Portable sensors detect fresh-water cyanotoxins

Toxic algae blooms are on the rise worldwide, but water engineers lack portable, real time detection methods. (Image: Warning sign on the Calooshatchee River, Florida, courtesy Sierra Club.)

What?

Novel sensors for detecting certain natural neurotoxins occurring in lake water have emerged. Increasingly strict global water standards are targeting highly toxic cyclic peptides called microcystins, a class of cyanotoxins produced globally by species of cyanobacteria (blue-green algae). Two new high-performance multidisciplinary approaches to the problem rely on sensors coated with toxin-specific materials: one employs a piezoelectric micro-cantilever for detection, while the other applies optical transduction and surface plasmon resonance (SPR) in a novel microarray format. Both approaches avoid the limitations of conventional lab equipment and methods, while boasting accuracies measured in picograms of toxin per milliliter of water.[1]

Why?

In conditions of the sort often found in warm, stagnant lakes, ponds, and water reservoirs, cyanobacteria populations can expand rapidly, or ‘bloom,’ producing some of the most potent toxins known.[2] These toxins threaten human and animal health, aquatic ecosystem sustainability, and economies.[3] Their increase in incidence and duration worldwide is partially driven by climate change, through excessive nutrient-laden stormwater runoff, water stagnation during prolonged droughts, and rising temperatures.[4]

Not all cyanobacteria blooms are toxic, however, and the types and levels of toxins may change over time. Consequently, although standard methods exist for analyzing some cyanotoxins, improved methods are needed for rapid, inexpensive, and reliable field analysis.[5] Liquid chromatography-tandem mass spectrometry (LC-MS/MS), enzyme-linked immunosorbent assays (ELISA), and other conventional cyanotoxin detection techniques may vary in accuracy and specificity, can be expensive, and are not field-deployable. They require that raw water samples be obtained from lakes, rivers, and other sources and transported to analytical laboratories. Typically containing a wide range of organic and inorganic contaminants, the samples must be properly handled and pretreated, including cleaning and concentrating before analysis.[6]

The US Environmental Protection Agency (EPA) and other organizations are actively funding research into portable, simple-to-use, quick-reacting biosensors that do not require sample concentration, isolating, or cleaning. The novel use of monoclonal antibodies with device-scale transduction techniques promises to make possible real-time monitoring, while providing water and health agencies a tool for accurate and prompt response and tracking.

Who, Where, and When?

Professor Raj Mutharasan, at Drexel University in Pennsylvania, announced a piezoelectric-excited millimeter-sized cantilever (PEMC) application for cyanotoxins in 2010.[7] The technology research and development of Professor Mutharasan’s Biosensors Laboratory team has been supported by the EPA, the USDA, the NSF, and the PA Department of Health.

Dr. Maria Cruz Moreno-Bondi, of the Chemical Optosensors Group and Laboratory of Applied Photochemistry (GSOLFA) research team at Complutense University of Madrid, reported on the latest achievement of her group’s evanescent-wave automated array biosensor at the end of last year.[8]

How?

Both biosensor devices indirectly detect and measure immunoreactions between toxin-specific monoclonal antibodies and the microcystins found in raw water samples.

The PEMC sensor is fabricated from a thin glass strip anchored at one end to a pressure-sensitive piezoelectric material (PZT). The glass is coated with monoclonal antibodies via amine coupling. As microcystins in the water sample bind to the coating, they increase the effective mass of the glass cantilever, lowering its resonant frequency. This frequency change can be detected via the PZT, to a precision of 1 picogram of toxin per milliliter of water.

The surface-plasmon-resonance biosensor uses a microscope slide as a planar waveguide, on whose surface a self-assembled monolayer of microcystin-leucine-arginine (MCLR) is covalently immobilized. Anti-MCLR monoclonal antibodies are added to the raw water sample, where some bind to the microcystin present while others bind to the antigen pattern on the sensor. The antibodies that bind to the sensor cause a shift in the slide’s refractive index, detectable by reflecting light off the reverse surface of the glass. The shift is thus inversely correlated to the amount of toxin present. The SPR device demonstrated a detection limit of 16 ± 3 ng/L and was reusable for at least 15 assay-regeneration cycles.

But?

Development toward practical application of both technologies continues. While numerous well-known and reliable SPR and microcantilever sensor devices already exist, their novel application as cyanotoxin sensor devices is limited by the availability of specific antigens and antibodies for the numerous microcystin variants, as well as for a range of other cyanotoxins, some more highly toxic.[9],[10] Protocols for data analysis and interpretation have yet to be established, and standardization must occur before the devices can be broadly employed.

Literature
Yanjun Ding and Raj Mutharasan, Highly Sensitive and Rapid Detection of Microcystin-LR in Source and Finished Water Samples Using Cantilever Sensors, Environmental Science & Technology, 2011 45(4), 1490-1496.
Herranz S, Marazuela MD, Moreno-Bondi MC. Biosens Bioelectron, Automated portable array biosensor for multisample microcystin analysis in freshwater samples, Epub, 2012.
Background
Ed. H Hudnell, Harmful, Cyanobacterial, and Algal Blooms. Cyanobacterial Harmful Algal Blooms: State of the Science and Research Needs, Springer (2008)

 

References

  1. Algae-Cyanotoxins, What Are They?, Accessed 2009.
  2. What Are Harmful Blooms?, Accessed 2012.
  3. Kathleen McAuliffe, Are Toxins in Seafood Causing ALS, Alzheimer's, and Parkinson's?, Discover Magazine, 22 July, 2011.
  4. Kathleen McAuliffe, Are Toxins in Seafood Causing ALS, Alzheimer's, and Parkinson's?, Discover Magazine, 22 July, 2011.
  5. Hans Paerl, Elisabeth Calandrino, and J. Huisman, The Algal Toxins Case, Proceedings of the NATO Advanced Study Institute on Sensor Systems for Biological Threats, 30 September-11 October 2007.
  6. Keith Loftin and Jennifer Graham, Guidelines for Design, Sampling, Analysis and Interpretation for Cyanobacterial Toxin Studies, 2010 National Water Quality Monitoring Conference, April 26 2010.
  7. Yanjun Ding and Raj Mutharasan, Highly Sensitive and Rapid Detection of Microcystin-LR in Source and Finished Water Samples Using Cantilever Sensors, Environ. Sci. Technol. 45 (4), 2011.
  8. S. Herranz, M.D. Marazuela, M.C. Moreno-Bondi, Automated portable array biosensor for multisample microcystin analysis in freshwater samples, Biosensors and Bioelectronics 33 (1), 2012.
  9. Biosensing Instrument Inc, Technical Notes: Principle of SPR detection - intensity profile and shift of the SPR angle.
  10. Anja Boisen et al, Cantilever-like micromechanical sensors, Rep. Prog. Phys. 74, 2011.

About the Author

Sunny Bains is a scientist, journalist, editor, Editorial Director of the The Briefing and Managing Director of Form & Content Media Ltd.

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