Although, graphene based FETs provide a label free, fast and portable mean of detecting heavy metal ions in liquid (i.e. water, blood etc.), there has not been a huge development on this. Why is that?
The work published are mainly from research institutes for discovery of novel phenomena. There are huge development work using graphene materials as sensors happened in the industries. This is why you hardly read papers on the development. If you want to know what industries do, the best way is to keep eyes on the scientific news or online company information. Some info you could find is from patents. Google scholar or Google search engine is a good starting point.