Hardware Reference
In-Depth Information
Computer
Peripheral Circuit
Signal generator
Buffers, amplifies,
and interface with
biochip
FPGA or
single-board
microcontroller
Analog feedback
from biochip
Sensing
system
Biochip
Fig. 2.5
The schematic of the cyberphysical digital microfluidic system. Software running on the
computer and the biochip are coupled by a peripheral circuit and a field-programmable gate array
(or a single-board microcontroller)
control software to voltage signals that can be directly applied to the electrodes of
the biochip.
Figure
2.5
shows a schematic representation of the cyberphysical system.
The system consists of a computer, a peripheral circuit, a single-board microcon-
troller, and the biochip. During the execution of a bioassay, the software running on
the computer sends control signals to the biochip. The software at the same time
receives feedback from the sensing system on the biochip through the single-board
microcontroller. The control software recomputes the schedule of fluidic operations,
module placement, and droplet pathways depending on sensor feedback. This
process is referred to as reconfiguration and the key idea is to use an on-chip sensing
system for concurrent monitoring of experiments. When an error is detected by
on-chip sensors, error propagation is prevented by the immediate discarding of the
abnormal droplet. The biochip implements error-recovery operations in subsequent
operations.
The closed-loop integration in cyberphysical microfluidics can also be used to
control the completion time of bioassays. For example, when measuring the glucose
in blood, serum samples need to be well-mixed with an enzymatic reagent [
19
].
During the mixing procedure, the status of the droplet is monitored by an image
sensor. The extent to which mixing has been completed can be quantified by
analyzing and comparing images of the droplet. Therefore, the control software
will force the biochip to continue mixing until the feedback information shows
that the droplets are sufficiently well-mixed. Hence without knowing the precise
mixer execution time in advance, the mixing operation can be precisely controlled,
and the on-chip measurement results for glucose concentration can be as precise
