Enzyme sensor for the electrochemical detection of the marine toxin okadaic acid

Advancing biological investigations using portable sensors for detection of sensitive samples

Portable biosensors are emerged as powerful diagnostic tools for analyzing intricately complex biological samples. These biosensors offer sensitive detection capabilities by utilizing biomolecules such as proteins, nucleic acids, microbes or microbial products, antibodies, and enzymes. Their speed, accuracy, stability, specificity, and low cost make them indispensable in forensic investigations and criminal cases. Notably, portable biosensors have been developed to rapidly detect toxins, poisons, body fluids, and explosives; they have proven invaluable in forensic examinations of suspected samples, generating efficient results that enable effective and fair trials. One of the key advantages of portable biosensors is their ability to provide sensitive and non-destructive detection of forensic samples without requiring extensive sample preparation, thereby reducing the possibility of false results. This comprehensive review provides an overview of the current advancements in portable biosensors for the detection of sensitive materials, highlighting their significance in advancing investigations and enhancing sensitive sample detection capabilities.

Single-stranded DNA binding protein coupled aptasensor with carbon-gold nanoparticle amplification for marine toxins detection assisted by a miniaturized absorbance reader

Okadaic acid (OA), one of the most widely distributed marine toxins worldwide poses a severe threat to human health. Previous sensing methods for OA detection are usually based on antigen-antibody binding mechanism. However, the drawbacks of antibodies especially the enzyme-labeled antibodies, such as the harsh storage condition and high cost, lead to significant challenges to OA detection in biological samples. To overcome these limitations, a single-stranded DNA binding protein (SSB) coupled aptasensor was developed for OA detection. SSB was incubated on the microplate as a substitute for conventional OA-protein conjugations. Carbon-gold nanoparticles were synthesized and labeled with horseradish peroxidase and thiol-modified aptamers to obtain a capture probe (CGNs@HRP-Apt) instead of the enzyme-labeled antibody for signal amplification. OA and SSB competed to bind with limited aptamers on CGNs@HRP-Apt probes followed by colorimetric assay to obtain the optical signals correlated to OA concentration. To achieve on-site detection, a miniaturized and multichannel absorbance reader (Smart-plate reader) was self-designed with full automation for OA detection. Utilizing the SSB coupled aptasensor and the Smart-plate reader, our approach enables cost-effective and on-site OA sensing with a detection range of 2.5-80 ppb and an ultra-low limit of detection of 0.68 ppb. Moreover, novel OA detection kits based on the SSB coupled aptasensor were prepared which can effectively reduce the cost by 15 times lower than that of commercial ELISA kits. Therefore, the developed platform provides a favorable and promising avenue for marine toxin detection in aquaculture and food safety.

A novel microfluidic system for the sensitive and cost-effective detection of okadaic acid in mussels

Okadaic acid (OA) is produced by marine dinoflagellates and it can be easily accumulated in shellfish, causing intoxications when consumed by humans. Consequently, there is a need for sensitive, reliable and cost-effective methods to detect OA in real samples. In this work, we developed a novel and affordable microfluidic system to detect OA based on the protein phosphatase 1 inhibition colorimetric assay. This enzyme was immobilized in a microfluidic chamber by physisorption in an alumina sol-gel. The results show good enzyme stability over time when maintained at 4 °C. The developed system was sensitive for OA standard solutions, presenting a limit of detection (LOD) of 11.6 nM over a large linear range (43.4 to 3095.8 nM). Our method revealed an LOD as low as 0.2 μg kg-1 and a linear range between 1.47 and 506 μg kg-1 for extracted mussel matrix, detecting OA concentrations in contaminated mussels much lower than the regulated limit (160 μg kg-1). The enzyme stability and reusability along with the simplicity and low cost associated with microfluidics systems make this method very interesting from a commercial point of view.

Current Trends and Challenges for Rapid SMART Diagnostics at Point-of-Site Testing for Marine Toxins

In the past twenty years marine biotoxin analysis in routine regulatory monitoring has advanced significantly in Europe (EU) and other regions from the use of the mouse bioassay (MBA) towards the high-end analytical techniques such as high-performance liquid chromatography (HPLC) with tandem mass spectrometry (MS). Previously, acceptance of these advanced methods, in progressing away from the MBA, was hindered by a lack of commercial certified analytical standards for method development and validation. This has now been addressed whereby the availability of a wide range of analytical standards from several companies in the EU, North America and Asia has enhanced the development and validation of methods to the required regulatory standards. However, the cost of the high-end analytical equipment, lengthy procedures and the need for qualified personnel to perform analysis can still be a challenge for routine monitoring laboratories. In developing regions, aquaculture production is increasing and alternative inexpensive Sensitive, Measurable, Accurate and Real-Time (SMART) rapid point-of-site testing (POST) methods suitable for novice end users that can be validated and internationally accepted remain an objective for both regulators and the industry. The range of commercial testing kits on the market for marine toxin analysis remains limited and even more so those meeting the requirements for use in regulatory control. Individual assays include enzyme-linked immunosorbent assays (ELISA) and lateral flow membrane-based immunoassays (LFIA) for EU-regulated toxins, such as okadaic acid (OA) and dinophysistoxins (DTXs), saxitoxin (STX) and its analogues and domoic acid (DA) in the form of three separate tests offering varying costs and benefits for the industry. It can be observed from the literature that not only are developments and improvements ongoing for these assays, but there are also novel assays being developed using upcoming state-of-the-art biosensor technology. This review focuses on both currently available methods and recent advances in innovative methods for marine biotoxin testing and the end-user practicalities that need to be observed. Furthermore, it highlights trends that are influencing assay developments such as multiplexing capabilities and rapid POST, indicating potential detection methods that will shape the future market.

Concentration cell-based potentiometric analysis for point-of-care testing with minimum background

One of the most critical problems of point-of-care testing is how to reduce the interference of background, especially under resource-limited conditions when sample pretreatment is not available. In this work we report a potentiometric method for point-of-care testing with minimum background. The method is based on the principles of a concentration cell which is a type of galvanic cells. It is an electrochemical cell having two carbon electrodes. The potential of each electrode is determined by ratio of a redox couple (i.e. Fe(CN)₆^4-/3-) on the electrode surface. On one electrode, the adsorbed enzyme catalyzes the oxidation of analyte by Fe(CN)₆^3- which produces Fe(CN)₆^4-. The shift of the potential was because of the analyte as well as the background. In the other channel, no enzyme was present so that the shift of the potential, if any, is owing to the background. By measuring the potential difference between the two electrodes (i.e. voltage of the concentration cell), analyte can be quantitatively determined with most of the background eliminated. As the proof-of-concept analyte, blood glucose is quantitatively detected using a voltammeter with acceptable selectivity and accuracy. Noble metal electrodes that are indispensable for conventional electrochemical sensing are not required. All these features simplify the fabrication procedure and reduce the cost for the detection. Therefore, we believe it is promising for electrochemical point-of-care testing.

Ultrasensitive and rapid immuno-detection of human IgE anti-therapeutic horse sera using an electrochemical immunosensor

Antivenom allergy disease mediated by patient IgE is an important public health care concern. To improve detection of hypersensitive individuals prior to passive antibody therapy, an amperometric immunosensor was developed to detect reactive human IgE. Whole horse IgG3 (hoIgG3) was immobilized onto the surface of carbon or gold screen-printed electrodes through a cross-linking solution of glutaraldehyde on a chitosan film. Sera from persons with a known allergic response to hoIgG3 or non-allergic individuals was applied to the sensor. Bound human IgE (humIgE) was detected by an anti-humIgE antibody through a quantitative amperometric determination by tracking via the electrochemical reduction of the quinone generated from the hydroquinone with the application of a potential of 25 mV. The optimal immunosensor configuration detected reactive humIgE at a dilution of 1:1800 of the human sera that represent a detection limit of 0.5 pg/mL. Stability testing demonstrated that through 20 cycles of a scan, the specificity and performance remained robust. The new immunosensor successfully detected humIgE antibodies reactive against hoIgG3, which could allow the diagnosis of potential allergenic patients needing therapeutic antivenom preparations from a horse.

New biorecognition molecules in biosensors for the detection of toxins

Biological and synthetic recognition elements are at the heart of the majority of modern bioreceptor assays. Traditionally, enzymes and antibodies have been integrated in the biosensor designs as a popular choice for the detection of toxin molecules. But since 1970s, alternative biological and synthetic binders have been emerged as a promising alternative to conventional biorecognition elements in detection systems for laboratory and field-based applications. Recent research has witnessed immense interest in the use of recombinant enzymatic methodologies and nanozymes to circumvent the drawbacks associated with natural enzymes. In the area of antibody production, technologies based on the modification of in vivo synthesized materials and in vitro approaches with development of "display "systems have been introduced in the recent years. Subsequently, molecularly-imprinted polymers and Peptide nucleic acid (PNAs) were developed as an attractive receptor with applications in the area of sample preparation and detection systems. In this article, we discuss all alternatives to conventional biomolecules employed in the detection of various toxin molecules We review recent developments in modified enzymes, nanozymes, nanobodies, aptamers, peptides, protein scaffolds and DNazymes. With the advent of nanostructures and new interface materials, these recognition elements will be major players in future biosensor development.

Graphene oxide-assisted non-immobilized SELEX of okdaic acid aptamer and the analytical application of aptasensor

Okadaic acid (OA) is a low-molecular-weight marine toxin from shellfish that causes abdominal pain, vomiting and diarrhea, i.e., diarrheic shellfish poisoning. In this study, a ssDNA aptamer that specifically binds to OA with high affinity was obtained via Systematic Evolution of Ligands by Exponential Enrichment (SELEX) assisted by graphene oxide (GO). This aptamer was then applied to fabricate a novel direct competitive enzyme-linked aptamer assay (ELAA). At the optimized conditions, this ELAA method showed a low detection limit (LOD of 0.01 ng/mL), wide linear range (from 0.025 to 10 ng/mL), good recovery rate (92.86–103.34% in OA-spiked clam samples) and repeatability (RSD of 2.28–4.53%). The proposed method can be used to detect OA in seafood products with high sensitivity and can potentially be adapted for the determination of other small molecular analytes.

Production of a soluble single-chain variable fragment antibody against okadaic acid and exploration of its specific binding

Okadaic acid is a lipophilic marine algal toxin commonly responsible for diarrhetic shellfish poisoning (DSP). Outbreaks of DSP have been increasing and are of worldwide public health concern; therefore, there is a growing demand for more rapid, reliable, and economical analytical methods for the detection of this toxin. In this study, anti-okadaic acid single-chain variable fragment (scFv) genes were prepared by cloning heavy and light chain genes from hybridoma cells, followed by fusion of the chains via a linker peptide. An scFv-pLIP6/GN recombinant plasmid was constructed and transformed into Escherichia coli for expression, and the target scFv was identified with IC-CLEIA (chemiluminescent enzyme immunoassay). The IC15 was 0.012 ± 0.02 μg/L, and the IC50 was 0.25 ± 0.03 μg/L. The three-dimensional structure of the scFv was simulated with computer modeling, and okadaic acid was docked to the scFv model to obtain a putative structure of the binding complex. Two predicted critical amino acids, Ser32 and Thr187, were then mutated to verify this theoretical model. Both mutants exhibited significant loss of binding activity. These results help us to understand this specific scFv-antigen binding mechanism and provide guidance for affinity maturation of the antibody in vitro. The high-affinity scFv developed here also has potential for okadaic acid toxin detection.

Evaluation of okadaic acid, dinophysistoxin-1 and dinophysistoxin-2 toxicity on Neuro-2a, NG108-15 and MCF-7 cell lines

Marine dinoflagelates from the genus Dynophisis are important producers of Diarrhetic Shellfish Poisoning (DSP) toxins which are responsible for human intoxications. The present work is an approach to study the relative toxicity of DSP toxins effects on Neuro-2a, NG108-15 and MCF-7 cell-lines. Certified standards of okadaic acid (OA), dinophysistoxin-1 (DTX-1) and dinophysistoxin-2 (DTX-2) were used. Our results show that the three toxins exhibit similar cytotoxicity in Neuro-2a and NG108-15 cell lines. Conversely, MCF-7 cells were the least sensitive to these toxins. DTX-1 displayed the most toxic effect in the three tested cell lines.

Biosensors in forensic analysis. A review

Forensic analysis is an important branch of modern Analytical Chemistry with many legal and socially relevant implications. Biosensors can play an important role as efficient tools in this field considering their well known advantages of sensitivity, selectivity, easy functioning, affordability and capability of miniaturization and automation. This article reviews the latest advances in the use of biosensors for forensic analysis. The different methodologies for the transduction of the produced biological events are considered and the applications to forensic toxicological analysis, classified by the nature of the target analytes, as well as those related with chemical and biological weapons critically commented. The article provides several Tables where the more relevant analytical characteristics of the selected reported methods are gathered.

Innovative detection methods for aquatic algal toxins and their presence in the food chain

Detection of aquatic algal toxins has become critical for the protection of human health. During the last 5 years, techniques such as optical, electrochemical, and piezoelectric biosensors or fluorescent-microsphere-based assays have been developed for the detection of aquatic algal toxins, in addition to optimization of existing techniques, to achieve higher sensitivities, specificity, and speed or multidetection. New toxins have also been incorporated in the array of analytical and biological methods. The impact of the former innovation on this field is highlighted by recent changes in legal regulations, with liquid chromatography-mass spectrometry becoming the official reference method for marine lipophilic toxins and replacing the mouse bioassay in many countries. This review summarizes the large international effort to provide routine testing laboratories with fast, sensitive, high-throughput, multitoxin, validated methods for the screening of seafood, algae, and water samples.

Inhibition equivalency factors for dinophysistoxin-1 and dinophysistoxin-2 in protein phosphatase assays: applicability to the analysis of shellfish samples and comparison with LC-MS/MS

The protein phosphatase inhibition assay (PPIA) is a well-known strategy for the determination of diarrheic shellfish poisoning (DSP) lipophilic toxins, which deserves better characterization and understanding to be used as a routine screening tool in monitoring programs. In this work, the applicability of two PPIAs to the determination of okadaic acid (OA), dinophysistoxin-1 (DTX-1), dinophysistoxin-2 (DTX-2), and their acyl ester derivatives in shellfish has been investigated. The inhibitory potencies of the DSP toxins on a recombinant and a wild PP2A have been determined, allowing the establishment of inhibition equivalency factors (IEFs) (1.1 and 0.9 for DTX-1, and 0.4 and 0.6 for DTX-2, for recombinant and wild PP2A, respectively). The PPIAs have been applied to the determination of OA equivalent contents in spiked and naturally contaminated shellfish samples. Results have been compared to those obtained by LC-MS/MS analysis, after application of the IEFs, showing good agreements.

Biosensors based on enzyme inhibition

The present chapter describes the use of biosensors based on enzyme inhibition as analytical tools. The parameters that affect biosensor sensitivity, such as the amount of immobilized enzyme, incubation time, and immobilization type, were critically evaluated, highlighting how the knowledge of enzymatic kinetics can help researchers optimize the biosensor in an easy and fast manner. The applications of these biosensors demonstrating their wide application have been reported. The objective of this survey is to give a critical description of biosensors based on enzyme inhibition, of their assembly, and their application in the environmental, food, and pharmaceutical fields.

Enzyme immobilization by entrapment within a gel network

This chapter provides a detailed description of the three immobilization methods based on the biomolecules entrapment into polymer matrices. The poly (vinyl alcohol) bearing styrylpyridinium groups (PVA-SbQ), a soluble pre-polymer bearing photo-cross-linkable groups, has widely been used to entrap enzymes, and several bioassays based on this immobilization matrix have been reported. Similarly, immobilization of enzymes via sol-gel has been described in this chapter. Sol-gel process is based on the ability to form solid metal or semi-metal oxides via the aqueous process of hydrolytically labile precursors. Enzymes can also be entrapped in an agarose gel. Contrary to synthetic polymers such as polyacrylamide, this matrix is biocompatible, non-toxic, provides natural microenvironment to the enzyme and also gives sufficient accessibility to electrons to shuttle between the enzyme and the electrode. The entrapment strategies are easy-to-perform, and permit to deposit enzyme, mediators, and additives in the same sensing layer. Moreover, the activity of the enzyme is preserved during the immobilization process, as biological element is not modified. Biosensors based on physically entrapped enzymes are often characterized by increased operational and storage stability.

A graphene-based electrochemical competitive immunosensor for the sensitive detection of okadaic acid in shellfish

A novel graphene-based voltammetric immunosensor for sensitive detection of okadaic acid (OA) was developed. A simple and efficient electrografting method was utilized to functionalize graphene-modified screen-printed carbon electrodes (GSPE) by the electrochemical reduction of in situ generated 4-carboxyphenyl diazonium salt in acidic aqueous solution. Next, the okadaic acid antibody was covalently immobilized on the carboxyphenyl modified graphene electrodes via carbodiimide chemistry. Square wave voltammetry (SWV) was used to investigate the stepwise assembly of the immunosensor. A competitive assay between OA and a fixed concentration of okadaic acid-ovalbumin conjugate (OA-OVA) for the immobilized antibodies was employed for the detection of okadaic acid. The decrease of the [Fe(CN)(6)](3-/4-) reduction peak current in the square wave voltammetry for various concentrations of okadaic acid was used for establishing the calibration curve. A linear relationship between the SWV peak current difference and OA concentration was obtained up to ~5000 ng L(-1). The developed immunosensor allowed a detection limit of 19 ng L(-1) of OA in PBS buffer. The matrix effect studied with spiked shellfish tissue extracts showed a good percentage of recovery and the method was also validated with certified reference mussel samples.

A simple colorimetric enzymatic-assay for okadaic acid detection based on the immobilization of protein phosphatase 2A in sol-gel

Okadaic acid (OA), a lipophilic toxin, is produced by Dinophysis and Prorocentrum, and causes diarrheic shellfish poisoning to humans. The mechanism of OA action is based on the reversible inhibition of protein phosphatase type 2A (PP2A) by the toxin. Therefore, this inhibition could be used to develop assay for OA detection. In this work, a colorimetric test based on the PP2A inhibition was developed for OA detection. PP2A from GTP and Millipore was immobilized on silica sol-gel, and the detection was performed. A limit of detection of 0.29 and 1.14 μg/L was respectively observed for enzyme from GTP and Millipore. The immobilization technique provided a tool to preserve the enzymatic activity, which is very unstable in solution. The PP2A immobilized sol-gel exhibited a storage stability of near 5 months, when microtiter plate with enzyme-immobilized polymer was kept at -18C°. The combination of the simplicity of the colorimetric method, along with long storage stability achieved by sol-gel immobilization, demonstrated the potentiality of this technique to be used for commercial purpose.

Development of a colorimetric inhibition assay for microcystin-LR detection: comparison of the sensitivity of different protein phosphatases

A colorimetric protein phosphatase (PP) inhibition test for the detection of microcystin-LR (MC-LR) has been developed. Three PP2As, one recombinant and two natural versions, as well as one PP1 produced by molecular engineering, were tested. First, assays were performed using the enzymes in solution to compare their sensitivity to MC-LR. The PP2A purchased from ZEU Immunotec and PP1 appeared more sensitive to the toxin than the other enzymes. With PP2A from ZEU Immunotec, the colorimetric test showed a detection limit of 0.0039 μg L(-1) and an IC(50) value of 0.21 μg L(-1). With PP1, the assay gave a detection limit of 0.05 μg L(-1) and an IC(50) value of 0.56 μg L(-1). Therefore, this assay allowed the detection of lower microcystin-LR (MC-LR) concentrations than the maximum level (1 μg L(-1)) recommended by the World Health Organisation (WHO). The main drawback of this PP-based approach in solution is poor enzyme stabilisation. To overcome this problem, enzymes were entrapped within either a photopolymer or an agarose gel. PP2A from ZEU Immunotec and PP1 were immobilised at the bottom of microwells. The agarose-based tests performed better than the photopolymer-based assay for all of the enzymes. Therefore, the agarose gel is a good candidate to replace the photopolymer, which is generally used in PP-immobilising membranes. The assays based on enzyme-entrapping agarose gels showed detection limits equal to 0.17 μg L(-1) and 0.29 μg L(-1) with immobilised PP2A from ZEU and PP1, respectively. In view of these performances, these tests can potentially be used for monitoring water quality.

Production of monoclonal antibody and application in indirect competitive ELISA for detecting okadaic acid and dinophytoxin-1 in seafood

BACKGROUND, AIM, AND SCOPE

Okadaic acid (OA) and analogues of dinophysistoxin (DTX) are key diarrheic shellfish poisoning (DSP) toxins, which possibly arouse DSP symptoms by consuming the contaminated shellfish. Because of the stable toxicity in high temperature and the long-term carcinogenicity, the outbreaks of DSP related to consumption of bivalve mollusks contaminated by DSP toxins pose a hazard to public health. Therefore, it is worth developing a fast and reliable analytical method for the detection of OA and analogues in shellfish. In this paper, an indirect competitive enzyme-linked immunosorbent assay (ELISA) (icELISA) for detecting OA and DTX-1 in seafood was developed based on monoclonal antibody (McAb).

METHODS

The OA was conjugated to human immunoglobulin G (IgG) and bovine serum albumin (BSA) by the active ester method as the immune antigen and the detective antigen. The spleen cells from BALB/c mice immunized with OA-IgG were fused with SP2/0 myeloma cells. A hybridoma cell line, which secreted McAb against OA, was selected by "limiting dilution" cloning. An icELISA was developed based on immobilized conjugate (OA-BSA) competing the McAb with the free OA in seafood sample.

RESULTS

A hybridoma cell line, which secreted IgG1 subclass monoclonal antibody (McAb) against OA, was selected. The IC(50) of the McAb for OA and dinophytoxin-1 (DTX-1) were 4.40 and 3.89 ng/mL, respectively. Based on the McAb, an indirect competitive ELISA for detection of OA and DTX-1 in seafood was developed. The regression equation was y = 54.713x - 25.879 with a coefficient correlation of R (2) = 0.9729. The linear range and the limit of detection were 0.4-12.5 and 0.45 ng/mL, respectively. The average recovery of OA and DTX-1 spiked shellfish was 82.29% with the coefficient of variation of 7.67%.

CONCLUSION

The developed icELISA is a fast, sensitive, and convenient assay for detecting of total amount of OA and DTX-1 in seafood.

Development of an efficient protein phosphatase-based colorimetric test for okadaic acid detection

Okadaic acid (OA), responsible for gastrointestinal problems, inhibits protein phosphatase 2A (PP2A). Therefore, the inhibition exerted by the toxin on PP2A could be used to detect the presence of OA in aqueous solution and in shellfish sample. In this work, two commercial PP2As (from ZEU Immunotec and Millipore) and one produced by molecular engineering (from GTP Technology) were tested. Enzymes were used in solution and also immobilized within a polymeric gel. In solution, best performances were obtained using PP2A purchased from ZEU Immunotec (Spain). OA was detected in aqueous solution in concentration as low as 0.0124 μg L(-1) using the enzyme from ZEU Immunotec whereas the detection limits were 0.47 μg L(-1) and 0.123 μg L(-1) with PP2As from Millipore and GTP Technology, respectively. Considering that the immobilization step contributes to stabilize the PP2A activity, enzymes were entrapped within a photopolymer and an agarose gel. These different polymeric matrices were optimized, tested and compared. Agarose gel seems to be a good alternative to the photopolymer largely used in our group. For instance, the IC(50) value obtained with the test based on PP2A from ZEU Immunotec immobilized within an agarose gel was 1.98 μg L(-1). This value was 1.8-fold lower than those obtained with the photopolymer test using the same enzyme. The proposed test is sensitive, fast and does not require expensive equipment. To evaluate the efficiency of the assay, PP inhibition tests based on PP2A from ZEU Immunotec in solution or immobilized within a gel were used for OA detection in contaminated shellfish.

A rapid enzymatic method for aflatoxin B detection

A novel method for aflatoxin B (AFB) determination is proposed. The AFB determination is based on acetylcholinesterase (AChE, from electric eel) inhibition, and the AChE residual activity is determined using the colorimetric method (Ellman's method). To select and optimize the analytical procedures, the investigation on type of AChE inhibition by AFB(1) was carried out. The AChE degree of inhibition by AFB(1) was independent of the incubation time and the enzyme concentrations, showing the reversibility of the inhibition. This reversibility of the inhibition permits a rapid analysis of AFB(1). In fact, only a 3-min analysis is required. For the development of AFB(1) assay, the pH, the reaction time, the temperature, and the substrate concentration were evaluated and optimized. The linear range of 10-60 ng/mL was assessed. To evaluate the selectivity of this method, the cross-reactivity with other aflatoxins, such as AFB(2) (aflatoxin B(2)), AFG(1) (aflatoxin G(1)), AFG(2) (aflatoxin G(2)), and AFM(1) (aflatoxin M(1)), was investigated. The suitability of the assay for AFB(1) quantification in barley was also evaluated. This study shows a new approach to detect aflatoxins based on enzyme inhibition with several advantages, such as the easiness of use, the rapidity, and the cost-effectiveness, demonstrating a possible use as screening method for this type of mycotoxins.

Biological methods for marine toxin detection

The presence of marine toxins in seafood poses a health risk to human consumers which has prompted the regulation of the maximum content of marine toxins in seafood in the legislations of many countries. Most marine toxin groups are detected by animal bioassays worldwide. Although this method has well known ethical and technical drawbacks, it is the official detection method for all regulated phycotoxins except domoic acid. Much effort by the scientific and regulatory communities has been focused on the development of alternative techniques that enable the substitution or reduction of bioassays; some of these have recently been included in the official detection method list. During the last two decades several biological methods including use of biosensors have been adapted for detection of marine toxins. The main advances in marine toxin detection using this kind of technique are reviewed. Biological methods offer interesting possibilities for reduction of the number of biosassays and a very promising future of new developments.

Use of biosensors as alternatives to current regulatory methods for marine biotoxins

Marine toxins are currently monitored by means of a bioassay that requires the use of many mice, which poses a technical and ethical problem in many countries. With the exception of domoic acid, there is a legal requirement for the presence of other toxins (yessotoxin, saxitoxin and analogs, okadaic acid and analogs, pectenotoxins and azaspiracids) in seafood to be controlled by bioassay, but other toxins, such as palytoxin, cyclic imines, ciguatera and tetrodotoxin are potentially present in European food and there are no legal requirements or technical approaches available to identify their presence. The need for alternative methods to the bioassay is clearly important, and biosensors have become in recent years a feasible alternative to animal sacrifice. This review will discuss the advantages and disadvantages of using biosensors as alternatives to animal assays for marine toxins, with particular focus on surface plasmon resonance (SPR) technology.

High-sensitive flow-based kinetic exclusion assay for okadaic acid assessment in shellfish samples

Episodes of shellfish contamination with okadaic acid (OA) are a human health threat that is causing increasing concern. As a way to overcome the shortcomings involved in the reference methods of analysis set by legislations, alternative procedures are envisaged. This paper describes the development of different immunosensors for the analysis of OA, focusing on the comparison of their sensitivity, precision, ease of use and sample matrix effects. Initially, a surface plasmon resonance (SPR)-based immunosensor was developed, which enabled the quantification of the toxin in mussel samples at concentrations in the range of the 160 microg kg(-1) European regulatory limit with good percentages of recovery. Nevertheless, calibration curves with spiked mussel samples showed that matrix effects could not be neglected. Alternatively, a flow-immunosensing system based on kinetic exclusion measurements was developed achieving the theoretical lowest limit of detection enabled by the affinity of the anti-OA antibody (IC(70)=0.03 microg L(-1) in the assay solution). This highly sensitive automated system allows rapid and reliable OA quantification, with no significant matrix effects for the analysis of spiked mussel and scallop samples. Performance features such as high sensitivity and precision, low limits of detection and simplicity of the analysis protocol, shows the biosensing-systems based on kinetic exclusion measurements for toxin detection in shellfish samples as highly performing tools for rapid and continuous screening.

Flow-injection electrochemical immunosensor for the detection of human IgG based on glucose oxidase-derivated biomimetic interface

A newly flow-through electrochemical immunosensor for monitoring IgG in human serum has been developed by using core-shell SiO(2)/Au nanocomposites and poly(amidoamine) G4 dendrimer as matrices. The ferrocenecarboaldehyde-labeled anti-IgG biomolecules were initially chemisorbed onto the nanoparticle surface, and then glucose oxidase (GOx), as a blocking reagent instead of bovine serum albumin (BSA), was backfilled onto the modified surface. The formation of the antibody-antigen complex by a simple one-step immunoreaction between the immobilized anti-IgG and IgG in sample solution introduced a barrier of direct electrical communication between the immobilized GOx and the base surface, and decreased the immobilized GOx toward the catalytic oxidation of glucose. The performance and factors influencing the performance of the immunosensor were evaluated. Under optimal conditions, the linear range of the developed immunosensor by using GOx as enhancer was from 5.0 x 10(-6) to 9.6 x 10(-4)mol/L with a detection limit of 8.0 x 10(-7)mol/L IgG (at 3delta), while the detection limit by using BSA was 1.5 x 10(-5)mol/L IgG (at 3delta) with the linear range from 3.5 x 10(-5) to 1.2 x 10(-3)mol/L. The selectivity, reproducibility and stability of the proposed immunosensor were acceptable. The IgG contents in 37 human serum samples obtained by the proposed method are identical with the data of clinical laboratory.

Sensors and Biosensors for the Determination of Small Molecule Biological Toxins

The following review of sensors and biosensors focuses on the determination of commonly studied small molecule biological toxins, including mycotoxins and small molecule neurotoxins. Because of the high toxicity of small molecule toxins, an effective analysis technique for determining their toxicity is indispensable. Sensors and biosensors have emerged as sensitive and rapid techniques for toxicity analysis in the past decade. Several different sensors for the determination of mycotoxins and other small molecule neurotoxins have been reported in the literature, and many of these sensors such as tissue biosensors, enzyme sensors, optical immunosensors, electrochemical sensors, quartz crystal sensors, and surface plasmon resonance biosensors are reviewed in this paper. Sensors are a practical and convenient monitoring tool in the area of routine analysis, and their specificity, sensitivity, reproducibility and analysis stability should all be improved in future work. In addition, accuracy field portable sensing devices and multiplexing analysis devices will be important requirement for the future.