Manipulation and characterization of red blood cells with alternating current fields in microdevices

Abstract

The motion of a suspension of erythrocytes (red blood cells, RBCs) in response to a high-frequency alternating current (AC) field in a microfluidic device is examined with parallel and orthogonal electrode configurations to delineate the various fundamental driving forces. Cell repulsion from the platinum electrodes due to electrode polarization interacting with cell membrane polarizations is observed to be the strongest force acting on the particles in the first few seconds of field application. We exploit this strong repulsion to concentrate the bioparticles between the microelectrodes to amplify multiparticle aggregation phenomenon and dielectrophoretic (DEP) manipulation in a small and well-characterized region within the microfluidic device. Secondary motions include RBC pearl chain formation along field lines due to particle polarization followed by classical dielectrophoretic motion of the chains across field lines to regions of weaker field. These are driven by far weaker dipole-dipole and field-dipole interactions than the preliminary electrode repulsions. RBC chain length and total aggregated cells are presented for a variety of AC frequencies and are significantly amplified by the electrode repulsion. Motion of particles away from the polarized electrode is found to be species- and age-sensitive and can stand by itself as a promising identification and separation mechanism. In a 0.1 S/m isotonic phosphate buffer saline medium, we observe the largest cell mobilities at an optimal frequency of approximately 1 MHz, corresponding to the inverse diffusion time across the double layer of the cell and across the electrode's polarized layer. This suggests that the dielectric responses of both particles and electrodes in the low MHz frequency range are mostly determined by normal electromigration of ions from the bulk to their interfaces. Sensitivity to RBC age and species suggests that the surface proteins and membrane ion channels can affect the capacitance of the interface to accommodate the ions from the bulk. Such surface ion accumulation and polarization mechanisms are different from the classical dielectric theories. The resonant frequency of electrode polarization at around 1 MHz falls between positive and negative dielectrophoretic resonant frequency peaks - suggesting that the double-layer polarization mechanism is a distinct and potentially important bioparticle manipulation tool.

Review Article—Dielectrophoresis: Status of the theory, technology, and applications

“…This problem has been reduced in a DEP microfluidic device in which 100 m diameter platinum wires, in a pin-plate configuration, span the entire depth of the DEP chamber and are energized with 15 Vpp voltages. 71 The fact that the parameter ͑E · ٌ͒E in Eq. ͑7͒ has units of V 2 m −3 provided the clue that, by miniaturizing the electrodes, DEP measurements could be improved, in terms of speed and the avoidance of thermal and electrolysis effects, using much smaller applied voltages.…”

A capillary dielectrophoretic chip for real-time blood cell separation from a drop of whole blood

“…Pearl chaining of red blood cells were formed along the AC field line due to particle polarization based on the previous studies. 45 Although pearl chaining of red blood cells were formed within seconds in the separation zone, which soon were dispersed and separated into the low electric field zone due to nDEP domination.…”

Designing a nano-interface in a microfluidic chip to probe living cells: Challenges and perspectives

“…Nonlinear electrophoresis circumvents the formation of ion gradients in the medium by alternating the orientation of the electric field at a rate that is greater than the reaction times at the electrodes (Ͼ10 kHz) (40). These alternating current fields are either uniform (parallel field lines) or nonuniform (curved, unequally spaced field lines) and allow for whole cells to be selectively manipulated based on conductivity and subsequent polarization of the cell and its membrane (41,42).…”