Development of a colloidal gold strip for rapid detection of ochratoxin A with mimotope peptide

Advances in phage display based nano immunosensors for cholera toxin

Cholera, a persistent global public health concern, continues to cause outbreaks in approximately 30 countries and territories this year. The imperative to safeguard water sources and food from Vibrio cholerae, the causative pathogen, remains urgent. The bacterium is mainly disseminated via ingestion of contaminated water or food. Despite the plate method's gold standard status for detection, its time-consuming nature, taking several days to provide results, remains a challenge. The emergence of novel virulence serotypes raises public health concerns, potentially compromising existing detection methods. Hence, exploiting Vibrio cholerae toxin testing holds promise due to its inherent stability. Immunobiosensors, leveraging antibody specificity and sensitivity, present formidable tools for detecting diverse small molecules, encompassing drugs, hormones, toxins, and environmental pollutants. This review explores cholera toxin detection, highlighting phage display-based nano immunosensors' potential. Engineered bacteriophages exhibit exceptional cholera toxin affinity, through specific antibody fragments or mimotopes, enabling precise quantification. This innovative approach promises to reshape cholera toxin detection, offering an alternative to animal-derived methods. Harnessing engineered bacteriophages aligns with ethical detection and emphasizes sensitivity and accuracy, a pivotal stride in the evolution of detection strategies. This review primarily introduces recent advancements in phage display-based nano immunosensors for cholera toxin, encompassing technical aspects, current challenges, and future prospects.

Recent Progress in Rapid Determination of Mycotoxins Based on Emerging Biorecognition Molecules: A Review

Mycotoxins are secondary metabolites produced by fungal species, which pose significant risk to humans and livestock. The mycotoxins which are produced from Aspergillus, Penicillium, and Fusarium are considered most important and therefore regulated in food- and feedstuffs. Analyses are predominantly performed by official laboratory methods in centralized labs by expert technicians. There is an urgent demand for new low-cost, easy-to-use, and portable analytical devices for rapid on-site determination. Most significant advances were realized in the field bioanalytical techniques based on molecular recognition. This review aims to discuss recent progress in the generation of native biomolecules and new bioinspired materials towards mycotoxins for the development of reliable bioreceptor-based analytical methods. After brief presentation of basic knowledge regarding characteristics of most important mycotoxins, the generation, benefits, and limitations of present and emerging biorecognition molecules, such as polyclonal (pAb), monoclonal (mAb), recombinant antibodies (rAb), aptamers, short peptides, and molecularly imprinted polymers (MIPs), are discussed. Hereinafter, the use of binders in different areas of application, including sample preparation, microplate- and tube-based assays, lateral flow devices, and biosensors, is highlighted. Special focus, on a global scale, is placed on commercial availability of single receptor molecules, test-kits, and biosensor platforms using multiplexed bead-based suspension assays and planar biochip arrays. Future outlook is given with special emphasis on new challenges, such as increasing use of rAb based on synthetic and naïve antibody libraries to renounce animal immunization, multiple-analyte test-kits and high-throughput multiplexing, and determination of masked mycotoxins, including stereoisomeric degradation products.

Mimotopes for Mycotoxins Diagnosis Based on Random Peptides or Recombinant Antibodies from Phage Library

Mycotoxins, the small size secondary metabolites of fungi, have posed a threat to the safety of medicine, food and public health. Therefore, it is essential to create sensitive and effective determination of mycotoxins. Based on the special affinity between antibody and antigen, immunoassay has been proved to be a powerful technology for the detection of small analytes. However, the tedious preparation and instability of conventional antibodies restrict its application on easy and fast mycotoxins detection. By virtue of simplicity, ease of use, and lower cost, phage display library provides novel choices for antibodies or hapten conjugates, and lead random peptide or recombinant antibody to becoming the promising and environmental friendly immune-reagents in the next generation of immunoassays. This review briefly describes the latest developments on mycotoxins detection using M13 phage display, mainly focusing on the recent applications of phage display technology employed in mycotoxins detection, including the introduction of phage and phage display, the types of phage displayed peptide/recombinant antibody library, random peptides/recombinant antibodies-based immunoassays, as well as simultaneous determination of multiple mycotoxins.

Mimotope-Based Immunoassays for the Rapid Analysis of Mycotoxin: A Review

Mycotoxins are toxic contaminants in foods and feeds that are naturally occurring and largely unavoidable. Determining their contents in these products is essential to protect humans from harm. Immunoassays of mycotoxins have been well-established because they are fast, sensitive, simple, and cost-effective. However, a major limitation of immunoassays is the requirement of toxic mycotoxins as competing antigens, standards, or competing tracers. Mimotopes are peptides or proteins that can specifically bind to antibodies and compete with analytes for binding sites by mimicking antigenic epitopes. They can be employed as substitutes for competing antigens, standards, or competing tracers to avoid use of mycotoxins. This review summarizes the production and functionalization of the two main kinds of mimotopes, mimic peptides and anti-idiotypic antibodies (Ab2), and their applications in rapid analysis of mycotoxins.

Green Enzyme-Linked Immunosorbent Assay Based on the Single-Stranded Binding Protein-Assisted Aptamer for the Detection of Mycotoxin

In this work, a green enzyme-linked immunosorbent assay (ELISA) based on the single-stranded binding protein (SSB)-assisted aptamer was designed for biosensing applications. Combined with the biotin-streptavidin (SA) system and the high catalytic activity of horseradish peroxidase (HRP), this SSB-assisted aptamer sensor was applied for the detection of aflatoxin B1, ochratoxin A, and zearalenone. In this novel ELISA, mycotoxin-protein conjugations were replaced by SSB to avoid the hazard of mycotoxin, whereas antibodies were replaced by aptamer to avoid the complex and tedious preparation of antibodies. In the absence of target mycotoxins, SSB can bind the aptamer-biotin specifically. Detection was performed using the strong combination of biotin and SA after adding SA-HRP and substrate/chromogen solution, thereby resulting in a strong yellow color signal. In the presence of target mycotoxins, the aptamer-biotin cannot bind to the SSB, thereby leading to a weak yellow color signal. Under optimal conditions, the designed method was successfully applied for the determination of real sample and exhibited high specificity and low limits of detection in corn (112 ng L^-1 for aflatoxin B1, 319 ng L^-1 for ochratoxin A, and 377 ng L^-1 for zearalenone). The green ELISA may also be extended to the detection of other biohazardous targets by changing the aptamer.

Rapid and sensitive detection of mycotoxins by advanced and emerging analytical methods: A review

Quantification of mycotoxins in foodstuffs is extremely difficult as a limited amount of toxins are known to be presented in the food samples. Mycotoxins are secondary toxic metabolites, made primarily by fungal species, contaminating feeds and foods. Due to the presence in globally used grains, it is an unpreventable problem that causes various acute and chronic impacts on human and animal health. Over the previous few years, however, progress has been made in mycotoxin analysis studies. Easier techniques of sample cleanup and advanced chromatographic approaches have been developed, primarily high-performance liquid chromatography. Few extremely sophisticated and adaptable tools such as high-resolution mass spectrometry and gas chromatography-tandem MS/MS have become more important. In addition, Immunoassay, Advanced quantitative techniques are now globally accepted for mycotoxin analysis. Thus, this review summarizes these traditional and highly advance methods and their characteristics for evaluating mycotoxins.

Environmental-friendly gold nanoparticle immunochromatographic assay for ochratoxin A based on biosynthetic mimetic mycotoxin-conjugates

Ochratoxin A (OTA) is a possibly carcinogenic mycotoxin which is one of the most abundant food contaminants. It can be normally monitored and detected by immunochromatographic assays (ICG) which have a good sensitivity and specificity and easy to operate. However, the development of normal ICG is based on traditional OTA-conjugates or chemosynthetic mimotope peptides, which are very high-cost reagents with a detrimental effect on the environment and operators. This study takes advantage of both biosynthetic mimetic OTA-conjugates and a convenient IGG to develop a novel environmental-friendly and low-cost ICG for the rapid detection of OTA. Qualitatively, the visual cut-off level of the developed ICG for OTA was 0.8 ng/ml, which is 10-fold more sensitive than the chemosynthetic mimotope peptide based ICG, while there is no cross-reaction with other mycotoxins. The assay takes only 15 min to acquire results visible to the naked eye. Quantitatively, the half inhibition concentration of the ICG setup with mimetic OTA-conjugates was 0.187 ng/ml, with a linear range of 0.015 to 0.5 ng/ml. These results demonstrate the potential to adapt the method for detecting other toxic mycotoxins.

Rapid and Simple Detection of Ochratoxin A using Fluorescence Resonance Energy Transfer on Lateral Flow Immunoassay (FRET-LFI)

The detection of mycotoxins is crucial because of their toxicity in plants, animals, and humans. It is very important to determine whether food products are contaminated with mycotoxins such as ochratoxin A (OTA), as mycotoxins can survive heat treatments and hydrolysis. In this study, we designed a fluorescence resonance energy transfer (FRET)-based system that exploits antibody-antigen binding to detect mycotoxins more rapidly and easily than other currently available methods. In addition, we were able to effectively counteract the matrix effect in the sample by using a nitrocellulose membrane that enabled fluorescence measurement in coffee samples. The developed FRET on lateral flow immunoassay (FRET-LFI) system was used to detect OTA at a limit of detection (LOD) of 0.64 ng∙mL-1, and the test can be completed in only 30 min. Moreover, OTA in coffee samples was successfully detected at a LOD of 0.88 ng∙mL-1, overcoming the matrix effect, owing to the chromatographic properties of the capillary force of the membrane. We believe that the developed system can be used as a powerful tool for the sensitive diagnosis of harmful substances such as mycotoxins and pesticides for environmental and food quality control monitoring.

Lateral flow assays for Ochratoxin A using metal nanoparticles: comparison of "adsorption-desorption" approach to linkage inversion assembled nano-aptasensors (LIANA)

Nano-aptamer probes were prepared and used in lateral flow colorimetric assays for the detection of Ochratoxin A (OTA). In this study, two approaches were examined using 5'-biotin-modified OTA aptamers and silver or gold nanoparticles (AgNP or AuNP). The first method used an "adsorption-desorption" approach wherein aptamers were adsorbed onto the metal nanoparticle surface. Upon the addition of OTA, the aptamer binds specifically to the target, releasing the NPs. The above solutions were applied on a lateral flow assay (LFA) and a detection limit of 6.3 nM was achieved with both metal nanoparticles. The second method used a labelled approach based on Linkage Inversion Assembled Nano-Aptasensors (LIANAs) using a DNA linker containing a 5'-5' linkage inversion (5'-5' linker) to assemble biotinylated aptamer-functionalized metal nanoparticles. In the presence of target, OTA specifically binds with its aptamer leading to release of the linker and disassembly of LIANA aggregates into dispersed nanoparticles. The same solutions were applied in LFA format and the lowest detection limit of 0.63 nM was achieved. The results indicated that the LIANA-based LFA strips were more sensitive than the "adsoprtion-desorption" LFAs. Both lateral flow assays are inexpensive, simple, and rapid to perform and produces results visible to the naked-eye.

Staining Traditional Colloidal Gold Test Strips with Pt Nanoshell Enables Quantitative Point-of-Care Testing with Simple and Portable Pressure Meter Readout

Traditional immunochromatographic test strips based on colloidal gold are effective devices for portable and low-cost point-of-care (POC) testing. Nevertheless, they still suffer from the limitation of qualitative or semiquantitative tests via naked-eye detection. Replacement of gold with other signal entities, such as magnetic particles or fluorescent particles, requires professional instrumentation to obtain quantitative results. A pressure-based assay with platinum nanoparticles (PtNPs) can provide quantitative results using a portable pressure meter but is also hampered by the long-term instability of PtNPs. Consequently, we developed a Pt-staining method based on test strips to create platinum nanoshells on the surface of colloidal gold. This method not only preserves the original advantages of colloidal gold with easy synthesis and decoration but also introduces PtNPs with excellent catalytic activity as signal labels to achieve sensitive quantitative detection. Myoglobin was tested as a model target, and the limit of detection was 5.47 ng/mL in 20% diluted serum samples, which satisfies the requirements for clinical monitoring of acute myocardial infarction. In addition, the two most common colloidal gold strips available in the marketplace were applied to demonstrate the compatibility of Pt-staining. Taking advantage of low cost, user-friendliness, compatibility, simplicity, and stability, colloidal gold test strips with Pt-staining are expected to satisfy the need for quantitative POC testing of biomarkers, especially in resource-limited regions.

Development of a new format of competitive immunochromatographic assay using secondary antibody-europium nanoparticle conjugates for ultrasensitive and quantitative determination of ochratoxin A

In this study, to enhance the sensitivity of conventional immunochromatographic assay (ICA) two strategies including using a high sensitive label and changing the assay format, were simultaneously applied to develop an ultrasensitive format of ICA. In new format, primary monoclonal antibody against ochratoxin A (OTA) was used without any labeling, and a secondary polycolonal antibody was labeled with europium fluorescent nanoparticles (EuNPs). Detection was performed in a single step by inserting the test strip into a microtube containing all reagents. The results were obtained within 12 min and read by a portable fluorescent strip reader. Salient features of the new format of ICA compared with conventional format include: (1) A 100-fold decrease in limit of detection (LOD) due to application of two amplification strategy; (2) Reduction in expensive monoclonal antibody consumption. The established method was evaluated for the quantitative determination of OTA with LOD as low as 0.4 pg mL^-1.

A Lateral Flow Strip Based Aptasensor for Detection of Ochratoxin A in Corn Samples

Ochratoxin A (OTA) is a mycotoxin identified as a contaminant in grains and wine throughout the world, and convenient, rapid and sensitive detection methods for OTA have been a long-felt need for food safety monitoring. Herein, we presented a new competitive format based lateral flow strip fluorescent aptasensor for one-step determination of OTA in corn samples. Briefly, biotin-cDNA was immobilized on the surface of a nitrocellulose filter on the test line. Without OTA, Cy5-labeled aptamer combined with complementary strands formed a stable double helix. In the presence of OTA, however, the Cy5-aptamer/OTA complexes were generated, and therefore less free aptamer was captured in the test zone, leading to an obvious decrease in fluorescent signals on the test line. The test strip showed an excellent linear relationship in the range from 1 ng·mL⁻¹ to 1000 ng·mL⁻¹ with the LOD of 0.40 ng·mL⁻¹, IC₁₅ value of 3.46 ng·mL⁻¹ and recoveries from 96.4% to 104.67% in spiked corn samples. Thus, the strip sensor developed in this study is an acceptable alternative for rapid detection of the OTA level in grain samples.

Bioinspired recognition elements for mycotoxin sensors

Mycotoxins are low molecular weight molecules produced as secondary metabolites by filamentous fungi that can be found as natural contaminants in many foods and feeds. These toxins have been shown to have adverse effects on both human and animal health, and are the cause of significant economic losses worldwide. Sensors for mycotoxin analysis have traditionally applied elements of biological origin for the selective recognition purposes. However, since the 1970s there has been an exponential growth in the use of genetically engineered or synthetic biomimetic recognition elements that allow some of the limitations associated with the use of natural receptors for the analyses of these toxins to be circumvented. This review provides an overview of recent advances in the application of bioinspired recognition elements, including recombinant antibodies, peptides, aptamers, and molecularly imprinted polymers, to the development of sensors for mycotoxins based on different transduction elements. Graphical abstract Novel analytical methods based on bioinspired recognition elements, such as recombinant antibodies, peptides, aptamers, and molecularly imprinted polymers, can improve the detection of mycotoxins and provide better tools than their natural counterparts to ensure food safety.

Silver Nanoparticle-Based Fluorescence-Quenching Lateral Flow Immunoassay for Sensitive Detection of Ochratoxin A in Grape Juice and Wine

A silver nanoparticle (AgNP)-based fluorescence-quenching lateral flow immunoassay with competitive format (cLFIA) was developed for sensitive detection of ochratoxin A (OTA) in grape juice and wine samples in the present study. The Ru(phen)32+-doped silica nanoparticles (RuNPs) were sprayed on the test and control line zones as background fluorescence signals. The AgNPs were designed as the fluorescence quenchers of RuNPs because they can block the exciting light transferring to the RuNP molecules. The proposed method exhibited high sensitivity for OTA detection, with a detection limit of 0.06 µg/L under optimized conditions. The method also exhibited a good linear range for OTA quantitative analysis from 0.08 µg/L to 5.0 µg/L. The reliability of the fluorescence-quenching cLFIA method was evaluated through analysis of the OTA-spiked red grape wine and juice samples. The average recoveries ranged from 88.0% to 110.0% in red grape wine and from 92.0% to 110.0% in grape juice. Meanwhile, less than a 10% coefficient variation indicated an acceptable precision of the cLFIA method. In summary, the new AgNP-based fluorescence-quenching cLFIA is a simple, rapid, sensitive, and accurate method for quantitative detection of OTA in grape juice and wine or other foodstuffs.

Recent advances in mycotoxins detection

Mycotoxins contamination in both food and feed is inevitable. Mycotoxin toxicity in foodstuff can occur at very low concentrations necessitating early availability of sensitive and reliable methods for their detection. The present research thrust is towards the development of a user friendly biosensor for mycotoxin detection at both academic and industrial levels to replace conventional expensive chromatographic and ELISA techniques. This review critically analyzes the recent research trend towards the construction of immunosensor, aptasensor, enzymatic sensors and others for mycotoxin detection with a reference to label and label free methods, synthesis of new materials including nano dimension, and transuding techniques. Technological aspects in the development of biosensors for mycotoxin detection, current challenges and future prospects are also included to provide a overview and suggestions for future research directions.

Rapid detection of ochratoxin A on membrane by dot immunogold filtration assay

BACKGROUND

Ochratoxin A (OTA), a widely distributed mycotoxin produced by certain species of Aspergillus and Penicillium, has been identified as a carcinogenic, hepatotoxic, teratogenic, nephrotoxic and immunotoxic toxin. To reduce the risk of OTA contamination, a rapid, inexpensive, suitable and on-site assay for its detection is required.

RESULTS

In this study a dot immunogold filtration assay (DIGFA) of OTA on high-flow nitrocellulose membrane was developed. Firstly colloidal gold was synthesized and colloidal gold-polyclonal antibody (PcAb) conjugates against OTA were prepared at the optimal colloidal gold-labeled pH value and package amount. Then the colloidal gold-PcAb conjugates were used to develop the OTA DIGFA. The results demonstrated a visual detection limit of approximately 10 ng mL(-1) OTA. In addition, this method had no cross-reaction with zearalenone, aflatoxin B1 or citrinin.

CONCLUSION

These results indicated that the developed DIGFA could be applied for the actual detection of samples without complicated steps.

Analytical methods for determination of mycotoxins: An update (2009-2014)

Mycotoxins are a problematic and toxic group of small organic molecules that are produced as secondary metabolites by several fungal species that colonise crops. They lead to contamination at both the field and postharvest stages of food production with a considerable range of foodstuffs affected, from coffee and cereals, to dried fruit and spices. With wide ranging structural diversity of mycotoxins, severe toxic effects caused by these molecules and their high chemical stability the requirement for robust and effective detection methods is clear. This paper builds on our previous review and summarises the most recent advances in this field, in the years 2009-2014 inclusive. This review summarises traditional methods such as chromatographic and immunochemical techniques, as well as newer approaches such as biosensors, and optical techniques which are becoming more prevalent. A section on sampling and sample treatment has been prepared to highlight the importance of this step in the analytical methods. We close with a look at emerging technologies that will bring effective and rapid analysis out of the laboratory and into the field.

Novel strategies to enhance lateral flow immunoassay sensitivity for detecting foodborne pathogens

Food contaminated by foodborne pathogens causes diseases, affects individuals, and even kills those affected individuals. As such, rapid and sensitive detection methods should be developed to screen pathogens in food. One current detection method is lateral flow immunoassay, an efficient technique because of several advantages, including rapidity, simplicity, stability, portability, and sensitivity. This review presents the format and principle of lateral flow immunoassay strip and the development of conventional lateral flow immunoassay for detecting foodborne pathogens. Furthermore, novel strategies that can be applied to enhance the sensitivity of lateral flow immunoassay to detect foodborne pathogens are presented; these strategies include innovating new label application, designing new formats of lateral flow immunoassay, combining with other methods, and developing signal amplification systems. With these advancements, detection sensitivity and detection time can be greatly improved.

Ultrasensitive and quantitative gold nanoparticle-based immunochromatographic assay for detection of ochratoxin A in agro-products

In most cases of mycotoxin detection, quantitation is critical while immunochromatographic strip tests are qualitative in nature. Moreover, the sensitivity of this technique is questioned. In order to overcome these limitations, an ultrasensitive and quantitative immunochromatographic assay (ICA) for rapid and sensitive quantitation of ochratoxin A (OTA) was developed. The assay was based on a competitive format and its sensitivity was improved by using a sensitive and selective OTA monoclonal antibody (OTA-mAb). The visible ICA results were obtained within 15 min, and in addition to visual examination, they were read by the rapid color intensity portable strip reader. The visual and computational detection limits (vLOD and cLOD, respectively) for ochratoxin A were 0.2 and 0.25 ng mL(-1), respectively. These values were lower than those reported by previous studies in a range 5-2500 folds. For validation, contaminated samples including wheat, maize, rice and soybean were assayed by ICA and a standard high performance liquid chromatography (HPLC). The results were in good agreement for both ICA and HPLC methods. The average recoveries of the HPLC were in the range 72-120% while the ICA values were from 76 to 104%, confirming the accuracy and sensitivity of this method.

An aptamer based surface plasmon resonance biosensor for the detection of ochratoxin A in wine and peanut oil

Ochratoxin A (OTA), as a kind of chlorophenolic mycotoxin, exist widely in plant origin food and is harmful to human. Herein, a surface plasmon resonance (SPR) biosensor using an anti-OTA aptamer immobilized sensor chip was developed to measure ochratoxin A (OTA) quantificationally through a straightforward direct binding assay. The streptavidin protein as a crosslinker was immobilized onto the surface of a sensor chip and the biotin-aptamer was captured through streptavidin-biotin interaction. The biosensor exhibited a detection range from 0.094 to 100ng/mL (linear range from 0.094 to 10ng/mL) of OTA with a lower detection limit of 0.005ng/mL. Detection of OTA in wine and peanut oil was further performed in the SPR biosensor using simple liquid-liquid extraction for sample pretreatments. Recoveries of ochratoxin A from spiked samples ranged from 86.9% to 116.5% and coefficients of variation (CVs) ranged from 0.2% to 6.9%. The developed methods in our studies showed good analytical performances with limits of detection much lower than the maximum residue limit, as well as a good reproducibility and stability.

Use of cloneable peptide-MBP fusion protein as a mimetic coating antigen in the standardized immunoassay for mycotoxin ochratoxin A

The quality of mycotoxin conjugates is essential to the development of reliability of immunoassays for mycotoxins. However, conventional mycotoxin conjugates are usually synthesized by chemical methods, which are harmful to the environment and yield unwanted cross-reactions. In this study, using ochratoxin A (OTA) as a model system, a selected OTA mimotope (phage-displayed peptide) that specifically binds to anti-OTA antibody was expressed as soluble and monovalent fusions to maltose binding protein (MBP). These prepared fusion proteins can serve as a mimetic coating antigen in both a quantitative chemiluminescent enzyme-linked immunoassay (CLEIA) and a qualitative dot immunoassay for OTA. One of the prepared mimetic coating antigen (L12-206-MBP)-based CLEIAs exhibited a half-inhibition concentration (IC50) of 0.82 ng/mL and a working range of 0.30-2.17 ng/mL, which resemble those of the conventional OTA-OVA conjugate-based immunoassay. The dot immunoassay developed with both the OTA-OVA conjugate and the mimetics showed identical visual cutoff values of 5 ng/mL. The mimetic coating antigen proposed here is an OTA-free product and can be prepared reproducibly as a homogeneous product and facilitates standardization of immunoassays for the mycotoxin OTA.

Development of a heterologous enzyme-linked immunosorbent assay for organophosphorus pesticides with phage-borne peptide

An enzyme-linked immunosorbent assay (ELISA) was developed to detect organophosphorus pesticides using a phage-borne peptide that was isolated from a cyclic 8-residue peptide phage library. The IC₅₀ values of the phage ELISA ranged from 1.4 to 92.1 μg L^-1 for eight organophosphorus pesticides (parathion-methyl, parathion, fenitrothion, cyanophos, EPN, paraoxon-methyl, paraoxon, fenitrooxon). The sensitivity was improved 120- and 2-fold compared to conventional homologous and heterologous ELISA, respectively. The selectivity of the phage ELISA was evaluated by measuring its cross-reactivity with 23 organophosphorus pesticides, among which eight were the main cross-reactants. The spike recoveries were between 66.1% and 101.6% for the detection of single pesticide residues of parathion-methyl, parathion and fenitrothion in Chinese cabbage, apple and greengrocery, and all of the coefficient of variation were less than or equal to 15.9%. Moreover, the phage ELISA results were validated by gas chromatography. The results indicate that isolating phage-borne peptides from phage display libraries is an alternative method for the development of a heterologous immunoassay and that the developed assay has a lower limit of detection than the chemically synthesized competitor assay.

Increased sensitivity of lateral flow immunoassay for ochratoxin A through silver enhancement

Silver nucleation on gold has been exploited for signal amplification and has found application in several qualitative and quantitative bio-sensing techniques, thanks to the simplicity of the method and the high sensitivity achieved. Very recently, this technique has been tentatively applied to improve the performance of gold-based immunoassays. In this work, the exploitation of the signal amplification due to silver deposition on gold nanoparticles has been first applied to a competitive lateral flow immunoassay (LFIA). The signal enhancement due to silver allowed us to strongly reduce the amount of the competitor and of specific antibodies employed to build an LF device for measuring ochratoxin A (OTA), thus permitting the attainment of a highly sensitive assessment of OTA contamination, with a sensitivity gain of more than 10-fold compared to the gold-based LFIA that used the same immunoreagents and to all previously reported LFIA for measuring OTA. In addition, a less sensitive "quantitative" LFIA could be established, by suitably tuning competitor and antibody amounts, which was characterized by reproducible and accurate OTA determinations (RSD% 6-12%, recovery% 82-117%). The quantitative system allowed a reliable OTA quantification in wines and grape musts at the microgram per liter level requested by the European legislation, as demonstrated by a highly results obtained through the quantitative silver-enhanced LFIA and a reference HPLC-FLD on 30 samples.

A lateral flow immunoassay for the rapid detection of ochratoxin A in wine and grape must

A one-step lateral flow immunoassay was developed for semiquantitatively detecting ochratoxin A (OTA) in wines and grape musts. Matrix-matched calibration curves carried out in blank wines showed a detection limit of 1 μg L(-1) and IC(50) of 3.2 μg L(-1). Relative standard deviations for intra- and interday precision were in the 20-40% range. A simple treatment of samples, which only included dilution with sodium bicarbonate and polyethylene glycol (4% w/v) for red and white wines and the further addition of ethanol (12% v/v) for grape musts, was established. The developed assay allowed OTA detection in 5 min and proved to be accurate and sensitive enough to allow the correct attribution of samples as compliant or noncompliant according to EU legislation. Results agreeing with those of a reference chromatographic method were obtained on 38 wines and 16 musts. Although some lateral flow devices aimed at detecting OTA have been previously described, this is the first assay capable of measuring the toxin in wine and grape must, which represent a major source of OTA dietary intake. Analytical performances of the method are comparable to or better than previously reported assays showed. In addition, the assay, including sample treatments, is extremely simple and rapid and can be effectively regarded as a one-step assay usable virtually anywhere.

Current development of microfluidic immunosensing approaches for mycotoxin detection via capillary electromigration and lateral flow technology

Mycotoxin contamination in the food chain has caused serious health issues in humans and animals. Thus, a rapid on-site and lab-independent detection method for mycotoxins, such as aflatoxins (AFTs), is desirable. Microfluidic chip based immunosensor technology is one of the most promising methods for fast mycotoxin assays. In this review, we cover the major microfluidic immunosensors used for mycotoxin analysis, via flow-through (capillary electromigration) and lateral flow technology. Sample preparation from different matrices of agricultural products and foodstuffs is summarized. The choice of materials, fabrication strategies, and detection methods for microfluidic immunosensors are further discussed in detail. The sensors application in mycotoxin determination is also outlined. Finally, future challenges and opportunities are discussed.

Lateral-flow immunoassays for mycotoxins and phycotoxins: a review

Natural toxin (for example mycotoxin and phycotoxin) contamination of food is of safety and economic concern, so much effort is devoted to the development of screening methods which enable the toxins to be continuously and widely monitored in food and feed. More generally speaking, rapid and non-instrumental assays for detection of a variety of food contaminants are generating ever-increasing scientific and technological interest because they enable high-throughput, economical, on-site monitoring of such contaminants. Among rapid methods for first-level screening of food contaminants, lateral-flow immunoassay (LFIA), also named immunochromatographic assay or immune-gold colloid immunoassay, has recently attracted scientific and industrial interest because of its attractive property of enabling very rapid, one-step, in-situ analysis. This review focuses on new aspects of the development and optimization of lateral-flow devices for mycotoxin and phycotoxin detection, including strategies for management of matrix interference and, particularly, for investigation of the improvements achieved by signal-enhancing strategies or by application of non-gold nanoparticle signal reporters.

A Gold Nanoparticle and Aflatoxin B1-BSA Conjugates Based Lateral Flow Assay Method for the Analysis of Aflatoxin B1

A rapid and simple immuno-chromatographic assay was developed to detect aflatoxin B1 (AFB1). The assay was based on a modified competitive binding format using colloidal gold and polyclonal antibody (Pab) conjugates. The anti-AFB1 Pab was immobilized to a defined detection zone on a porous nitrocellulose membrane and colloidal gold particles were conjugated to AFB1-BSA which served as a detection reagent. The AFB1-containing sample was added to the membrane and allowed to move with AFB1-BSA-coated particles dried on the conjugation pad. The mixture was then passed along the porous membrane by capillary action past the Pab in the detection zone, which captured AFB1 or AFB1-BSA. AFB1 in the sample inhibits binding of AFB1-BSA conjugated gold particles to the Pab and prevents formation of a red color dot. In the absence of AFB1, AFB1-BSA conjugated gold particles bound to the Pab, give a red color within this detection zone. With this method, 10 μg/mL of AFB1 was detected in less than 10 min. The developed AFB1 assay also showed no cross reaction to Ochratoxin A (OTA).