Sensing Membrane Potential by Inorganic Semiconductor Nanorods

Unraveling emergent brain activities requires simultaneous recording of action potentials from a large number of neurons. Electrical recording methods such as patch clamp and optical recording by voltage sensing dyes and proteins have been developed for years and are widely utilized. However, such techniques have insufficient spatial and/or temporal resolutions and/or suffer from poor photostability, posing a need for probes that circumvent these limitations. Improved probes, with high sensitivity and photostability, could afford the study of large neural networks (in a large filed-of-view) and/or at very high spatial resolution. Using bandgap-engineering and colloidal synthesis methods, we have synthesized seeded semiconductor (SC) nanorods (NRs) with Type-II heterojunctions that exhibit a large Quantum Confined Stark Effect (QCSE) at room temperature (1). For using these NRs as voltage sensors, however, one needs to impart them with membrane-protein like properties so that they can be stably inserted into the membrane. We report here spontaneous insertion of SC NRs into liposomes and cell membranes by functionalizing them with specially designed peptides. We provide evidences for insertion from cryo transmission electron microscopy (TEM) and polarized light microscopy. We also report on first attempts to sense membrane potential with these particles with single-particle sensitivity. With further improvements, SC NRs could potentially be used to study signals from whole neural networks in a large field-of-view. Moreover, successful implementation of SC NRs would allow for the analysis of voltage signals at the nano- (single synapse-) scale.∗Equal contributions(1) Park, K.; Deutsch, Z.; Li, J. J.; Oron, D.; Weiss, S., Single Molecule Quantum-Confined Stark Effect Measurements of Semiconductor Nanoparticles at Room Temperature. ACS Nano 2012,6 (11), 10013-10023.