Low-Cost Microdevices for Point-of-Care Testing - Point-of-Care Diagnostics on a Chip - page 6

techniques (chemical, electrical, or magnetic) [ 22 ]. Several novel size-based separa-
tion methods force a stream of cells through a series of channels by hydrodynamic
flow switching, electrokinetic flow switching, dielectrophoresis, electrowetting-
assisted flow switching, or valves [ 5 ] which provide predictable and reproducible
cell movement [ 22 ]. These methods do not employ the use of any proteins or
biologies to achieve cell separation, hence, these size-based devices would have
longer shelf lives. Affinity-based methods include the specific capture of cells
using antibodies such as with magnetic beads coated with antibodies, which is
a common laboratory protocol and can be miniaturized easily. Another affinity-
based method makes use of dielectrophoresis. This method makes use of the
differential response of cells to electric fields due to their density, physiological,
and metabolic states. Other approaches involve lysing the undesired cells, leaving
behind the desired cells in the reaction chamber [ 23 ]. This technique can reduce
the processing time and therefore avoid cell damage from prolonged contact with
lysis agents and centrifugation [ 22 ]. These approaches are easily implemented
on microfluidic devices and usually followed by downstream analysis such as
fluorescence microscopy or proteomics/genomics analysis following the lysing of
the captured cells [ 24 ].

1.3.3 Nucleic Acids

Clinical diagnoses can be made based on the analysis of DNA or RNA sequences.
Nucleic acid detection and analysis can identify the type of infection or pathogen
and diseases. It can be used in prenatal diagnosis of inherited disorders, clinical dis-
ease diagnosis (genetic disease, infection, disease staging, drug resistance mutation,
and pathogen presence/abundance), and forensic investigations. Nucleic acid testing
(NAT) offers detection that is highly sensitive (due to amplification) and specific
(due to specific base pairing of complementary nucleotides). NAT also reduces the
window period between infection and detectability of disease. Currently available
clinical tests mostly target infectious diseases, for instance, HIV (diagnosis and viral
load monitoring), H1N1 influenza, tuberculosis, and group B streptococcal disease.
These available systems are mainly used in hospitals and centralized laboratories
with complex operation steps and high-cost instruments [ 25 ]. In order to achieve
NAT for POC diagnosis, fully integrated system is preferable; for instance, to avoid
contamination issues, reduce worker steps, and deliver rapid results.

1.3.4 Small Molecules

Analyzing electrolytes from body fluids is used to monitor health parameters in
disease prevention. The ranges of electrolytes (Na C ,K C ,Cl ,Ca 2 C ), general

chemistries (pH, urea, glucose), blood gases (pCO 2 ,pO 2 /, and hematology