Biomedical Engineering Reference
In-Depth Information
NMs open new avenues to develop various novel biosensors. These NM-based
biosensors, nanobiosensors, make use of electrochemical and optical proper-
ties of NMs. These nanobiosensors are expected to demonstrate improved limit
of detection, sensitivity, ease of use, reproducibility, low cost, portability, and
selectivity.
3-5
The size of NMs that is comparable to the dimensions of biomo-
lecular probes and to biological analytes makes them excellent components of
biosensors.
6-12
In this chapter, nanobiosensors that involve NMs for detection of various
biomolecules that are useful in the clinical diagnosis of different types of dis-
eases will be discussed. These diseases may be genetic, metabolic, or caused by
infectious disease-causing agents. Various types of NM-based nanobiosensors
will be presented and a few protocols will be discussed.
4.2 NANOBIOSENSORS UNIQUE PROPERTIES
The booming nanotechnology industry has revived interest in the development
of novel sensing systems as well as the enhancement of the performance of bio-
analytical assays.
13-15
Recent advances in material science and synthetic chem-
istry have made it possible to produce high-quality nanomaterials in the form
of nanoparticles (NPs; nanotubes, nanorods, nanospheres, nanowires), nanoar-
rays, and their composites.
16,17
These NMs have been used for the develop-
ment of biosensors
6,7,10-12,14,18-20
because of their significant advantages over
microscale and bulk materials that include (a) size-tunable properties, (b) large
surface-volume ratio, (c) shape-dependent properties, (d) lower energy con-
sumption, (e) miniaturized biosensors, and (f) low cost.
Bottom-up nanotechnology approaches are offering a large series of NMs
with special interest for biosensing systems. Investigations of these materials
are gaining interest due to the size- and shape-dependent physical, chemical,
and electrochemical properties which make them extremely useful in sensing
and biosensing applications.
21
The size and composition sometimes make NMs
even more attractive than the corresponding bulk structure. A target binding
event (i.e. DNA hybridization or immunoreaction) occurring on the NP's surface
may have a significant effect on its optical (change of the light absorption/
emission) or electrochemical properties (oxidation/reduction current onto a
transducing platform) offering novel alternatives for bioanalysis. For example,
compounds consisting of metal NPs of group II-VI which are semiconductors
like CdSe, ZnSe, CdTe, etc., also called quantum dots (QDs)
22
as well as gold
nanoparticles (AuNPs) are of special interest because of their properties. QDs
are highly fluorescent and in comparison with organic dyes (such as rhodamine)
are 20 times as bright, 100 times as stable against photobleaching, and one-third
as wide in spectral line width.
23
Thus, QDs present an enormous potential for
biosensors applications for fluorescence detection. The most interesting property
of QDs for fluorescence detection is the very small number of QDs necessary to
produce a signal. Indeed, several studies have reported flickering of some speci-
mens, a phenomenon that is due to the blinking of a small number of QDs.
23,24
