Introduction - Hardware/Software Co-Design and Optimization for Cyberphysical Integration in Digital Microfluidic Biochips - page 8

Fig. 1.3 Several generations of fabricated and packaged digital microfluidic biochips [ 21 ]

Figure 1.3 [ 21 ] shows several generations of fabricated and packaged digital
microfluidic biochips. The electrodes in these devices are fabricated on printed
circuit boards (PCBs). Similar biochips have been fabricated on glass and silicon,
and demonstrated for a wide variety of biomedical assays, including on-chip
chemistry for DNA sequencing [ 1 ], multiplexed real-time polymerase chain reaction
[ 22 ], protein crystallization for drug discovery [ 23 ], and cytotoxicity assays [ 24 ].
The process of fabricating microfluidic biochips on silicon wafers is described
in [ 25 ]. In this process, the wafer is coated with a layer of SiO 2 , which is used as
the bulk insulation layer. Figure 1.4 a shows electrodes fabricated on a silicon wafer.
Two metal layers are deposited to form the interconnects. A cross-sectional view of
a silicon-based biochip is shown in Fig. 1.4 b[ 25 ].
The silicon-based microfluidic biochip in [ 25 ] can be used to generate and
manipulate droplets that have volumes of 300 pl, and the actuation voltages required
for dispensing and transporting a droplet are 11.4 V and 7.2 V, respectively.

1.1.3 Sensing Systems

The development of integrated biomedical analysis systems requires miniaturized,
integrated, and robust sensing systems. Sensing systems on biochips can be
recognized into three categories based on their working principle, i.e., droplet
visualization monitoring system, on-chip capacitative sensor, and on-chip photode-
tector. More details about each of these systems are provided below.