Production of monoclonal antibodies with broad specificity and development of an immunoassay for microcystins and nodularin in water

Effect of pretreatment approach on the ELISA-based detection of cyanotoxins in water: Analysis and application

Common cyanotoxins, such as microcystins and nodularins, are produced by frequently occurring harmful cyanobacterial algal blooms in freshwater systems. The required routine monitoring of microcystins and nodularins in drinking water and ambient water demands cost-efficient and reliable enzyme-linked immunosorbent assay kits. We validated the performance of a self-produced broad-spectrum enzyme-linked immunosorbent assay kit and investigated two different methods of mitigating the matrix effects to elucidate the effect of the respective pretreatment approaches recommended by China and the United States on the quantitative detection of cyanotoxins in surface water. We found that the enzyme-linked immunosorbent assay kit achieved a detection limit of 0.15 μg/L with a linear detection range from 0.27 μg/L to 1.87 μg/L for microcystin-LR (the most studied and widely distributed cyanotoxin). The matrix effects could be mitigated both by dilution of water samples with an optimal dilution ratio and dilution of antibody with the buffer containing phosphate buffer solution (10×), bovine serum albumin (1 %) and ethylene diamine tetraacetic acid (0.5 %). In terms of the surface water samples being tested, the concentrations of microcystins and nodularins measured based on pretreatment approach recommended by the United States were 1- 5 times that measured based on pretreatment approach recommended by China, indicating that the pretreatment approach of China overlooks cyanotoxins. In addition, all the measured total microcystins and nodularins of the surface water samples were below the health advisory limit (1.6 μg/L) for microcystins in drinking water proposed by the United States Environmental Protection Agency for school-age children and adults. Our research could provide significant information for outbreak warnings and risk management of harmful cyanobacterial algal blooms.

Rapid Immunochemical Methods for Anatoxin-a Monitoring in Environmental Water Samples

Algal blooms that contaminate freshwater resources with cyanotoxins constitute, nowadays, a global concern. To deal with this problem, a variety of analytical methods, including immunochemical assays, are available for the main algal toxins, for example, microcystins, nodularins, and saxitoxins, with the remarkable exception of anatoxin-a. Now, for the first time, highly sensitive, enantioselective immunoassays for anatoxin-a have been validated using homemade monoclonal antibodies. Two competitive enzyme-linked immunosorbent assays were developed in different formats, with detection limits for (+)-anatoxin-a of 0.1 ng/mL. Excellent recovery values between 82 and 117%, and coefficients of variation below 20%, were observed using environmental water samples fortified between 0.5 and 500 ng/mL. In addition, a lateral-flow immunochromatographic assay was optimized for visual and instrumental reading of results. This test showed a visual detection limit for (+)-anatoxin-a of 4 ng/mL. Performance with a reader was validated in accordance with the European guidelines for semiquantitative rapid methods for small chemical contaminants. Thus, at a screening target concentration of 2 ng/mL, the probability of a blank sample to be classified as “suspect” was as low as 0.2%. Finally, the optimized direct enzyme immunoassay was validated by comparison with high-performance liquid chromatography-tandem mass spectroscopy data and showed a good correlation (r = 0.995) with a slope of 0.94. Moreover, environmental water samples containing more than 2 ng/mL of anatoxin-a were detected by the developed dipstick assay. These results provide supplementary and complementary strategies for monitoring the presence of anatoxin-a in water.

ELISA-Based Method for Variant-Independent Detection of Total Microcystins and Nodularins via a Multi-immunogen Approach

Required routine monitoring of microcystins (MCs) and nodularins (NODs) in water samples, as posed by U.S. EPA Unregulated Contaminant Monitoring Rule 4, demands cost-effective, reliable, and sensitive detection methods. To target as many MC and NOD variants as possible, we developed an indirect competitive enzyme-linked immunosorbent assay (ELISA) with group-specific monoclonal antibodies for variant-independent detection of total MCs and NODs. In this ELISA method, the mice monoclonal antibodies presenting both high affinities and broad-spectrum recognition capabilities against MCs and NODs were self-produced by designing MC hapten-based multi-immunogens to minimize specificity for the particular variant. Their high affinities and variant-independent binding capabilities against MCs and NODs were validated by both wet lab and in silico methods. The developed ELISA method achieved a limit of detection of below 0.3 μg/L for 13 MC/NOD variants, well with the reported best cross-reactivities of 60-127% relative to MC-LR. As a case study, this ELISA method was used to map the variations of intracellular and extracellular total MCs/NODs in the Luoma Lake drinking water source, China, in July, 2020. Its capability to measure total MCs/NODs with high sensitivity and high throughput in a simple and affordable way would truly be a disruptive technology capable of changing our understanding of bloom/toxin dynamics and having obvious implications for monitoring efforts.

A Mini-Review on Detection Methods of Microcystins

Cyanobacterial harmful algal blooms (CyanoHABs) produce microcystins (MCs) which are associated with animal and human hepatotoxicity. Over 270 variants of MC exist. MCs have been continually studied due of their toxic consequences. Monitoring water quality to assess the presence of MCs is of utmost importance although it is often difficult because CyanoHABs may generate multiple MC variants, and their low concentration in water. To effectively manage and control these toxins and prevent their health risks, sensitive, fast, and reliable methods capable of detecting MCs are required. This paper aims to review the three main analytical methods used to detect MCs ranging from biological (mouse bioassay), biochemical (protein phosphatase inhibition assay and enzyme linked immunosorbent assay), and chemical (high performance liquid chromatography, liquid chromatography-mass spectrometry, high performance capillary electrophoresis, and gas chromatography), as well as the newly emerging biosensor methods. In addition, the current state of these methods regarding their novel development and usage, as well as merits and limitations are presented. Finally, this paper also provides recommendations and future research directions towards method application and improvement.

Recent developments in the methods of quantitative analysis of microcystins

Cyanotoxins are produced by the toxic cyanobacterial species present in algal blooms formed in water bodies due to nutrient over-enrichment by human influences and natural environmental conditions. Extensive studies are available on the most widely encountered cyanotoxins, microcystins (MCs) in fresh and brackish water bodies. MC contaminated water poses severe risks to human health, environmental sustainability, and aquatic life. Therefore, commonly occurring MCs should be monitored. Occasionally, detection and quantification of these toxins are difficult due to the unavailability of pure standards. Enzymatic, immunological assays, and analytical techniques like protein phosphatase inhibition assay, enzyme-linked immunosorbent assay, high-performance liquid chromatography, liquid chromatography-mass spectrometry, and biosensors are used for their detection and quantification. There is no single method for the detection of all the different types of MCs; therefore, various techniques are often combined to yield reliable results. Biosensor development offered a problem-solving approach in the detection of MCs due to their high accuracy, sensitivity, rapid response, and portability. In this review, an endeavor has been made to uncover emerging techniques used for the detection and quantification of the MCs.

Predicting cyanobacteria bloom occurrence in lakes and reservoirs before blooms occur

With increased global warming, cyanobacteria are blooming more frequently in lakes and reservoirs, severely damaging the health and stability of aquatic ecosystems and threatening drinking water safety and human health. There is an urgent demand for the effective prediction and prevention of cyanobacterial blooms. However, it is difficult to effectively reduce the risks and loss caused by cyanobacterial blooms because most methods are unable to successfully predict cyanobacteria blooms. Therefore, in this study, we proposed a new cyanobacterial bloom occurrence prediction method to analyze the probability and driving factors of the blooms for effective prevention and control. Dominant cyanobacterial species with bloom capabilities were initially determined using a dominant species identification model, and the principal driving factors of the dominant species were then analyzed using canonical correspondence analysis (CCA). Cyanobacterial bloom probability was calculated using a newly-developed model, after which, the probable mutation points were identified and thresholds for the principal driving factors of cyanobacterial blooms were predicted. A total of 141 phytoplankton data sets from 90 stations were collected from six large-scale hydrology, water-quality ecology, integrated field surveys in Jinan City, China in 2014-2015 and used for model application and verification. The results showed that there were six dominant cyanobacterial species in the study area, and that the principal driving factors were water temperature, pH, total phosphorus, ammonia nitrogen, chemical oxygen demand, and dissolved oxygen. The cyanobacterial blooms corresponded to a threshold water temperature range, pH, total phosphorus (TP), ammonium nitrogen level, chemical oxygen demand, and dissolved oxygen levels of 19.5-32.5 °C, 7.0-9.38, 0.13-0.22 mg L^-1, 0.38-0.63 mg L^-1, 10.5-17.5 mg L^-1, and 4.97-8.28 mg L^-1, respectively. Comparison with research results from other global regions further supported the use of these thresholds, indicating that this method could be used in habitats beyond China. We found that the probability of cyanobacterial bloom was 0.75, a critical point for prevention and control. When this critical point was exceeded, cyanobacteria could proliferate rapidly, increasing the risk of cyanobacterial blooms. Changes in driving factors need to be rapidly controlled, based on these thresholds, to prevent cyanobacterial blooms. Temporal and spatial scales were critical factors potentially affecting the selection of driving factors. This method is versatile and can help determine the risk of cyanobacterial blooms and the thresholds of the principal driving factors. It can effectively predict and help prevent cyanobacterial blooms to reduce the global probability of occurrence, protect the health and stability of water ecosystems, ensure drinking water safety, and protect human health.

Portable Multiplex Immunochromatographic Assay for Quantitation of Two Typical Algae Toxins Based on Dual-Color Fluorescence Microspheres

A multiplex immunochromatographic assay (ICA) based on dual-color fluorescent microspheres (FMs) as a sensitive label was developed for the first time. Two typical algae toxins, microcystin-LR (MC-LR) and okadaic acid (OA), were chosen as proof-of concept targets to evaluate the feasibility of this ICA format. Commercial red- and green-colored FMs were selected to couple with monoclonal antibodies as fluorescent probes. The use of dual-wavelength FMs as labels guaranteed a lower consumption of material strips, lower sample volume, and shorter reaction time without increasing the length of ICA strips. Under optimal conditions, the multiplex FM-ICA could be completed in 20 min and reached limits of detection for the simultaneous determination of MC-LR and OA in fish samples, which were 0.074 and 2.42 μg/kg, respectively. The developed technique was validated using artificially spiked and naturally contaminated fish samples. Ultra-high-performance liquid chromatography-tandem mass spectrometry was used as confirmatory technique. In summary, this portable ICAs detection mode based on dual-wavelength FMs provided a reliable and sensitive on-site detection of multiple contaminants in food samples, which opens a new field for application of FMs in food safety.

Development of Time-Resolved Fluoroimmunoassay for Detection of Cylindrospermopsin Using Its Novel Monoclonal Antibodies

Cylindrospermopsin (CYN) is a cyanotoxin that is of particular concern for its potential toxicity to human and animal health and ecological consequences due to contamination of drinking water. The increasing emergence of CYN around the world has led to urgent development of rapid and high-throughput methods for its detection in water. In this study, a highly sensitive monoclonal antibody N8 was produced and characterized for CYN detection through the development of a direct competitive time-resolved fluorescence immunoassay (TRFIA). The newly developed TRFIA exhibited a typical sigmoidal response for CYN at concentrations of 0.01–100 ng mL⁻¹, with a wide quantitative range between 0.1 and 50 ng mL⁻¹. The detection limit of the method was calculated to be 0.02 ng mL⁻¹, which is well below the guideline value of 1 μg L⁻¹ and is sensitive enough to provide an early warning of the occurrence of CYN-producing cyanobacterial blooms. The newly developed TRFIA also displayed good precision and accuracy, as evidenced by low coefficients of variation (4.1–6.5%). Recoveries ranging from 92.6% to 108.8% were observed upon the analysis of CYN-spiked water samples. Moreover, comparison of the TRIFA with an ELISA kit through testing 76 water samples and 15 Cylindrospermopsis cultures yielded a correlation r² value of 0.963, implying that the novel immunoassay was reliable for the detection of CYN in water and algal samples.