Biomedical Engineering Reference
In-Depth Information
We next apply the droplet-trace-based array-partitioning method to the
multiplexed bioassay example. Initially, six partitions are created for the four
droplet traces of Reagents 1 and 2 and Samples 1 and 2, with the two traces
corresponding to the mixed samples going to Detector 1 and Detector 2.
Three more partitions are created for the three trace-overlapping regions,
respectively. Next, time-span overlap is checked for the three spatially over-
lapping partitions (Partitions 3, 4, and 5). Since there is no temporal overlap
of droplets being manipulated in both Partitions 3 and 5, only five pins are
needed for each of them. Partition 4 is recognized as a mixer; thus, only five
pins are needed for it. In the next step, time span overlap is checked for all
partition pairs. The six partitions corresponding to four droplets traces and
two detector paths merge into two partitions (Partitions 1 and 2). Finally,
the Connect-5 algorithm is applied. The partitions and the pin-assignment
results are shown in Figure 3.12.
We therefore see that array partitioning and pin assignment are effective
in reducing the input bandwidth, while maintaining the same throughput
that is obtained for a directly addressable array. Five partitions are suffi-
cient for preventing interference between multiple droplets on the array,
as shown in Figure 3.12. Since only five control pins are necessary for full
control of a single droplet within each partition, only 25 out of the possible
225 control pins are necessary, that is, only 11.11% of the total number of
electrodes. This represents a significant reduction in input bandwidth with-
out sacrificing throughput.
3.2 Cross-Referencing-Based Droplet Manipulation Method
In this section, we present an alternative implementation of pin-
constrained biochips. We present a droplet manipulation method based on
a “cross-referencing” addressing method that uses “row” and “columns”
to access electrodes [62]. By mapping the droplet movement problem to
the clique partitioning problem from graph theory, the proposed method
allows simultaneous movement of a large number of droplets on a micro-
fluidic array. This in turn facilitates high-throughput applications on a
pin-constrained biochip.
3.2.1 Cross-referencing Addressing
A pin-constrained biochip based on the cross-referencing addressing
method is first proposed in [39]. This method allows control of an N × M
grid array with only N + M control pins. The electrode rows are patterned
on both the top and bottom plates, and placed orthogonally. In order to
activate a cell on the grid array, the electrode row and column that the cell
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