Biomedical Engineering Reference
In-Depth Information
is not excessive, most microfluidic modules on the array are not affected, and
they do not need not to be reconfigured. As discussed in the Section 2.3.2,
the incorporation of defect tolerance in the design flow ensures a high prob-
ability of partial reconfigurability of the modules; that is, it is very likely that
the defective biochip can be made usable via partial reconfiguration.
For each affected module, we search the array for available defect-free areas
for partial reconfiguration. This can be accomplished fast, because the search
space is restricted to the layouts in the modules' time duration. Once a mod-
ule is relocated, the algorithm updates the corresponding layout and starts
the search for the next module. Resources' binding and scheduling results are
not changed. Only the placement of defective modules is modified. Therefore,
this method is much faster compared to a complete resynthesis procedure.
In some cases, there may not be a sufficient number of defect-free cells
to carry out partial reconfiguration for some defective modules. We, there-
fore, introduce a new method called
partial resynthesis
. The key idea here is
to truncate the bioassay and carry out resynthesis only for the modules that
start later than the earliest in-use defective module. Although in the worst
case—that is, if the first in-use module is defective and cannot be relocated—
this partial resynthesis procedure may take as much time as complete resyn-
thesis, it is faster on average than the complete resynthesis procedure.
Using these two methods, the complexity of performing postmanufacture
processing for defect tolerance can be greatly reduced compared to resynthesis.
The time needed to complete a set of bioassays is also significantly decreased.
2.4 Simulation Results
In this section, we evaluate the defect-tolerant droplet-routing-aware synthe-
sis method by using it to design a biochip for a real-life protein assay.
Recently, the feasibility of performing a colorimetric protein assay on a
digital microfluidic biochip has been successfully demonstrated [38]. Based
on the Bradford reaction [9], the protocol for a generic droplet-based color-
imetric protein assay is as follows. First, a droplet of the sample, such as
serum or some other physiological fluid containing protein, is generated
and dispensed into the biochip. Buffer droplets, such as 1 M NaOH solu-
tion, are then introduced to dilute the sample to obtain a desired dilution
factor (
DF
). This on-chip dilution is performed using multiple hierarchies
of binary mixing/splitting phases, and is referred to as the interpolating
serial dilution method [9]. The mixing of a sample droplet of protein con-
centration
C
and a unit buffer droplet results in a droplet with twice the unit
volume, and concentration
C
/2. The splitting of this large droplet results in
two unit-volume droplets of concentration
C
/2 each. Continuing this step
in a recursive manner using diluted droplets as samples, an exponential
