Nanoparticle-based biosensors and bioassays - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 441

detection with polymerase chain reaction (PCR)-like sensitivity. Such protocols couple
the amplifi cation features of nanoparticle-biomolecule assemblies with highly sensi-
tive optical or electrochemical transduction schemes. Multi-amplifi cation protocols,
combining several nanomaterial-based amplifi cation units and processes, can also be
designed for addressing further the high sensitivity demands of modern bioassays.
There has also been a substantial interest recently in using biomolecules to construct
nanostructured architectures [1, 9] and in tailoring and functionalizing the surfaces of
nanoparticles [2, 9]. Nanoparticle-based biosensors thus offer great potential for DNA
and protein diagnostics and can have a profound impact upon bioanalytical chemistry.
The applications of nanoparticles in biosensors can be classifi ed into two categories
according to their functions: (1) nanoparticle-modifi ed transducers for bioanalytical
applications and (2) biomolecule-nanoparticle conjugates as labels for biosensing and
bioassays. We intend to review some of the major advances and milestones in biosensor
development based upon nanoparticle labels and their roles in biosensors and bioassays
for nucleic acids and proteins. Moreover, we focus on some of the key fundamental prop-
erties of certain nanoparticles that make them ideal for different biosensing applications.
14.2 WHYNANOPARTICLES?
The unique properties of nanoscale materials offer excellent prospects for design-
ing highly sensitive and selective bioassays of nucleic acids and proteins. The crea-
tion of such designer nanomaterials for specifi c biosensing and bioassay applications
greatly benefi ts from being able to vary the size, composition, and shape of the mate-
rials and hence tailor their physical and chemical properties. Owing to the tiny size
of nanomaterials, their properties are strongly infl uenced by the binding of target bio-
molecules. Nanoparticles of different compositions and dimensions have been widely
used in recent years as versatile and sensitive tracers for the electronic, optical, and
microgravimetric transduction of different biomolecular recognition events [4-8]. The
enormous signal enhancement associated with using nanoparticle amplifying labels
and with forming nanoparticle-biomolecule assemblies provides the basis for ultrasen-
sitive optical and electrical detection with PCR-like sensitivity. Such protocols couple
the amplifi cation features of nanoparticle-biomolecule assemblies with highly sensi-
tive optical or electrochemical transduction schemes. Multi-amplifi cation protocols,
combining several nanomaterial-based amplifi cation units and processes, can also be
designed for addressing further the high sensitivity demands of modern bioassays. The
unique catalytic properties of metal nanoparticles stimulate their enlargement by the
same metal or another one to offer substantial signal amplifi cation. It is possible also
to dramatically increase the number of tags per binding event (and achieve an enor-
mous signal amplifi cation) by encapsulating numerous signal-generating molecules
within a nanoparticle host. These nanomaterial-based biosensing and bioassays can be
combined with additional amplifi cation processes, such as surface preconcentration or
enzymatic recycling. The following sections discuss nanoparticle labels for ultrasensi-
tive optical and electronic biosensing, and bioassays.