Korean researchers developed a liquid-ion gated FET-type graphene-based aptasensor with highly sensitive and selective responses to various mercury ion concentrations. This sensor was shown to be a good detector of mercury in mussels.
Aptasensors are bio-sensors that use aptamers (artificial oligonucleotides: DNA or RNA) as a recognition element. The sensors developed in korea used a single-layer graphene sheet that was functionalized using an aptamer. This sensor is not just very sensitive and fast, but it's also flexible and highly stable mechanically.
More info on Aptamers at the US National Library of Medicine