Dielectrophoretic Characterization and Continuous Separation of Cells in a PDMS Microfluidic Device with Sidewall Conducting PDMS Composite Electrodes - Bioanalysis Advanced Materials Methods and Devices - page 170

three layers are wall, membrane, and cytoplasm [ 27 ]. The CM factor is then
given by

e cell e m
e cell þ

K ðÞ¼ (11.3)

2 e m

where e cell is the effective complex permittivity of the cell. Using the smeared-out
sphere approach [ 28 ], one can obtain the effective complex permittivity of the cell
as

2
4

3
5

r 2 3

2 e 23 e 1
e 23 þ 2 e 1

r 1

þ

e cell ¼ e 1 (11.4)

r r 2 3

e 23 e 1
e 23 þ 2 e 1

and

2
4

3
5

r 3 3

2 e 3 e 2
e 3 þ 2 e 2

r 2

þ

e 23 ¼ e 2 (11.5)

r 3 3

e 3 e 2
e 3 þ

r 2

2 e 2

where e 1 , e 2 , e 3 , r 1 , r 2 , and r 3 are the complex permittivities and radii of (1) yeast cells'
wall, cytoplasm, and nucleus or (2) bacterial cells' wall, membrane, and cytoplasm,
respectively.

11.3 PDMS Microfluidic Device with Sidewall Conducting
PDMS Composite Electrodes

Conducting PDMS composites were synthesized by adding 1 m m silver (Ag)
particles into PDMS gel and using them as sidewall DEP electrodes in a PDMS-
based micro flow device, as shown in Fig. 11.2a . The device fabrication processes
were elaborated in detail in our previous work [ 22 ]. The device has a 200

m wide

m

and 1,400 m long separation channel with four branch channels connected to inlets

A and B and outlets C and D. The branch channels A, B, C, and D are 100, 115, 50,
and 170

m

m wide, respectively. The depth of all channels is 40 m. Four 100 m

m m m

wide AgPDMS electrodes with 100 m separating gaps apart were embedded along

m

a sidewall of the separation channel.
The following key functions of such a device have been demonstrated: (1) DEP
characterization of cells in stagnant flow, (2) continuous-flow separation of cells
from latex particles by polarizability, and (3) continuous-flow separation of
microparticles by size. The DEP characterization of yeast and bacterial cells was