Determination of aflatoxin M1 in milk samples by means of an inductively coupled plasma mass spectrometry-based immunoassay

Molecularly imprinted polymer based on covalent organic framework coated steel substrate as the mass spectrometric ionization source for the direct detect of aflatoxins in complex food matrices

Ambient mass spectrometry allows direct analysis of various sample types with minimal or no pretreatment. However, due to the influence of matrix effects, there are sensitivity and issues in analyzing trace analytes in complex food samples. In this work, we developed a spray mass spectrometry platform based on SSS@TPBD-TPA@MIPs (Stainless steel substrate (SSS), terephthalaldehyde (TPA), N, N, N', N'-tetrakis(p-aminophenyl)-p-phenylenediamine (TPBD), molecularly imprinted polymer (MIP)), for rapid, in situ, high-throughput, highly enrichment efficiency and highly selective trace analysis of aflatoxins. By simplifying the sample pretreatment and directly applying high voltage for ESI-MS, the analysis can be completed within 1 min. The established method base on SSS@TPBD-TPA@MIPs exhibited high sensitivity and accuracy when determine trace level AFs in maize and peanuts. The results demonstrated a good linear relationship within the range of 0.01-10 μg/L, with the determination coefficient (R2) ≥ 0.9956. The limits of detection (LODs) was 0.035-0.3 ng/mL and limits of quantitation (LOQs) was 0.12-0.99 ng/mL, with acceptable recovery rate of 82.09-115.66 % and good repeatability represented by the relative standard deviation (RSD) less than 17.43 %. Furthermore, SSS@TPBD-TPA@MIPs exhibited excellent reusability, with more than 8 repeated uses, and showed good adsorption performance.

Highly sensitive detection of aflatoxin B1 byCRISPR/Cas12a-assisted single nanoparticle counting

CRISPR (clustered regularly interspaced short palindromic repeats) and CRISPR-associated protein (Cas) have gained extensive applications in bioassays. However, CRISPR-based detection platforms are often hampered by limited analytical sensitivity, while nucleic acid-based amplification strategies are usually indispensable for additional signal enhancement with potential risks of amplification leakages. To address these challenges, an amplification-free CRISPR-based bioassay of aflatoxin B1 (AFB1) was proposed by applying single nanoparticle counting. Single-particle mode inductively coupled plasma mass spectrometry (Sp-ICPMS) has been regarded as a sensitive tool for nanoparticle counting since one nanoparticle can generate considerable signals above backgrounds. With AFB1, activator strands were introduced to initiate the trans-cleavage of CRISPR/Cas12a for cutting the nanoparticles-tagged-magnetic beads, which were transduced to nanoparticle count signals after separation. Finally, a pico-mole level limit-of-detections (LODs) with moderate selectivity was achieved. Certified reference materials (CRMs) analysis and recovery tests were conducted with promising results. To our best knowledge, this is the first report of the single particle counting-based CRISPR/Cas12a biosensing study.

A novel multimode biosensor for sensitive detection of AFB1 in food based on Mxenes nano enzymes

In this work, Ti₃C₂ nano-enzymes (Ti₃C₂ NEs) materials with simulated peroxidase activity and fluorescence quenching properties were prepared. Then Ti₃C₂ NEs was functionalized using 6-carboxyfluorescein (FAM) labeled Aflatoxin B₁ (AFB₁) aptamers to construct a novel multimode nano enzyme biosensor for the detection of AFB₁ in peanuts. Based on the fluorescence quenching characteristics and the superior simulated peroxidase activity of Ti₃C₂ NE_S and the specific binding of the aptamer to AFB₁, the sensitive and rapid fluorescence/colorimetric/smart phone detection of AFB₁ have been achieved, with detection limits of 0.09 ng mL^-1, 0.61 ng mL^-1 and 0.96 ng mL^-1, respectively. The analytical method provided can not only detect AFB₁ in multiple modes, but also has a wider detection range, lower limit of detection (LOD) and better recovery rate, and can achieve on-site accurate detection of AFB₁ content in peanuts, which has great application potential in the field of food quality testing.

Mach-Zehnder Interferometric Immunosensor for Detection of Aflatoxin M1 in Milk, Chocolate Milk, and Yogurt

Aflatoxin M1 (AFM1) is detected in the milk of animals after ingestion of aflatoxin B1-contaminated food; since 2002, it has been categorized as a group I carcinogen. In this work, a silicon-based optoelectronic immunosensor for the detection of AFM1 in milk, chocolate milk, and yogurt has been developed. The immunosensor consists of ten Mach-Zehnder silicon nitride waveguide interferometers (MZIs) integrated on the same chip with the respective light sources, and an external spectrophotometer for transmission spectra collection. The sensing arm windows of MZIs are bio-functionalized after chip activation with aminosilane by spotting an AFM1 conjugate with bovine serum albumin. For AFM1 detection, a three-step competitive immunoassay is employed, including the primary reaction with a rabbit polyclonal anti-AFM1 antibody, followed by biotinylated donkey polyclonal anti-rabbit IgG antibody and streptavidin. The assay duration was 15 min with limits of detection of 0.005 ng/mL in both full-fat and chocolate milk, and 0.01 ng/mL in yogurt, which are lower than the maximum allowable concentration of 0.05 ng/mL set by the European Union. The assay is accurate (% recovery values 86.7-115) and repeatable (inter- and intra-assay variation coefficients <8%). The excellent analytical performance of the proposed immunosensor paves the way for accurate on-site AFM1 determination in milk.

Ultrasensitive determination of β-conglutin food allergen by means an aptamer assay based on inductively coupled plasma mass spectrometry detection

The overall objective of this work is the evaluation of different competitive aptamer assays based on inductively coupled plasma mass spectrometry (ICP-MS) detection for the determination of β-conglutin (food protein allergen from lupin) in flour samples. To this end, two competitive aptamer assay schemes were developed using either thiolated aptamers chemisorbed onto gold nanoparticles (AuNPs) or biotinylated aptamers linked to streptavidin-AuNPs. The influence of ICP-MS detection mode (i.e., conventional vs single particle) on assay performance was explored. In the case of the thiolated aptamer, the limit of detection (LoD) obtained using the single particle mode was improved 2-fold as compared to the LoD provided by the conventional mode. With regards to the biotinylated aptamer, the use of the conventional mode provided a 5-fold improvement of LoD as compared to that obtained for the single particle one. Using the optimized conditions, the best LoD of 2 pM was obtained with the biotinylated aptamer operating with conventional ICP-MS detection. When compared to previous reports using the same aptamer in a competitive assay, the developed method significantly improved the LoD by at least an order of magnitude. Different flour samples containing lupin were successfully analyzed according to European Conformity guidelines for the analysis of food contaminants.

Developments in mycotoxin analysis: an update for 2017-2018

This review summarises developments that have been published in the period from mid-2017 to mid-2018 on the analysis of various matrices for mycotoxins. Analytical methods to determine aflatoxins, Alternaria toxins, ergot alkaloids, fumonisins, ochratoxins, patulin, trichothecenes, and zearalenone are covered in individual sections. Advances in sampling strategies are discussed in a dedicated section, as are methods used to analyse botanicals and spices, and newly developed comprehensive liquid chromatographic-mass spectrometric based multi-mycotoxin methods. This critical review aims to briefly discuss the most important recent developments and trends in mycotoxin determination as well as to address limitations of the presented methodologies.

Evaluation of different competitive immunoassays for aflatoxin M1 determination in milk samples by means of inductively coupled plasma mass spectrometry

Haptens (i.e. biomolecules which molecular weight is lower than 10 kDa) determination by inductively coupled plasma mass spectrometry (ICP-MS) is usually performed by means of competitive immunoassays. In these immunoassays, analyte quantification is indirectly carried out using two different tracer species (i.e. antibodies or antigen-protein conjugates). However, the benefits (and drawbacks) derived from using a given tracer species have not been systematically investigated so far. The goal of this work is to evaluate the influence of the tracer species employed in competitive immunoassays on the analytical figures of merit for aflatoxin M₁ (AFM₁) determination in milk samples. To this end, three different strategies have been developed and evaluated, namely: (i) antibody binding inhibition assay (ABIA); (ii) capture inhibition assay (CIA); and (iii) capture bridge inhibition assay (CBIA). Experimental results show that the use of the antibody as tracer species (as in the ABIA approach) affords better analytical figures of merit for AFM₁ determination than using the antigen-protein conjugate as the tracer one (as in the CIA and CBIA strategies). The limit of detection afforded by ABIA strategy (i.e. 0.1 ng kg^-1) for AFM₁ determination was 1000-fold and 50-fold lower regarding the CIA and CBIA strategies, respectively. In the case of the ABIA approach, the characteristics of the metal nanoparticle label employed to detect the tracer species is critical on the analytical figures of merit. However, when the hapten-protein conjugates are used as tracer species, immunocomplex formation is severely hampered by steric effects caused by the protein moiety and, consequently, the characteristics of the metal nanoparticle label is not critical in the immunoassay performance. The different immunoassay strategies were successfully validated for AFM₁ determination in milk samples using a certified reference material of whole milk powder (ERM-BD283) according to European Conformity guidelines for analytical methods of food contaminants and mycotoxins. Compared to ELISA, the immunoassay developed for AFM₁ determination in milk samples improve limits of detection up to 10-fold.

Quantum dots: from fluorescence to chemiluminescence, bioluminescence, electrochemiluminescence, and electrochemistry

During the past decade, nanotechnology has become one of the major forces driving basic and applied research. As a novel class of inorganic fluorochromes, research into quantum dots (QDs) has become one of the fastest growing fields of nanotechnology today. QDs are made of a semiconductor material with tunable physical dimensions as well as unique optoelectronic properties, and have attracted multidisciplinary research efforts to further their potential bioanalytical applications. Recently, numerous optical properties of QDs, such as narrow emission band peaks, broad absorption spectra, intense signals, and remarkable resistance to photobleaching, have made them biocompatible and sensitive for biological assays. In this review, we give an overview of these exciting materials and describe their potential, especially in biomolecules analysis, including fluorescence detection, chemiluminescence detection, bioluminescence detection, electrochemiluminescence detection, and electrochemical detection. Finally, conclusions are made, including highlighting some critical challenges remaining and a perspective of how this field can be expected to develop in the future.