Cross-scale electric manipulations of cells and droplets by frequency-modulated dielectrophoresis and electrowetting

Abstract

Two important electric forces, dielectrophoresis (DEP) and electrowetting-on-dielectric (EWOD), are demonstrated by dielectric-coated electrodes on a single chip to manipulate objects on different scales, which results in a dielectrophoretic concentrator in an EWOD-actuated droplet. By applying appropriate electric signals with different frequencies on identical electrodes, EWOD and DEP can be selectively generated on the proposed chip. At low frequencies, the applied voltage is consumed mostly in the dielectric layer and causes EWOD to pump liquid droplets on the millimetre scale. However, high frequency signals establish electric fields in the liquid and generate DEP forces to actuate cells or particles on the micrometre scale inside the droplet. For better performance of EWOD and DEP, square and strip electrodes are designed, respectively. Mammalian cells (Neuro-2a) and polystyrene beads are successfully actuated by a 2 MHz signal in a droplet by positive DEP and negative DEP, respectively. Droplet splitting is achieved by EWOD with a 1 kHz signal after moving cells or beads to one side of the droplet. Cell concentration, measured by a cell count chamber before and after experiments, increases 1.6 times from 8.6 x 10(5) cells ml(-1) to 1.4 x 10(6) cells ml(-1) with a single cycle of positive DEP attraction. By comparing the cutoff frequency of the voltage drop in the dielectric layer and the cross-over frequency of Re(fCM) of the suspended particles, we can estimate the frequency-modulated behaviors between EWOD, positive DEP, and negative DEP. A proposed weighted Re(fCM) facilitates analysis of the DEP phenomenon on dielectric-coated electrodes.

Digital Microfluidic System with Vertical Functionality

“…A major application of DµF is as a platform for biological assays and cell manipulation [3,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]. Technological advances that have enabled these applications have included improvements to automated proteomics [9,23,33], DEP-based protein and cell sorting [34][35][36], complete mammalian cell culture on-chip [37], and cell spheroid development [38].…”

Transmittance tuning by particle chain polarization in electrowetting-driven droplets

“…The presented results demonstrate cross-scale electric manipulations based on our study of digital microfluidic cell/ particle concentrator. 21 We previously reported cell/particle concentrated toward strong or weak electric field regions by dielectrophoresis ͑DEP͒ 22,23 using nonuniform electric fields. Instead of using nonuniform electric fields, here we apply uniform electric fields to polarize and drive the particles.…”

“…As analyzed by the simplified equivalent circuit of the parallel plate device, 21,26,27 in order to have efficient voltage drop across the dielectric layer, the frequency of the applied voltage should be limited below several kilohertz. The low frequency voltage essential to EWOD is demonstrated by V LF in Fig.…”

Single cell kinase signaling assay using pinched flow coupled droplet microfluidics

“…The capillary electrophoresis system was automatized to analyze $3.5 cells/min. [4][5][6][7][8][9][10] Compared with these methods, the droplet based technology is attractive [11][12][13][14][15][16][17][18][19][20][21] because of its ultra high throughput cell encapsulations ($1000 droplets/s) [22][23][24] and accurate fluidic controls. Accordingly, a wide range of droplet base single cell polymerase chain reactions (PCR) were carried out in previous studies.…”