Emerging roles of the aptasensors as superior bioaffinity sensors for monitoring shellfish toxins in marine food chain

Dual-mode monolithic column with zwitterion antifouling and aptamer affinity for online specific recognition of okadaic acid

Developing a functional media for precise identification of trace shellfish toxin would underpin the effective assessment of marine pollution. Herein, a novel monolithic column with a dual-mode strategy integrating antifouling and aptamer bionic affinity recognition was proposed for online specific identification of the marine toxin okadaic acid (OA). The zwitterionic monomer 2-(methacryloyloxy)ethylphosphorylcholine (MPC) and aptamers were synergistically employed to enable efficient reduction of matrix interferences and selective capture of target OA. Preparation optimization, characterization, and fouling-resistant mechanism of the dual-mode bionic monolith were evaluated. The zwitterion phosphorylcholine MPC introduced into the monolith significantly improved the fouling resistance to biomass substrates, meanwhile the aptamers were able to provide a high specific recognition capacity. Coupled with LC-MS, the as-prepared monolith provided an effective approach for highly selective and sensitive identification of OA. Good recovery yields of over 90 % in shellfish tissue extracts and human serum were achieved with a sensitive limit of detection (LOD) as low as 0.1 ng/mL, as well as excellent specificity and low interference from proteins, fatty acids and analogues. Applied to popular shellfishes (such as clams, mussels, and oysters) and serum samples, trace OA toxin was accurately distinguished and quantified with satisfactory recoveries as 93.8 ± 2.2 % - 99.9 ± 1.9 % (n = 3). Compared to the traditional HLB cartridge and other materials in the LC-MS method, the resulting anti-fouling aptamer monolith provided a more advanced online analysis mode with higher sensitivity and better resolution of OA in biological samples. It might provide an attractive access to an online bionic recognition platform with LC-MS for efficient, anti-interference and sensitive specific detection of trace marine toxin OA in biological samples.

Recent Advances in Food Safety Detection: Split Aptamer-Based Biosensors Development and Potential Applications

Ensuring food safety is a shared responsibility across the entire food supply chain, encompassing manufacturers, processors, retailers, consumers, and regulatory bodies. However, traditional detection methods have several limitations, including slow processing times, high costs, limited sensitivity, and susceptibility to false positives or negatives. These shortcomings underscore the urgent need for faster, more accurate, and cost-effective detection technologies. Aptamers and aptasensors have emerged as promising alternatives. Aptamers offer advantages over traditional recognition probes due to their high affinity and specificity for diverse targets. The aptasensors enable rapid detection, cost reduction, shelf life extension, and minimal batch-to-batch variability, making them highly suitable for food safety applications. Detecting small molecules such as toxins, antibiotics, pesticides, contaminants, and heavy metals remains challenging due to steric hindrance, nonspecific binding, and reduced accuracy. Recent advancements in aptamer technology have focused on pre- and postmodifications to enhance detection performance. One of the most promising innovations is the development of split aptamers. These engineered aptamers, designed to operate in segments known as split aptamers, offer improved flexibility and binding specificity, effectively addressing the challenges of detecting small-sized targets. This review examines the evolution of aptamers and aptasensors, focusing on their application in detecting small molecules that are essential to food safety. It reported the strategies for modifying and optimizing selected aptamers, providing details on developing split aptamers as a promising approach to address the unique challenges of small-molecule detection. Additionally, recent advancements in split aptamer technology and its integration into aptasensor development are highlighted, showcasing how these innovations are revolutionizing the detection of food safety hazards by overcoming the limitations of traditional detection methods.

Past, Current and Future Techniques for Monitoring Paralytic Shellfish Toxins in Bivalve Molluscs

Paralytic shellfish poisoning is a threat to human health caused by the consumption of shellfish contaminated with toxins of the saxitoxin class. Human health is protected by the setting of regulatory limits and the analysis of shellfish prior to sale. Both robust toxicity data, generated from experiments fitting into the ethical 3R framework, and appropriate analysis methods are required to ensure the success of this approach. A literature review of in vivo animal bioassays and in vitro and analytical methods showed that in vitro methods are the best option to screen shellfish for non-regulatory purposes. However, since neither the receptor nor antibody binding of paralytic shellfish toxin analogues correlate with toxicity, these assays cannot accurately quantify toxicity in shellfish nor be used to calculate toxicity equivalence factors. Fully replacing animals in testing is rightfully the ultimate goal, but this cannot be at a cost to human health. More modern technology, such as organ-on-a-chip, represent an exciting development, but animal bioassays cannot currently be replaced in the determination of toxicity. Analytical methods that employ toxicity equivalence factors calculated using oral animal toxicity data result in an accurate assessment of the food safety risk posed by paralytic shellfish toxin contamination in bivalve molluscs.

Prevalence of lipophilic phycotoxins with different forms in the benthic environments of a typical mariculture bay

Lipophilic phycotoxins (LPTs) are toxic and lipophilic secondary metabolites produced by toxic microalgae, which pose a serious threat to marine shellfish culture industries. LPTs were systematically investigated in bottom seawater, suspended particulate matter (SPM), sediment, and sediment porewater of Laizhou Bay, a typical mariculture bay in China, to understand the chemical diversity and environment behaviors of LPTs in the benthic environments. Okadaic acid (OA), pectenotoxin-2 (PTX2), dinophysistoxin-1 (DTX1), azaspiracid-2 (AZA2), gymnodimine (GYM), pectenotoxin-2 seco acid (PTX2 SA), 7-epi- pectenotoxin-2 seco acid (7-epi-PTX2 SA), 13-desmethylspirolide C (SPX1), yessotoxin (YTX) and homo YTX (h-YTX) were detected in the benthic environment of Laizhou Bay in spring, indicating that LPTs are rich in chemical diversity. OA and PTX2 were dominant in bottom seawater and porewater; PTX2 and PTX2 SA were dominant in SPM; and PTX2 and AZA2 were dominant in sediments, but AZA2 was present in sediments only. At the bottom seawater-SPM interface, the average proportion of LPTs in the dissolved phase (DP) (84.35%) was significantly higher than in the particulate phase (PP) (15.65%), indicating that LPTs were mainly distributed to the DP in the bottom seawater. At the sediment-porewater interface, a considerable variation exists in the partitioning behavior of different groups of LPTs, with abundant PTX2 and OA in DP, while the AZA2 and YTX group of LPTs were present in PP. The concentration of total lipophilic phycotoxins (∑LPTs) in the bottom seawater ranged from 8.07 ng L-1 to 37.11 ng L-1, with an average of 22.63 ng L-1, showing that the spatial distribution characteristics of ∑LPTs of the northern farshore are higher than in the southern nearshore. Concentrations of ∑LPTs in sediment and porewater ranged from 1.51 ng kg-1-32.67 ng kg-1 (mean: 17.32 ng kg-1) and 17.32 ng L-1-226.54 ng L-1 (mean: 88.72 ng L-1), respectively. Notably, the concentration of ∑LPTs in porewater is significantly higher than in bottom and surface seawater, indicating that the potential harm of LPTs to benthos needs more attention.

Perspectives in Aptasensor-Based Portable Detection for Biotoxins

Biotoxins are pervasive in food and the environment, posing significant risk to human health. The most effective strategy to mitigate the risk arising from biotoxin exposure is through their specific and sensitive detection. Aptasensors have emerged as pivotal tools, leveraging aptamers as biorecognition elements to transduce the specificity of aptamer-target interactions into quantifiable signals for analytical applications, thereby facilitating the meticulous detection of biotoxins. When integrated with readily portable devices such as lateral flow assays (LFAs), personal glucose meters (PGMs), smartphones, and various meters measuring parameters like pH and pressure, aptasensors have significantly advanced the field of biotoxin monitoring. These commercially available devices enable precise, in situ, and real-time analysis, offering great potential for portable biotoxin detection in food and environmental matrices. This review highlights the recent progress in biotoxin monitoring using portable aptasensors, discussing both their potential applications and the challenges encountered. By addressing these impediments, we anticipate that a portable aptasensor-based detection system will open new avenues in biotoxin monitoring in the future.

Assembly of a multivalent aptamer for efficient inhibition of thermostable direct hemolysin toxicity induced by Vibrio parahaemolyticus

Thermostable direct hemolysin (TDH) is a key virulence factor of Vibrio parahaemolyticus, capable of causing seafood-mediated outbreaks of gastroenteritis, posing a threat to the aquatic environment and global public health. In the present study, we explored a multivalent aptamer-mediated inhibition strategy to mitigate TDH toxicity. Based on the characteristic structure of TDH, a stable multivalent aptamer, Ap3-5, was rationally designed by truncation, key fragment evolution, and end fixation. Ap3-5 exhibited strong affinity (Kd=39.24 nM), and thermal (Tm=57.6 °C) and enzymatic stability. In silico studies also revealed that Ap3-5 occupied more active sites of TDH and covered its central pore, indicating its potential as a blocking agent for inhibiting TDH toxicity. In the hemolysis assay, Ap3-5 significantly suppressed the hemolytic effect of TDH. A cellular study revealed a substantial (∼80 %) reduction in TDH cytotoxicity. Supporting these findings, in vivo trials confirmed the inhibitory action of Ap3-5 on both the acute and intestinal toxicity of TDH. Overall, benefiting from the strong binding affinity, high stability, and multisite occupation of the multivalent aptamer with TDH, Ap3-5 displayed robust potential against TDH toxicity by inhibiting membrane pore formation, providing a new approach for alleviating bacterial infections.

Spatiotemporal distribution of lipophilic shellfish toxins in plankton and shellfish in the offshore regions of Shandong province, China

Lipophilic shellfish toxins (LSTs) threaten the ecosystem health and seafood safety. To comprehensively investigate the spatiotemporal distribution of common LSTs in phytoplankton, zooplankton and economic shellfish, three cruises were conducted in five typical offshore aquaculture regions of Shandong province, China, including Haizhou Bay, Jiaozhou Bay, Sanggou Bay, Sishili Bay and Laizhou Bay, in spring (March-April), summer (July-August) and autumn (November-December). This study revealed significant variability in the composition and content of LSTs in phytoplankton samples collected from different regions. Pectenotoxin-2 (PTX2), dinophysistoxin-1 (DTX1) and okadaic acid (OA) were mainly detected in the ranges of not detected (nd)-5045 pmol g-1 dry weight (dw), nd-159 pmol g-1 dw, and nd-154 pmol g-1 dw, respectively. In zooplankton, DTX1 and OA were the predominant components of LSTs, with the highest levels of ∑LSTs in spring ranging from nd to 406 pmol g-1 dw. Spearman's correlation analysis between LSTs and environmental factors indicated significant correlations for the contents of homo-yessotoxin (hYTX), gymnodimine-A (GYM-A), and spirolide-1 (SPX1) with these factors. Totally relatively low levels of LSTs with dominative DTX1 were detected in economic shellfish, which showed a low risk to seafood safety for human health.

Toward Sensitive and Reliable Immunoassays of Marine Biotoxins: From Rational Design to Food Analysis

Marine biotoxins are metabolites produced by algae that can accumulate in shellfish or fish and enter organisms through the food chain, posing a serious threat to biological health. Therefore, accurate and rapid detection is an urgent requirement for food safety. Although various detection methods, including the mouse bioassay, liquid chromatography-mass spectrometry, and cell detection methods, and protein phosphatase inhibition assays have been developed in the past decades, the current detection methods cannot fully meet these demands. Among these methods, the outstanding immunoassay virtues of high sensitivity, reliability, and low cost are highly advantageous for marine biotoxin detection in complex samples. In this work, we review the recent 5-year progress in marine biotoxin immunodetection technologies such as optical immunoassays, electrochemical immunoassays, and piezoelectric immunoassays. With the assistance of immunoassays, the detection of food-related marine biotoxins can be implemented for ensuring public health and preventing food poisoning. In addition, the immunodetection technique platforms including lateral flow chips and microfluidic chips are also discussed. We carefully investigate the advantages and disadvantages for each immunoassay, which are compared to demonstrate the guidance for selecting appropriate immunoassays and platforms for the detection of marine biotoxins. It is expected that this review will provide insights for the further development of immunoassays and promote the rapid progress and successful translation of advanced immunoassays with food safety detection.

Molecularly imprinted metal-organic frameworks assisted cloth and paper hybrid microfluidic devices for visual detection of gonyautoxin

Marine algal toxin contamination is a major threat to human health. Thus, it is crucial to develop rapid and on-site techniques for detecting algal toxins. In this work, we developed colorimetric cloth and paper hybrid microfluidic devices (μCPADs) for rapid detection of gonyautoxin (GTX1/4) combined with molecularly imprinted polymers. In addition, the metal-organic frameworks (MOFs) composites were applied for this approach by their unique features. Guanosine serves as a dummy template for surface imprinting and has certain structural advantages in recognizing gonyautoxin. MOF@MIPs composites were able to perform a catalytic color reaction using hydrogen peroxide-tetramethylbenzidine for the detection of GTX1/4. The cloth-based sensing substrates were assembled on origami μPADs to form user-friendly, miniaturized colorimetric μCPADs. Combined with a smartphone, the proposed colorimetric μCPADs successfully achieved a low limit of detection of 0.65 μg/L within the range of 1-200 μg/L for rapid visual detection of GTX1/4. Moreover, the GTX1/4 of real shellfish and seawater samples were satisfactorily detected to indicate the application prospect of the μCPADs. The proposed method shows good potential in the low-cost, stable establishment of assays for the rapid detection of environmental biotoxins.

Selection, characterization, and biosensing applications of DNA aptamers targeting cyanotoxin BMAA

Scientists have established a connection between environmental exposure to toxins like β-N-methylamino-l-alanine (BMAA) and a heightened risk of neurodegenerative disorders. BMAA is a byproduct from certain strains of cyanobacteria that are present in ecosystems worldwide and is renowned for its bioaccumulation and biomagnification in seafood. The sensitivity, selectivity, and reproducibility of the current analytical techniques are insufficient to support efforts regarding food safety and environment monitoring adequately. This work outlines the in vitro selection of BMAA-specific DNA aptamers via the systematic evolution of ligands through exponential enrichment (SELEX). Screening and characterization of the full-length aptamers was achieved using the SYBR Green (SG) fluorescence displacement assay. Aptamers BMAA_159 and BMAA_165 showed the highest binding affinities, with dissociation constants (Kd) of 2.2 ± 0.1 μM and 0.32 ± 0.02 μM, respectively. After truncation, the binding affinity was confirmed using a BMAA-conjugated fluorescence assay. The Kd values for BMAA_159_min and BMAA_165_min were 6 ± 1 μM and 0.63 ± 0.02 μM, respectively. Alterations in the amino proton region studied using solution nuclear magnetic resonance (NMR) provided further evidence of aptamer-target binding. Additionally, circular dichroism (CD) spectroscopy revealed that BMAA_165_min forms hybrid G-quadruplex (G4) structures. Finally, BMAA_165_min was used in the development of an electrochemical aptamer-based (EAB) sensor that accomplished sensitive and selective detection of BMAA with a limit of detection (LOD) of 1.13 ± 0.02 pM.

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.

A label-free ratiometric fluorescent aptasensor based on a peroxidase-mimetic multifunctional ZrFe-MOF for the determination of tetrodotoxin

A Fe/Zr bimetal-organic framework (ZrFe-MOF) is utilized to establish a ratiometric fluorescent aptasensor for the determination of tetrodotoxin (TTX). The multifunctional ZrFe-MOF possesses inherent fluorescence at 445 nm wavelength, peroxidase-mimetic activity, and specific recognition and adsorption capabilities for aptamers, owing to its organic ligand, and Fe and Zr nodes. The peroxidation of o-phenylenediamine (OPD) substrate generates fluorescent 2,3-diaminophenazine (OPDox) at 555 nm wavelength, thus quenching the inherent fluorescence of ZrFe-MOF because of the fluorescence resonance energy transfer (FRET) effect. TTX aptamers, which are absorbed on the material surface without immobilization or fluorescent labeling, inhibit the peroxidase-mimetic activity of ZrFe-MOF. It causes the decreased OPDox fluorescence at 555 nm wavelength and the inverse restoration of ZrFe-MOF fluorescence at 445 nm wavelength. With TTX, the aptamers specifically bind to TTX, triggering rigid complex release from ZrFe-MOF surface and reactivating its peroxidase-mimetic activity. Consequently, the two fluorescence signals exhibit opposite changes. Employing this ratiometric strategy, the determination of TTX is achieved with a detection limit of 0.027 ng/mL and a linear range of 0.05-500 ng/mL. This aptasensor also successfully determines TTX concentrations in puffer fish and clam samples, demonstrating its promising application for monitoring trace TTX in food safety.

Monthly distribution of lipophilic marine biotoxins and associated microalgae in the South Sea Coast of Korea throughout 2021

Aquaculture farms have been established along the South Sea Coast of Korea, supplying most of the seafood consumed domestically. However, annual harmful algal blooms pose a potential threat to seafood safety. This study aimed to determine the spatial and seasonal distributions of 12 lipophilic marine biotoxins (LMTs) in phytoplankton and mussels in the region in 2021. Solid-phase adsorption toxin tracking (SPATT) was used to monitor the cumulative compositions of LMTs in seawater. LMT concentrations were also determined in twelve commercially available species of domestic shellfish to evaluate the potential risks to human health. Gonyaulux spinifera and Dinophysis acuminata, causative microalgae of yessotoxins (YTXs) and pectenotoxins (PTXs), respectively, showed high densities in the region from May to July. This period corresponded to high LMT concentrations in phytoplankton and mussels. Phytoplankton mainly contained PTX-2 and homo-YTX, with a maximum concentration of 2300 ng g-1 wet weight (ww) in May. In contrast, mussels mainly contained homo-YTX and YTX, with a maximum concentration of 1300 ng g-1 ww in July. LMTs-producing microalgae showed low densities and concentrations after July, whereas mussels accumulated toxins until September. In the SPATT sampler, more diverse LMTs were detected than in seawater, phytoplankton, and mussels. For example, dinophysistoxin-1 and azaspiracid-2 were detected only in SPATT. YTXs were detected in domestic seafood samples, including mussels, red scallops, and pen shells, but the concentrations were below the European Food Safety Agency recommended standard of 3.75 mg YTX-eq. kg-1. Moreover, the hazard quotient was less than 100 in all scenarios, indicating that the human health risk was not significant. This study provides valuable data on monthly distribution patterns of LMTs in the South Sea Coast of Korea and can serve as baseline data for future management policies of marine biotoxins.

Exonuclease-based aptasensors: Promising for food safety and diagnostic aims

As of today's requirement, developing cost-effective smart sensing tools with ultrahigh sensitivity for food safety insurance is of special importance. For this purpose, aptamer-based biosensors (aptasensors) powered by the superiorities of the recycling signal amplification strategies have been expanded especially. Target recycling supported by enzymes is an appealing approach for implementing signal amplification. As the supreme biocatalyst enzymes, exonucleases can inaugurate signal improvement by involving a single target in a process would result in appreciable repeating cycles of the cleavage of the phosphodiester bonds between the building blocks of the nucleic acid strands, and also, their terminals. Although there are diverse substances for catalyzing amplification strategies, including nanoparticles, carbon-based nanocomposites, and quantum dots (QDs), exonucleases are of superiority over them by simplifying the amplification process with no need for the complicated pre-treatment processes. The outstanding selectivity and great sensitivity of the aptasensors tuned by amplification potency of exonucleases nominate them as the promising sensing tools for label-free, ease-of-use, cost-effective, and real-time diagnosis of diverse targets. Here, we summarize the achievements and perspectives in the scientific branch of aptasensor design for the qualitative monitoring of diverse targets by cooperation of exonucleases with the conspicuous potential for the signal amplification. Finally, some results are expressed to provide a comprehensive viewpoint for developing novel nuclease-based aptasensors in the future.

Simultaneous screening of multiple diarrhetic shellfish poisons with group-specific split aptamers and silver nanocluster beacon

Poisoning events concerning diarrhetic shellfish poisons (DSPs) are increasing continually. It is extremely necessary to develop simple analysis methods for screening simultaneously different types of DSPs from food-related samples. Okadaic acid (OA) and its analogues, i.e., dinophysistoxin-1 (DTX-1) and dinophysistoxin-2 (DTX-2), are the prevalent DSPs. Herein, a facile and label-free fluorescent aptasensor targeting the three DSPs was constructed with a pair of group-specific split aptamers and silver nanocluster beacon. In presence of the targets, the DNA templates attached at the ends of the split aptamers would be dragged close to trigger enhanced fluorescence signals from silver nanoclusters. The aptasensor offered high sensitivity and good selectivity, with limit of detection of 2.282 nmolL^-1, 19.38 nmolL^-1, and 13.61 nmolL^-1 for OA, DTX-1, and DTX-2, respectively. Moreover, the applicability of aptasensor was well verified with shellfish and seawater samples. This study provides good reference for further exploration on analysis methods for food-related molecules.

Mismatched duplexed aptamer-isothermal amplification-based nucleic acid-nanoflower for fluorescent detection of okadaic acid

We developed a highly sensitive fluorescent assay to detect okadaic acid (OA), a prevalent aquatic toxin posing serious health risks. Our approach uses a mismatched duplexed aptamer (DA) immobilized on streptavidin-conjugated magnetic beads (SMBs) to create a DA@SMB complex. In the presence of OA, the cDNA unwinds, hybridizes with a G-rich segment pre-encoding circular template (CT), and undergoes rolling circle amplification (RCA) to produce G-quadruplexes, which are detected using the fluorescent dye thioflavine T (ThT). The method has a LOD of 3.1 × 10^-3 ng/mL, a linear range of 0.1 ∼ 1.0 × 10³ ng/mL, and was successfully applied to shellfish samples with spiked recoveries of 85.9% ∼ 102.2% and RSD less than 13%. Furthermore, instrumental analysis confirmed the accuracy and reliability of this rapid detection method. Overall, this work represents a significant advancement in the field of rapid aquatic toxin detection and has important implications for public health and safety.

Recent Advances in Aptasensing Strategies for Monitoring Phycotoxins: Promising for Food Safety

Phycotoxins or marine toxins cause massive harm to humans, livestock, and pets. Current strategies based on ordinary methods are long time-wise and require expert operators, and are not reliable for on-site and real-time use. Therefore, it is urgent to exploit new detection methods for marine toxins with high sensitivity and specificity, low detection limits, convenience, and high efficiency. Conversely, biosensors can distinguish poisons with less response time and higher selectivity than the common strategies. Aptamer-based biosensors (aptasensors) are potent for environmental monitoring, especially for on-site and real-time determination of marine toxins and freshwater microorganisms, and with a degree of superiority over other biosensors, making them worth considering. This article reviews the designed aptasensors based on the different strategies for detecting the various phycotoxins.