Fiber-Optic Raman Probes for Biomedical and Pharmaceutical Applications - Emerging Raman Applications and Techniques in Biomedical and Pharmaceutical Fields - page 34

fibers and has a diameter of 600 m [28]. The other is made of HOF with a

ball lens and has a diameter of 640

μ

m [37].
The narrowest diameter fiber-optic Raman probes are single optical fiber,
which were employed by Santos et al., Koljenovic et al., and Nijssen et al. for

μ

high wave number > 2800 cm − 1 spectroscopy [39-41]. Although the probes
are limited to collection of scatter from CH, NH and OH were used success-
fully in identifying basal cell carcinoma tissue with high accuracy. The FSB
intensity in the high wave number region is much smaller than that in the
fingerprint region because there is no silica Raman scatter and if the fiber is
chosen carefully, little. Simple designs become possible. The simplest consists
of a single unfiltered optical fiber that delivers the excitation light to the sam-
ple and serves to collect the Raman scatted light. Santos et al. tested different
fiber core cladding and coating materials [39]. They recommended low-OH sil-
ica core-silica clad fibers with an acrylate coating and a black nylon jacket
for minimal Raman scatter and fluorescence. With this fiber the background
is flat [39]. In addition, the fluorescence of the sample is weaker because the
high wave number region corresponds to the long wavelength region, in which
molecules usually do not emit fluorescence.
Only a few types of vibrations can be observed in the high wave number
region. Bands appearing between 2800 and 3000 cm − 1 are the symmetric and
asymmetric stretching modes of the CH 2 and CH 3 groups [38]. A broadband
near 3300 cm − 1 is due to the NH stretching mode of protein and other amides.
A broad feature near 3400 cm − 1 is the OH stretching mode of water. Diseased
tissue can be detected by high wave number Raman spectroscopy if it has
molecular compositional and structural changes that alter the frequencies of
these vibrational modes.

2.3.1 Development of the Miniaturized Fiber-Optic Raman Probe

In Sect. 2.2 the optical properties of the fiber, filters, and spectrometers were
described and their interrelated properties explained. In this section the op-
tical design considerations for Raman probe made of bundled fibers will be
discussed. The need to suppress FSB from the fibers and the need to couple
the fibers properly to the spectrograph are largely the same as in the probes
employing single fibers. For measurements in the fingerprint wave number re-
gion, it is necessary to suppress the FSB generated in the optical fibers used
for delivery of the excitation light and those used for the collection of the
scattered light [26]. To suppress the FSB, a BP filter is attached at the distal
end of the fiber delivering the excitation light and an LP filter is attached at
the distal end of the fiber used to collect the Raman scattered light to block
the strong Rayleigh scattered light.
We developed a micro-Raman probe (MRP) with a total diameter of

600 m to use with an intravascular endoscope [28]. To develop this MRP,

it was important to consider the following three parameters when selecting
the optical fiber: (1) R b , (2) NA, and (3) core diameter. The first parameter

μ