Hydrodynamic flow profiling in microchannel structures by single molecule fluorescence correlation spectroscopy

In this paper we demonstrate high spatial resolution hydrodynamic flow prof iling in silicon wafer based microchannels using single molecule fluorescen ce correlation spectroscopy (FCS). We have used confocal fluorescence micro scopy to detect single tetramethylrhodamine (TMR-4-dUTP) biomolecules trave rsing a similar to 1 fL volume element defined by an argon laser beam focus . By elevating a (similar to 10(-10) M) reservoir of diluted analyte, a con tinuous hydrodynamic flow through the microstructure could be accomplished. The microchannel was then scanned with a diffraction-limited focus in simi lar to 1-mu m steps in both the vertical and the horizontal directions to d etermine the now profile across a 50 x 50 mu m(2) channel. The now profile measured was parabolic in both dimensions, thereby showing a Poiseuille lam inar now profile. Future microstructures can hereby be nondestructively inv estigated with the use of high spatial resolution confocal correlation micr oscopy.