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 5nm and a time resolution of 117 ms using one excitation wavelength.