Cell-Free Detection of Heavy Metals for Rapid, in-Field Water Quality Testing

The ability to detect contaminants, such as heavy metals, in water is critical to health and safety in both field-forward and resource-poor environments. Nature and bioengineers have devised biosensors that respond to a variety of analytes; however, deployment of these sensors remains a challenge. For cell-based sensors, these challenges include the nutrient requirements of living cells and concerns surrounding the potential release of genetically modified organisms in the environment. Cell-free protein synthesis (CFPS) is a powerful tool that is being harnessed for the development of biosensors due to the ability of CFPS systems to detect an array of analytes, including those that are toxic to living systems, and their potential to address other limitations of whole-cell biosensors. CFPS systems can be freeze-dried onto paper substrates, and following rehydration, a visualizable reporter protein is produced in response to the presence of 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. Sensor optimization using an acoustic liquid handler and specificity data are also presented. These cell-free sensors are able to detect heavy metal concentrations at or below US Military Exposure Guidelines in under 30 minutes, and we demonstrate the simultaneous detection of multiple metal species in one assay. In addition to heavy metals, the CFPS approach described here can be expanded in the future to detect a wider range of contaminants, including toxic compounds and pathogens.