Chemistry Reference
In-Depth Information
Recent studies have demonstrated that CNTs exhibit strong electrocatalytic activity for a wide range of
compounds, such as neurotransmitters, hydrogen peroxide, ascorbic and uric acid, cytochrome c, hydrazines,
hydrogen sulfide, amino acids and deoxyribonucleic acid (DNA). Their potential applications in
electrochemical sensors and biosensors due to their high conductivity are also reported [40].
Finally, an emergent nanomaterial is
graphene
, constituted by a single-atom-thick and two-dimensional
carbon material. It has attracted great attention for being a novel alternative to carbon nanotubes in biosensing,
as it had demonstrated its capabilities in many applications. An example of its application is the glucose sensor
where the glucose or glutamate molecules were detected by the change of graphene conductance in a transistor
platform showing exceptional electronic properties [41]. Some variation in the sensing platform such as a
transistor with suspended gate modified with graphene could improve the signal and decrease the noise [42].
18.2.3
Other detection principles
Electrochemiluminescence
(ECL) is an optical and electrical phenomenon in which a material emits light
in response to an electric current or electrical field. One important application of ECL is in enzyme
biosensors based on cadmium sulfide nanocrystals (CdS NCs) in situ formed onto the surface of
multi-walled carbon nanotubes (MWCNTs). The MWCNT-CdS can react with H
2
O
2
generating strong
and stable ECL emission in neutral solution [43] (See Figure 18.3a). By following the same procedure,
(b)
(a)
h
n
h
n
h
n
ACh
Ch
H
2
O
2
Channel without stress
Deflection
ACh
E
ChO
CdS
CdS
CdS
CdS
CdS
CdS
e
-
e
-
e
-
PIGE
PIGE
Channel under stress
(c)
Gold
layer
Experimental
line
Signal
generator
Sensing layer
Phase detector
Waveguide layer
Piezoelectric substrate
Phase detector
Gold IDTs
Experimental
line
SAW
Figure 18.3
Some examples of other detection alternatives.
(a) Electroluminiscence: Schematic diagram of
the multi-wall carbon nanotubes (MWCNT): Cadmium sulfide (CdS), acetylcholine esterase (AChE), ECL
biosensor for detection of neurotransmitter acetylcholine (Ach). Adapted from [43] with permission from Wiley-
Blackwell © 2009; (b) schematic of an embedded metal-oxide semiconductor field-effect transistor (MOSFET)
cantilever system. Adapted from [46] © Annual Reviews 2009; and (c) surface acoustic wave sensor (SAW): a
sinusoidal voltage is applied to the input (input interdigitated transducer - IDT), which develops an alternating
electric field that is translated into a mechanical SAW by the piezoelectric effect. The velocity of the SAW is
affected by mass loading, fluid viscosity and temperature on the surface of the substrate. Adapted from [45]
© Expert Reviews 2009.
