Nitric oxide (NO) electrochemical sensors - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 10

20 sec

1600

y 1.3583x 16.15

R 2 0.9985

1200

800

400

0

0 300 600 900 1200

Concentration/nM

Time (s)

FIGURE 1.3 Response of WPI's ISO-NOP007 NO sensor to increasing concentration of NO produced
by introduction of SNAP to a solution of CuCl. (Reprinted with permission from Wiley Publishing [77].)

The NO generated from the reaction is then used to calibrate the sensor. Since the
conversion of NO 2 to NO is stoichiometric (and KI and H 2 SO 4 are present in excess)
the fi nal concentration of NO generated is equal to the concentration of KNO 2 in the
solution. Hence, the concentration of NO can be easily calculated by simple dilution
factors. Experiments have demonstrated that NO generated from this reaction will per-
sist suffi ciently long enough to calibrate an NO sensor. However, since this technique
involves the use of a strong acid, which can damage the delicate selective membranes
of most NO microsensors, it is only suitable for use with Clark type stainless steel
encased NO sensors such as the ISO-NOP. Figure 1.4 illustrates the amperometric
response of a 2.0 mm ISO-NOP sensor following exposure to increasing concentrations
of NO. The sensor responds rapidly to NO and reaches steady state current within a
few seconds. The data generated from Fig. 1.4 is then used to construct a fi nal cali-
bration curve (Fig. 1.4, inset). The calibration curve illustrates the good linearity that
exists between NO concentration and the current produced by its oxidation.

1.5 CHARACTERIZATION OF NO ELECTRODES

NO sensors can be characterized in terms of sensitivity, detection limit, selectivity,
response time, stability, linear range, lifetime, reproducibility, and biocompatibility.
Sensor stability is important especially when measuring low NO concentrations. For
example, when measuring low NO concentrations it must be the case that the noise