Scientists capture real-time electrical activity of a beating heart using graphene 'camera' Bay Area scientists have captured the real-time electrical activity of a beating heart, using a sheet of graphene to record an optical image -- almost like a video camera -- of the faint electric fields generated by the rhythmic firing of the heart's muscle cells. The graphene camera represents a new type of sensor useful for studying cells and tissues that generate electrical voltages, including groups of neurons or cardiac muscle cells. To date, electrodes or chemical dyes have been used to measure electrical firing in these cells. But electrodes and dyes measure the voltage at one point only; a graphene sheet measures the voltage continuously over all the tissue it touches.