The ability to detect heavy metals and other contaminants in water is critical for health and safety in both field-forward and resource-poor environments. The power of biology is being leveraged to develop biosensors capable of responding to a wide variety of analytes; however, deployment of these sensors remains a challenge. For cell-based sensors, these challenges include nutrient and cold chain requirements of living cells and concerns surrounding the potential release of genetically modified organisms in the environment. Biosensors based on cell-free expression (CFE) systems hold great potential for providing rapid, in-field detection capabilities. CFE systems can be freeze-dried onto paper substrates, and following rehydration at the point of need, a visualizable reporter protein is produced in response to the target analyte. These paper-based sensors are cheap, disposable, simple to use, and multiplexible. This work shows a tri-service effort to develop cell-free biosensors for arsenic, cadmium, and mercury. Within 30 minutes, all three sensors are able to detect heavy metals at or below Military Exposure Guideline (MEG) levels, and the arsenic and mercury sensors achieve detection limits below the World Health Organization (WHO) recommended levels. The sensors are further being evaluated and improved for field-relevant conditions: Each sensor shows robust performance using an NSF test water standard that mimics rain water, and lyophilization of the sensors on paper is being optimized. In addition to heavy metals, the CFE approach described here can be expanded in the future to detect a wider range of contaminants, including toxic compounds and pathogens. Ultimately, a panel of different CFE sensors could be combined onto a single paper ticket, allowing for the simultaneous detection of multiple hazardous contaminants in water.

Paper-based, cell-free detection of heavy metals for in-field water quality testing

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ACS Fall 2022

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