Point-of-Use Detection of Organosulfate Contaminants Associated with Cyanotoxins in Water Using Electrochemical Methods
Authors: Willis Christina Nicole , Misra Mano , Mohanty Swomitra 
Published: February 2020

Cyanobacteria, more commonly referred to as blue-green algae, often grow in stagnant water such as lakes and have been linked to many adverse health effects. Several species of cyanobacteria produce nerve or liver toxins called cyanotoxins, and by the time they are in concentrations large enough to be visible to the human eye (known as algal blooms), these toxins are already at harmful concentrations. Because cyanobacteria are not readily visible at low concentrations, it is important to develop analytical sensing methods of their associated toxins. In the state of Utah the species most commonly responsible for poisoning are Anabaena, Aphanizomenon and Microcystis. Of particular importance is the class of cyanotoxins known as cylindrospermopsin (CYN). It is produced by both Anabaena and Aphanizomenon cyanobacteria, two of the three species most often responsible for poisoning, and is proven to be cytotoxic, dermatotoxic, genotoxic, hepatotoxic in vivo, developmentally toxic and possibly carcinogenic. The cyanobacteria that most commonly produce CYN bloom mid-water, making it extremely difficult to visibly detect during the early stages of development. Most forms of the toxin are extracellular in water, making detection easier by eliminating the need for processing the bacteria itself. Cylindrospermopsin (an organosulfate) has an active sulfonate ester functional group, which can be exploited for electrochemical sensing with minimal sample preparation. Current methods are most commonly chromatographic, including Gas Chromatography/ Mass Spectrometry (GCMS) and Liquid Chromatography (i.e. HPLC or LCMS), but can also employ biological assays. The biggest problem with these techniques are the time, sample preparation and expensive equipment associated with them, making them non-ideal for point of use sensing. In order for regular testing of affected waters to be plausible, it is imperative to develop a sensor which can be used easily, inexpensively and without the need for highly trained technicians with access to laboratory grade equipment. Specific detection of sulfonate functional groups will be the main focus of this work, as the presence of organosulfates is strictly monitored at waste treatment plants, making such a sensor useful outside of cyanotoxin-specific applications. This work will describe emerging techniques for electrochemical organosulfate detection using a modified titanium dioxide (TiO2) nanotube electrode surface. This electrode type, paired with the proper metal functionalization, has proven to be highly specific in detecting VOC biomarkers in previous work. The use of this sensor will now be expanded to water-based applications. The first step in the work is to determine the appropriate metal functionalization, which will bind with the sulfonate group at a specific applied voltage and change the current proportionally to the concentration of sulfonate present. A method of this type gives results within minutes, requires little to no sample preparation, and can have extremely low limits of detection due to a baseline current in the nanoamp range. Preliminary cyclic voltammetry experiments using methane sulfonic acid show interaction with tin-oxide at a copper electrode surface, which suggests tin as a possibility for inexpensive metal functionalization at a TiO2 electrode.