Simultaneous determination of toxins in algae and water samples by high-performance liquid chromatography with triple quadrupole mass spectrometry

ATP-Responsive Strand Displacement Coupling with DNA Origami/AuNPs Strategy for the Determination of Microcystin-LR Using Surface-Enhanced Raman Spectroscopy

The DNA origami-mediated self-assembly strategy has emerged as a powerful tool in surface-enhanced Raman spectroscopy (SERS). However, these self-assembly approaches typically do not possess high detection specificity. Herein, a novel strategy based on adenosine triphosphate (ATP)-responsive strand displacement (ARSD) coupling with DNA origami/AuNPs for SERS analysis of microcystin-LR (MC-LR) is presented. In the presence of MC-LR and ATP molecules, nucleic acid sensing structures fabricated with anti-MC-LR aptamer (T1) and ATP aptamer (T2) were triggered to release the remaining ATP. In addition, DNA origami-assisted assembly results in the formation of homogeneous plasmonic nanostructures for Raman enhancement via strong plasmonic coupling. After the binding in the gaps of functionalized DNA origami/AuNPs, the Raman shift of the ATP molecules becomes detectable, leading to increased SERS intensity in 734 cm^-1. A linear response to MC-LR was obtained in the concentration range of 1.56-50 μg·L^-1, and the limit of detection (LOD) was 0.29 μg·L^-1. Combined with the solid-phase extraction sample pretreatment for extraction and 10-fold concentration, this proposed method was successfully used to detect MC-LR type in real lake-water samples with good recoveries of 98.4-116% and relative standard deviations of 1.9-6.7%. Furthermore, for the detection of MC-LR in contaminated lake-water samples, the results of the developed method and ultrahigh-performance liquid chromatography-tandem mass spectrometry were found to be in agreement with relative errors between -12 and 2.4%. The proposed strategy provides a sensitive recognition and signal amplification platform for trace MC-LR analysis as well as innovative nucleic acid sensing structures for toxin analysis more generally.

Rapid detection of mcyG gene of microcystins producing cyanobacteria in water samples by recombinase polymerase amplification combined with lateral flow strips

Nowadays, cyanobacteria blooms and microcystins (MCs) pollution are threatening water safety and public health. In this study, a rapid detection method was established for detecting MCs producing cyanobacteria. The MC synthesis gene mcyG was measured through recombinase polymerase amplification combined with lateral flow strips (LF-RPA) technology. The target gene mcyG was amplified at a temperature range of 37-45 °C, and the amplification time to detect mcyG was only 15 min at 37 °C. The optimal reaction conditions were confirmed using single dependent variable experiments, suggesting that the best probe dosage for 50 μL of the reaction mixture was 0.2 μL, the best dilution ratio of products was 1/100, and the best loading volume was 10 μL. The specificity test proved that the LF-RPA assay could distinguish MCs producing cyanobacteria from nontoxic algae well. Within 35 min of amplification time, the detection limit of the LF-RPA assay was 10³ copies/mL mcyG and 10⁴ cells/mL Microcystis aeruginosa FACHB-905. Overall, the LF-RPA assay could detect MCs producing cyanobacteria in water samples quickly and accurately, and it has a great promise to be applied for monitoring the MCs producing cyanobacteria blooms in natural waters.

Rapid and sensitive detection of nodularin-R in water by a label-free BLI aptasensor

Contamination of freshwater with nodularin-R (NOD-R) represents a significant global environmental and public health concern. However, ethical problems and technical difficulties surrounding the current detection methods for NOD-R necessitate further studies to devise appropriate alternatives within a regulatory monitoring regime. In this work, we employed an aptamer as a specific recognition element and developed a biolayer interferometry (BLI) biosensor platform for NOD-R detection. The aptasensor we propose displayed a broad detection range from 40 to 600 nM NOD-R (and a linear response range from 40 to 200 nM), and achieved a detection limit as low as 167 pM. In addition, the aptamer-based biosensor was shown to possess high selectivity, as well as good reproducibility and stability. We believe that this novel aptamer-based biosensor provides a potential alternative for the sensitive and rapid detection of NOD-R.

Development and single-laboratory validation of a UHPLC-MS/MS method for quantitation of microcystins and nodularin in natural water, cyanobacteria, shellfish and algal supplement tablet powders

A simple, rapid UHPLC-MS/MS method has been developed and optimised for the quantitation of microcystins and nodularin in wide variety of sample matrices. Microcystin analogues targeted were MC-LR, MC-RR, MC-LA, MC-LY, MC-LF, LC-LW, MC-YR, MC-WR, [Asp3] MC-LR, [Dha7] MC-LR, MC-HilR and MC-HtyR. Optimisation studies were conducted to develop a simple, quick and efficient extraction protocol without the need for complex pre-analysis concentration procedures, together with a rapid sub 5min chromatographic separation of toxins in shellfish and algal supplement tablet powders, as well as water and cyanobacterial bloom samples. Validation studies were undertaken on each matrix-analyte combination to the full method performance characteristics following international guidelines. The method was found to be specific and linear over the full calibration range. Method sensitivity in terms of limits of detection, quantitation and reporting were found to be significantly improved in comparison to LC-UV methods and applicable to the analysis of each of the four matrices. Overall, acceptable recoveries were determined for each of the matrices studied, with associated precision and within-laboratory reproducibility well within expected guidance limits. Results from the formalised ruggedness analysis of all available cyanotoxins, showed that the method was robust for all parameters investigated. The results presented here show that the optimised LC-MS/MS method for cyanotoxins is fit for the purpose of detection and quantitation of a range of microcystins and nodularin in shellfish, algal supplement tablet powder, water and cyanobacteria. The method provides a valuable early warning tool for the rapid, routine extraction and analysis of natural waters, cyanobacterial blooms, algal powders, food supplements and shellfish tissues, enabling monitoring labs to supplement traditional microscopy techniques and report toxicity results within a short timeframe of sample receipt. The new method, now accredited to ISO17025 standard, is simple, quick, applicable to multiple matrices and is highly suitable for use as a routine, high-throughout, fast turnaround regulatory monitoring tool.

Role of illumination intensity in microcystin development using Microcystis aeruginosa as the model algae

Microcystis aeruginosa (M. aeruginosa) is one of the most common genera of cyanobacteria in algal blooms. In the present work, the impact of the illumination intensity on the growth of M. aeruginosa has been studied and a grinding method for the extraction of intracellular microcystins (MCs) was developed. The variations of algal density, pH, total phosphorus (TP), and total nitrogen (TN) have been investigated during MCs' culturing period. Results showed that the extraction efficiency of MC-YR by the grinding method was 275% higher than the sonication method, and the extraction efficiencies of MC-RR and MC-LR by the grinding method were similar to the sonication method. The optimal illumination intensity for M. aeruginosa was found to be 19-38 μmol m^-2 s^-1 with suitable pH range of 7.5-10.5. Active release of extracellular MCs was not significantly observed when illumination intensities were ≤ 38 μmol m^-2 s^-1. Furthermore, the intracellular MC yields under different illumination intensities were found to be a relatively stable level. However, excess illumination intensity (≥ 47 μmol m^-2 s^-1) led to the lysis of algal cell and increased the concentrations of extracellular MCs, with MC-RR as the dominant compound. The calculated intracellular/extracellular MCs ratios for MC-RR, MC-LR, and MC-YR were 2.38 (N = 100, SD = 2.44), 2.68 (N = 64, SD = 3.48), and 1.25 (N = 30, SD = 1.64), respectively. Strong illumination intensity and cell lysis were found to be the two major factors influencing the release of extracellular MCs.

New SPE-LC-MS/MS method for simultaneous determination of multi-class cyanobacterial and algal toxins

Cyanobacterial and algal toxins comprise a large group of harmful metabolites, belonging to different chemical classes, with a variety of chemical structures, physicochemical properties and toxic activities. In this study, a fast, simple and sensitive analytical method was developed for the simultaneous determination of multi-class cyanobacterial and algal toxins in water. The target compounds were: Cylindrospermopsin, Anatoxin-a, Nodularin, 12 Microcystins ([D-Asp3]MC-RR, MC-RR, MC-YR, MC-HtyR, [D-Asp3]MC-LR, MC-LR, MC-HilR, MC-WR, MC-LA, MC-LY, MC-LW and MC-LF), Okadaic acid and Domoic acid. Analytes were determined using liquid chromatography-tandem mass spectrometry (LC-MS/MS). A dual Solid Phase Extraction (SPE) cartridge assembly was applied for the extraction of target compounds from water. Optimized SPE parameters included cartridge material, initial sample pH, sequence of the cartridges in the SPE assembly as well as composition and volume of the elution solvent. The method was validated, providing acceptable mean recoveries and reproducibility for most analytes. Limits of detection were at the ngL^-1 level. The method was successfully applied in real lake water samples from Greece, where a wide range of Microcystins were detected for the first time, at concentrations ranging from 0.034 to 63μgL^-1.

Molecular tools to detect anatoxin-a genes in aquatic ecosystems: Toward a new nested PCR-based method

Over the last few decades, cyanobacterial mass occurrence has become a recurrent feature of aquatic ecosystems. This has led to ecosystem exposure and health hazards associated with cyanotoxin production. The neurotoxin anatoxin-a and its homologs can be synthesized by benthic cyanobacterial species in lotic systems, but also by planktonic lacustrine species such as Dolichospermum (also known as Anabaena). However, only a few studies have focused on anatoxin-a occurrence and its biosynthesis genes in freshwater lakes. The initial aim of this study was to evaluate the molecular tools available in the literature to detect anatoxin-a biosynthesis genes in lacustrine environments. Having tested different sets of PCR primers, we found that that some sets of primers, such as anxC, were too specific and did not amplify anatoxin-a biosynthesis genes in all producing strains. On the other hand, some sets of primers, such as atxoa, seemed not to be specific enough, amplifying numerous non-specific bands in environmental samples, especially those from sediments. Furthermore, anaC and anaF amplification exhibited different band intensities during electrophoresis, suggesting a high variation in number of gene copies between samples. As a result, we proposed a new nested PCR-based method which considerably improved the amplification of the anaC gene in our environmental samples, eliminating non-specific bands and weak detections. Using this tool, our study also highlighted that anatoxin-a genes are widely distributed throughout freshwater lakes. This suggests the need for further ecological investigations into anatoxin-a in these ecosystems.

Simultaneous analysis of ten phytohormones in Sargassum horneri by high-performance liquid chromatography with electrospray ionization tandem mass spectrometry

Phytohormones have attracted wide attention due to their important biological functions. However, their detection is still a challenge because of their complex composition, low abundance and diverse sources. In this study, a novel method of high-performance liquid chromatography with electrospray ionization tandem mass spectrometry was developed and validated for the simultaneous determination of ten phytohormones including indole-3-acetic acid, isopentenyladenine, isopentenyl adenosine, trans-zeatin riboside, zeatin, strigolactones, abscisic acid, salicylic acid, gibberellin A3, and jasmonic acid in Sargassum horneri (S. horneri). The phytohormones were extracted from freeze-dried S. horneri with methanol/water/methanoic acid (15:4:1, v/v/v) analyzed on a Hypersil Gold C18 column and detected by electrospray ionization tandem triple quadrupole mass spectrometry in the multiple reaction monitoring mode. The experimental conditions for the extraction and analysis of phytohormones were optimized and validated in terms of reproducibility, linearity, sensitivity, recovery, accuracy, and stability. Distributions of the phytohormones in the stems, blades, and gas bladder of the S. horneri in drift, fixed, and semi-fixed growing states were investigated for the first time. The observed contents of the phytohormones in S. horneri range from not detected to 5066.67 ng/g (fresh weight). Most phytohormones are distributed mainly in the stems of S. horneri in drift and semi-fixed states.

Graphene oxide-assisted non-immobilized SELEX of okdaic acid aptamer and the analytical application of aptasensor

Okadaic acid (OA) is a low-molecular-weight marine toxin from shellfish that causes abdominal pain, vomiting and diarrhea, i.e., diarrheic shellfish poisoning. In this study, a ssDNA aptamer that specifically binds to OA with high affinity was obtained via Systematic Evolution of Ligands by Exponential Enrichment (SELEX) assisted by graphene oxide (GO). This aptamer was then applied to fabricate a novel direct competitive enzyme-linked aptamer assay (ELAA). At the optimized conditions, this ELAA method showed a low detection limit (LOD of 0.01 ng/mL), wide linear range (from 0.025 to 10 ng/mL), good recovery rate (92.86–103.34% in OA-spiked clam samples) and repeatability (RSD of 2.28–4.53%). The proposed method can be used to detect OA in seafood products with high sensitivity and can potentially be adapted for the determination of other small molecular analytes.

Multi-detection method for five common microalgal toxins based on the use of microspheres coupled to a flow-cytometry system

Freshwater and brackish microalgal toxins, such as microcystins, cylindrospermopsins, paralytic toxins, anatoxins or other neurotoxins are produced during the overgrowth of certain phytoplankton and benthic cyanobacteria, which includes either prokaryotic or eukaryotic microalgae. Although, further studies are necessary to define the biological role of these toxins, at least some of them are known to be poisonous to humans and wildlife due to their occurrence in these aquatic systems. The World Health Organization (WHO) has established as provisional recommended limit 1μg of microcystin-LR per liter of drinking water. In this work we present a microsphere-based multi-detection method for five classes of freshwater and brackish toxins: microcystin-LR (MC-LR), cylindrospermopsin (CYN), anatoxin-a (ANA-a), saxitoxin (STX) and domoic acid (DA). Five inhibition assays were developed using different binding proteins and microsphere classes coupled to a flow-cytometry Luminex system. Then, assays were combined in one method for the simultaneous detection of the toxins. The IC50's using this method were 1.9±0.1μg L(-1) MC-LR, 1.3±0.1μg L(-1) CYN, 61±4μg L(-1) ANA-a, 5.4±0.4μg L(-1) STX and 4.9±0.9μg L(-1) DA. Lyophilized cyanobacterial culture samples were extracted using a simple procedure and analyzed by the Luminex method and by UPLC-IT-TOF-MS. Similar quantification was obtained by both methods for all toxins except for ANA-a, whereby the estimated content was lower when using UPLC-IT-TOF-MS. Therefore, this newly developed multiplexed detection method provides a rapid, simple, semi-quantitative screening tool for the simultaneous detection of five environmentally important freshwater and brackish toxins, in buffer and cyanobacterial extracts.

State of knowledge and concerns on cyanobacterial blooms and cyanotoxins

Cyanobacteria are ubiquitous microorganisms considered as important contributors to the formation of Earth's atmosphere and nitrogen fixation. However, they are also frequently associated with toxic blooms. Indeed, the wide range of hepatotoxins, neurotoxins and dermatotoxins synthesized by these bacteria is a growing environmental and public health concern. This paper provides a state of the art on the occurrence and management of harmful cyanobacterial blooms in surface and drinking water, including economic impacts and research needs. Cyanobacterial blooms usually occur according to a combination of environmental factors e.g., nutrient concentration, water temperature, light intensity, salinity, water movement, stagnation and residence time, as well as several other variables. These environmental variables, in turn, have promoted the evolution and biosynthesis of strain-specific, gene-controlled metabolites (cyanotoxins) that are often harmful to aquatic and terrestrial life, including humans. Cyanotoxins are primarily produced intracellularly during the exponential growth phase. Release of toxins into water can occur during cell death or senescence but can also be due to evolutionary-derived or environmentally-mediated circumstances such as allelopathy or relatively sudden nutrient limitation. Consequently, when cyanobacterial blooms occur in drinking water resources, treatment has to remove both cyanobacteria (avoiding cell lysis and subsequent toxin release) and aqueous cyanotoxins previously released. Cells are usually removed with limited lysis by physical processes such as clarification or membrane filtration. However, aqueous toxins are usually removed by both physical retention, through adsorption on activated carbon or reverse osmosis, and chemical oxidation, through ozonation or chlorination. While the efficient oxidation of the more common cyanotoxins (microcystin, cylindrospermopsin, anatoxin and saxitoxin) has been extensively reported, the chemical and toxicological characterization of their by-products requires further investigation. In addition, future research should also investigate the removal of poorly considered cyanotoxins (β-methylamino-alanine, lyngbyatoxin or aplysiatoxin) as well as the economic impact of blooms.

Innovative detection methods for aquatic algal toxins and their presence in the food chain

Detection of aquatic algal toxins has become critical for the protection of human health. During the last 5 years, techniques such as optical, electrochemical, and piezoelectric biosensors or fluorescent-microsphere-based assays have been developed for the detection of aquatic algal toxins, in addition to optimization of existing techniques, to achieve higher sensitivities, specificity, and speed or multidetection. New toxins have also been incorporated in the array of analytical and biological methods. The impact of the former innovation on this field is highlighted by recent changes in legal regulations, with liquid chromatography-mass spectrometry becoming the official reference method for marine lipophilic toxins and replacing the mouse bioassay in many countries. This review summarizes the large international effort to provide routine testing laboratories with fast, sensitive, high-throughput, multitoxin, validated methods for the screening of seafood, algae, and water samples.

Simultaneous quantification of flavonol glycosides, terpene lactones, biflavones, proanthocyanidins, and ginkgolic acids in Ginkgo biloba leaves from fruit cultivars by ultrahigh-performance liquid chromatography coupled with triple quadrupole mass spectrometry

On the basis of liquid chromatography coupled with triple quadrupole mass spectrometry working in multiple reaction monitoring mode, an analytical method has been established to simultaneously determine flavonol glycosides, terpene lactones, biflavones, proanthocyanidins, and ginkgolic acids in Ginkgo biloba leaves. Chromatographic separation was carried out on an Acquity BEH C₁₈ column (100 mm × 2.1 mm, 1.7 μm) with gradient elution of acetonitrile and 0.10% formic acid (v/v) at a flow rate of 0.4 mL/min, and column temperature 30°C. The developed method was validated in terms of linearity, accuracy, precision, stability, and sensitivity. The optimized method was successfully applied to analyze twenty-two G. biloba leaf samples of fruit cultivars collected from different places in China. Furthermore, hierarchical clustering analysis (HCA) was performed to evaluate and classify the samples according to the contents of the twenty-four chemical constituents. All of the results demonstrated that the developed method was useful for the overall evaluation of the quality of G. biloba leaves, and this study was also helpful for the comprehensive utilization and development of G. biloba resources.