Biomedical Engineering Reference
In-Depth Information
concurrently in a direct-addressing-based chip. These advantages are quan-
titatively evaluated using a real chip example in Subsection 3.3.4.
3.3.3 broadcast Addressing for Multifunctional biochips
Broadcast addressing can also be applied to multifunctional biochips, that is,
biochips targeting the execution of a set of (multiple) predetermined bioas-
says. For each target bioassay, droplet routing and schedule information are
collected, and activation sequences are calculated. Next, for each electrode, we
merge the activation sequences from the different assays and obtain a collec-
tive activation sequence. Note that the compatibility of activation sequences
is independent of the ordering of the sequences. Therefore, the merging of
activation sequences can be carried out in any arbitrarily chosen order.
Once the collective activation sequences are derived, the same steps as
described in Subsection 3.3.2 are carried out to derive the electrode parti-
tions and the wiring (connection of input pins to electrodes) plan. Note
that the longer the activation sequences, the more specified the entries
(i.e., “1” and “0” exist), and the less compatibility we observe. Therefore,
multifunctionality may necessitate a larger number of input control pins for
the proposed broadcast-addressing method. This trade-off is evaluated in
the next section.
3.3.4 experimental results
In this section, we evaluate the proposed broadcast-addressing method by
applying it to pin-constrained design of biochips for a multiplexed immuno-
assay, a representative protein assay, and the polymerase chain reaction
(PCR) procedure.
Each assay is first mapped to a 15 × 15 electrode array controlled using the
direct-addressing scheme. Next, the proposed broadcast-addressing method
is used to reduce the number of control pins.
3.3.4.1 Multiplexed Assay
We first map the multiplexed biochemical assay described in Subsection 3.1.4.
Figure 3.34 shows the flowchart for the multiplexed assays in the form of a
sequencing graph. For each sample or reagent, two droplets are dispensed
into the array. Four pairs of droplets, that is, {
S
1
,
R
1
}, {
S
1
,
R
2
}, {
S
2
,
R
1
}, and
{
S
2
,
R
2
}, are routed together in sequence for the mixing operation. Mixed
droplets are finally routed to the detection site for analysis.
As discussed in Subsection 3.1.4, the multiplexed bioassays were mapped
to a digital microfluidic platform containing a 15 × 15 array, as shown in
Figure 3.11. A depiction of the droplet pathways for multiplexed glucose and
lactase assays is given in Figure 3.11.
