Self-assembled monolayer-based immunoassays for okadaic acid detection in seawater as monitoring tools

Marine toxins in seafood: Recent updates on sample pretreatment and determination techniques

Marine toxins can lead to varying degrees of human poisoning, often resulting in fatal symptoms and causing significant economic losses in seafood-producing regions. To gain a deeper comprehension of the role of marine toxins in seafood and their impact on the environment, it is imperative to develop rapid, cost-effective, environmentally friendly, and efficient methods for sample pretreatment and determination to mitigate adverse impacts of marine toxins. This review presents a comprehensive overview of advancements made in sample pretreatment and determination techniques for marine toxins since 2017. The advantages and disadvantages of various technologies were critically examined. Additionally, the current challenges and future development strategies for the analysis of marine toxins are provided.

Ultrasensitive fluorescence detection of gonyautoxins in seawater using a novel molecularly imprinted nanoprobe

Gonyautoxins (GTXs), a group of potent neurotoxins belonging to paralytic shellfish toxins (PSTs), are often associated with harmful algal blooms of toxic dinoflagellates in the sea and represent serious health and ecological concerns worldwide. In the study, a highly selective and sensitive fluorescence nanoprobe was constructed based on photoinduced electron transfer recognition mechanism to rapidly detect GTXs in seawater, using specific entrapment of molecularly imprinted polymers (MIPs) combined with fluorescence analyses. The green emissive fluorescein isothiocyanate was grafted in a silicate matrix as a signal transducer and fluorescence intensity of the nanoprobe with a core-shell structure exhibited a strong enhancement due to efficient analyte blockage in a short response time. Under optimal conditions, the developed MIPs nanoprobe presented an excellent analytical performance for spiked seawater samples including a recovery from 94.44 % to 98.23 %, a linear range between 0.018 nmol L-1 and 0.36 nmol L-1, as well as good accuracy. Furthermore, the method had extremely high sensitivity, with limit of detection obtained as 0.005 nmol L-1 for GTXs and GTX2/3. Finally, the nanoprobe was applied for the determination of GTXs in seven natural seawater samples with GTXs mixture (0.035-0.058 nmol L-1) or single GTX2/3 (0.033-0.050 nmol L-1), and the results agreed well with those of a UPLC-MS/MS method. The findings of our study suggest that the constructed MIPs-based fluorescence enhancement nanoprobe was suitable for rapid, selective and ultrasensitive detection of GTXs, particular GTX2/3, in natural seawater samples.

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.

Cyclodextrin polymers as passive sampling materials for lipophilic marine toxins in Prorocentrum lima cultures and a Dinophysis sacculus bloom in the NW Mediterranean Sea

Cyclodextrins, cyclic oligomers that form a conical structure with an internal cavity, are proposed as new and sustainable materials for passive sampling of lipophilic marine toxins. Two applicability scenarios have been tested. First, disks containing β-cyclodextrin-hexamethylene diisocyanate (β-CD-HDI) and β-cyclodextrin-epichlorohydrin (β-CD-EPI) polymers were immersed in Prorocentrum lima cultures for different days (2, 12 and 40). LC-MS/MS analysis showed capture of free okadaic acid (OA) and dinophysistoxin-1 (DTX1) by cyclodextrins at contents that increased with immersion time. Cyclodextrins resulted more efficient in capturing DTX1 than OA. In a second experiment, disks containing β-CD-HDI, β-CD-EPI, γ-CD-HDI and γ-CD-EPI were deployed in harbor waters of El Masnou (NW Mediterranean Sea) during a Dinophysis sacculus bloom in February 2020. Free OA and pectenotoxin-2 (PTX2) were captured by cyclodextrins. Toxin contents were higher at sampling points and sampling weeks with higher D. sacculus cell abundance. In this case, PTX2 capture with cyclodextrins was more efficient than OA capture. Therefore, cyclodextrins have provided information regarding the toxin profile of a P. lima strain and the spatial and temporal dynamics of a D. sacculus bloom, proven efficient as passive sampling materials for environmental monitoring.

A multi-channel handheld automatic spectrometer for wide range and on-site detection of okadaic acid based on specific aptamer binding

Okadaic acid (OA) is one of the marine toxins that are widely distributed and harmful to humans. However, the current detection methods for OA involve complex procedures, need long detection time, and rely on large-scale laboratory equipment. In this work, a multi-channel handheld automatic spectrometer (MHAS) based on a spectral sensor was developed with the advantages of small size, simple operation and low cost. It could achieve rapid detection within 30 s and a wide spectral detection range of 470-780 nm with a broadband LED as the light source and a microplate containing 8 wells as a sample cell. Moreover, through the combination of gold nanoparticles (AuNPs) and aptamer-OA34, a highly sensitive and rapid system for OA detection was established with a LOD of 1.80 μg L^-1 and a wide detection range of 20-10 000 μg L^-1, which is comparable to a microplate reader. Compared with other studies, the proposed MHAS realized rapid on-site detection of OA with a wider detection range, shorter detection time and higher portability. Therefore, the MHAS promises to be a stable and efficient optical detection instrument for on-site detection in the fields of food safety, disease diagnosis and environmental monitoring.

A Novel Enzyme-Based SPR Strategy for Detection of the Antimicrobial Agent Chlorophene

Chlorophene is an important antimicrobial agent present in disinfectant products which has been related to health and environmental effects, and its detection has been limited to chromatographic techniques. Thus, there is a lack of research that attempts to develop new analytical tools, such as biosensors, that address the detection of this emerging pollutant. Therefore, a new biosensor for the direct detection of chlorophene in real water is presented, based on surface plasmon resonance (SPR) and using a laccase enzyme as a recognition element. The biosensor chip was obtained by covalent immobilization of the laccase on a gold-coated surface through carbodiimide esters. The analytical parameters accomplished resulted in a limit of detection and quantification of 0.33 mg/L and 1.10 mg/L, respectively, fulfilling the concentrations that have already been detected in environmental samples. During the natural river's measurements, no significant matrix effects were observed, obtaining a recovery percentage of 109.21% ± 7.08, which suggested that the method was suitable for the fast and straightforward analysis of this contaminant. Finally, the SPR measurements were validated with an HPLC method, which demonstrated no significant difference in terms of precision and accuracy, leading to the conclusion that the biosensor reflects its potential as an alternative analytical tool for the monitoring of chlorophene in aquatic environments.

Recent progress in micro/nano biosensors for shellfish toxin detection

Shellfish toxins, as one kind of marine toxin, have attracted worldwide attention due to their severe threat to food safety and human health. Therefore, it is highly essential and urgent to develop a low-cost and convenient method to detect these toxins. With the rapid advance in microfabrication processes, micro/nano biosensors provide novel approaches to address this issue. In addition to their features of low cost, portability, easy operation, high efficiency and high bioactivity, micro/nano biosensors have great potential to realize on-the-spot, rapid detection of shellfish toxins. This review focuses on the most recent advances in the development of micro/nano biosensors for shellfish toxin detection. These biosensors are mainly classified into five categories according to their transducer detection principles, which include optical devices, electrochemical sensors, electrochemiluminescence, field-effect transistors, and acoustic devices. Sensor strategies, toxin analytes, biosensitive elements, coupling methods and field detection performance are highlighted to discuss the applications of shellfish toxin detection. With advances in sensor technology, biomaterials, microfabrication and miniaturized electronics, micro/nano biosensors applied to in-field fast detection of shellfish toxins are expected to play a critical role in food safety, environmental monitoring, and foreign trade in the foreseeable future. Finally, the current challenges and future development trends of micro/nano biosensors for shellfish toxin detection are discussed.

Monitoring and warning of lipophilic marine algal toxins in mariculture zone based on toxin profiles of phytoplankton

Some toxigenic dinoflagellates can produce lipophilic marine algal toxins (LMATs), which are potent threats to marine breeding industries. In this study, a new method based on the profiling analysis of six LMAT classes in phytoplankton was developed for the monitoring and warning of LMATs in mariculture zones. This method was applied to monitor and evaluate LMATs in the Jiaozhou Bay and the Changjiang estuary in China. Results demonstrated that the occurrence and spatiotemporal variations of LMATs in mariculture zones can be revealed by the toxin profiles of phytoplankton, indicating the method's effectiveness for the comprehensive monitoring of the composition and levels of various LMATs in coastal aquaculture zones. The method was further used as an alarm for potential pollution risk from LMATs in mariculture zones at an early stage. The "alert" thresholds of LMAT pollution in the mariculture zones were preliminarily proposed based on the statistical data analysis of LMATs in phytoplankton in three typical mariculture areas in China. This study is the first to conduct simultaneous monitoring and warning of multi-class LMATs based on toxin profiles of phytoplankton, thereby providing new insight into the monitoring and early warning of natural poisonous pollutants in coastal aquaculture zones around the world.

Determination of Lipophilic Marine Biotoxins in Mussels Harvested from the Adriatic Sea by LC-MS/MS

Lipophilic marine biotoxins include okadaic acid, pectenotoxin, yessotoxin and azaspiracid groups. The consumption of contaminated molluscs can lead to acute food poisoning syndromes depending on the exposure level. Regulatory limits have been set by Regulation (European Community, 2004a) No 853/2004 and LC-MS/MS is used as the official analytical method according to Regulation (European Community, 2011) No 15/2011. In this study specimens of mussels (Mytilus galloprovincialis) were collected along the coasts of the central Adriatic Sea during the years 2015–2017 and analyzed by the European harmonized Standard Operating Procedure. The method was validated for linearity, specificity, repeatability and reproducibility and it revealed able to be used for the detection of the lipophilic marine biotoxins. Levels of okadaic acid, pectenotoxin, yessotoxin and its analogs were detected at different concentrations in 148 (37%) out of a total of 400 samples, always below the maximum limits, except for 11 (4.3%) of them that were non-compliant because they exceeded the regulatory limit. Moreover, some samples were exposed to a multi-toxin mixture with regards to okadaic acid, yessotoxin and 1-Homo yessotoxin. Following these results, the aquaculture farms from which the non-compliant samples derived were closed until the analytical data of two consecutive samplings returned favorable. Besides the potential risk of consumption of mussels contaminated by lipophilic marine biotoxins, these marine organisms can be considered as bio-indicators of the contamination status of the marine ecosystem.