Microfluidics for Biologists Fundamentals and Applications

various new techniques. Table 2.1 represents various fabrication techniques
corresponding to the stated techniques along with their characteristics features
and problems involved with these modifications.
The characterised DEP modules have been used for various applications, includ-
ing separation, concentration etc. DEP of various nanoparticles like polystyrene
particles and polystyrenes particles mixed with Saccharomyces cerevisiae cells [ 93 ]
is carried out in asymmetric insulator traps. This kind of DEP has resulted in
separation of particles on the basis of size. It was observed that large size particles
leave the system earlier than those of the smaller size particles. This separation
scheme has been observed valid for individual particles as well as for mixture of
cells and polystyrene particles. DEP of DNAs is also carried out by various authors.

Table 2.1 Fabrication techniques for accomplishing DEP

Dielectrophoresis

technique Fabrication techniques Characteristic features Problem

Metal

electrode

DEP [ 83 ]

2D metal

electrodes

• Metal deposition
  (Sputtering)
  
  
  • Voltage requirement:
    10 s of volts
  
  
  
  

Electrode

fouling

• Polymer patterning • Volume 30 μm from
  
  
  • Etching bottom
    3D metal
    electrodes
    [ 84 ]
  
  
  
  


• Electrodeposition
  (Gold electrodes)


• Thick film photoli-
  thography (Doped Sili-
  con Electrodes [ 85 ])
  Insulator
  based
  DEP

Insulator

matrices

[ 86 ]

Channel filled with

dielectric beads or shapes

Higher

voltage

requirement

Insulator

structures

[ 87 ]

• Glass based: Symmetric repeated insu-
  lator structures of various
  shapes

✓Wet etching

• Polymer based [ 88 ]:
  ✓Injection moulding
  ✓Micromilling
  ✓Photolithography
  Contactless
  DEP [ 89 ]

Electrodes not solid but

conducting fluid

Liquid

electrode

DEP [ 90 ]

Metal patterning and

polymer

photolithography

Vertical equipotential

surface creation at side

walls

Light

induced

DEP [ 91 ]

Light excites photocon-

ductive layer and create

an electric field gradient

Carbon

electrode

DEP [ 92 ]

• Low voltage
  requirement


• Lower electrolysis of
  sample


• More chemical stability
  than metal electrodes

2 Microfluidics Overview 67