Charge-based particle separation in microfluidic devices using combined hydrodynamic and electrokinetic effects.

Area of Science:

• Microfluidics
• Biophysics
• Analytical Chemistry

Background:

• Particle separation is crucial in various scientific fields.
• Existing microfluidic techniques often face limitations in efficiency and specificity.
• Controlling particle behavior within microchannels requires understanding complex fluid dynamics and electrokinetic phenomena.

Purpose of the Study:

• To present a novel microfluidic approach for charge-based particle separation.
• To introduce and demonstrate the phenomenon of flow-induced electrokinetic trapping (FIET).
• To exploit FIET for separating particles with different zeta potentials.

Main Methods:

• Employing a microfluidic device with a recirculating flow pattern generated by opposing pressure-driven and electro-osmotic flows.
• Utilizing diverging/converging channel segments to induce flow-induced electrokinetic trapping (FIET).
• Separating charged particles based on their zeta potential differences in non-uniform microchannels.

Main Results:

• Demonstrated successful trapping and preconcentration of charged particles when their net velocity approaches zero.
• Achieved particle separation using FIET in a non-uniform microchannel, separating polystyrene beads with varying zeta potentials.
• Theoretical analysis confirmed that trapping occurs when electrokinetic and pressure-driven velocities are equal and opposite.

Conclusions:

• FIET is a viable mechanism for charge-based particle separation in microfluidic devices.
• The electrophoretic mobility (zeta potential) of particles dictates the conditions required for effective trapping and separation.
• This method offers a predictable way to separate particles based on their surface charge characteristics.