Aqueous chloramine sensors based on molecules acting as switchable dopant sites on graphene-like carbon films

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Water is fundamentally important to most aspects of our existence. One of the most important monitoring parameters of drinking water quality is the level of disinfectants. If their levels are too low, microorganisms can grow in the water, which are harmful to our health. If the disinfectant levels are too high, the disinfectants themselves may be harmful, or at least unpleasant to humans. After primary disinfection at the water treatment plant is complete, disinfectant levels have to be maintained throughout the water distribution system (secondary disinfection). Chloramination is increasingly used for this purpose instead of chlorination. While its persistence is a benefit during distribution, monochloramine is harder to detect (it is odorless) and remove (it is stable) at the consumer end. For applications in health care, aqua culture, swimming pools, and in the food and beverage industry, however, complete removal of chloramines by filtration is imperative. Filter lifetime is difficult to judge just by age or water volume since it is more directly a function of filter capacity and contaminant load. Ideally, a sensor immediately after the filter could warn of breaches due to defects or exhausted capacity. Here we focus on the development of a chloramine sensor for point-of-use water filters. This work will build on a novel sensor design that our research team has recently demonstrated as effective for detecting free chlorine in drinking water. The design is based on our finding that aniline oligomers are capable of being oxidized by the free chlorine in water, thus switching on their ability to act as p-dopants for carbon nanotube films. A simple chemiresistor configuration can quantitatively detect the significant conductivity change of the nanocarbon film due to the dopant switching, and hence serve as a quantitative redox sensor across the entire relevant range. Preliminary data indicates that these sensors can also be used to detect and distinguish a variety of redox-active species. The same sensing principle can be applied to pH or other analytes by using different selectively switchable dopant molecules. Hence, we propose to develop a sensing array capable of quantitatively detecting chloramines in relevant applications for our industrial partner, 3M Canada.**