Microfluidic Mixing and Analog On-Chip Concentration Control Using Fluidic Dielectrophoresis.

Microfluidic platforms capable of complex on-chip processing and liquid handling enable a wide variety of sensing, cellular, and material-related applications across a spectrum of disciplines in engineering and biology. However, there is a general lack of available active microscale mixing methods capable of dynamically controlling on-chip solute concentrations in real-time. Hence, multiple microfluidic fluid handling steps are often needed for applications that require buffers at varying on-chip concentrations.

Fluidic dielectrophoresis: The polarization and displacement of electrical liquid interfaces.

Traditional particle-based dielectrophoresis has been exploited to manipulate bubbles, particles, biomolecules, and cells. In this work, we investigate analytically and experimentally how to utilize Maxwell-Wagner polarization to initiate fluidic dielectrophoresis (fDEP) at electrically polarizable aqueous liquid-liquid interfaces. In fDEP, an AC electric field is applied across a liquid electrical interface created between two coflowing fluid streams with different electrical properties.

Maxwell-Wagner polarization and frequency-dependent injection at aqueous electrical interfaces.

We demonstrate a new type of alternating current (ac) interfacial polarization and frequency-dependent fluid displacement phenomenon at a liquid-liquid electrical interface. Two fluid streams--one with a greater electrical conductivity and the other a greater dielectric constant--are made to flow side by side in a microfluidic channel. An ac electric field is applied perpendicular to the interface formed between the liquid lamellae, and fluid is observed to displace across the liquid-liquid interface.