Detection of heavy metal ions using protein-functionalized microcantilever sensors

Microcantilevers functionalized with metal-binding protein, AgNt84-6, are demonstrated to be sensors for the detection of heavy metal ions like Hg ²⁺ and Zn²⁺. AgNt84-6, a protein that has the ability to bind multiple atoms of Ni²⁺, Zn²⁺, Co²⁺, Cu²⁺, Cd²⁺ and Hg²⁺ was attached to the gold-coated side of silicon nitride cantilevers via linker groups. Upon exposure to 0.1 mM HgCl₂ and 0.1 mM ZnCl₂ solutions, the microcantilevers underwent bending corresponding to an expanding gold side. Exposure to a 0.1 mM solution of MnCl₂ solution did not result in a similar bending indicating a weak or no interaction of Mn²⁺ ions with the AgNt84-6 protein. The microcantilever bending data were consistent with data from electrophoresis carried out on SDS-PAGE gels containing metal ions that showed protein interaction with Zn²⁺ ions but not with Mn²⁺ ions. Thus, we demonstrate that microcantilever bending can be used to discriminate between metal ions that bind and do not bind to AgNt84-6 protein in real time.