Nanocavity sensor arrays are powerful devices for parallel extracellular recordings of action potentials from cell networks. The sensors combine a high spatial resolution and seal resistance between cell and electrode with low electrode impedances, allowing low-noise electrophysiological measurements of individual cells in a network without the use of CMOS technology. In this paper, we present a new protocol for the simple fabrication of nanocavity sensors, which enables easy modification of standard microelectrode arrays. Our approach enables processing of devices with improved sensor characteristics and flexibility regarding electrode area and aperture size with minimal effort. We characterize the sensors by impedance spectroscopy and demonstrate their applicability by recording action potentials of individual cardiomyocyte-like cells growing in a network on the chip surface.