Biomedical Engineering Reference
In-Depth Information
Fig. 1.4
HemoCue WBC System and Daktari CD4 cell counter. (
a
) Picture of the HemoCue
WBC System for total white blood cell count (Taken from www.hemocue.com with permission
from HemoCue Corporation). (
b
) Picture of the portable Daktari CD4 cell counting system that is
currently undergoing performance evaluations (Image courtesy of Daktari Diagnostics, Inc)
1.4.2
Cell-Based Assays
POC testing for cell-based diagnostics has been increasingly important in hematol-
ogy laboratory practices. It involves the numeration of specific cell types, typically
white blood cells, from whole blood for the diagnosis, monitoring, and staging
of diseases such as HIV/AIDS. A common use of microfluidics for POC cellular
analysis is to replace traditional, resource-intensive technologies such as those used
for flow cytometry and cellular biosensors. Such microfluidic methods may involve
cell (or microparticle) separation based on size [
45
] and are based on methods such
as filtration [
46
], laminar flow [
47
], dielectrophoretic force [
48
], optical gradient
force [
49
], magnetic force [
50
], and acoustic force [
51
]. Other methods are based
on antibody-specific capture of cells [
52
].
POC testing has been increasingly important in hematology practices, especially
in obtaining white cell counts. The HemoCue WBC system (HemoCue AB,
Sweden) measures total white blood cells in just 10Lofsample[
53
] and consists
of a photomicroscope, a microcuvette holder, and an LCD display (Fig.
1.4
a). It
is able to operate on batteries and has low power consumption, making it suitable
for POCT. The Chempaq analyzer is a self-contained system that uses differential
impedance to detect different types of cells to return full blood counts within
3min [
54
].
Due to the pressing need for a point-of-care CD4 T-lymphocyte enumeration
method for the management of HIV/AIDS epidemic, especially in underserved
regions, much work has been done to develop a microfluidic approach. A lysate
impedance measurement method has been developed where the specific cells of
interest are captured and lysed, and the resulting change in impedance is measured
