Hardware Reference
In-Depth Information
Fig. 1.7
Circuit for
capacitive sensing of
biochip [
28
]
Fig. 1.8
A droplet with
particle contamination [
29
]
particles or another small droplet that contains a different reagent. A contaminating
particle changes the capacitance of the droplet. This difference can be detected and
monitored by capacitive sensors. The minimum radius of a contaminating particle
that can be detected by the capacitive sensor has been derived using theoretical
calculations in [
29
].
By using the experimental setup shown in Fig.
1.9
[
30
], the relationship between
the volume of droplet and the capacitance of a unit cell can be measured. During the
measurement procedure, liquid is injected from the top of an electrode of the digital
microfluidic biochip via a hole using a syringe pump. The flow rate of injected liquid
is set as a constant, hence the volume of the droplet can be calculated based on the
pumping time. By repeating the measurement procedures, the relationship about
the volume of the droplet and the capacitance of electrode pair can be determined.
Using this relationship and calibrated curve, the precise location and volume of
each droplet can be estimated based on the feedback from capacitive sensors during
bioassay execution.
1.1.3.3
Photodetectors and Optical Sensing
Photodetectors are widely used for sensing because they convert the intensity of
fluorescence of droplet on chip into electrical signals [
31
-
33
]. These electrical
signals can subsequently be applied as the feedback to the control software of the
biochip.
