Sensors - Hierarchical Nanostructures for Energy Devices - page 260

d n 3 r 4 n g | 4

Figure 11.7 SEM image of IrO 2 nanowires grown on a Pt microwire (a-b) and

current-time recordings (c) obtained at the 25 mm Pt wire (red) and
IrO 2 -Pt (blue) microelectrodes upon increasing the concentration of
NADH in 0.005 M PBS solution (pH 7.4) at E ¼ 0.3 V (c) (adapted from
ref. 36 with permission).

. of 2.9 m Acm 2 (mM) 1 and an LOD of 5 mM with a response time of less than

10 s at an applied potential of 0.3 V as shown in Figure 11.7(c).
In summary, the surface-to-volume ratio is greatly enhanced in hier-
archical nanostructures compared to their dense and compact counterparts.
It is believed that the improvement in sensing performance in electro-
chemical sensors exploiting hierarchical metal oxide nanostructures may be
attributed to the increased surface area on which the sensing reaction oc-
curs. Furthermore, the nano-sized feature guarantees that most of the ma-
terial experiences a change in electrical property enabling a measurable
signal at a slight change in analyte concentration, leading to higher sensi-
tivity. In addition, the hierarchical nanostructure allows facile diffusion and
mass transport for analyte molecules resulting in an immediate sensing
reaction, which means an ultra-fast response/recovery of sensors.

11.4.3 SERS Sensors
As a different type of transduction mechanism from the two previously
mentioned types of sensors, surface enhanced Raman spectroscopy or