Low-Cost Microdevices for Point-of-Care Testing - Point-of-Care Diagnostics on a Chip - page 11

using electrodes integrated on-chip [ 55 ]. This is the underlying technology behind
the Daktari CD4 system, a POC microdevice developed by Daktari Diagnostics
that is portable, handheld, and does not require complex sample processing [ 24 ]
(Fig. 1.4 b). Another method, being commercialized by LabNow, uses semiconduc-
tor quantum dots to label captured CD4 cells, and an automated software is then
used to analyze the fluorescent images [ 56 ]. An interesting use of microfluidics to
create POC microdevices for cell-based assays is the integration of commercially
available fiber optics with the microdevices so as to miniaturize the whole system
by reducing any required optical and mechanical hardware [ 57 ]. Finally, the Pima
CD4 test is being tested in the developing world [ 58 ].
We have utilized ultrasensitive chemiluminescence for detection of CD4 cells

on a microfluidic platform [ 59 ]. Compared to other optical-based LOC approaches
for CD4 counting, this method used an instrument that requires no external light
source and no image processing to produce a digitally displayed result only seconds
after running the test.

C

1.4.3 Nucleic Acid Amplification Testing

In order to perform nucleic acid testing on a microfluidic chip, the main function-
alities that have to be integrated on-chip include sample preparation, nucleic acid
amplification, and the detection of the amplified product. While these steps can be
easily integrated together and performed in a general laboratory, miniaturization of
such disparate processes onto a single microfluidic chip is still a topic of intense
research [ 60 - 62 ]. A fully integrated system could avoid contamination, reduce
worker steps, and deliver rapid results. However, most of the devices that have been
reported are single-function and require separate modules for detection and analysis
due to the challenges involved in combining and miniaturizing these functionalities
into a cost-effective, simple, and robust platform which these processes require
much effort and time [ 25 , 60 ].

1.4.3.1 Sample Preparation

After biological samples are collected, cell isolation and lysis followed by nucleic
acid extraction, purification, and preconcentration may be performed [ 63 ]. This
“sample processing” or “sample preparation” step has been less developed than
other assay steps because of its intrinsic complexity. Moreover, contamination
and inhibitors for subsequent amplification steps, and nucleic acid degradation are
also critical and influence diagnostic testing as these factors impede quantitative
assessment of the analyte in question, leading to misinterpretation of results
[ 62 , 64 ]. Therefore, sample preparation tends to be performed off-chip (using
laboratory equipment such as centrifuge), while amplification and detection can be
accomplished in microfluidic systems [ 65 ]. Nonetheless, efforts have been made