Measurements of diffusion coefficients in 1-D micro- and nanochannels using shear-driven flows

Abstract

The present paper describes a method for measuring the molecular diffusion coefficient of fluorescent molecules in microfluidic systems. The proposed static shear-driven flow method allows one to perform diffusion measurements in a fast and accurate manner. The method also allows one to work in very thin (i.e. submicron) channels, hence allowing the investigation of diffusion in highly confined spaces. In the deepest investigated channels, the obtained results were comparable to the existing literature values, but when the channel size dropped below the micrometer range, a significant decrease (more than 30%) in molecular diffusivity was observed. The reduction of the diffusivity was most significant for the largest considered molecules (ssDNA oligomers with a size ranging between 25 to 100 bases), but the decrease was also observed for smaller tracer molecules (FITC). This decrease can be attributed to the interactions of the analyte molecules with the channel walls, which can no longer be neglected when the depth of the channel reaches a critical value. The change in diffusivity seems to become more explicit as the molecular weight of the analytes increases.

Carbon Nanotube–Polymer Composite for Light‐Driven Microthermal Control

“…[23,24] Second, the fluid sample inside the microchannel has a volume of as little as 720 pL and, consequently, a small heat capacity. [25][26][27] Under NIR laser irradiation, the PL-BSA-SWNT-PDMS microchannels underwent significant changes in temperature when the laser power was pulsed on and off (see Figure 3 e). The maximum temperature at laser powers of 1, 3, and 5 W increased from 25 8C to 30, 35, and 44 8C, respectively.…”

Direct Observation of Transitions between Surface-Dominated and Bulk Diffusion Regimes in Nanochannels

“…Overall, these are the dominant contributions to an effective diffusion coefficient which is strongly decreased when measuring the diffusion of proteins in nano-confinements 9,12,24 . …”

Near-Wall Motion of Caged Fluorescent Dye in Microchannel Flows Obtained from Evanescent Wave Molecular Tagging

“…where ∆t is the frame interval of the CCD camera, are the variances of the fluorescent intensity profile at t = t i and t i+1 , respectively, which were calculated by fitting the profiles with a Gaussian function (18) . This operation was applied to the captured images just after 74 ms of the UV laser exposure.…”

“…On the other hand, in the past experiments, the uncaged dye convected to the streamwise direction is of interest in spite of the dye dispersion in the depthwise direction, which has been hardly detected by MTV with volume illumination. The effect of velocity gradient on the molecule dispersion affects significantly the performance of chromatographic separations using microfluidic device (18) , however, none of the experiments has focused on the near-wall behavior. The optical diagnostic with the near-wall resolution is required to extend our understanding of the molecule adsorption effect on interfacial flow and the molecule dispersion near the wall.…”