We will report on efforts to develop voltage sensing inorganic nanoparticles that self‐insert into the cell membrane and optically record, non‐invasively, action potential on the single paticle level. Bandgap‐engineered colloidal semiconductor nanoparticles, dubbed voltage‐sensing nanoparticles (vsNPs) that display large quantum‐confined Stark effect (QCSE) at room temperature and on the single particle level were developed. QCSE measurements of several types of fluorescent colloidal semiconductor quantum dots (QDs) and nanorods (NRs) were performed. It was shown that charge separation across one (or more) heterostructure interface(s) with type‐II band alignment (and the associated induced dipole) is crucial for an enhanced QCSE. Surface functionalization that impart membrane‐protein like properties was developed. We will discuss the possible utility of these nanoparticles for voltage sensing on the nanoscale, and in particular, their suitability for action potential recording.