Raman Microscopy and Imaging: Applications to Skin Pharmacology and Wound Healing - Emerging Raman Applications and Techniques in Biomedical and Pharmaceutical Fields - page 365

The optical image is shown in Fig. 15.3a. Five significant factors whose
loadings in the 800-1140 cm − 1 spectral region are shown in Fig. 15.3b were
extracted. Score images for each factor are given in Fig. 15.3c. Three of the
score images and their corresponding loadings are easily correlated with known
spatial regions of skin. Thus, factor 1 corresponds to the SC, factor 4 to the
viable epidermis, and factor 5 to the dermis. The skin thickness of the SC
determined from factor score images is consistent with the known properties
of pigskin as seen in the optical image.
The two remaining factor score images (factors 2 and 3) highlight particu-
lar features within the viable epidermis not generally evident in optical micro-
graphs and demonstrate a major advantage of the Raman approach, namely
the ability to extract molecular structure/composition information from data
generated at particular tissue sites. The process of assigning the chemical ori-
gin of a particular image feature is demonstrated for factor 2 (Fig. 15.3c) in
Fig. 15.4a-c. An average spectrum of the stratum corneum as labeled (top
spectrum in each of Fig. 15.4a-c) is compared with an average spectrum lo-
calized to the small spectral region highlighted in Fig. 15.3c (labeled factor 2).
Both spectra display strong bands near 1058, 1130, 1296, 2880, and 2850 cm − 1
(Fig. 15.4b and c). These bands are assigned [26, 27] to lipid C-C stretching
(1058, 1130 cm − 1 )andCH 2 stretching modes (2850 and 2880 cm − 1 )ofcon-

formationally ordered (all- trans ) chains, and lipid CH 2 twisting 1296 cm − 1 .
In addition, the bands observed at 605 and 700 cm − 1 (Fig. 15.4a) arise from

Fig. 15.4. Averaged Raman spectra from within the SC ( top ) and lipid ( bot-
tom ) regions as noted in Fig. 15.3b and c as factors 1 and 2, respectively. a The
590-780 cm − 1 region with bands at 605 and 700 cm − 1 assigned to cholesterol as
marked. b The 800-1380 cm − 1 region displays three major bands (1058, 1130, and
1296 cm − 1 ) characteristic for ordered (all- trans ) lipid chains. c The C-H stretching
2800-3000 cm − 1 region with symmetric 2850 cm − 1 and asymmetric 2880 cm − 1
methylene stretching modes noted. The frequencies of the bands are consistent con-
formationally ordered chains