The electrophotonic biosensor integrates silicon photonics with electrochemistry into a single technology. This multi-modal biosensor provides a number of unique capabilities that extend the functionality of conventional silicon photonics. For example, by combining the complementary information revealed by simultaneous electrochemical and photonic measurements, it is possible to provide unique insights into on-surface electrochemical processes. Furthermore, the ability to create electrochemical reactions directly on the silicon surface provides a novel approach for engineering the chemical functionality of the photonic sensors. The electrophotonic biosensor thus represents a critical advance towards the development of very high-density photonic sensor arrays for multiplexed diagnostics.