Towards refining Raman spectroscopy-based assessment of bone composition

Abstract

Various compositional parameters are derived using intensity ratios and integral area ratios of different spectral peaks and bands in the Raman spectrum of bone. The ν1-, ν2-,ν3-, ν4 PO43−, and ν1 CO32− bands represent the inorganic phase while amide I, amide III, Proline, Hydroxyproline, Phenylalanine, δ(CH3), δ(CH2), and ν(C–H) represent the organic phase. Here, using high-resolution Raman spectroscopy, it is demonstrated that all PO43− bands of bone either partially overlap with or are positioned close to spectral contributions from the organic component. Assigned to the organic component, a shoulder at 393 cm−1 compromises accurate estimation of ν2 PO43− integral area, i.e., phosphate/apatite content, with implications for apatite-to-collagen and carbonate-to-phosphate ratios. Another feature at 621 cm−1 may be inaccurately interpreted as ν4 PO43− band broadening. In the 1020–1080 cm−1 range, the ~ 1047 cm−1ν3 PO43− sub-component is obscured by the 1033 cm−1 Phenylalanine peak, while the ~ 1076 cm−1ν3 PO43− sub-component is masked by the ν1 CO32− band. With ν1 PO43− peak broadening, ν2 PO43− integral area increases exponentially and individual peaks comprising the ν4 PO43− band merge together. Therefore, ν2 PO43− and ν4 PO43− band profiles are sensitive to changes in mineral crystallinity.