Nitric oxide (NO) electrochemical sensors - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 14

of this type of NO sensor is about 50-100 nM of NO/ºC, while the temperature induced
response of a carbon fi ber NO microelectrode is less than 10nM of NO/ºC. Thus,
when measuring NO, the temperature should be carefully monitored simultaneously.
A change in pH can also induce a background current change of NO electrodes. Usually
a change of 1 pH can cause a 50-100 pA current change on Clark type NO sensors.
1.6 SELECTED APPLICATIONS OF NO ELECTRODES
Several hundred research papers have been published over the last decade describing
the amperometric detection of NO in biological systems. This is mainly due to the
fact that these type of electrochemical sensors are the only way NO can be measured
in vivo in biological systems. Because there has been such an explosion in the develop-
ment of NO microsensors, these measurements can now be made in a variety of bio-
logical tissues and organs, as well as on the cellular level without signifi cant damage to
the system. This section will point out several examples where NO microsensors were
used to determine a variety of biological effects [78].
Determinations of NO in a variety of biological systems have been made. For exam-
ple, measurement of NO has been made in eyes [79-81], gastrointestinal tract [82, 83],
brain tissue [47, 50, 84-87], kidney and kidney tubule fl uid [88-93], rat and guinea
pig isolated and intact hearts [94, 95], rat spinal cord [96], human monocyte cells
[97], human endothelial cells [98], mitochondria [99, 100], rat penis corpus caverno-
sum [101], granulocytes [102], invertebrate ganglia and immunocytes [103], choroidal
endothelial cells [104], cancer cells [105, 106], peripheral blood [107], human blood
[108], human leukocytes [109], platelets [110-112], ears [113, 114], plants [115-118],
and pteropod mollusk [119].
Levine and coworkers fi rst reported on the real-time profi ling of kidney tubular
fl uid nitric oxide concentration in vivo [89, 91]. In the 2001 publication, a modifi ed
version of a combination NO electrode (WPI, ISONOP007) was successfully used to
measure NO concentration profi les along the length of a single nephron of a rat kidney
tubular segment. Since it was shown that the electrode is sensitive to NO in the rat
tubule it was used to detect NO concentration differences in rat kidney tubules before
and after 5/6 nephrectomy. The results clearly showed that the NO concentration was
much higher in nephrectomized rats vs unnephrectomized rats.
In a recent publication, investigators used a specially customized ISO-NOP sensor to
monitor, in real time, NO production in the stomach and esophagus of human patients
[82]. In this method a patient fi rst swallowed two NO electrodes (see Fig. 1.6), which
were then withdrawn slowly at 1cm increments every 2min. The investigators were
then able to establish a profi le of NO concentration in the upper gastrointestinal tract.
Simonsen's group has performed some elegant work over the years on NO release
characteristics from rat superior mesenteric artery. Initially, Simonsen's group simul-
taneously monitored artery relaxation and NO concentration in the artery using a NO
microsensor in response to various drugs [120]. NO concentration was monitored via
an ISONOP30 electrode, purchased from WPI and inserted into the artery lumen using