A Sensor for Detecting Aqueous Cu²⁺ That Functions in a Just-Add-Water Format

There is growing concern around the negative health impacts associated with contamination of drinking water by harmful chemicals. Technology that enables fast, cheap, and easy detection of ions and small molecules in drinking water is thus important for reducing the incidence of these negative health impacts. Here, we describe a sensor for detecting Cu²⁺ in water that provides colorimetric results in 15 min or less and functions in a just-add-water format. The sensor contains cheap reagents including salts, buffer, oxidant, chromogen, surfactant, and optionally a chelating agent. The sensor is assembled and lyophilized for shelf-stability and field-deployment. Rehydrating the sensor with water containing Cu²⁺ results in chromogen oxidation and blue color formation to visually indicate the presence of Cu²⁺. The sensor demonstrates high selectivity toward Cu²⁺ against other metal cations, functionality in field samples, shelf-stability, and can be tuned to activate at different Cu²⁺ threshold concentrations. This sensor thus has the potential to meet a variety of needs, such as point-of-need testing for Cu²⁺ to ensure water supplies meet health guidelines, such as the United States Environmental Protection Agency's Lead and Copper Rule.