Towards refining Raman spectroscopy-based assessment of bone composition

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 [Formula: see text] (1)-, [Formula: see text] (2)-,[Formula: see text] (3)-, [Formula: see text] (4) PO(4)(3−), and [Formula: see text] CO(3)(2−) bands represent the inorganic phase while amide I, amide III, Proline, Hydroxyproline, Phenylalanine, δ(CH(3)), δ(CH(2)), and [Formula: see text] (C–H) represent the organic phase. Here, using high-resolution Raman spectroscopy, it is demonstrated that all PO(4)(3−) 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 [Formula: see text] (2) PO(4)(3−) 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 [Formula: see text] (4) PO(4)(3−) band broadening. In the 1020–1080 cm(−1) range, the ~ 1047 cm(−1) [Formula: see text] (3) PO(4)(3−) sub-component is obscured by the 1033 cm(−1) Phenylalanine peak, while the ~ 1076 cm(−1) [Formula: see text] (3) PO(4)(3−) sub-component is masked by the [Formula: see text] (1) CO(3)(2−) band. With [Formula: see text] (1) PO(4)(3−) peak broadening, [Formula: see text] (2) PO(4)(3−) integral area increases exponentially and individual peaks comprising the [Formula: see text] (4) PO(4)(3−) band merge together. Therefore, [Formula: see text] (2) PO(4)(3−) and [Formula: see text] (4) PO(4)(3−) band profiles are sensitive to changes in mineral crystallinity.