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

In this paper we demonstrate high spatial resolution hydrodynamic flow profiling in silicon wafer based microchannels using single molecule fluorescence correlation spectroscopy (FCS). We have used confocal fluorescence microscopy to detect single tetramethylrhodamine (TMR-4-dUTP) biomolecules traversing 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 continuous hydrodynamic flow through the microstructure could be accomplished. The microchannel was then scanned with a diffraction-limited focus in similar to 1-mu m steps in both the vertical and the horizontal directions to determine 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 laminar now profile. Future microstructures can hereby be nondestructively investigated with the use of high spatial resolution confocal correlation microscopy.