Nanoscale materials and devices could play a unique role in biological and biomedical application due to their small size, minimal invasiveness, multifunctionality, and enhanced biocompatibility. In this talk, I will focus on discussing our recent progress of developing novel nanoscale field-effect transistor (FET) based devices to measure transmembrane potential change from inside living electrogenic cells. Compared to other available recording methods, these FET based intracellular measurement devices allow for unprecedented miniaturization and integration of probes, thus enabling electrophysiology studies of subcellular neuronal structures and large scale, high resolution mapping from neuronal networks.