Hardware Reference
In-Depth Information
a
b
c
Electrode
with defect
Original
transportation path
Adjusted
transportation path
R
1
R
2
D
1
D
2
M
1
Mixer assigned for
M
1
Fig. 5.5
(
a
) Sequencing graph for the dispensing and mixing of two droplets; (
b
) placement of the
output port of reservoirs and the mixer; (
c
) an example of defect tolerance by droplet rerouting
of electrodes [
7
,
8
]. There is no pre-assigned specific region for mixer modules;
all the mixing/splitting operations are performed on the electrodes lying between
the output ports of reservoirs. Let D
1
and D
2
denote two dispensing operations
from reservoirs R
1
and R
2
respectively, and let M
1
represent a mixing operation
between these two droplets (Fig.
5.5
a). Figure
5.5
b shows a possible placement of
these modules, in which the droplets dispensed from R
1
and R
2
are mixed on the
electrode array between these two reservoirs.
By placing the output of reservoirs on the circular electrode path, the defect
tolerance of PCR biochips can be enhanced. An example is shown in Fig.
5.5
c.
Two droplets are scheduled to be mixed together, and their original transportation
paths are indicated by the arrows. When a defect is present on the layout, the
transportation paths of these two droplets are dynamically adjusted. Therefore, using
an alternative droplet transportation path, the PCR biochip can execute bioassays
despite the presence of the defect.
5.4.2
Droplet Routing on Low-Cost PCR Biochip
In Sect.
5.3.3
, when determining the placement of devices, all the reservoirs are
considered as indistinguishable devices. However, in order to execute a given
bioassay on the PCR biochip, we have to allocate reservoirs for each sample/reagent
used in the bioassay.
When multiple operations need to be concurrently performed on a low-cost
biochip with “electrode ring” structure, the routing paths of droplets may have
conflicts. An example is shown in Fig.
5.6
. Here we assume that reagents x
1
to x
7
shown in Fig.
3.10
are stored in reservoirs R
1
to R
2
.
As defined by the sequencing graph (Fig.
3.10
), the droplets dispensed from
reservoirs R
1
and R
4
need to be mixed together in operation M
5
, and the droplets
dispensed from R
3
and R
5
need to be mixed together in operation M
3
. We assume
that the positions of outputs for R
1
, R
3
, R
4
,andR
5
are placed like Fig.
5.6
.Inorder
to perform mixing operation M
3
and M
5
, the droplets dispensed from R
1
, R
3
, R
4
,
and R
5
need to be transported in the directions indicated by the arrows in Fig.
5.6
.
It is easy to observe that in order to avoid the head-on collisions, these four droplets
cannot be transported on the biochip concurrently. Hence the mixing operations M
3
and M
5
cannot be executed in parallel.
