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Real-time pulsatile voltage signals
Heart rate at 200 beats/minute
0.95
Blood flow
0.949
4 mm
0.948
2 cm
MEMS sensor
0.947
Catheter
0.946
0.945
Aorta
0.944
0
2
4
6
8
10
12
(a)
Time (second)
(b)
Figure 16.16. In vivo testing. (a) Catheter-based polymer sensor in the thoracic
aorta of NZW rabbit. Contrast dye was injected to delineate the diameter of the
aorta in relation to that of the catheter. (b) Voltage signal output (v) was
detected by the sensor over time. The respiratory rate of the rabbit was at
30/minutes. The peaks and troughs reflect systoles and diastoles.
oxidative modification of circulating LDL. The MEMS LC as a lab-on-a-chip
platform minimizes sample volume and patient discomfort, thus, providing an
efficacious venue to detect clinical markers such as the levels of circulating
oxidized LDL for early diagnosis of unstable angina and prevention of acute
coronary syndrome.
Chromatography has made the separation of molecules possible in a fast and
efficient manner. Protein molecules are separated according to their physical
properties such as their size, shape, charge, hydrophobicity, and affinity for other
molecules. High performance liquid chromatography (HPLC) enables the separa-
tion of molecules under high pressure in a stainless steel column filled with beads.
Although liquid chromatography (LC) column is normally made of capillary
tubes due to fluidics limitations, the miniaturization of the column can enhance
separation performance (Fig. 16.17). When identical separation chemistry applies,
separated peak width is independent of column internal diameter. The ''band-
width'' of peaks is more distinct for the smaller columns with smaller beads [38].
MEMS-based LC provides high pressure compatibility of the microfluidic devices
for operating HPLC [39]. The column is packed with conventional LC stationary
phase support materials such as microbeads with surface functional groups. A
self-aligned, channel-anchoring technique has been developed to increase the
pressure rating of the Parylene microfluidic devices from 30 to at least 800 psi.
MEMS-based LC also minimizes the input sample volume to less than 1 m L from
the patients.
Purified LDL samples suspended in PBS solution were obtained from human
blood plasma at the Atherosclerosis Research Unit at the University of Southern
California. When the MEMS LC column was packed with ion-exchange
 
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