Several methods have been developed to detect microcystins in various water matrices. Reliable analytical techniques include chromatographic methods (e.g., LC/MS/MS) and enzyme-linked immunosorbent assay (ELISA). LC/MS/MS detects and quantifies precisely very low microcystin levels, and it can differentiate between microcystin congeners. However, the method is limited by a lack of standards and requires highly technical skills. ELISA is a routine methodology to analyze water samples for microcystins. ELISA is inexpensive and easy to perform in the field or laboratory and does not require highly skilled personnel. Both techniques detect various cyanotoxins in water samples; however, the main drawbacks are the lack of instrument portability and the inability for real-time detection of MC-LR in real water samples. There is an urgent need for the development of a sensor that is portable, sensitive, and capable for point-of-use detection of microcystins. Such sensors would alert the presence of cyanotoxins in water in real-time, which is important considering that the prevention of toxins from entering a drinking water treatment plant or appropriate adjustment of chemical treatment are critical to provide safe drinking water.
Biosensors are powerful analytical tools, known for their ability to detect various targets in environmental and medical applications. Specifically, electrochemical sensors with aptamer-based recognition systems have gained popularity due to their specificity, sensitivity, quick response, low cost, and portability compared to conventional methods. Aptamers are short fragments of nucleic acid (DNA or RNA) selected and amplified by a process called Systematic Evolution of Ligands by Exponential Enrichment (SELEX) developed in 1990. Target analyte is bound to randomly generated single-stranded sequences (about 20–80 nucleotides in length) with constant 5′ and 3′ ends that serve as primers. Bound sequences are amplified by polymerase chain reaction for DNA sequences or reverse transcription polymerase chain reaction for RNA sequences. The single-stranded nucleic acid molecules fold around the target analyte yielding a three-dimensional stable structure, offering an excellent affinity bioreceptor for biosensing.
University of Cincinnati researchers have developed a sensor that detects toxins from algal blooms that taint surface water such as rivers, lakes and streams. Early detection of these toxins can aid water treatment plants to adjust the treatment strategy to keep the dangerous substances from contaminating drinking water. The research is led by Dionysios Dionysiou, professor of environmental engineering. Project collaborators included researchers from across several disciplines at UC: Vesselin Shanov, professor of chemical engineering; Ryan White, associate professor of electrical engineering and chemistry; and Bill Heineman, distinguished research professor of chemistry. Researchers from the Environmental Protection Agency—Armah de la Cruz and Eunice Varughese—also contributed.
The researchers created an electrochemical aptamer-based sensor that detects and measures microcystin cyanotoxin in water. Microcystins are the toxic byproducts of harmful algal blooms, which develop when fertilizer used in agriculture leaches into bodies of water. Exposure through drinking water may cause liver damage, tumor growth and gastroenteritis.
Once the cyanotoxins are detected in the finished drinking water it’s more challenging to remove—which occurred in Toledo, Ohio, in 2014 and led to a do-not-drink order for 500,000 consumers. Early detection with the sensor in the freshwater source, such as Lake Erie in the Toledo case, would alert water treatment plants to the presence of the toxins before the water enters the treatment facility. Conventional treatment processes are not always efficient in removing cyanotoxins. Contaminated water with these toxins is harder to treat. If the toxins pass several treatment stages, an unfortunate increase in the cost and major difficulties in the general management of a treatment plant is expected.
Using water samples taken from Lake Erie and other Ohio bodies of water, the researchers employed their sensor to successfully detect and measure the amount of a specific type of microcystin commonly found in the region. The next step for future research is to expand the types of toxins the sensor can detect and create a prototype device to be used in the field.
The authors focused on microcystins which are very commonly found here in Ohio and other places, but there are other important toxins, they want to develop modified sensors that can be selective for other toxins, as well as sensing devices that can detect and quantitatively measure multiple cyanotoxins in water.
A novel electrochemical sensing approach has been developed for the detection of MC-LR using surface-confined [Ru(NH3)6]3+ as redox mediator. Sensing surfaces of highly packed immobilized aptamers were capable of recording decreasing SWV signals after the addition of MC-LR in redox-free buffer. The dose–response curve was linearly proportional to the logarithm of the MC-LR concentration in a dynamic range of concentrations. Higher concentrations of MC-LR resulted in lower SWV percent signal changes with the highest being 60% and a calculated LOD of 9.2 pM. Sensitivity and selectivity of the sensor were good. The sensor may be applicable to detect MC-LR in drinking water samples rather than lake samples. This study suggests a new strategy for the detection of toxins in water using an aptamer with localized conformational changes that provides limited conformational change and thus small electrochemical signal changes.
Vasileia Vogiazi, Armah A. de la Cruz, Eunice A. Varughese, William R. Heineman, Ryan J. White*, and Dionysios D. Dionysiou. Sensitive Electrochemical Detection of Microcystin-LR in Water Samples Via Target-Induced Displacement of Aptamer Associated [Ru(NH3)6]3+. ACS EST Engg. 2021, 1, 11, 1597–1605. https://doi.org/10.1021/acsestengg.1c00256