Tracking the Dynamics of Single Quantum Dots: Beating the Optical Resolution Twice

Using particle tracking routines the location of single point light sources can be determined with an accuracy of a few nanometers. By using quantum dots (QDs) emitting at different wavelengths, the measurement of the distance between these point light sources, which are closer than the optical resolution of 200-nm, was achieved. The nanocrystals have major advantages over conventional chromophores in higher quantum yield, more photostability, and the possibility of different emission wavelengths by an excitation with a single wavelength. The colocalization of two single QDs at the least distance of 40-nm can be measured with a standard deviation of 5-nm and a time resolution of 117-ms using one excitation wavelength.