Biomedical Engineering Reference
In-Depth Information
that no change in dipole moment occurs during their vibrations; the same
principle applies to monatomic molecules or ions. However, diatomic mol-
ecules made up of basal atoms that are different do display some infrared
absorption due to the occurrence of dipole moment changes [31].
A general principle that can be applied when it comes to infrared radia-
tion absorption is that covalent bonding between unlike atoms gives rise to
infrared absorption. Molecules and materials that are partly covalent and
partly ionic, such as materials that are partly organic and partly inorganic,
will show absorption because of that portion of their bonding that is covalent
in nature. Another general principle that can be applied is that all organic
substances absorb infrared radiation [31].
The infrared spectrum is recorded by passing a beam of infrared light
through the sample and recording the changes at the energy level of the
photons as a result of interactions with the sample. This can be done with
a monochromatic beam, which changes in wavelength over time. However,
using a Fourier transform (FT) instrument makes it possible to measure
all wavelengths at once. The aim is to measure the quality and quantity of
transmittance or absorbance of each different wavelength by a sample that
can produce transmittance or absorbance spectrum.
FTIR and Raman Spectrometry
Raman and FTIR are two of the available spectroscopic techniques (Figure 1.8).
Although there are some other spectroscopic methods, including fluorescence
spectroscopy [30,31,32], nuclear magnetic resonance (NMR)  [33], magnetic
resonance (MR) spectroscopy [34,35,36], and ultraviolet-visible (UV-Vis) spec-
troscopy [37], Raman and FTIR are the techniques that are most often used.
This is mainly because of the advantages of these techniques, such as having a
simple analysis procedure and being noninvasive in nature.
FTIR and Raman are potential tools for noninvasive optical tissue diag-
nosis. These techniques have become a significant analytical method for
biomedical applications. The measurements are nondestructive to tissue
and only very small amounts of material (micrograms to nanograms) are
required. In some studies, sensitivity and specificity values of more than 90%
for distinguishing cancer from normal tissues have been reported [38−41].
Furthermore, such analysis yields structural information concerning the
conformational order in complex natural tissues. The methods are employed
to find more conservative ways of analysis to measure characteristics within
tumour tissue and cells, which would allow accurate and precise assignment
of functional groups, bonding types, and molecular conformations. Spectral
bands in vibrational spectra are molecule specific and provide direct infor-
mation about biochemical composition. These bands are relatively narrow,
 
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