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 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)
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
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