Fluorescence correlation spectroscopy with sub-diffraction-limited resolution using near-field optical probes

We report fluorescence correlation spectroscopy (FCS) measurements using near-field scanning optical microscopy (NSOM) probes to produce a sub-diffraction-limited observation area. An order of magnitude reduction in the area compared to confocal FCS has been achieved. We also demonstrate a simple means to model the autocorrelation decay due to diffusion within the excitation profile at the NSOM probe aperture. The use of probes with smaller …