Safe drinking water is a priority for soldiers on field duty but water testing can be impractical. Now US scientists have developed an easy-to-use, portable water-screening device powered by a battery pack.

The toxicity sensor and automated cell maintenance system are stored in a case that is easy to transport

Mark Widder, at the US Army Center for Environmental Health Research, Fort Detrick, and colleagues, grew a monolayer of mammalian cells on a fluidic chip's electrodes. They injected water samples into the chip and electrically monitored the cells' response. They showed that the cells' impedance (resistance to current) changed when the water contained toxins.

Cellular impedance is a proven monitor of chemically induced toxicity, explains Widder. For example, toxins may affect cell membrane porosity, which leads to a change in a cell's resistance. But until now, the difficulty in keeping cells healthy for extended periods has limited their use in portable sensors.

Widder's sensor integrates the impedance-measuring chip with automated cell maintenance - a computer-controlled pump delivers cell-culture media to the cells from a bag attached to the lid of the device's case. Using this simple system, which is powered by a rechargeable battery, the group kept the cells healthy and responsive for up to four months and showed they could detect five different pollutants.

'The system does not require trained technicians and a cell-culture facility,' comments Widder. 'All that is required of the operator is to reconstitute the pre-packaged cell media in 20 millilitres of water sample, temperature equilibrate the sample with a control sample then inject the two samples.' He adds that the pump-controlling computer also analyses the impedance measurements.

Eugen Gheorghiu, an expert in impedance-based analysis and biosensors at the International Centre of Biodynamics, Bucharest, Romania, says that although the samples' concentrations were high and he wonders about the sensor's sensitivity, the method 'is a promising development that could pave the way to wider applicability and relevance of cell-based lab-on-a-chip platforms'.

Widder acknowledges that the sensitivity may not be good enough for drinking water standards but says that it meets military exposure guidelines. The team are continuing to work on the sensitivity, he adds. They have also developed an enhanced version of the device that incorporates multiple biochips, enabling analysis of multiple samples. The team will perform field testing after they complete laboratory validation, says Widder.

Frances Galvin

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