Page 17 - Vibrational Spectroscopic Imaging for Biomedical Applications

Preface

he renaissance of vibrational spectroscopy into an imaging
technique has happened in the past 10 years, thanks to the
Tadvent of multichannel detection technology, integration of
microscopy, and optimization of data acquisition time and analysis.
The rich information content provided by infrared and Raman tech-
niques make them suitable for biomedical applications. The data
obtained is available through a simple univariate analysis, and in the
case of complex applications like cancer diagnoses, the data acquisi-
tion, sampling, and analyses must be integrated in a coherent manner.
The unique advantage of observing an entire field of view rapidly in
the infrared imaging technique permitted applications that allowed
for (1) monitoring dynamic processes, (2) spatially resolved spectros-
copy of large or multiple samples, and (3) enhancement of spatial
resolution due to retention of radiation throughput. An emerging
biomedical application in infrared imaging is tissue histopathology,
in which Fourier transform IR (FTIR) imaging has been proposed as
a solution that can potentially help pathologists. It provides an objec-
tive and reproducible assessment of diseases in a manner that is easily
understood by clinicians. The other developments witnessed in recent
years are the incorporation of reflective substrates, integration of attenu-
ated total internal reflection (ATR) elements with microscopy and large
sample imaging, various sample forming, grazing angle, and multi-
sample accessories. The utilization of ATR accessory in tissue samples
provides a high-spatial resolution image, which would further assist in
tissue histopathology and thus in diagnosis of diseases.
Unlike in IR spectroscopy, the Raman spectrum of water is weak,
allowing good spectra to be acquired of species in aqueous solution.
Owing to this unique advantage, biological samples like cells can be
measured in their typical environments, for example, in a buffer
solution or special culture medium. Using confocal Raman imaging,
currently we are able to acquire depth profiles of spectra at a
nanometer resolution. However, in some cases, long integration times
are required because of the weak intrinsic Raman signal. Nanoparticle-
based SERS imaging, by contrast, has proven to be a potential
technique to provide a much stronger signal and hence shorter
xv