Researchers genetically modified E.coli bacteria to detect amount of arsenic in drinking water. These E.coli will activate arsenic switch, whose gene in turn activate breakdown of lactic acid. Through litmus test we can observe a change in pH level, and presence of arsenic in water. Arsenic detector is built by using principle of synthetic biology, which aims to identify function of genetic part or a particular DNA sequences. These parts are matched together to form new genetic circuits, creating novel biological functions within living organisms, like bacteria.

Source: www.technologyreview.com