Biomedical Engineering Reference
In-Depth Information
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Figure 1.30
Detection of nucleic acid duplex formation via excitation of a dye with
the quantum dot -based emission.
Scattered light produced with a lower frequency than the excitation radiation is
termed Stokes scattering, whereas that with a higher frequency that that for
excitation is called anti-Stokes scattering. The data obtained from the method
is somewhat analogous to that found for infrared spectroscopy, i.e. molecular
vibrational information, although the selection rules for the Raman process are
different and involve induced polarizability in the target molecule. Although
not considered biosensor technology, conventional Raman spectroscopy, in a
wide variety of forms such as micro-Raman spectroscopy, has found wide-
spread use in the examination of biological fluids, bacteria, cells and tissue. For
several excellent examples the reader is directed to the references within ref. 93.
We take one example from our own work,
96
where the technique was employed
in the study of acute mouse brain injury with specific reference to the motor
cortex. Tissue subject to deliberate damage showed a quite different Raman
signature from a healthy brain sample. Interestingly the Raman spectra
correlated with makers for apoptosis, cell death.
A system closer to the concept of a biosensor is surface enhanced Raman
spectroscopy (SERS) associated with ultra-small metal particles.
138,139
SERS
involves the highly significant enhancement of Raman signals, 10
3
to 10
6
in
magnitude, when metal particles such as those fabricated from silver, gold or
copper, for example, are employed in the Raman experiment. Much as
associated with SPR described above, the SERS effect is connected to surface
plasmon physics at the interfaces of, for example, two materials. The metals are
formed in nanoparticles (some years ago these were considered to be in the
realm of colloid chemistry!) in many different shapes. A different method to
generate nanoparticles placed on substrates is the approach known as photo-or
electron beam lithography (which will be very familiar to the electronic
engineer).
