Nitric oxide (NO) electrochemical sensors - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 7

Ag/AgCI

WPI
membrane

Sensing
element

100 nm

≈ 150 µ m

FIGURE 1.2 Illustration of WPI's ISO-NOPNM 100 nm combination NO nanosensor. (Reprinted with
permission from Elsevier Publishing [45].)

sensor was constructed using a 7 m carbon fi ber that was etched with an Ar ion beam

to result in fi bers with diameters in the 100 nm range. These 100 nm fi bers were then
used to construct combination electrodes, as described above. These sensors are capa-
ble of making NO measurements on the cellular level. Later in 2000, our group devel-
oped a unique “microchip” combination sensor [46]. This sensor is quite unique in its
design but its principle of operation is the same as for all the other combination elec-
trodes presented in this section. Briefl y, a 5000 Å thick carbon fi lm was deposited on
an Si wafer by RF sputtering. This carbon layer was then covered with a resist layer.
A number of 2

µ

µ m diameter carbon electrodes were then exposed by a dry etching

process in a 50 m

away from its nearest neighbor. An Ag/AgCl reference electrode and a Pt counter elec-
trode were added to the wafer surface. The surface was then modifi ed with WPI's pro-
prietary gas permeable, NO-selective membrane and made ready for use. The resulting
sensor (ISO-NOP-MC) exhibited an extremely low NO detection limit on the order
of 300 pM, great selectivity against ascorbic acid, nitrite and dopamine and a superior
response time.

50 array on the wafer surface, where each carbon electrode is 20 µ

1.3.4 Other NO electrodes
Various other types of carbon fi ber NO sensors, which utilize a variety of different
coatings, have been described. Coatings used for these sensors include: conducting
and non-conducting polymers [47-51]; multiple membranes [52, 53]; ruthenium [54];
iridium and palladium [55]; heated-denatured cytochrome c [56]; Nafi on-Co (II)-1,10-
phenanthroline[57]; ferrioxamine [58]; a microcoaxial microelectrode was reported
for in vivo nitric oxide measurement [59]; siloxane polymer [60]; Nafi on and cellulose
[61]; Hb/phosphatidylcholine fi lms [62]; hemoglobin-DNA fi lm [63] and ionic poly-
mers; and

α -cyclodextrin [64]. Recently, Mizutani's group reported the coating of a

10 m Pt disc electrode with a cross-linked sol-gel Langmuir-Blodgett fi lm of siloxane

polymer to render the electrode permselective for NO [51]. Schoenfi sch's group
recently reported the addition of a sol-gel fi lm to a Pt electrode for NO detection [65].
Meyerhoff's group described an improved planar amperometric NO sensor based on a

µ