Dual excitation wavelength system for combined fingerprint and high wavenumber Raman spectroscopy

Abstract

A fiber optic probe-based Raman spectroscopy system using a single laser module with two excitation wavelengths, at 680 and 785 nm, has been developed for measuring the fingerprint and high wavenumber regions using a single detector. This system is simpler and less expensive than previously reported configurations of combined fingerprint and high wavenumber Raman systems, and its probe-based implementation facilitates numerous in vivo applications. The high wavenumber region of the Raman spectrum ranges from 2800–3800 cm−1 and contains valuable information corresponding to the molecular vibrations of proteins, lipids, and water, which is complimentary to the biochemical signatures found in the fingerprint region (800–1800 cm−1), which probes DNA, lipids, and proteins. The efficacy of the system is demonstrated by tracking changes in water content in tissue-mimicking phantoms, where Voigtian decomposition of the high wavenumber water peak revealed a correlation between the water content and type of water-tissue interactions in the samples. This dual wavelength system was then used for in vivo assessment of cervical remodeling during mouse pregnancy, a physiologic process with known changes in tissue hydration. The system shows that Raman spectroscopy is sensitive to changes in collagen content in the fingerprint region and hydration state in the high wavenumber region, which was verified using an ex vivo comparison of wet and dry weight. Simultaneous fingerprint and high wavenumber Raman spectroscopy will allow precise in vivo quantification of tissue water content in the high wavenumber region, paired with the high biochemical specificity of the fingerprint region.

Immunobiology of Cervix Ripening

“…In a recent longitudinal study of women during pregnancy, this approach proved useful to identify many peaks that reflected extracellular matrix proteins, actin, and blood in the cervix that change throughout pregnancy and postpartum (173). This approach has also been used to study changes in fatty acid lipids, proteins, and amino acids the cervix in mice during pregnancy (174), as well as water content in non-pregnant and mice at term (175). Whether clear resolution of potentially overlapping peaks that correspond to signatures of known molecules in the inflammatory process of remodeling awaits further study.…”

A modification for the calculation of water depth profiles in oil‐treated skin by in vivo confocal Raman microscopy

“…Various analytical methodologies have been employed to measure water in the SC , for example, infrared spectroscopy , electrical capacitance , trans‐epidermal water loss (TEWL) and confocal Raman microscopy (CRM) . Among them, Raman spectroscopy is considered a powerful method to accurately measure water mass percentage depth profiles in the SC . Huizinga et al introduced a method using the depth profiles of CRM of the eye and calculated water profiles in the high wavenumber region (HWN) by the ratio of the OH water band (3350‐3550 cm −1 ) to the keratin CH 3 band (2910‐2965 cm −1 ).…”

Predicting the Refractive Index of Tissue Models Using Light Scattering Spectroscopy

“… 1 The range 1216–1300 cm –1 presents a doublet at 1248 and 1271 cm –1 (amide III 29 ), while the range 1431–1507 cm –1 corresponds to CH 3 and CH 2 deformations. 29 , 33 The range between 1562 and 1800 cm –1 presents contributions from both protein (amide I 29 , 33 centered at 1665 cm –1 and assigned to disordered protein structure, 34 , 35 with a shoulder at 1635 cm –1 associated with denatured triple helices 35 ) and water (bending mode at 1635 cm –1 ). 36 , 37 Highly hydrated gelatin is expected to be more disordered than gels of lower water content, where a larger proportion of alpha helices are expected to be present.…”