Microfluidic dielectrophoretic sorter using gel vertical electrodes

Abstract

We report the development and results of a two-step method for sorting cells and small particles in a microfluidic device. This approach uses a single microfluidic channel that has (1) a microfabricated sieve which efficiently focuses particles into a thin stream, followed by (2) a dielectrophoresis (DEP) section consisting of electrodes along the channel walls for efficient continuous sorting based on dielectric properties of the particles. For our demonstration, the device was constructed of polydimethylsiloxane, bonded to a glass surface, and conductive agarose gel electrodes. Gold traces were used to make electrical connections to the conductive gel. The device had several novel features that aided performance of the sorting. These included a sieving structure that performed continuous displacement of particles into a single stream within the microfluidic channel (improving the performance of downstream DEP, and avoiding the need for additional focusing flow inlets), and DEP electrodes that were the full height of the microfluidic walls ("vertical electrodes"), allowing for improved formation and control of electric field gradients in the microfluidic device. The device was used to sort polymer particles and HeLa cells, demonstrating that this unique combination provides improved capability for continuous DEP sorting of particles in a microfluidic device. V C 2014 AIP Publishing LLC.

3-D In-Bi-Sn Electrodes for Lab-on-PCB Cell Sorting

“…The frequency and actuation used are similar to the optimal frequency and actuation parameters for a similar, previously published system [13]. A frequency of 1 MHz produces a positive DEP force in cells with intact membranes (i.e., highcytoplasmic conductivity relative to the media conductivity), but produces a small negative DEP force in cells with compromised membranes (i.e., when the media and cytoplasmic conductivity are nearly equal).…”

“…Despite the advantages of vertical electrode use for DEP separations, the fabrication can be challenging, generally requiring a series of photolithographic steps [13] and, in the case of electroplating, fine electrical current control to fabricate these 3-D structures and then to seal the device [10]. Various methods have been proposed to circumvent these difficulties such as contactless DEP and insulator-based DEP [14].…”

“…Finally, both aliquots are recombined at a 1:1 ratio in a lowconductivity DEP buffer consisting of 8.5% sucrose (wt/vol), 0.3% dextrose (wt/vol), and 0.725% Roswell Park Memorial Institute (vol/vol); final conductivity and pH are 100 μS/cm and 7.38, respectively. Low-conductivity buffer is used to enable sorting of biological cells using positive DEP, as shown previously [7], [13], [24]. The final concentration of each cell type is 1E6/ml.…”

“…In live cells, PI is unable to penetrate the cell membrane and no staining results, but dead cells' membranes are porated, granting the dye entry. Upon binding to the dead cells' exposed nucleic acids, PI fluoresces under an excitation wavelength of 561 nm [13]. Finally, both aliquots are recombined at a 1:1 ratio in a lowconductivity DEP buffer consisting of 8.5% sucrose (wt/vol), 0.3% dextrose (wt/vol), and 0.725% Roswell Park Memorial Institute (vol/vol); final conductivity and pH are 100 μS/cm and 7.38, respectively.…”

Continuous sheathless microparticle and cell patterning using CL-SSAWs (conductive liquid-based standing surface acoustic waves)

“…Therefore, electrode channels have been the most promising substitute for patterned metal electrodes in various electric microfluidic devices, including electrophoretic and dielectrophoretic applications. [18][19][20] Although channel-based threedimensional electrodes can generate a uniform electric field across the microchannel, the applicability of these techniques for microparticle manipulation can be limited because the device performance depends on the electrical properties of the microparticles and the suspending medium. On the other hand, acoustic methods manipulate target particles depending on relative physical properties (size, deformability, density, etc.)…”