Biomedical Engineering Reference
In-Depth Information
associated with a test droplet and its “target region.” A target region for a
droplet includes the cells that are traversed by this droplet. The proposed
method can be viewed as carrying out a single-droplet scan-like test in dif-
ferent target regions in parallel; therefore, we refer to this method as the
parallel scan-like method
.
4.1.1 Off-line Test and Diagnosis
In off-line testing, test droplets are dispensed from the test droplet source
to the start electrodes of their target regions. Since we use columns/rows
as target regions, the start electrodes are located on the array boundary,
as shown in Figure 4.3. For each target region, the start electrode acts as
the test-droplet source for the underlying single-droplet scan-like method.
Therefore, we refer to start electrodes here as pseudosources. Starting from
these pseudosources, test droplets are routed in parallel (similar to a water-
fall in nature) to the electrodes at the other end of the corresponding target
regions. These endpoints are referred to as pseudosinks. Finally, the test
droplets are routed to the sink reservoir. Note that in the preceding method,
we assume that a microfluidic array has only one source and one sink
reservoir to facilitate chip packaging and reduce fabrication cost. Dispensed
from the single source, test droplets are aligned one by one and routed in
sequence, like components in an assembly line, along the periphery nodes to
their pseudosources. The reverse process is carried out when the test drop-
lets are routed from the pseudosink to the sink reservoir.
As in [28], the test outcome is read out using the capacitive sensing circuit
located at the sink reservoir. The major enhancement here is that multiple
test droplets can be detected at the sink. Instead of a single pulse, the capaci-
tive sensing circuit can detect a pulse sequence corresponding to multiple
test droplets
(see Figure 4.4)
.
Different fault patterns (i.e., groups of failing
cells) are mapped to different pulse sequences.
Sufficient spacing between droplets must always be maintained during
droplet routing [27]. Therefore, in order to avoid unintentional merging of
Te st droplets
Pseudo-sources
Source
Source
Ta rget regions
Sink
1
2
3
1
2
3
Figure 4.3
Example of target regions and pseudosources.
