The ability to measure electrochemical reactions on single nanoparticle electrodes reveals how local structural and surface heterogeneity impacts electrochemical performance. However, integrating traditional electrochemical techniques with single nanoparticle measurements remains an experimental challenge and typically does not allow many individual nanoparticles to be interrogated simultaneously. Optical readouts of electrochemical reactions provide a solution to this challenge, allowing reactions on many nanoparticles to be followed in parallel, while providing single nanoparticle sensitivity. However, optical readouts are traditionally limited to a specific subset of redox-active probes that show a change in their optical signature upon a change in their redox state, limiting the scope and applicability of the approach. This talk will discuss using pH sensitive probes to follow spectroscopically-silent redox reactions such as hydrogen production on single nanoparticle electrodes.