Although many of us may balk at the thought of drinking arsenic, the toxic chemical does occur naturally in the drinking water of some regions – and its levels definitely need to be monitored. An inexpensive new device allows people in developing countries to do so, and it works with a smartphone.

Developed by a team at the University of Edinburgh, the flat rectangular tool incorporates 384 tiny wells, joined together by microfluidic channels. Each well in turn contains genetically-altered Escherichia coli bacteria, suspended in a gel.

When a water sample is introduced, it flows through the channels, going into each well. If any arsenic is present in that water, the bacteria will react by producing fluorescent proteins. The E. coli in different parts of the device have different sensitivities to arsenic, so they will likewise produce differing amounts of fluorescence.

The result is an illuminated pattern, which is read by the camera of an attached smartphone. An app on that phone subsequently analyzes that pattern and then displays the water sample's arsenic levels, in a volume bar-type layout.

According to the university, the device is much more sensitive than other arsenic biosensors, it can be operated in the field with minimal training, and it's also quite cheap to use – each test costs about 30 pence, or around 40 US cents.

"We tested our sensors with samples from wells in a village in Bangladesh," says lead scientist, Dr. Baojun Wang. "The arsenic levels reported by the sensors was consistent with lab-based standard tests, demonstrating the device's potential as a simple low-cost-use monitoring tool."

A paper on the study was recently published in the journal Nature Chemical Biology.