Abstract

An optical switch exhibits two stable and selectively addressable states, a fluorescent state and a non-fluorescent state, which can be reversibly interconverted upon irradiation with different wavelengths of light. Efficient molecular optical switches are strongly desired for improved protein tracking in living cells and they are potentially very useful for far- field fluorescence imaging with improved resolution. Because suitable optical switches reversibly undergo light-induced transitions between two thermally stable states, and the transitions are saturable, a spatial intensity distribution of two laser wavelengths (one to switch off the fluorophore and another to reactivate fluorescence) featuring a local minimum might allow fluorescence imaging at the nanoscale. Conceptually similar to stimulated-emission depletion (STED) microscopy optical switches promise similar spatial resolution, but require much lower laser intensities. Here we review different concepts that use reversible saturable optical fluorescence transitions (RESOLFT) and discuss the requirements optical switches have to fulfill. In addition, we address the problem of selective in vivo labeling of target molecules with chemical switches, i.e. optical switches that are activated upon specific labeling to target molecules in living cells.

© 2007 SPIE