Hardware Reference
In-Depth Information
In order to reduce the number of control pins and to control the digital
microfluidic array without significantly affecting the reconfigurability of the
biochip, a number of design of optimization techniques have been published
in the literature. These techniques can be categorized as being either bioassay-
independent [
5
,
6
] or bioassay-specific [
7
-
9
]. In bioassay-independent techniques
such as the use of a bus-phase addressing [
5
] or cross-referencing [
6
], the number
of control pins required for addressing the electrodes is independent of the target
application. For example, analogous to row/column-based addressing in memories,
cross-referencing requires m
C
n pins for an m
n array of electrodes. Bioassay-
specific pin-assignment methods lead to fewer control pins since they utilize
knowledge about the operation schedule, module placement, and droplet routing
pathways of the target bioassay.
Prior methods on bioassay-specific pin assignment suffer from three main
drawbacks. First, these techniques are not effective for the design of multi-functional
biochips, which can be reconfigured post-fabrication for different applications by
loading the appropriate control software. General purpose (application-independent)
biochips, where software can be used as a differentiator, offer the promise of
higher production volume and reduced cost. Second, fluid-handling operations on an
application-specific biochip are constrained by the pre-determined pin-assignment.
Hence it is impossible to perform post-fabrication tuning of the bioassay protocol,
schedule, and droplet routing. Finally, it is difficult to estimate the number of
control pins a priori since the number of pins is application-dependent. The
cross-referencing technique described above is application-independent; however, it
requires a special electrode structure which both top and bottom plates are divided
into discrete electrode arrays. This results in increased complexity and higher
manufacturing cost [
6
].
To overcome the above drawbacks, we propose a new method to generate pin-
assignment configurations. This method does not depend on actuation sequences of
electrodes, or does the scheduling and the routing of droplets. Any target application
can be mapped to the array without any restriction on droplet manipulation.
Therefore, the degree of freedom for droplet movement is maximized.
The main contributions of this chapter are as follows:
1. An analysis of pin-actuation conflicts and freedom of movement of a single
droplet in all feasible directions (Sect.
6.2
).
2. The derivation of necessary and sufficient conditions for control-pin sharing to
ensure high flexibility in the concurrent movement of two droplets (Sect.
6.2
).
3. An integer linear programming model for designing a pin-assignment with the
smallest number of pins (Sect.
6.3
).
4. A graph-theoretic method to formulate an acceptance test for a pin-assignment
configuration and a lower bound on the number of pins (Sect.
6.4
).
5. A heuristic algorithm that generates a pin-assignment configuration for biochips
(Sect.
6.4
).
6. Extension of the study from 1
volume droplets to 2
and even larger droplets
(Sect.
6.5
).
