Hardware Reference
In-Depth Information
Control electrode group (CEG)
: An electrode on which the droplet rests at
any given time and all other electrodes that have direct contact with the droplet are
defined as the elements of the control electrode group (CEG).
For a 1
droplet, its CEG includes the central electrode on which the droplet
rests and all the non-diagonally adjacent electrodes, see Fig.
6.1
a. Most bioassays
executed on biochips only include the transportation of 1
droplets, hence we only
discuss the case of 1
droplets on the biochip in the following sections (Sect.
6.2.2
through Sect.
6.4
). The pin-assignment problem associated with biochips that have
larger droplets on them is discussed in Sect.
6.5
.
Control pin group (CPG)
: All pins that are connected to the electrodes in the
CEG are defined as the elements of the control pin group (CPG).
When multiple fluid-handling operations are performed on a biochip with a
given pin-assignment configuration, pin-actuation conflicts must be considered. An
example is shown in Fig.
6.1
b, where droplets D
1
and D
2
are on the array, and they
are scheduled to move concurrently in the directions of the arrows. The groups of
control pins for D
1
and D
2
are {A, B, H} and {A, C, D, H}, respectively. Note that
Pin A and Pin H are common (shared) control pins for droplets D
1
and D
2
.Inorder
to move D
1
in the designated direction, the voltages applied to A, B, H should be
set as “Low”, “Low”, and “High”, respectively. Similarly, in order to move droplet
D
2
, the voltages of A, C, D, H should be set as “High”, “Low”, “Low”, and “Low”,
respectively. Thus, the movement of D
1
requires the application of “High” voltage
on Pin H, while the movement of D
2
requires the application of “Low” voltage on
Pin H. The movements of D
1
and D
2
cannot be implemented concurrently since it is
impossible to apply these different voltages to Pin H at the same time. This problem
is referred to as “conflict in pin-actuation signals”.
6.2.2
Control-Pin Sharing and Concurrent Movement
of Droplets
To analyze pin-actuation conflicts, we consider an electrode array with any arbitrary
pin-assignment configuration. Assume that Droplet 1 and Droplet 2 are on two
arbitrarily chosen electrodes in the array and their control electrode groups are
written as CEG
1
and CEG
2
, respectively, and these control electrode groups have
no overlap with each other. The central electrodes of CEG
1
and CEG
2
are written
as E
1C
and E
2C
, respectively. Note that any pin-actuation conflict involving more
than two droplets can be studied as a two-droplet problem by examining all possible
pairs of droplets.
Without loss of generality, we first assume that two electrodes E
11
and E
12
in
CEG
1
share one pin (Pin A). Then we have the following scenarios, which are
exhaustively enumerated by Cases (1.a)
(1.c):
