Study of bacterial metal resistance protein-based sensitive biosensors for heavy metal monitoring

A capacitive signal transducer was used with metal-resistance (SmtA) and metal regulatory (MerR) proteins to construct sensitive biosensors for monitoring heavy metal ions. The proteins were overexpressed in E. coli, purified and immobilized on a gold electrode modified with self-assembled thiol layers. The protein-modified electrode was used as the working electrode in an electrochemical cell placed in a flow injection system. Both the metallothionein from the cyanobacterium Synechococcus PCC 7942 and the MerR regulatory protein from transposon Tn501 enabled monitoring of Cu2+, Hg2+, Zn2+, and Cd2+ starting from femtomolar concentrations. The metal ions were bound differentially and the shape of the binding curves may sense conformational changes related to the biological roles of the proteins.