Page 164 - Vibrational Spectroscopic Imaging for Biomedical Applications

140 Cha pte r F i v e

High

(b) Low
(a)

(c)

FIGURE 5.7 (a) Developing spores along a branching structure of Neurospora.
(b) The sFTIR map recorded with 8 μm pixel and step size, processed for the
−1
intensity of a CH-stretch band at 2854 cm , (c) Raman map acquired on the
lower right branch, 1 μm pixel and step size, 785 nm laser line. [(a) and
(b) reproduced from Ref. 16, with permission of Wiley-Blackwell.]
branch is a fragment that broke during sample acquisition and fell
onto the clean gold surface several mm from the growing colony.
Effectively, the spatial resolution with IR only reveals the general
shape of the branched structure, processing on the CH band
2
indicates lipid within the developing spores. The Raman map has
–1
been processed to show the intensity of the band at 1050 cm ,
typical of the cell wall in this species.
5.5.3 Detection of Crystalline Materials by IR and Raman
In the case of inclusions with fairly high purity, an accurate identity
of the compound can sometimes be made. For example, calcium
hydroxyapatite in calcified tissues, atherosclerotic plaque content, 49
50
and silicone in lymph nodes from patients with breast implants 65
have all been reported. We recently identified elevated deposits of
crystalline creatine in the brain tissue from a transgenic model for
Alzheimer disease using a combination of sFTIR and Raman micros-
66
copy. Creatine, with 18 atoms, has a possible 48 vibrational modes,
plus combinations and overtones. The spectral signature is extraordi-
narily distinctive, as each mode or combination appears at a unique
frequency with a unique intensity relative to all the other peaks, and
are easy to detect against the background of normal tissue (Fig. 5.8).
Crystalline compounds can also be associated with fungal
symbionts, such as lichen. For example, usnic acid, a polyketide and
secondary metabolite of certain lichens that has valuable biomedical
properties and also is believed to provide some protective functions
for lichen. More than 800 such natural products have been identified,
most of them are polyketides that have been discovered to possess
multiple useful properties. The lichen Cladonia may be found on all
the continents; C. uncialis is a slow-growing lichen that can readily
be found in North American forests (Fig. 5.9). The lichen grows over