Nitric oxide (NO) electrochemical sensors - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 3

subsequent years a range of highly specialized and sensitive NO electrodes have
been developed offering detection limits for NO ranging from below 1 nM up to
100 M [21]. Most recently, a unique range of high sensitivity NO sensors based

on a membrane coated activated carbon microelectrode with diameters ranging from
200

µ

m down to 100 nm have been developed by this lab. These electrodes exhibit
superior performance during NO measurement and feature a detection limit of less
than 0.1 nM NO.

µ

1.2 PRINCIPLES OF DETERMINATION OF NO BY
ELECTROCHEMICAL SENSORS

NO can be oxidized or reduced on an electrode surface. Since the reduction potential
of NO is close to that of oxygen which causes huge interference NO measurement,
therefore, usually oxidation of NO is used for measurement of NO. NO oxidation on
solid electrodes proceeds via an “EC mechanism” electrochemical reaction [22] fol-
lowed by chemical reaction [23]. First, one-electron transfer from the NO molecule to
the electrode occurred and resulted in the formation of a cation:

NO (1)
NO is immediately, irreversibly converted into nitrite in the presence of OH ,
since it is a relatively strong Lewis acid:

e

NO →

NO OH

→ HNO 2 (2)

According to equation 2, the rate of the chemical reaction increases with the
increase of pH.
Among the several electrochemical techniques that have been shown to be use-
ful for the measurement of NO, the most popular is amperometry. This technique uses
the model set forth by Clark and Lyons in 1962 for continuous gas monitoring during
cardiovascular surgery [24]. Generally, this technique involves applying a fi xed (poise)
voltage potential to a working electrode, versus a reference electrode, and monitoring
the very low redox current produced (e.g. pAs) by the oxidation of NO. This technique
has proven to be very useful for NO detection due to its fast response time, which is less
than a few seconds, and its high sensitivity. As a result it is possible to monitor changes
in NO concentration on biologically relevant time scales and concentrations, which are
typically in the nm range. A multitude of other electrochemical techniques have been
used to detect NO including differential pulse voltammetry (DPV), differential normal
pulse voltammetry (DNPV), linear scanning voltammetry (LSV), square wave voltam-
metry (SWV), and fast scan voltammetry (FSV). These methods typically employ a
classical three-electrode confi guration consisting of a working electrode, reference elec-
trode, and a counter electrode. Scanning techniques, with the exception of fast scanning
voltammetry, require approximately ten seconds for the voltammogram to be recorded,
which precludes its use in most NO research applications. Moreover, since scanning
voltammetry-based NO instrumentation is not commercially available, NO researchers