We have developed a new technique for fluorescence correlation spectroscopy (FCS) using an optical fiber probe, as is employed in nearfield scanning optical microscopy under the illumination-collection hybrid mode. A small observation volume beyond the diffraction limit makes it possible to apply FCS to concentrated solutions with high spatial resolution. Owing to the large transmission efficiency of the probe, correlation traces with an adequate signal-to-noise ratio resulted. We performed FCS measurements for fluorescent particles to demonstrate the validity of the method.
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