Nitric oxide (NO) electrochemical sensors - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 4

typically prefer to use the two-electrode amperometric technique. Since the amperomet-
ric method is so widely used the discussion below will focus on this technique.

1.3 FABRICATION OF ELECTRODES FOR NO
DETERMINATION

1.3.1 Clark type NO electrodes
The fi rst described electrochemical NO sensor was based on a classical Clark electrode
design, where NO was directly oxidized on the working electrode surface [25]. The
NO sensor was composed of a fi ne platinum wire and a separate silver wire, which
were then inserted into a glass micropipette. The micropipette was then fi lled with
30 mM NaCl and 0.3 mM HCl and sealed at the tip with a chloroprene rubber mem-
brane. The platinum (working) electrode was positioned close to the surface of the
membrane. The silver wire was then used as the reference/counter electrode. Although
such electrodes could be used to measure NO, their inherent low sensitivity, narrow
linear concentration measurement range and fragility rendered them unsuitable for
most research applications. In 1992, utilizing the Clark type design, WPI produced the
fi rst commercial electrochemical NO sensor (ISO-NOP) for use with their NO detec-
tion meter (ISO-NO). The ISO-NOP sensor consisted of a platinum wire disk working
electrode and an Ag/AgCl reference electrode. Both electrodes were encased within a
protective Faraday-shielded stainless steel sleeve. The tip of the sleeve was covered with
a NO-selective membrane and the sleeve itself contained an electrolyte. The rugged
design of this sensor made it extremely convenient in many research applications and
the sensor became widely used and established in numerous NO measurement research
applications. The basic design of this type of NO sensor is illustrated in Fig. 1.1 [26].

Stainless steel
sleeve Gas permeable

membrane

Locking cap

Probe
handle

Combination
working/counter
electrode
FIGURE 1.1

Connection
to meter

Illustration of WPI's ISO-NOP NO sensor. (Reprinted with permission from Frontiers in

Bioscience [26].)