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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 32, Number 2
BKCSDE 32(2)
February 20, 2011 

Characterization of the Surface Contribution to Fluorescence Correlation Spectroscopy Measurements
Salina A. Chowdhury, Manho Lim*
Fluorescence correlation spectroscopy, Rhodamine 123, Free diffusion, Surface-molecule interaction, Surface hydrophobicity
the diffusion of molecules in a solution at the single-molecule level. FCS is strongly affected by many factors such as the stability of the excitation power, photochemical processes, mismatch between the refractive indices, and variations in the cover glass thickness. We have studied FCS near the surface of a cover glass by using rhodamine 123 as a fluorescent probe and have observed that the surface has a strong influence on the measurements. The temporal autocorrelation of FCS decays with two characteristic times when the confocal detection volume is positioned near the surface of the cover glass. As the position of the detection volume is moved away from the surface, the FCS autocorrelation becomes one-component decaying; the characteristic time of the decay is the same as the faster-decaying component in the FCS autocorrelation near the surface. This observation suggests that the faster component can be attributed to the free diffusion of the probe molecules in the solution, while the slow component has its origin from the interaction between the probe molecules and the surface. We have characterized the surface contribution to the FCS measurements near the surface by changing the position of the detection volume relative to the surface. The influence of the surface on the diffusion of the probe molecules was monitored by changing the chemical properties of the surface. The surface contribution to the temporal autocorrelation of the FCS strongly depends on the chemical nature of the surface. The hydrophobicity of the surface is a major factor determining the surface influence on the free diffusion of the probe molecules near the surface.
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