Programmable Hybrid Integrated Circuit/Microfluidic Chips - Point-of-Care Diagnostics on a Chip - page 23

Cell inlet

Reagent
inlets

Microfluidic chamber

Droplets

Droplet makers

Integrated circuit

∼ 5 × 5 mm

Fig. 2.1 An illustration of a hybrid integrated circuit/microfluidic chip for point-of-care diagnos-
tics. The device contains an integrated circuit with a microfluidic chamber built on top. Cells and
reagents enter through the inlets. Single cells and droplets are pinched off into the microfluidic
chamber where they are positioned and analyzed

used to release cell contents, merge droplets, and heat the chip. All make use of
alternating electric fields in different frequency bandwidths.
Dielectrophoresis (DEP) is a phenomenon where dielectric objects are attracted
to electric field maxima. The object's polarizability relative to the surrounding
medium determines the strength of DEP. It comes in two flavors, positive DEP
and negative DEP, as seen in Fig. 2.2 . With positive DEP, a dielectric particle is
more polarizable than the surrounding medium and is attracted to the electric field
maxima . This is shown with the upper particle of Fig. 2.2 . In negative DEP, seen at
the bottom of Fig. 2.2 , the particle is less polarizable than the surrounding medium
and is pushed away from the electric field maximum. This is analogous to a helium-
filled balloon. Even though gravity is pulling it down, it floats upward because it is
less dense than the surrounding air.
The force generated by dielectrophoresis is described by the following equa-
tions [ 19 ]: