Optical Waveguide-Based Biosensors Using Noble Metal Nanoparticles - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 78

of biological warfare agents 7 is an extremely signiicant problem.
For many biosensing techniques, the analyte must wear an
electrochemical or spectroscopic signature. Unfortunately, a lot of
biochemical species do not wear such signatures. Hence, labeling
of the analyte is then required. However, the labeling procedures
are often tedious and sometimes may lead to errors. Alternatively,
a second recognition biomolecule (e.g., use of second antibody in
enzyme-linked immunosorbent assay, ELISA) which can produce
an electrochemical or spectroscopic signature will be used.
Nevertheless, the use of a second recognition molecule not only
lengthens the analysis time and complicates the procedures but also
increases cost. Furthermore, both approaches do not allow real-
time detection of the analyte. Hence, development of label-free and
real-time biosensors with additional characteristics such as high
sensitivity and selectivity, portable for point-of-care, easy to use, and
cost-effective is extremely necessary.
Much biosensor research has been devoted to the evaluation of
the relative merits of various label-free signal transduction methods
including optical, piezoelectric, and impedimetric. Although each
of these methods has its individual strengths and weaknesses, a
strong case has been made that optical sensors, in particular those
based on evanescent electromagnetic ields such as surface plasmon
resonance (SPR) at planar gold surfaces, are the methods of choice
in many biosensing applications today. 8 Unfortunately, SPR sensors
require bulky and expensive optical equipment and hence are
dificult to be miniaturized.
The development of portable biosensors composed of a highly
miniaturized signal transducer element that enables point-of-care
applications is one of the important driving forces in biosensor
research. 1 Also important are their potential capabilities for on-site,
in situ , in vivo , remote sensing, and disposable use. In these situations,
it is necessary to utilize sensor platforms that have as many of the
desirable characteristics of SPR sensors as possible, but also can be
easily conigured in a miniaturized format, and minimize the time
required to achieve measurable signals, and the volume of sample
required.
Recently, scientiic community has begun to explore alternative
strategies for the development of new optical sensing platforms
based on the extraordinary optical properties of noble metal
nanoparticles (NMNP). 9-11 These nanoparticles characteristically