Biomedical Engineering Reference
In-Depth Information
Electrochemical detection methods are popular for quantitative analysis of blood
parameters [ 77 ]. The iSTAT device from Abbott Laboratories (Abbott Park, IL,
USA), which uses microfabricated thin-film electrodes to measure levels of elec-
trolytes, general chemistries, blood gases, and hematocrit, has an electrochemical
detection system which includes amperometry, voltammetry, and conductance,
depending on the analyte [ 5 ]. The iSTAT device uses disposable cartridges for
performing sample preconcentration and separation, and a portable instrument
for electrochemical detection [ 12 ]. Conventional glucose meters are also based
on electrochemical assays [ 77 , 78 ]. However, devices that feature electrochemical
detection have several disadvantages with regard to POC testing. Electrodes are
required to be integrated onto the disposable, increasing per-test costs; detecting
hundreds of simultaneous reactions at once is difficult to achieve with electrodes;
and incompatibilities exist between capabilities of existing microelectronics fabri-
cation facilities and specifications of sensors, with regard to dimensions, materials,
passivation layer, and others [ 5 , 77 ]. With the increasing availability of cheap, high-
quality optoelectronic components such as CCDs and laser diodes, optical detection
may be more suited for POC testing of blood chemistry parameters. For situations
where semiquantitative analysis is sufficient, paper-based microfluidic devices may
be attractive [ 78 , 79 ].
1.4.5
Hematology
The most widely tested hematology parameters in point-of-care situations are
hemoglobin and hematocrit (for anemia, red blood cell transfusion therapy, and
acute hemodilution during surgery), and coagulation/clotting time (for cardiac
surgical and catheterization procedures) [ 80 ]. Sphere Medical (Cambridge, United
Kingdom) has developed a microanalyzer technology with silicon chips for signal
processing and sensing based on three transducer technologies: potentiometry,
amperometry, and conductimetry. Different membranes and receptor materials are
used to cover the sensors to detect specific analytes. The technology can measure
hematocrit and small molecule analytes.
Activated clotting time, activated partial thromboplastin time, and prothrombin
time are monitored for high-dose heparin therapy (a blood clot inhibitor) and
blood-thinning medications (such as warfarin). Companies with POC instruments
for monitoring coagulation include Medtronic (Minneapolis, MN, USA), Abbott
Diagnostics (Abbott Park, IL, USA), Roche Diagnostics (Indianapolis, IN, USA),
and Hemosense (owned by Alere) (Waltham, MA, USA).
1.5
Outlook
Over the last decade, microdevices for point-of-care testing have generated great
progress in both academic and industrial laboratories. Several challenges remain
before these technologies can be translated to be effective POC tests, including
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