A smartphone-based fluorescent biosensor with metal-organic framework biocomposites and cotton swabs for the rapid determination of tetrodotoxin in seafood.

BACKGROUND: Tetrodotoxin (TTX) is a potent neurovirulent marine biotoxin that is present in puffer fish and certain marine animals. It is capable of causing severe neurotoxic symptoms and even death when consumed through contaminated seafood. Due to its high toxicity, developing an effective assay for TTX determination in seafood has significant benefits for food safety and human health. Currently, it remains challenging to achieve on-site determination of TTX in seafood. To facilitate mass on-site assays, more affordable technologies utilizing accessible equipment that require no skilled personnel are needed. RESULTS: A smartphone-based portable fluorescent biosensor is proposed for TTX determination by using metal-organic framework (MOF) biocomposites and cotton swabs. Oriented antibody (Ab)-decorated and fluorescent quantum dot (QD)-loaded MOF biocomposites (QD@MOF*Ab) are rapidly synthesized for binding targets and fluorescent responses by utilizing the tunability of zinc-based MOF. Moreover, facile Ab-immobilized household cotton swabs are utilized as TTX capture tools. TTX forms sandwich immune complexes with QD@MOF*Ab probes, achieving signal amplification. These probes are excited by a portable device to generate bright fluorescent signals, which can be detected by the naked eye, and TTX quantitative results are obtained using a smartphone. When observed with the naked eye, the limit of detection (LOD) is 0.4 ng/mL, while intelligent quantitation presents an LOD of 0.13 ng/mL at logarithmic concentrations of 0.2-400 ng/mL. SIGNIFICANCE: This biosensor is convenient to use, and an easy-to-operate analysis is completed within 15 min, thus demonstrating excellent performance in terms of detection speed and portability. Furthermore, it successfully determines TTX contents in puffer fish and clam samples, demonstrating its potential for monitoring seafood. Herein, this work provides a favorable rapid sensing platform that is easily portable.

Automated Patch Clamp for the Detection of Tetrodotoxin in Pufferfish Samples.

Tetrodotoxin (TTX) is a marine toxin responsible for many intoxications around the world. Its presence in some pufferfish species and, as recently reported, in shellfish, poses a serious health concern. Although TTX is not routinely monitored, there is a need for fast, sensitive, reliable, and simple methods for its detection and quantification. In this work, we describe the use of an automated patch clamp (APC) system with Neuro-2a cells for the determination of TTX contents in pufferfish samples. The cells showed an IC50 of 6.4 nM for TTX and were not affected by the presence of muscle, skin, liver, and gonad tissues of a Sphoeroides pachygaster specimen (TTX-free) when analysed at 10 mg/mL. The LOD achieved with this technique was 0.05 mg TTX equiv./kg, which is far below the Japanese regulatory limit of 2 mg TTX equiv./kg. The APC system was applied to the analysis of extracts of a Lagocephalus sceleratus specimen, showing TTX contents that followed the trend of gonads > liver > skin > muscle. The APC system, providing an in vitro toxicological approach, offers the advantages of being sensitive, rapid, and reliable for the detection of TTX-like compounds in seafood.

Sudden peak in tetrodotoxin in French oysters during the summer of 2021: Source investigation using microscopy, metabarcoding and droplet digital PCR.

Tetrodotoxin (TTX) is a potent neurotoxin causing human intoxications from contaminated seafood worldwide and is of emerging concern in Europe. Shellfish have been shown to contain varying TTX concentrations globally, with concentrations typically higher in Pacific oysters Crassostrea gigas in Europe. Despite many decades of research, the source of TTX remains unknown, with bacterial or algal origins having been suggested. The aim of this study was to identify potential source organisms causing TTX contamination in Pacific oysters in French coastal waters, using three different techniques. Oysters were deployed in cages from April to September 2021 in an estuary where TTX was previously detected. Microscopic analyses of water samples were used to investigate potential microalgal blooms present prior or during the peak in TTX. Differences in the bacterial communities from oyster digestive glands (DG) and remaining flesh were explored using metabarcoding, and lastly, droplet digital PCR assays were developed to investigate the presence of Cephalothrix sp., one European TTX-bearing species in the DG of toxic C. gigas. Oysters analysed by liquid chromatography-tandem mass spectrometry contained quantifiable levels of TTX over a three-week period (24 June-15 July 2021), with concentrations decreasing in the DG from 424 µg/kg for the first detection to 101 µg/kg (equivalent to 74 to 17 µg/kg of total flesh), and trace levels being detected until August 13, 2021. These concentrations are the first report of the European TTX guidance levels being exceeded in French shellfish. Microscopy revealed that some microalgae bloomed during the TTX peak, (e.g., Chaetoceros spp., reaching 40,000 cells/L). Prokaryotic metabarcoding showed increases in abundance of Rubritaleaceae (genus Persicirhabdus) and Neolyngbya, before and during the TTX peak. Both phyla have previously been described as possible TTX-producers and should be investigated further. Droplet digital PCR analyses were negative for the targeted TTX-bearing genus Cephalothrix.

Temporal variation in the concentrations and profiles of paralytic shellfish toxins and tetrodotoxin in scallop (Mizuhopecten yessoensis) and bloody clam (Anadara broughtonii) collected from the coast of Miyagi Prefecture, Japan.

For food safety, the concentrations and profiles of paralytic shellfish toxins (PSTs) and tetrodotoxin were examined in economically important scallops and bloody clams collected from the coast of the Miyagi Prefecture, Japan. PSTs were the major toxins in both species. The tetrodotoxin concentration in scallops increased in summer, although the highest value (18.7 µg/kg) was lower than the European Food Safety Authority guideline threshold (44 µg/kg). This confirmed the safety for tetrodotoxin in this area.

Tetrodotoxins in Tissues and Cells of Different Body Regions of Ribbon Worms Kulikovia alborostrata and K. manchenkoi from Spokoynaya Bay, Sea of Japan.

Nemerteans, or ribbon worms, possess tetrodotoxin and its analogues (TTXs), neurotoxins of bacterial origin, which they presumably use for capturing prey and self-defense. Most TTXs-containing nemertean species have low levels of these toxins and, therefore, have usually been neglected in studies of TTXs functions and accumulation. In the present study, Kulikovia alborostrata and K. manchenkoi, two closely related species, were analyzed for TTXs distribution in the body using the HPLC-MS/MS and fluorescence microscopy methods. The abundance of TTXs-positive cells was determined in the proboscis, integument, and digestive system epithelium. As a result, six TTXs-positive cell types were identified in each species; however, only four were common. Moreover, the proportions of the toxins in different body parts were estimated. According to the HPLC-MS/MS analysis, the TTXs concentrations in K. alborostrata varied from 0.91 ng/g in the proboscis to 5.52 ng/g in the precerebral region; in K. manchenkoi, the concentrations ranged from 7.47 ng/g in the proboscis to 72.32 ng/g in the posterior body region. The differences observed between the two nemerteans in the distribution of the TTXs were consistent with the differences in the localization of TTXs-positive cells. In addition, TTXs-positive glandular cell types were found in the intestine and characterized for the first time. TTXs in the new cell types were assumed to play a unique physiological role for nemerteans.

Assessing the Toxicity of Lagocephalus sceleratus Pufferfish from the Southeastern Aegean Sea and the Relationship of Tetrodotoxin with Gonadal Hormones.

Given the dramatic increase in the L. sceleratus population in the southeastern Aegean Sea, there is growing interest in assessing the toxicity of this pufferfish and the factors controlling its tetrodotoxin (TTX) content. In the present study, liver, gonads, muscle and skin of 37 L. sceleratus specimens collected during May and June 2021 from the island of Rhodes, Greece, were subjected to multi-analyte profiling using liquid chromatography-tandem mass spectrometry (LC-MS/MS) in order to quantitate TTX and evaluate whether this biotoxin interrelates with hormones. TTX and its analogues 4-epiTTX, 11-deoxyTTX, 11-norTTX-6-ol, 4,9-anhydroTTX and 5,11/6,11-dideoxyTTX were detected in all tissue types. Liver and gonads were the most toxic tissues, with the highest TTX concentrations being observed in the ovaries of female specimens. Only 22% of the analyzed muscle samples were non-toxic according to the Japanese toxicity threshold (2.2 µg TTX eq g-1), confirming the high poisoning risk from the inadvertent consumption of this species. Four steroid hormones (i.e., cortisol, testosterone, androstenedione and ß-estradiol) and the gonadotropin-releasing hormone (GnRH) were detected in the gonads. Androstenedione dominated in female specimens, while GnRH was more abundant in males. A positive correlation of TTX and its analogues with ß-estradiol was observed. However, a model incorporating sex rather than ß-estradiol as the independent variable proven to be more efficient in predicting TTX concentration, implying that other sex-related characteristics are more important than specific hormone-regulated processes.

New Vectors of TTX Analogues in the North Atlantic Coast: The Edible Crabs Afruca tangeri and Carcinus maenas.

Tetrodotoxin (TTX) and its analogues are naturally occurring toxins historically responsible for human poisoning fatalities in Eastern Asia. It is typically linked to the consumption of pufferfish and, to a lesser extent, marine gastropods and crabs. In the scope of a comprehensive project to understand the prevalence of emergent toxins in edible marine organisms, we report, for the first time, the detection of TTX analogues in the soft tissues of edible crabs, the European fiddler crab (Afruca tangeri) and green crab (Carcinus maenas), harvested in southern Portugal. No TTX was detected in the analyzed samples. However, three TTX analogues were detected-an unknown TTX epimer, deoxyTTX, and trideoxyTTX. These three analogues were found in the European fiddler crab while only trideoxyTTX was found in the green crab, suggesting that the accumulation of TTX analogues might be influenced by the crabs' different feeding ecology. These results highlight the need to widely monitor TTX and its analogues in edible marine species in order to provide adequate information to the European Food Safety Authority and to protect consumers.

Determination of Multiple Neurotransmitters through LC-MS/MS to Confirm the Therapeutic Effects of Althaea rosea Flower on TTX-Intoxicated Rats.

Tetrodotoxin (TTX) inhibits neurotransmission in animals, and there is no specific antidote. In clinical practice in China, Althaea rosea (A. rosea flower) extract has been used to treat TTX poisoning. In this work, the efficacy of the ethyl acetate fraction extract of A. rosea flower in treating TTX poisoning in rats was investigated. A high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed to determine nine neurotransmitters in rat brain tissue, including γ-aminobutyric acid (GABA), dopamine (DA), 5-hydroxytryptamine (5-HT), noradrenaline (NE), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 5-hydroxyindole-3-acetic acid (5-HIAA), epinephrine (E), and tyramine (Tyn). The detoxifying effect of A. rosea flower was verified by comparing the changes in neurotransmitters' content in brain tissue before and after poisoning in rats. The assay was performed in multiple reaction monitoring mode. The quantification method was performed by plotting an internal-standard working curve with good linearity (R2 > 0.9941) and sensitivity. Analyte recoveries were 94.04-107.53% (RSD < 4.21%). Results indicated that the levels of 5-HT, DA, E, and NE in the brains of TTX-intoxicated rats decreased, whereas the levels of GABA, Tyn, and 5-HIAA showed an opposite trend, and HVA and DOPAC were not detected. The levels of all seven neurotransmitters returned to normal after the gavage administration of ethyl acetate extract of A. rosea flower to prove that the ethyl acetate extract of A. rosea flower had a therapeutic effect on TTX poisoning. The work provided new ideas for studies on TTX detoxification.

Levels of Tetrodotoxins in Spawning Pufferfish, Takifugu alboplumbeus.

Tetrodotoxin (TTX), also known as pufferfish toxin, is an extremely potent neurotoxin thought to be used as a biological defense compound in organisms bearing it. Although TTX was thought to function as a chemical agent for defense and anti-predation and an attractant for TTX-bearing animals including pufferfish, it has recently been demonstrated that pufferfish were also attracted to 5,6,11-trideoxyTTX, a related compound, rather than TTX alone. In this study, we attempted to estimate the roles of TTXs (TTX and 5,6,11-trideoxyTTX) in the pufferfish, Takifugu alboplumbeus, through examining the location of TTXs in various tissues of spawning pufferfish from Enoshima and Kamogawa, Japan. TTXs levels in the Kamogawa population were higher than those in the Enoshima population, and there was no significant difference in the amount of TTXs between the sexes in either population. Individual differences were greater in females than in males. However, the location of both substances in tissues differed significantly between sexes: male pufferfish accumulated most of their TTX in the skin and liver and most of their 5,6,11-trideoxyTTX in the skin, whereas females accumulated most of their TTX and 5,6,11-trideoxyTTX in the ovaries and skin.

Tetrodotoxin Detection in Japanese Bivalves: Toxification Status of Scallops.

Tetrodotoxin (TTX), or pufferfish toxin, has been frequently detected in edible bivalves around the world during the last decade and is problematic in food hygiene and safety. It was reported recently that highly concentrated TTX was detected in the midgut gland of the akazara scallop Chlamys (Azumapecten) farreri subsp. akazara collected in coastal areas of the northern Japanese archipelago. The toxification of the bivalve was likely to involve the larvae of the flatworm, Planocera multitentaculata. However, the overall status of bivalve TTX toxification has not been elucidated. In this study, 14 species/subspecies of bivalves from various Japanese waters were subjected to LC-MS/MS analysis to reveal TTX toxification state, demonstrating that the Pectinidae, including C. farreri akazara, Chlamys farreri nipponensis, Chlamys (Mimachlamys) nobilis, and Mizuhopecten yessoensis, accumulated TTX in their midgut gland. Many individuals of C. farreri akazara and C. farreri nipponensis were found with high concentrations of TTX, while C. nobilis and M. yessoensis exhibited low concentrations. The extent of TTX accumulation in C. farreri akazara and C. farreri nipponensis varied widely by region and season. Curiously, no other bivalve species investigated in this study showed evidence of TTX. These results suggest that monitoring for TTX, like other shellfish toxins, is necessary to ensure that pectinid bivalves are a safe food resource.

Interlaboratory Evaluation of Multiple LC-MS/MS Methods and a Commercial ELISA Method for Determination of Tetrodotoxin in Oysters and Mussels.

BACKGROUND: Given the recent detection of tetrodotoxin (TTX) in bivalve molluscs but the absence of a full collaborative validation study for TTX determination in a large number of shellfish samples, interlaboratory assessment of method performance was required to better understand current capabilities for accurate and reproducible TTX quantitation using chemical and immunoassay methods. OBJECTIVE: The aim was to conduct an interlaboratory study with multiple laboratories, using results to assess method performance and acceptability of different TTX testing methods. METHODS: Homogenous and stable mussel and oyster materials were assessed by participants using a range of published and in-house detection methods to determine mean TTX concentrations. Data were used to calculate recoveries, repeatability, and reproducibility, together with participant acceptability z-scores. RESULTS: Method performance characteristics were good, showing excellent sensitivity, recovery, and repeatability. Acceptable reproducibility was evidenced by HorRat values for all LC-MS/MS and ELISA methods being less than the 2.0 limit of acceptability. Method differences between the LC-MS/MS participants did not result in statistically different results. Method performance characteristics compared well with previously published single-laboratory validated methods and no statistical difference was found in results returned by ELISA in comparison with LC-MS/MS. CONCLUSION: The results from this study demonstrate that current LC-MS/MS methods and ELISA are on the whole capable of sensitive, accurate, and reproducible TTX quantitation in shellfish. Further work is recommended to expand the number of laboratories testing ELISA and to standardize an LC-MS/MS protocol to further improve interlaboratory precision. HIGHLIGHTS: Multiple mass spectrometric methods and a commercial ELISA have been successfully assessed through an interlaboratory study, demonstrating excellent performance.

Simultaneous analysis of paralytic shellfish toxins and tetrodotoxins in human serum by liquid chromatography coupled to Q-Exactive high-resolution mass spectrometry.

Paralytic shellfish toxins (PSTs) and tetrodotoxins (TTXs) are powerful neurotoxins. Previous research reported that PSTs and TTXs are found together in seafoods and may pose a serious hazard to public health. In this study, a new analytical method combining modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged, Safe) with high-performance liquid chromatography coupled to Q-Exactive Orbitrap high-resolution mass spectrometry was developed and validated for the quantification of 10 PSTs and 2 TTXs in human serum. Chromatographic separation was achieved using the HILIC TSK-Gel Amide-80 column. The mass spectrometer was operated in full scan/dd-MS2(data-dependent MS2) mode, and for quantification analysis. The dd-MS2 resolution was set to 17,500 fullwidthat halfmaximum （FWHM）. Results showed that methanol with 1 % (v/v) acetic acid extraction combined with 50 mg graphitized carbon black (GCB) and 50 mg octadecyl bonded silica gel (C18) was most suitable for purification. The mean recovery for all toxins ranged from 85.3 % to 118.2 % (RSD < 12 %). The limits of detection and quantification for human serum were in the ranges of 0.67-2.61 and 2.23-8.69 ng mL-1, respectively. The method was applied to analyze toxins in serum samples obtained from three poisoned patients in a case of poisoning caused by consumption of toxin-contaminated gastropoda (Bullacta exerata). The study has important application for rapid and accurate diagnosis of PSTs and TTXs toxin poisoning patients in clinic.

High-performance and -efficiency cardiomyocyte-based potential biosensor for temporal-specific detection of ion channel marine toxins.

Paralytic shellfish toxins (e.g., saxitoxin, STX; gonyautoxin-2, GTX-2) and tetrodotoxin (TTX) are highly toxic and widely distributed ion channel marine toxins which specifically block the voltage-dependent sodium channels (VDSCs), causing great harm to human health. It is urgent to exploit new detection methods with high specificity and high efficiency. Here, a portable high-throughput cardiomyocyte-based potential biosensor was established with cardiomyocytes, a 16-well microelectrodes (MEs) sensor and a robust 32-channel recording system, which presented high-quality and high-consistency extracellular field potential (EFP) signals in each well with a long duration of 80 h. The feature parameters, including firing rate (FR), spike amplitude (SA), spike slope (SS), spike duration (SD) and field potential duration (FPD), were extracted from EFP to quantitatively assess the toxic effects of these ion channel toxins. Importantly, the biosensor showed temporal specificity and parametric selectivity under toxin treatments, and FR, SS and SD were the optimal parameters to STX, TTX and GTX-2, respectively. This biosensor can rapidly detect 0.29 ng/mL STX, 0.30 ng/mL TTX and 0.16 ng/mL GTX-2 within 5 min, 10 min and 15 min, respectively. Thus, our novel multi-well cardiomyocyte-based biosensor will be a promising tool for high-effective detection of ion channel toxins.

Establishment and characterization of the ovary cell line derived from two-spot puffer Takifugu bimaculatus and its application for gene editing and marine toxicology.

Takifugu bimaculatus is a marine fish with high nutritional value. Its ovary contains tetrodotoxin (TTX) which is a severe neurotoxin that limits its edible value of it. To understand the mechanism of oogenesis and production of TTX in T. bimaculatus, an ovarian cell line named TBO from an adolescent ovary was established. TBO was composed of fibroblast-like cells that expressed the ovarian follicle cells marker gene Foxl2 and highly expressed TTX binding protein 2 (PSTBP2) but did not express the germ cells marker gene Vasa. Therefore, TBO seems to be mainly composed of follicle cells and possibly a small percentage of oocytes. Electroporation was used to successfully transfect the pEGFP-N1 and pNanog-N1 vectors into the TBO cell line with a high transfection efficiency. The morphological changes and survival rates of the exposed cells proved that this cell line was effective for exposure to conotoxins (CTXs), another group of toxins related to food safety. Furthermore, PSTBP2 was knocked out in TBO using CRISPR/Cas9 technology, showing that sgRNA2 could mutate PSTBP2. The results suggested that TBO will be more convenient, efficient, and rapid for reproduction and toxicology investigation, and gene editing. This study laid the groundwork for future research into the fish gonadal cell culture and food-related marine toxins. In conclusion, a cell line has been generated from T. bimaculatus, which might represent a valuable model for fish studies in the fields of toxicology and gene editing.

Simultaneous determination of 13 paralytic shellfish toxins and tetrodotoxin in marine shellfish by porous graphitic carbon solid-phase extraction and hydrophilic interaction chromatography-tandem mass spectrometry.

The lethal neurotoxins, paralytic shellfish toxins (PSTs), and tetrodotoxin (TTX) have recently been found in marine shellfish from many coastal states. Herein, we applied a sensitive and reliable ultra-performance hydrophilic interaction chromatography (HILIC)-tandem mass spectrometry (MS) method to determine 13 PSTs and TTX in marine shellfish using a porous carbon solid-phase extraction (SPE). This in-house validation study required the development of a novel chromatographic separation using a HILIC-Z column, which was necessary to retain highly polar compounds. Using acetonitrile as the organic phase and ammonium formate-formic acid buffer as the aqueous phase, the quantitative analysis was carried out with an external standard method in the multiple reaction monitoring modes using positive electrospray ionization. To reduce interference, 1% aqueous acetic acid extracts of the shellfish samples were cleaned up by ion-pair SPE using a porous graphitic carbon cartridge. The calibration curves for PSTs and TTX were linear (R2 > 0.995), and the sensitivity was good, with limits of detection (LODs) of 1.7-13.7 µg/kg, and limits of quantitation (LOQs) of 5.2-41.0 µg/kg. The recoveries were 76.5-95.5% with RSDs of 3.1-12.0%. Finally, We applied the method for the determination of PSTs and TTX in three batches of Nassarius showing excellent method accuracy against expected values.

[Tetrodotoxin Content of the Small Gastropod Nassarius sufflatus].

Severe tetrodotoxin (TTX) poisoning due to small gastropods has been documented in Japan. In this study, we investigated the TTX content of the muscles and viscera of Nassarius sufflatus collected off the coast of Futaoi Island, Shimonoseki, Yamaguchi Prefecture, Japan, to prevent the occurrence of TTX poisoning caused by this small gastropod. Live specimens were obtained, and their muscles and viscera were collected. Test solutions were prepared from tissues of specimens and analyzed for TTX by HPLC-fluorescence detection. TTX was detected in both tissues at concentrations ranging from <0.1 to 18.2 µg/g for muscle and <0.1 to 130.7 µg/g for viscera. These results suggested that N. sufflatus accumulates TTX not only in its viscera but also in its muscles, and that precautions should be taken to prevent food poisoning due to this gastropod.

[Detection of Tetrodotoxin in Vomit and Urine from a Patient Suffering from Pufferfish Poisoning].

We experienced a pufferfish poisoning case where no food residue was available to detect a causative agent. However, tetrodotoxin (TTX) was detected in vomit and urine samples from a patient using LC-MS/MS. Furthermore, we found a significant matrix effect in this analysis, indicating that the retention time of vomit and urine was not identical to the TTX standard solution and measured values multiplied by the dilution factors were not constant. Elimination of this matrix effect was attained by dilution of samples based on the retention time of the TTX standard solution, i.e., 10-time dilution of vomit test sample for LC-MS/MS analysis or 100-200-time dilution of urine one. Further research on urine analytical methods revealed that when TTX concentrations were too low to identify its peak on a chromatogram, TTX could be identified through a dilution procedure. It also showed that the application of the matrix-added TTX standard solution was effective for quantitative analysis under the influence of the matrix.

Development of a Proton-Enhanced ESI UPLC-MS/MS Method for the Determination of Tetrodotoxin.

Tetrodotoxin (TTX) is a kind of low-molecular-weight non-protein neurotoxin. It is one of the most potent neurotoxins found in nature, and it is found in puffer fish and various marine biota. The low sensitivity of previous analytical methods limited their application in puffer fish organ samples. This study established a method for the accurate and fast determination of TTX by reversed ultra-performance liquid chromatography coupled with proton-enhanced electron spray ionization-tandem mass spectrometry. The method yields good peak shapes, high sensitivity and low coeluted interferences. The method was successfully applied to determine TTX in puffer fish tissue samples of about 0.2 g.

Does Ocean Sunfish Mola spp. (Tetraodontiformes: Molidae) Represent a Risk for Tetrodotoxin Poisoning in the Portuguese Coast?

Tetrodotoxin (TTX) is a potent neurotoxin naturally occurring in terrestrial and marine organisms such as pufferfish. Due to the risk of TTX poisoning, fish of Tetraodontidae family and other puffer-related species must not be placed in the EU markets. This restriction applies to fish of the family Molidae even though no data on toxins' occurrence is available. In this study, the presence of TTX and its analogues was investigated in the main edible tissue (the white muscle) and the main xenobiotics storage organ (the liver) of ocean sunfish Mola spp. (n = 13) from the South Portuguese coast. HILIC-MS/MS analyses did not reveal TTX in the analyzed samples, suggesting an inexistent or very limited risk of TTX poisoning.

Simple and fast determination of tetrodotoxin in human plasma based on hydrophilic-interaction/ion-exchange mixed-mode solid phase extraction combined with liquid chromatography-tandem mass spectroscopy.

In this study, we developed and validated a simple, fast and sensitive LC-MS/MS method for the measurement of tetrodotoxin (TTX) in human plasma. Three HILIC-type solid phase extraction (SPE) carriers (PSA, silica, Siphila i HILIX) with different stationary phase functional groups were compared. The Siphila i HILIX SPE plate containing multi-carboxyl groups was finally selected due to obviously better extraction recovery of TTX (about 80% of recovery from plasma samples) than the other two and no significant matrix effects were observed, which was speculated to have mixed-mode synergistic effects of hydrophilic interaction and ion exchange. 100µL plasma sample was precipitated rapidly with acetonitrile containing 1% trichloroacetic acid, and filtrates were loaded onto Siphila i HILIX 96 well SPE plate. After washed with 95% acetonitrile, TTX was eluted with 200µL of 50% acetonitrile containing 1% trichloroacetic acid. 2µL of elution solution was directly injected into LC-MS/MS and the total run time on a BEH amide column was 4.5 min. The method avoids the evaporation and ultrafiltration processes which is simple and timesaving (<30 min). TTX and internal standard (arginine-15N4) were monitored in positive mode using m/z 320.3→162.2 (quantification transition for TTX), 320.3→284.1 (confirmation transition for TTX) and 179.2→63.0 (transition for IS), respectively. The method was linear in the range of 0.1-20 ng/mL for TTX with the low limit of quantification (S/N > 10) of 0.1 ng/mL; the intra- and inter-assay accuracies were in the range of 98.5%-99.8% (relative standard deviations, RSDs ≤ 5.92%) and 98.8-99.5% (RSDs ≤ 6.23%), respectively. Biases of spiking analysis were ranged from -7.00% to 7.43% for healthy human plasma samples (RSDs ≤ 8.83%) and from -5.00% to 3.93% for hemolytic, high triglyceride, high cholesterol and high bilirubin plasma samples (RSDs ≤ 6.40%), which proved the good anti-interference property of the method. The results showed that the method is sensitive, accurate, specific, reliable, and can be used to monitor the concentration of TTX in plasma to meet the needs of clinical research and poisoning screening.