Hardware Reference
In-Depth Information
Fig. 1.5
Setup of droplet
visualization system: two
CCD cameras are fixed on the
biochip platform to get top
view and side view of
droplets [
26
]
CCD Camera
XYZ
Positioner
Droplet
Fig. 1.6
Mixing of fluorescein and KCl droplets [
27
]
1.1.3.2
Capacitive Sensors
The upper and lower electrodes in each unit cell of the microfluidic biochip form a
parallel-plate capacitor. The capacitance associated with the pair of electrodes can
be measured by the resistor-capacitor (RC) circuit shown in Fig.
1.7
[
28
]. Since the
droplet's permittivity is different from that of the filler medium of the biochip, the
capacitance of a unit cell will change when a droplet is moved towards it. In this
way, the movement of a droplet can be monitored.
Capacitive sensors can also be used to detect whether the droplet is contaminated
by particles. As shown in Fig.
1.8
[
29
], a droplet may be contaminated by dust
