sensitivity (limit of quantification, 5 μg/kg for amicarbazone and desamino amicarbazone, and 10 μg/kg for isopropyl-2-hydroxy-desamino amicarbazone). Finally, the established method was successfully applied to determine the residues of amicarbazone and its metabolites in 49 real samples of grain and soybean.

Rabbit Monoclonal Antibody-Based Lateral Flow Immunoassay Platform for Sensitive Quantitation of Four Sulfonamide Residues in Milk and Swine Urine

Based on the available rabbit monoclonal antibody (RabMAb), a rapid and sensitive lateral flow immunoassay (LFA) platform has been developed for quantitative detection of four sulfonamide residues(SRs) of sulfadiazine (SD), sulfathiazole (STZ), sulfapyridine (SP), and sulfamethoxazole (SMX).Within the designed LFA competitive format assay, which was based on antigen-antibody properties, the hapten conjugate N1-[4-(carboxymethyl)-2-thiazolyl] sulfanilamide linked to protein ovalbumin (TS-OVA) and goat anti-rabbit antibody were sprayed as capture and control reagents, respectively, and then the antibody was conjugated to colloidal gold particles as the detection reagent. With quantitative assessment aided by a colorimetric strip reader, the sensitivities of the established LFA method for SD, STZ, SP, and SMX were 0.91 ng mL−1, 0.10ng mL−1,0.12ng mL−1, and 2.13ng mL−1, and the half-maximum inhibition concentrations (IC50) were 5.19 ng mL−1, 1.25 ng mL−1, 0.66 ng mL−1, and 24.14 ng mL−1, respectively. The recoveries at three spiked levels (5, 20, 50 ng mL−1for SD, STZ, and SP; 20, 50, 100 ng mL−1 for SMX) were in the range of 78.02–135.10% and 76.40–137.16% for milk and swine urine, respectively. More importantly, the detection performance of the established platform was consistent with that of in-parallel LC-MS/MS analysis. In conclusion, the proposed LFA platform has showed the potential for fast, sensitive and relatively accurate quantification of four sulfonamide residues in practical uses.

Reduced graphene oxide and gold nanoparticle composite-based solid-phase extraction coupled with ultra-high-performance liquid chromatography-tandem mass spectrometry for the determination of 9 mycotoxins in milk

A reliable solid-phase extraction (SPE) procedure using reduced graphene oxide and gold nanoparticle (rGO/Au) composite as sorbent was proposed for purification and enrichment of aflatoxin B1 (AFB1), aflatoxin M1 (AFM1), ochratoxin A (OTA), zearalenone (ZEA), α-zearalenol (α-ZOL), β-zearalenol (β-ZOL), zearalanone (ZAN), α-zearalanol (α-ZAL) and β-zearalanol (β-ZAL) in milk. Main parameters affecting the performance of SPE procedure were thoroughly investigated. The optimized conditions included 2% acetonitrile in water as the loading solution, 5% methanol in water as the washing solution, and methanol/acetonitrile/formic acid (50/49/1, v/v/v) as the elution solvent. Satisfactory linearity (R2 ≥ 0.992), high sensitivity (limit of quantification in the range of 0.02-0.18 ng mL-1), adequate recovery (70.2-111.2%), and acceptable precision (RSD, 2.0-14.9%) were obtained when the optimal sample pretreatment protocol was combined with ultra-high-performance liquid chromatography-tandem mass spectrometry detection. The applicability of the validated method was further verified in real milk samples.

Relationship between environmental conditions, TRI5 gene expression and deoxynivalenol production in stored Lentinula edodes infected with Fusarium graminearum

This study made the first attempt to relate the production of deoxynivalenol (DON) to the expression of TRI5 gene in Fusarium graminearum as a function of interacting environmental factors (water activity (aw) (0.95-0.98), temperature (20-30 °C) and incubation time (7 day-28 day)), so as to investigate its production mechanisms in Lentinula edodes. Changes in temperature, water activity and incubation time could significantly (P<0.01) affect DON production and TRI5 gene expression. The highest DON concentration (793.5±27.4 μg/kg) and TRI5 gene expression (2−ΔΔCt=38.8±4.8) were observed when the cultures were incubated at 20 °C and 0.98 aw for 21 days. Multi-regression analysis was performed and nonlinear models based on polynomial equations were established to uncover the individual effects of temperature, water activity and incubation time as well as their interactions on DON production and TRI5 gene expression. The established model was further used to develop contour maps to predict the DON production ...

Development and Validation of a Liquid Chromatography-Tandem Mass Spectrometry Method Coupled with Dispersive Solid-Phase Extraction for Simultaneous Quantification of Eight Paralytic Shellfish Poisoning Toxins in Shellfish

In this study, a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed for simultaneous determination of eight paralytic shellfish poisoning (PSP) toxins, including saxitoxin (STX), neosaxitoxin (NEO), gonyautoxins (GTX1–4) and the N-sulfo carbamoyl toxins C1 and C2, in sea shellfish. The samples were extracted by acetonitrile/water (80:20, v/v) with 0.1% formic and purified by dispersive solid-phase extraction (dSPE) with C18 silica and acidic alumina. Qualitative and quantitative detection for the target toxins were conducted under the multiple reaction monitoring (MRM) mode by using the positive electrospray ionization (ESI) mode after chromatographic separation on a TSK-gel Amide-80 HILIC column with water and acetonitrile. Matrix-matched calibration was used to compensate for matrix effects. The established method was further validated by determining the linearity (R2 ≥ 0.9900), average recovery (81.52–116.50%), sensitivity (limits of detection (LODs): 0.33–5.52 μg·kg−1; limits of quantitation (LOQs): 1.32–11.29 μg·kg−1) and precision (relative standard deviation (RSD) ≤ 19.10%). The application of this proposed approach to thirty shellfish samples proved its desirable performance and sufficient capability for simultaneous determination of multiclass PSP toxins in sea foods.

Reduced Graphene Oxide-Gold Nanoparticle Nanoframework as a Highly Selective Separation Material for Aflatoxins

Graphene-based materials have been studied in many applications, owing to the excellent electrical, mechanical, and thermal properties of graphene. In the current study, an environmentally friendly approach to the preparation of a reduced graphene oxide-gold nanoparticle (rGO-AuNP) nanocomposite was developed by using L-cysteine and vitamin C as reductants under mild reaction conditions. The rGO-AuNP material showed a highly selective separation ability for 6 naturally occurring aflatoxins, which are easily adsorbed onto traditional graphene materials but are difficult to be desorbed. The specificity of the nanocomposite was evaluated in the separation of 6 aflatoxin congeners (aflatoxin B1, aflatoxin B2, aflatoxin G1, aflatoxin G2, aflatoxin M1 and aflatoxin M2) from 23 other biotoxins (including, ochratoxin A, citrinin, and deoxynivalenol). The results indicated that this material was specific for separating aflatoxin congeners. The synthesized material was further validated by determining the recovery (77.6–105.0%), sensitivity (limit of detection in the range of 0.05–0.21 μg kg−1), and precision (1.5–11.8%), and was then successfully applied to the separation of aflatoxins from real-world maize, wheat and rice samples.