Simultaneous measurements of the flow velocities in a microchannel by wide/evanescent field illuminations with particle/single molecules

Abstract

A laser-induced fluorescence imaging method was developed to simultaneously measure flow velocities in the middle and near wall of a channel with particles or single molecules, by selectively switching from the wide field excitation mode to the evanescent wave excitation mode. Fluorescent microbeads with a diameter of 175 nm were used to calibrate the system, and the collisions of microbeads with channel walls were directly observed. The 175 nm microbeads velocities in the main flow and at 275 nm from the bottom of the channel were measured. The measured velocities of particles or single molecules in two positions in a microchannel were consistent with the calculated value based on Poiseuille flow theory when the diameter of a microbead was considered. The errors caused by Brownian diffusion in our measurement were negligible compared to the flow velocity. Single lDNA molecules were then used as a flowing tracer to measure the velocities. The velocity can be obtained at a distance of 309.0 ¡ 82.6 nm away from bottom surface of the channel. The technique may be potentially useful for studying molecular transportation both in the center and at the bottom of the channel, and interactions between molecules and microchannel surfaces. It is especially important that the technique can be permitted to measure both velocities in the same experiment to eliminate possible experimental inconsistencies.

Optofluidic microscope and its applications in biology

“…Additional functionalities can be built into the OFM systems. For example, the capability to perform fluorescence imaging [15,27] or Raman imaging [28] can be added In fact, the on-chip nature of the OFM easily enables multispectral analysis. A series of OFM device, each selective for a given wavelength band, can be built along a single microfluidic channel.…”

Analysis Laboratory on a Chip

“…Utilizing this system, we developed a novel method for simultaneous measurement of flow velocities in the middle and near wall of a microchannel with particles or single molecules. 34 In addition, we found that the numbers of molecules probed in the evanescent field decreased with an increase of molecular weight because of steric hindrance. 35 This interesting phenomenon might be helpful for studying undefined molecular interactions at extremely low concentrations without need of separations.…”

Studying Interfacial Transport With Evanescent Wave-Based Particle Velocimetry and Thermometry

“…Evanescent wave-based particle velocimetry methods have been used by various researchers to study Poiseuille and electroosmotic flows and hindered Brownian diffusion [5][6][7]. A number of groups have also used zinc sulfide-overcoated cadmium selenide quantum dots, which emit in the visible portion of the spectrum [8], and fluorescently labeled DNA molecules [9], as flow tracers for evanescent-wave velocimetry.…”