The automatic dispenser (Iso-Flow, Imagene Technology, Hanover, NH, USA) was used for this purpose. seawater, river water, and fish samples. The total duration of the sample pretreatment and LFIA was 25/40 min for water/fish samples, ensuring testing rapidity. The developed test system provides sensitive control of raw materials and food products and can be used to detect OA at all stages of the food industry ?from sea to fork? chains. Keywords: aquatic toxins, okadaic acid, immunochromatography, nanozyme, food safety 1. Introduction Among the dangerous food contaminants, a special place belongs to aquatic toxinsthe metabolites of cyanobacteria and microalgae inhabiting both fresh and saltwater bodies [1,2,3]. The cyanobacteria and microalgae producing cyanotoxins and phycotoxins, respectively, are initial links of food chains. Aquatic toxins may RRx-001 accumulate in different marine or freshwater macroorganisms including mollusks and fish [4,5]. Consumption of contaminated food can cause severe acute poisoning in humans. Regular intake of trace amounts of aquatic toxins leads to long-term chronic disorders, such as hepatotoxicity, oncological diseases, neuro-, immuno-, embryotoxic effects, etc. [6]. Phycotoxin okadaic acid (OA), produced by and dinoflagellates, belongs to the priority aquatic toxins [7]. These algae, widespread in the coastal waters of different regions, cause the so-called red tides during their active reproduction [4]. The action of lipophilic and heat-resistant OA is expressed in the inhibition of protein phosphatases; because OA poisoning mainly consists of disorders of the gastrointestinal tract, it is classified as a diarrheic shellfish poisoning (DSP) toxin [7,8]. High concern about the pervasion of toxic substances into aquaculture foodstuffs has led to official regulations and monitoring of aquatic toxins in products for human consumption. Thus, the maximum residue level (MRL) established in the EU countries for OA in mollusk tissues is 0.16 g/g [9]. Initially, biotests on living organisms were used to monitor aquatic toxins [10]. However, due to ethical issues and difficulties with harmonization, biotests have been replaced by instrumental methods. Liquid/gas chromatography-mass spectrometry (LC/GC-MS) is traditionally used to determine aquatic toxins [11,12]. LC/GC-MS is an RRx-001 accurate and sensitive method for the selective identification and quantification of individual toxins and their derivatives. Its disadvantages include expensive and complex instrumentation as well as the thorough sample preparation (most often by solid-phase extraction), RRx-001 which significantly increases the labor and time requirements of the analysis. Therefore, continuous mass monitoring of toxins content in mariculture products by instrumental analytical methods is expensive, difficult, and impractical. Rapid and sensitive qualitative detection (yes/no) and (semi-)quantitation of aquatic toxins require simple, productive, and low-cost methods that provide information on the presence and level of toxins quickly and with minimal effort. Lateral flow test systems with immune recognition of analytes fully met these requirements [13,14]. Lateral flow immunoassay (LFIA) of OA is described in several studies [15,16,17,18]. All the reported assays are based on the direct LFIA format, Rabbit Polyclonal to NM23 where anti-OA specific antibodies are conjugated with gold nanoparticles (AuNPs) as a marker. Among real samples, only the seafood matrix was tested for OA content. Our previous investigations in this field were aimed at multiplex determination of OA, domoic acid, and microcystin-LR as representatives of DSP, amnestic shellfish poisoning toxins, and hepatotoxins, respectively [19,20]. Besides, the enhanced LFIA of OA with cascade signal amplification was implemented [21]. In this study, several clones of anti-OA monoclonal antibodies (MAbs) were produced and tested. Instead of common AuNPs, bimetallic core@shell Au@Pt nanozyme was synthesized and used as a catalytic label with peroxidase-mimic catalytic properties. Au@Pt label was attached to anti-species antibodies to perform the indirect format of the LFIA. In contrast to the direct assay, in the indirect one, the unproductive immune binding without signal change is excluded, which contributes to the assay sensitivity [22]. Among other advantages of the indirect LFIA, the significant saving in specific antibodies and the application of labeled anti-species antibodies as a universal reagent should.