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

Area of Science:

• Physical Chemistry
• Chemical Engineering
• Nanotechnology

Background:

• Accurate measurement of molecular diffusion is crucial for understanding transport phenomena in microfluidic devices.
• Investigating diffusion in confined spaces, such as submicron channels, presents unique challenges and opportunities.
• Existing methods may lack the speed, accuracy, or resolution for studying diffusion in highly confined environments.

Purpose of the Study:

• To develop and validate a novel method for measuring molecular diffusion coefficients in microfluidic systems.
• To investigate the impact of channel confinement on molecular diffusivity.
• To explore the relationship between molecular size, channel dimensions, and diffusion behavior.

Main Methods:

• Utilized a static shear-driven flow method for rapid and accurate diffusion measurements.
• Employed microfluidic channels with varying depths, including submicron dimensions.
• Measured the diffusion of fluorescent molecules, including FITC and single-stranded DNA (ssDNA) oligomers.

Main Results:

• The static shear-driven flow method provided fast and accurate diffusion measurements.
• A significant decrease (over 30%) in molecular diffusivity was observed in channels below 1 micrometer.
• The reduction in diffusivity was most pronounced for larger molecules (25-100 base ssDNA) and also observed for smaller molecules (FITC).

Conclusions:

• Molecular diffusion is significantly reduced in highly confined microfluidic channels (submicron scale).
• Analyte-wall interactions become dominant in submicron channels, hindering molecular movement.
• The observed decrease in diffusivity is dependent on molecular weight and channel depth, highlighting the importance of confinement effects.