Microfluidic mixing using contactless dielectrophoresis.

Area of Science:

• Microfluidics
• Biotechnology
• Applied Physics

Background:

• Microfluidic devices are crucial for manipulating small fluid volumes.
• Achieving efficient mixing, especially for low-diffusivity samples, remains a significant challenge in laminar flow regimes.
• Traditional dielectrophoresis (DEP) methods face limitations due to direct electrode-fluid contact.

Purpose of the Study:

• To present the first experimental evidence of mixing enhancement using contactless dielectrophoresis (cDEP) in microfluidic systems.
• To investigate the impact of chamber geometry and operating parameters on mixing efficiency in cDEP.
• To explore the potential of cDEP for mixing challenging biological samples.

Main Methods:

• Fabrication of microfluidic devices with rectangular and circular chambers in PDMS.
• Utilizing pressure-driven flow of deionized water with 0.5 μm beads.
• Imposing dielectrophoresis (DEP) force via capacitively coupled electrodes (cDEP) without direct fluid contact.
• Conducting mixing tests across a range of flow rates (0.005–1 mL/h) and AC signal parameters (0–300 V, 100–600 kHz).

Main Results:

• Demonstrated significant mixing enhancement in microfluidic systems using cDEP.
• Observed rapid mixing when the timescales of bulk fluid motion and DEP motion were synchronized.
• Identified rectangular mixing chambers as more efficient than circular ones.
• Showcased the capability of cDEP to overcome limitations of standard DEP by avoiding direct electrode contact.

Conclusions:

• Contactless dielectrophoresis (cDEP) provides an effective method for enhancing mixing in microfluidic devices.
• The cDEP approach offers a viable solution for mixing low-diffusivity biological samples, a critical task in microscale laminar flows.
• Rectangular chamber designs combined with cDEP show superior mixing performance compared to circular designs.