Fluidic dielectrophoresis: The polarization and displacement of electrical liquid interfaces

Abstract

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. When potentials as low as 2 volts are applied, we observe a frequency-dependent interfacial displacement that is dependent on the relative differences in the electrical conductivity (Δσ) and dielectric constant (Δɛ) between the two liquids. At low frequency this deflection is independent of dielectric constant, while at high frequency it is independent of electrical conductivity. At intermediate frequencies, we observe an fDEP cross-over frequency that is independent of applied voltage, sensitive to both fluid electrical properties, and where no displacement is observed. An analytical fDEP polarization model is presented that accurately predicts the liquid interfacial cross-over frequency, the dependence of interfacial displacement on liquid electrical conductivity and dielectric constant, and accurately scales the measured fDEP displacement data. The results show that miscible aqueous liquid interfaces are capable of polarizing under AC electric fields, and being precisely deflected in a direction and magnitude that is dependent on the applied electric field frequency.

Monitoring microfluidic interfacial flows using impedance spectroscopy

“…Recently, a new type of electrokinetic flow was discovered in the vicinity of laminar liquid interfaces formed between two miscible aqueous electrolytes [28]. The phenomenon is known as fluidic dielectrophoresis (fDEP), which describes the ability to deflect a laminar liquid interface across a microchannel using an external AC electric field [29]. The interface is created using a microfluidic T-channel device where two fluids are forced to flow side-by-side.…”

“…fDEP motion is created using a perpendicular electric field produced from an array of parallel point electrodes integrated on the surface of the microfluidic channel (Fig 1a). For a liquid interface subjected to a time varying monochromatic electric field, the displacement is directly proportional to the real part of the interface polarizability factor, , which is function of field frequency ( ), electrical conductivity and permittivity [29]:…”

“…When an alternating current (AC) electric field was applied perpendicular to the direction of flow, the laminar interface polarized and the fluid electrohydrodynamically displaced across the flow channel. The motion of the fluid interface was shown to be an effective electrokinetic method for assessing fluid electrical conductivity and dielectric constant [29], and for detecting biomolecular binding [30]. In order to perform these fluidic measurements, however, the liquid interface required constant optical monitoring with confocal microscopy.…”

A microscopic physical description of electrothermal‐induced flow for control of ion current transport in microfluidics interfacing nanofluidics

“…For such, both steady and alternating electric fields as well as hybrid DC/AC voltage signals have been broadly employed to deal with particle and liquid contents in microfluidics [41][42][43][44][45][46][47][48]. For such, both steady and alternating electric fields as well as hybrid DC/AC voltage signals have been broadly employed to deal with particle and liquid contents in microfluidics [41][42][43][44][45][46][47][48].…”

“…The fast development of micro-machining technology in the last 10 years has allowed for an ease with which microelectrode structures can be patterned and then integrated into microfabricated fluidic networks. For such, both steady and alternating electric fields as well as hybrid DC/AC voltage signals have been broadly employed to deal with particle and liquid contents in microfluidics [41][42][43][44][45][46][47][48].…”