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Marine biotoxins are a diverse group of naturally occurring toxic secondary metabolites produced by marine dinoflagellates, diatoms, cyanobacteria, and other aquatic microorganisms. Many of these toxins are associated with harmful algal blooms (HABs), in which toxin-producing phytoplankton proliferate rapidly under favorable environmental conditions. Once introduced into aquatic ecosystems, marine biotoxins may persist in water and sediments or accumulate in shellfish, fish, and higher trophic organisms, creating potential risks to aquatic ecosystems, seafood safety, drinking water security, and public health. The increasing occurrence and geographic distribution of HAB events have made marine biotoxin surveillance an important component of environmental monitoring and water quality management. Nutrient enrichment, agricultural runoff, coastal urbanization, rising water temperatures, altered precipitation patterns, and changes in water circulation can all influence bloom formation and toxin dynamics. As a result, monitoring strategies increasingly require sensitive and scalable analytical approaches capable of detecting trace levels of diverse toxins across environmental and food matrices.
Marine biotoxins encompass chemically and biologically diverse compounds that can be broadly categorized according to their toxicological effects and mechanisms of action. Major groups relevant to environmental and food safety monitoring include paralytic shellfish toxins, diarrhetic shellfish toxins, amnesic shellfish toxins, neurotoxic shellfish toxins, and cyanobacterial toxins.
Fig. 1 Molecular Mechanisms of Major Marine Biotoxins
Paralytic shellfish toxins are a family of potent neurotoxins primarily associated with dinoflagellates such as Alexandrium, Gymnodinium, and Pyrodinium species. Saxitoxin (STX) is the best-known member of this group, together with neosaxitoxin, gonyautoxins, and decarbamoyl saxitoxins. PSTs exert their neurotoxic effects primarily by interacting with voltage-gated sodium channels on neuronal membranes, thereby interfering with sodium ion influx and action potential propagation. Exposure can result in neurological symptoms ranging from tingling and numbness to muscular paralysis and, in severe cases, respiratory failure.
Diarrhetic shellfish toxins include Okadaic Acid (OA) and dinophysistoxins such as DTX-1 and DTX-2, which are mainly associated with Dinophysis and Prorocentrum species. Okadaic acid inhibits serine/threonine protein phosphatases PP1 and PP2A, disrupting intracellular phosphorylation pathways and contributing to epithelial dysfunction and gastrointestinal toxicity. These toxins are associated with increased intestinal permeability, gastrointestinal inflammation, fluid secretion, and diarrhea, making their monitoring important for seafood safety and environmental surveillance.
Amnesic shellfish poisoning is primarily associated with Domoic Acid, a neuroexcitatory amino acid produced by several Pseudo-nitzschia diatom species. Domoic acid acts on kainate and AMPA glutamate receptors, and excessive receptor activation can lead to calcium influx, excitotoxicity, oxidative stress, and neuronal damage. Severe exposure may result in neurological effects including memory impairment, seizures, and other neurobehavioral abnormalities.
Brevetoxins are polyether neurotoxins produced by Karenia brevis and are commonly associated with red tide events. Unlike saxitoxins, brevetoxins activate voltage-gated sodium channels by stabilizing their open configuration, resulting in persistent sodium influx, membrane depolarization, and neuronal hyperexcitability. Their environmental impact extends beyond aquatic organisms and seafood safety, as HAB events involving brevetoxins can contribute to fish mortality, marine mammal poisoning, and respiratory irritation in humans exposed to toxin-containing aerosols.
Cyanobacteria can produce a range of toxins that are particularly relevant to freshwater ecosystems and drinking water monitoring. Major cyanotoxins include Microcystins, Cylindrospermopsin, Anatoxin-a, and Nodularins. The occurrence of these toxins in freshwater systems has increased interest in sensitive monitoring approaches capable of supporting drinking water safety, environmental surveillance, and early detection of toxic cyanobacterial blooms.
The occurrence and persistence of harmful algal blooms are influenced by multiple interacting environmental factors rather than a single cause. Nutrient enrichment from agricultural runoff, industrial activities, and wastewater can increase nitrogen and phosphorus availability, promote eutrophication, and stimulate the proliferation of toxin-producing phytoplankton. At the same time, rising water temperatures, altered precipitation patterns, and stronger water-column stratification associated with climate change may create conditions favorable for bloom formation and persistence. Hydrodynamic conditions and microbial ecosystem interactions can further influence the accumulation, distribution, and biosynthesis of marine biotoxins. Once produced, toxins may be transported through aquatic food webs and accumulate in shellfish, fish, and higher trophic organisms, resulting in bioaccumulation and trophic transfer. The complex relationship between environmental conditions, bloom development, toxin production, and biological accumulation highlights the need for monitoring strategies that can detect toxins across different stages of environmental and food-chain exposure.
Fig. 2 Bioaccumulation and Trophic Transfer of Marine Biotoxins
The structural diversity and low concentrations of marine biotoxins present significant challenges for environmental monitoring. Immunological technologies have become valuable tools for addressing these challenges because they combine sensitive molecular recognition with relatively simple and scalable assay formats. Compared with instrumental methods such as LC-MS/MS, immunoassays can provide more accessible and cost-effective approaches for routine screening of marine toxins in water, seafood, aquaculture, and environmental samples. Because many marine biotoxins are low-molecular-weight compounds with limited immunogenicity, they generally require hapten-carrier conjugation to generate an immune response. Consequently, hapten structure, conjugation chemistry, antibody affinity, specificity, and cross-reactivity are important considerations in the development of marine toxin immunoassays.
ELISA is one of the most widely used immunological approaches for marine biotoxin analysis, particularly for routine screening and high-throughput monitoring. Because many marine toxins are small molecules with limited antigenic epitopes, competitive ELISA formats are commonly employed. These assays can provide sensitive detection at trace concentrations while requiring relatively modest instrumentation, making them suitable for routine laboratories, field-oriented monitoring programs, and large-scale environmental surveillance.
ELISA-based methods have been developed for a broad range of marine and aquatic toxins, including:
In monitoring workflows, immunoassays can serve as screening tools to identify potentially contaminated samples, while LC-MS/MS or other instrumental methods may subsequently be used for confirmatory analysis and more detailed toxin characterization.
Lateral flow immunoassays provide a complementary approach when rapid, portable testing is required. Their relatively simple workflow, limited sample preparation requirements, short turnaround time, and minimal instrumentation make them particularly suitable for field deployment. These characteristics are valuable during HAB outbreaks, seafood harvest monitoring, and emergency environmental assessments, where rapid information can support timely decisions regarding water quality, harvesting, or further laboratory analysis.
Antibody-based technologies can also be applied beyond direct detection. Immunoaffinity columns (IACs) use immobilized antibodies to selectively capture target toxins from complex samples, enabling selective purification and enrichment before instrumental analysis. This approach can be applied to seawater samples, shellfish extracts, and other complex environmental matrices to improve toxin recovery, reduce matrix interference, and enhance the performance of downstream LC-MS/MS analysis. Immunoaffinity purification therefore provides a useful bridge between highly selective antibody recognition and high-specificity instrumental detection.
The integration of antibody recognition with biosensor technologies is further expanding the potential applications of immunological marine toxin detection. Antibody-based biosensors can combine selective molecular recognition with rapid signal transduction, supporting the development of real-time monitoring, multiplex detection, automated sensing, and ultra-trace analysis platforms. Examples include electrochemical immunosensors, surface plasmon resonance (SPR) systems, fluorescence immunosensors, and chemiluminescent biosensors.
Advances in recombinant antibody engineering, phage display, and single-chain variable fragment (scFv) technologies are also creating opportunities to improve antibody specificity and assay performance. These developments may support the next generation of marine toxin monitoring systems, particularly where rapid, multiplexed, or highly sensitive detection is required.
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