Tunable Bidirectional Electroosmotic Flow for Diffusion-Based Separations.

Area of Science:

• Microfluidics and Lab-on-a-Chip Technology
• Separation Science
• Biotechnology

Background:

• Current on-chip separation methods face challenges in efficiently separating molecules and particles with varying diffusivities.
• Controlling fluid dynamics at the microscale is crucial for achieving precise separations.
• Electroosmotic flow (EOF) is a key mechanism in microfluidic devices but requires advanced control for complex separations.

Purpose of the Study:

• To introduce and validate a new on-chip separation concept utilizing bidirectional flow.
• To demonstrate the ability to tune dispersion regimes for selective retention and transport of species.
• To provide a theoretical framework and practical guidelines for designing and operating such a system.

Main Methods:

• Development of a microfluidic system capable of generating bidirectional electroosmotic flow (EOF) using alternating current (AC) field-effect electrodes.
• Experimental demonstration of separation using mixtures of particles, antibodies, and dyes.
• Theoretical analysis to model species transport and diffusion under controlled flow conditions.

Main Results:

• Successful separation of low-diffusivity species (particles, antibodies) from high-diffusivity species (dyes) was achieved.
• The system effectively created distinct transport regimes: ballistic for low diffusivity and diffusion-dominated for high diffusivity.
• Experimental outcomes aligned with theoretical predictions, validating the system's design principles.

Conclusions:

• The proposed bidirectional flow system offers a novel and effective approach for on-chip separation based on diffusivity.
• This method provides tunable control over molecular and particle dispersion, enabling selective retention and advection.
• The findings offer valuable engineering guidelines for the design and optimization of advanced microfluidic separation devices.