Abstract: An electro-optical device using a plasmonic metasurface. The electro-optical device includes an electro-optical substrate and an array(s) of plasmonic unit cells forming a plasmonic metasurface fabricated on the substrate, where each of the plasmonic unit cells mimics a field-effect transistor. In each of the plasmonic unit cells, there is a drain and a source antenna separated from each other via a gap. In such a structure, a gate contact is not required thereby simplifying device fabrication. Furthermore, the device can be scaled to cover a large frequency range and have a flexible optical response, which is used to detect the presence of biomolecules. For example, the presence of a biomolecule is detected by observing a change in the electrical properties of the substrate in the gap region caused by a change in the substrate temperature which was caused by a change in the optical absorption of the plasmonic unit cell(s).