Magnetic Nanoparticle-Based Fluorescence Immunoassay for Determination of Ochratoxin A in Milk

Unravelling the potential of magnetic nanoparticles: a comprehensive review of design and applications in analytical chemistry

The study of nanoparticles has emerged as a prominent research field, offering a wide range of applications across various disciplines. With their unique physical and chemical properties within the size range of 1-100 nm, nanoparticles have garnered significant attention. Among them, magnetic nanoparticles (MNPs) exemplify promising super-magnetic characteristics, especially in the 10-20 nm size range, making them ideal for swift responses to applied magnetic fields. In this comprehensive review, we focus on MNPs suitable for analytical purposes. We investigate and classify them based on their analytical applications, synthesis routes, and overall utility, providing a detailed literature summary. By exploring a diverse range of MNPs, this review offers valuable insights into their potential application in various analytical scenarios.

Advances in Aptamer-Based Conjugate Recognition Techniques for the Detection of Small Molecules in Food

Small molecules are significant risk factors for causing food safety issues, posing serious threats to human health. Sensitive screening for hazards is beneficial for enhancing public security. However, traditional detection methods are unable to meet the requirements for the field screening of small molecules. Therefore, it is necessary to develop applicable methods with high levels of sensitivity and specificity to identify the small molecules. Aptamers are short-chain nucleic acids that can specifically bind to small molecules. By utilizing aptamers to enhance the performance of recognition technology, it is possible to achieve high selectivity and sensitivity levels when detecting small molecules. There have been several varieties of aptamer target recognition techniques developed to improve the ability to detect small molecules in recent years. This review focuses on the principles of detection platforms, classifies the conjugating methods between small molecules and aptamers, summarizes advancements in aptamer-based conjugate recognition techniques for the detection of small molecules in food, and seeks to provide emerging powerful tools in the field of point-of-care diagnostics.

Recent advances in nanomaterial-based optical biosensors for food safety applications: Ochratoxin-A detection, as case study

Global population growth tremendously impacts the global food industry, endangering food safety and quality. Mycotoxins, particularly Ochratoxin-A (OTA), emerge as a food chain production threat, since it is produced by fungus that contaminates different food species and products. Beyond this, OTA exhibits a possible human toxicological risk that can lead to carcinogenic and neurological diseases. A selective, sensitive, and reliable OTA biodetection approach is essential to ensure food safety. Current detection approaches rely on accurate and time-consuming laboratory techniques performed at the end of the food production process, or lateral-flow technologies that are rapid and on-site, but do not provide quantitative and precise OTA concentration measurements. Nanoengineered optical biosensors arise as an avant-garde solution, providing high sensing performance, and a fast and accurate OTA biodetection screening, which is attractive for the industrial market. This review core presents and discusses the recent advancements in optical OTA biosensing, considering engineered nanomaterials, optical transduction principle and biorecognition methodologies. Finally, the major challenges and future trends are discussed, and current patented OTA optical biosensors are emphasized for a particular promising detection method.

A Chemiluminescence Enzyme Immunoassay Based on Biotinylated Nanobody and Streptavidin Amplification for Diazinon Sensitive Quantification

The advantages of genetic modification and preferable physicochemical qualities make nanobody (Nb) easy to develop a sensitive and stable immunosensor platform. Herein, an indirect competitive chemiluminescence enzyme immunoassay (ic-CLEIA) based on biotinylated Nb was established for the quantification of diazinon (DAZ). The anti-DAZ Nb, named Nb-EQ1, with good sensitivity and specificity, was obtained from an immunized library via a phage display technique, where the molecular docking results indicated that the hydrogen bond and hydrophobic interactions between DAZ and complementarity-determining region 3 and framework region 2 in Nb-EQ1 played a critical role in the Nb-DAZ affinity processes. Subsequently, the Nb-EQ1 was further biotinylated to generate a bi-functional Nb-biotin, and then an ic-CLEIA was developed for DAZ determination via signal amplification of the biotin-streptavidin platform. The results showed that the proposed method based on Nb-biotin had a high specificity and sensitivity to DAZ, with a relative broader linear range of 0.12-25.96 ng/mL. After being 2-folds dilution of the vegetable samples matrix, the average recoveries were 85.7-113.9% with a coefficient of variation of 4.2-19.2%. Moreover, the results for the analysis of real samples by the developed ic-CLEIA correlated well with that obtained by reference method GC-MS (R² ≥ 0.97). In summary, the ic-CLEIA based on biotinylated Nb-EQ1 and streptavidin recognition demonstrated itself to be a convenient tool for the quantification of DAZ in vegetables.

Competitive ELISA based on pH-responsive persistent luminescence nanoparticles for autofluorescence-free biosensor determination of ochratoxin A in cereals

An accurate and sensitive competitive enzyme-linked immunosorbent assay (ELISA) based on persistent luminescence nanoparticles Zn₂GeO₄:Mn²⁺, Eu³⁺ (ZGME) was developed for detecting ochratoxin A (OTA), a powerfully toxic mycotoxin usually found in grains. As a signal output element of autofluorescence-free biosensors, ZGME can be integrated into ELISA with glucose oxidase (GOx)-binding OTA molecules due to its excellent pH-responsive persistent luminescence. In the absence of OTA, the OTA-GOx conjugate was captured by the anti-OTA monoclonal antibody (anti-OTA mAb) pre-coated on the 96-well plate. The results indicate a decrease in the pH value of the solution, which triggered the quenching of ZGME luminescence due to GOx-dependent gluconic acid production. The presence of OTA inhibited the binding of OTA-GOx on the plate, thus decreasing the production of gluconic acid and increasing the persistent luminous intensity of ZGME. Under the optimized concentrations of anti-OTA mAb and OTA-GOx, quantitative determination of OTA was achieved by plotting the increase or decrease in persistent luminescence intensity of ZGME at 535 nm. In this study, the linear range was from 0.1 μg L^-1 to 63 μg L^-1, and the limit of detection (LOD) was as low as 0.045 μg L^-1. In five food samples (corn grit, brown rice, soybean, rice, and wheat), the results exhibited good stability and repeatability, with a recovery range from 81.3% to 94.4% and a relative standard deviation (RSD) of less than 4.2%. Hence, the established method provides a sensitive, accurate, and autofluorescence-free approach for the determination of OTA in different grain samples.

Occurrence of Ochratoxin A in Different Types of Cheese Offered for Sale in Italy

The detection of Ochratoxin A (OTA) in the milk of ruminants occurs infrequently and at low levels, but its occurrence may be higher in dairy products such as cheese. The aim of this study was to investigate the presence of OTA in cheeses purchased in the metropolitan city of Bologna (Italy) and the surrounding area. For the analysis, a LC-MS/MS method with a limit of quantification (LOQ) of 1 µg/kg was used. OTA was detected in seven out of 51 samples of grated hard cheese (concentration range 1.3-22.4 µg/kg), while it was not found in the 33 cheeses of other types which were also analysed. These data show a low risk of OTA contamination for almost all types of cheese analysed. To improve the safety of cheese marketed in grated form, more regulations on cheese rind, which is the part most susceptible to OTA-producing moulds, should be implemented or, alternatively, producers should consider not using the rind as row material for grated cheese. It would be interesting to continue these investigations particularly on grated hard cheeses to have more data to update the risk assessment of OTA in cheese, as also suggested by EFSA in its 2020 scientific opinion on OTA.

Simultaneous determination of ochratoxin A and enterotoxin A in milk by magnetic nanoparticles based fluorescent immunoassay

Ochratoxin A (OTA) and staphylococcus enterotoxin A (SEA) are highly toxic contaminants and have induced human health problems. They commonly occur in milk and milk products. A competitive fluorescent immunoassay was developed for rapid and simultaneous determination of these toxins in milk samples. The procedure was based on the competitive immunoreactions between antigens in sample and antigen-fluorescent dye conjugates with immobilised antibodies on magnetic nanoparticles (MNPs). Each monoclonal antibody specifically recognises its corresponding toxin (antigen), and there is no cross-reactivity in the assay. First, monoclonal antibodies against OTA and SEA were produced. The activity of the obtained antibodies was determined by fluorescent-linked immunosorbent assay. Then, the monoclonal antibodies were immobilised on MNPs. The amounts of immobilised anti-OTA antibody and anti-SEA antibody were determined to be 20 and 22 μg mL^-1, respectively. The antigen-fluorescent dye conjugates OTA-OVA-ATTO620 and SEA-FITC were prepared. The optimal amount of immobilised antibodies for competitive immunoassay was determined. It was found that the linear range of OTA in buffer was larger (0.001-100 ng mL^-1) than the linear range of SEA (0.001-20 ng mL^-1). The results for simultaneous determination of OTA and SEA in sixfold diluted milk were almost the same in buffer; the linear range for OTA was from 0.005  to 100 ng mL^-1 and for SEA from 0.005  to 20 ng mL^-1. The detection limit for both OTA and SEA in milk was 0.004 ng mL^-1. The developed method took half the time of the individual assays (20 min). The assay was evaluated using spiked milk samples. The influences of somatic cell count, fat, pH and protein concentration in milk on immunoassay were studied. In summary, this developed immunoassay could provide an effective and rapid approach for detecting multi-toxins in milk samples.