Multiplexed mycotoxins determination employing white light reflectance spectroscopy and silicon chips with silicon oxide areas of different thickness

Photonic Microbead Array Digital Time-Resolved Fluorescence Ultrasensitive Platform for Simultaneous Detection of Multiple Mycotoxins

Limitations in the sensitivity, linear detection range, and cross-reaction of lateral flow immunoassays mainly hamper their application in rapid screening for multiple targets. In this work, we designed a new time-resolved fluorescence immunoassay (TRFIA) platform to overcome these limitations. This platform uses europium chelate polystyrene (PS@Eu) nanoparticles conjugated with monoclonal antibodies to sense multiple mycotoxins. We employed a competitive TRFIA protocol in which the conjugated PS@Eu was used on the surfaces of photonic microbead arrays (PMAs). The TRFIA signal of PMAs on the pad was recorded with the digital time-resolved fluorescence reader. The developed TRFIA shows wide detection linear ranges (0.01-1000 ng/mL for DON, 0.1-100 ng/mL for OTA, and 0.01-100 ng/mL for AFB1), low limits of detection (LODs) (7.9 pg/mL for DON, 18 pg/mL for OTA, and 7.7 pg/mL for AFB1), good specificity, good recovery ratios (76.68-117.26%), and good reproducibility in grain samples. The simulated fluorescence enhancement effect of PMA indicated that the electric field distribution on the surface of PS@Eu on PMA is twice higher than that on the surface of PS@Eu. The new TRFIA for three kinds of mycotoxins was 1000-fold more sensitive than the classical TRFIA, and it has great potential application in rapid screening for multiple targets.

Highly Sensitive Microarray Immunoassay for Multiple Mycotoxins on Engineered 3D Porous Silicon SERS Substrate with Silver Nanoparticle Magnetron Sputtering

A high-throughput, rapid, and highly sensitive surface-enhanced Raman spectroscopy (SERS) microarray for screening multiple mycotoxins has been developed on a three-dimensional silver nanoparticle porous silicon (3D AgNP-Psi) SERS substrate, which was easy to be engineered by electrochemical etching and magnetron sputtering technology. The etching current density, etching waveform, and target material for magnetron sputtering have been investigated to obtain an optimal 3D SERS substrate. The optimized 3D AgNP-Psi SERS substrate showed an enhancement factor of 2.3 × 107 at 400 mA/cm2 constant current density etching for 20 s and Ag target magnetron sputtering for 200 nm thickness on the surface of Psi. The simulation electric field distribution showed the near-field enhancement can reach 3× higher than that of AuNPs. A protein microarray has been designed to screen multiple mycotoxins by AuNP Raman tags and a competitive immunoassay protocol on the surface of the 3D SERS substrate. The SERS protein microarray displayed wide linear detection ranges of 0.001-100 ng/mL for ochratoxin A, 0.01-100 ng/mL for aflatoxin B1, 0.001-10 ng/mL for deoxynivalenol, along with pg/mL low limit of detection, good recovery rates, repeatability, and reproducibility. The 3D SERS protein microarray is easily engineered and has a great potential application in medicine, environment, and food industry fields.

Simultaneous Detection of SARS-CoV-2 Nucleoprotein and Receptor Binding Domain by a Multi-Area Reflectance Spectroscopy Sensor

The COVID-19 pandemic has emphasized the urgent need for point-of-care methods suitable for the rapid and reliable diagnosis of viral infections. To address this demand, we report the rapid, label-free simultaneous determination of two SARS-CoV-2 proteins, namely, the nucleoprotein and the receptor binding domain peptide of S1 protein, by implementing a bioanalytical device based on Multi Area Reflectance Spectroscopy. Simultaneous detection of these two proteins is achieved by using silicon chips with adjacent areas of different silicon dioxide thickness on top, each of which is modified with an antibody specific to either the nucleoprotein or the receptor binding domain of SARS-CoV-2. Both areas were illuminated by a single probe that also collected the reflected light, directing it to a spectrometer. The online conversion of the combined reflection spectra from the two silicon dioxide areas into the respective adlayer thickness enabled real-time monitoring of immunoreactions taking place on the two areas. Several antibodies have been tested to define the pair, providing the higher specific signal following a non-competitive immunoassay format. Biotinylated secondary antibodies and streptavidin were used to enhance the specific signal. Both proteins were detected in less than 12 min, with detection limits of 1.0 ng/mL. The assays demonstrated high repeatability with intra- and inter-assay coefficients of variation lower than 10%. Moreover, the recovery of both proteins from spiked samples prepared in extraction buffer from a commercial self-test kit for SARS-CoV-2 collection from nasopharyngeal swabs ranged from 90.0 to 110%. The short assay duration in combination with the excellent analytical performance and the compact instrument size render the proposed device and assay suitable for point-of-care applications.

Is chemical analysis suitable for detecting mycotoxins in agricultural commodities and foodstuffs?

The assessment of the risks of mycotoxins to humans through consuming contaminated foods resulted in specific legislation that evaluates the presence, quantities, and type of mycotoxins in agricultural commodities and foodstuffs. Thus, to ensure compliance with legislation, food safety and consumer health, the development of suitable analytical procedures for identifying and quantifying mycotoxins in the free or modified form, in low-concentration and in complex samples is necessary. This review reports the application of the modern chemical methods of analysis employed in mycotoxin detection in agricultural commodities and foodstuffs. It is reported extraction methods with reasonable accuracy and those present characteristics according to guidelines of Green Analytical Chemistry. Recent trends in mycotoxins detection using analytical techniques are presented and discussed, evaluating the robustness, precision, accuracy, sensitivity, and selectivity in the detection of different classes of mycotoxins. Sensitivity coming from modern chromatographic techniques allows the detection of very low concentrations of mycotoxins in complex samples. However, it is essential the development of more green, fast and more suitable accuracy extraction methods for mycotoxins, which agricultural commodities producers could use. Despite the high number of research reporting the use of chemically modified voltammetric sensors, mycotoxins detection still has limitations due to the low selectivity from similar chemical structures of mycotoxins. Furthermore, spectroscopic techniques are rarely employed due to the limited number of reference standards for calibration procedures.

Advanced biosensors for mycotoxin detection incorporating miniaturized meters

Advanced biosensors, considered as emerging technologies, are capable of accurate, quantitative and real-time analysis for point-of-care testing (POCT) applications. Moreover, the integrating of miniaturized meters into these advanced biosensors makes them ideally appropriate for portable, sensitive and selective detection of biomolecules. Miniaturized meters including PGMs (personal glucose meters), thermometer, pressuremeter, pH meter, etc. are the most accurate devices and wide availability in the market, exhibiting a promising potential towards detection of small molecule mycotoxins. In this article, we introduce and analyze the recent advancements for sensing of mycotoxins measured by handheld meters since the first report in 2012. Furthermore, limitations and challenges for versatile meters application against mycotoxins in food matrix are highlighted. By overcoming the bottleneck problems, we believe the miniaturized meters-based biosensor platform will provide great possibilities for mycotoxins analysis and launch them to the market.

Simultaneous determination of procalcitonin and interleukin-6 in human serum samples with a point-of-care biosensing device

The simultaneous determination of two inflammatory diseases biomarkers, namely procalcitonin (PCT) and interleukin-6 (IL-6), in human serum samples employing a Point-of-Care device based on Multi Area Reflectance Spectroscopy is presented. Dual-analyte detection was achieved using silicon chips with two silicon dioxide areas of different thickness, one functionalized with an antibody specific for PCT and the other with an antibody specific for IL-6. The assay included reaction of immobilized capture antibodies with mixtures of PCT and IL-6 calibrators with the biotinylated detection antibodies, streptavidin and biotinylated-BSA. The reader provided for the automated execution of the assay procedure, as well as for the collection and processing of the reflected light spectrum, the shift of which is correlated to analytes concentration in the sample. The assay was completed in 35 min and the detection limits for PCT and IL-6 were 2.0 and 0.01 ng/mL respectively. The dual-analyte assay was characterized by high reproducibility (the intra- and inter-assay coefficients of variation were less than 10% for both analytes) and accuracy (the percent recovery values ranged from 80 to 113% for both analytes). Moreover, the values determined for the two analytes in human serum samples with the assay developed were in good agreement with the values determined for the same samples by clinical laboratory methods. These results support the potential of the proposed biosensing device application for inflammatory biomarkers determination at the Point-of-Need.

Development of a Point-of-Care System Based on White Light Reflectance Spectroscopy: Application in CRP Determination

The development of methods and miniaturized systems for fast and reliable quantitative determinations at the Point-of-Care is a top challenge and priority in diagnostics. In this work, a compact bench-top system, based on White Light Reflectance Spectroscopy, is introduced and evaluated in an application with high clinical interest, namely the determination of C-Reactive protein (CRP) in human blood samples. The system encompassed all the necessary electronic and optical components for the performance of the assay, while the dedicated software provided the sequence and duration of assay steps, the reagents flow rate, the real-time monitoring of sensor response, and data processing to deliver in short time and accurately the CPR concentration in the sample. The CRP assay included two steps, the first comprising the binding of sample CRP onto the chip immobilized capture antibody and the second the reaction of the surface immunosorbed CRP molecules with the detection antibody. The assay duration was 12 min and the dynamic range was from 0.05 to 200 μg/mL, covering both normal values and acute inflammation incidents. There was an excellent agreement between CRP values determined in human plasma samples using the developed device with those received for the same samples by a standard diagnostic laboratory method.

Fast and Sensitive Determination of the Fungicide Carbendazim in Fruit Juices with an Immunosensor Based on White Light Reflectance Spectroscopy

Carbendazim is a systemic benzimidazole-type fungicide with broad-spectrum activity against fungi that undermine food products safety and quality. Despite its effectiveness, carbendazim constitutes a major environmental pollutant, being hazardous to both humans and animals. Therefore, fast and reliable determination of carbendazim levels in water, soil, and food samples is of high importance for both food industry and public health. Herein, an optical biosensor based on white light reflectance spectroscopy (WLRS) for fast and sensitive determination of carbendazim in fruit juices is presented. The transducer is a Si/SiO₂ chip functionalized with a benzimidazole conjugate, and determination is based on a competitive immunoassay format. Thus, for the assay, a mixture of an in-house developed rabbit polyclonal anti-carbendazim antibody with the standards or samples is pumped over the chip, followed by biotinylated secondary antibody and streptavidin. The WLRS platform allows for real-time monitoring of biomolecular interactions carried out onto the Si/SiO₂ chip by transforming the shift in the reflected interference spectrum caused by the immunoreaction to effective biomolecular adlayer thickness. The sensor is able to detect 20 ng/mL of carbendazim in fruit juices with high accuracy and precision (intra- and inter-assay CVs ≤ 6.9% and ≤9.4%, respectively) in less than 30 min, applying a simple sample treatment that alleviates any "matrix-effect" on the assay results and a 60 min preincubation step for improving assay sensitivity. Excellent analytical characteristics and short analysis time along with its small size render the proposed WLRS immunosensor ideal for future on-the-spot determination of carbendazim in food and environmental samples.

Recent Advances in Mycotoxin Analysis and Detection of Mycotoxigenic Fungi in Grapes and Derived Products

Mycotoxins are secondary metabolites of filamentous fungi that can cause toxic effects in human and animal health. Most of the filamentous fungi that produce these mycotoxins belong to four genera, namely, Aspergillus, Penicillium, Fusarium, and Alternaria. Mycotoxigenic fungi, along with mycotoxins, create a constant and serious economic threat for agriculture in many terms, counting product losses due to crop contamination and food spoilage, as well malnutrition when considering nutritional quality degradation. Given the importance of robust and precise diagnostics of mycotoxins and the related producing fungi in the grape food chain, one of the most important agricultural sectors worldwide, the present review initially delivers a comprehensive presentation of mycotoxin reports on grape and derived products, including a wide range of commodities such as fresh grapes, raisins, wine, juices, and other processed products. Next, based on worldwide regulations’ requirements for mycotoxins, and referring to the relative literature, this work presents methodological approaches for mycotoxin determination, and stresses major methods for the detection of fungal species responsible for mycotoxin production. The principle of function and basic technical background on the available analytical and molecular biology techniques developed—including chromatography, mass spectrometry, immunochemical-based assays, biosensors, and molecular assays—is briefly given, and references for their application to grape and derived product testing are highlighted.

Developments in mycotoxin analysis: an update for 2019-2020

This review summarises developments on the analysis of various matrices for mycotoxins published in the period from mid-2019 to mid-2020. Notable developments in all aspects of mycotoxin analysis, from sampling and quality assurance/quality control of analytical results, to the various detection and quantitation technologies ranging from single mycotoxin biosensors to comprehensive instrumental methods are presented and discussed. Aside from sampling and quality control, discussion of this past year’s developments is organised by detection and quantitation technology and covers chromatography with targeted or non-targeted high resolution mass spectrometry, tandem mass spectrometry, detection other than mass spectrometry, biosensors, as well as assays that use alternatives to antibodies. This critical review aims to briefly present the most important recent developments and trends in mycotoxin determination as well as to address limitations of the presented methodologies.

Highly Sensitive Simultaneous Detection of Multiple Mycotoxins Using a Protein Microarray on a TiO2-Modified Porous Silicon Surface

A new protein microarray method for multiplex mycotoxin detection in parallel has been established on a stable TiO₂-modified porous silicon (PSi) surface. A typical competitive immunoassay microarray protocol has been developed for simultaneous detection of multiplex mycotoxins including aflatoxin B₁ (AFB₁), ochratoxin A (OTA), and fumonisin B₁ (FB₁) on the TiO₂-PSi surface. The epoxy groups were selected to modify the surface of a TiO₂-PSi wafer for the immobilization of artificial antigens of mycotoxins because of their high signal-to-noise ratios. Under optimal conditions, the developed method showed wide linear detection ranges of 0.01-1 ng/mL for OTA, 0.001-1 ng/mL for AFB₁, and 0.01-1 ng/mL for FB₁ and low limit of detections (LODs) of 0.433 ng/mL for OTA, 0.243 ng/mL for AFB₁, and 0.093 ng/mL for FB₁. The microarray method can specifically identify the three mycotoxins and their analogues. The recovery rates in real samples were within 75-120%, which were in agreement with that of the classical ELISA method. The new method has great application potential for rapid, sensitive, and high-throughput screening of multiplex mycotoxins and other target molecules.

Fast Deoxynivalenol Determination in Cereals Using a White Light Reflectance Spectroscopy Immunosensor

Deoxynivalenol (DON) is a mycotoxin produced by certain Fusarium species and found in a high percentage of wheat and maize grains cultured worldwide. Although not so toxic as other mycotoxins, it exhibits both chronic and acute toxicity, and therefore methods for its fast and accurate on-site determination are highly desirable. In the current work, we employ an optical immunosensor based on White Light Reflectance Spectroscopy (WLRS) for the fast and sensitive immunochemical label-free determination of DON in wheat and maize samples. The assay is completed in 12 min and has a quantification limit of 2.5 ng/mL in buffer corresponding to 125 μg/kg in whole grain which is lower than the maximum allowable concentrations set by the regulatory authorities for grains intended for human consumption. Several extraction protocols have been compared, and the highest recovery (>90%) was achieved employing distilled water. In addition, identical calibration curves were received in buffer and wheat/maize extraction matrix providing the ability to analyze the grain samples using calibrators in buffer. Recoveries of DON from spiked wheat and maize grain samples ranged from 92.0(±4.0) to 105(±4.0)%. The analytical performance of the WLRS immunosensor, combined with the short analysis time and instrument portability, supports its potential for on-site determinations.

Controlling orientation, conformation, and biorecognition of proteins on silane monolayers, conjugate polymers, and thermo-responsive polymer brushes: investigations using TOF-SIMS and principal component analysis

Control over orientation and conformation of surface-immobilized proteins, determining their biological activity, plays a critical role in biointerface engineering. Specific protein state can be achieved with adjusted surface preparation and immobilization conditions through different types of protein-surface and protein-protein interactions, as outlined in this work. Time-of-flight secondary ion mass spectroscopy, combining surface sensitivity with excellent chemical specificity enhanced by multivariate data analysis, is the most suited surface analysis method to provide information about protein state. This work highlights recent applications of the multivariate principal component analysis of TOF-SIMS spectra to trace orientation and conformation changes of various proteins (antibody, bovine serum albumin, and streptavidin) immobilized by adsorption, specific binding, and covalent attachment on different surfaces, including self-assembled monolayers on silicon, solution-deposited polythiophenes, and thermo-responsive polymer brushes. Multivariate TOF-SIMS results correlate well with AFM data and binding assays for antibody-antigen and streptavidin-biotin recognition. Additionally, several novel extensions of the multivariate TOF-SIMS method are discussed.

Graphical abstract