Slide- and Micoarray-Based Biosensors Using Noble Metal Nanoparticles - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 59

afinity-based, label-free signal transduction of biomolecular
recognition events, and most of them provide real-time information
about interfacial binding reactions. Some examples of those are
mechanical, 2,3 magnetic, 4,5 electric, 6 and optical methods 7 . Optical
techniques, in particular noble metal ilm-based surface plasmon
resonance (SPR), 8,9 are the most common among these methods
(see Fig. 4.2). There are some reasons for this. First, since they all
rely on changes in refractive index induced by biomolecular binding
reactions conined to the interface, there is, in principle, no limitation
on the nature of the interactions that can be probed. Second, because
there is a linear relationship between refractive index increment and
the concentration of biomolecule, the changes in signal are generally
proportional to the number of bound molecules, and it is possible
to translate the signal into absolute mass uptake. Third, the readout
process does not affect the molecules, and many of the optical
techniques are compatible with miniaturization and microluidics.
Figure 4.2 Schematic illustration of propagating surface plasmon
resonance. The sensor surface is deposited with gold thin ilm
and attached with antibodies. (A) The sensor surface is gold
with antibodies attached to it. (B) As the target analyte binds
to the antibodies, the refractive index shifts and the relected
light moves from original angle ( θ 1 ) to larger angle ( θ 2 ).