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 $$\nu $$ ν 1-, $$\nu $$ ν 2-,$$\nu $$ ν 3-, $$\nu $$ ν 4 PO43−, and $$\nu_{1} $$ ν 1 CO32− bands represent the inorganic phase while amide I, amide III, Proline, Hydroxyproline, Phenylalanine, δ(CH3), δ(CH2), and $$\nu $$ 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 $$\nu $$ ν 2 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 $$\nu $$ ν 4 PO43− band broadening. In the 1020–1080 cm−1 range, the ~ 1047 cm−1$$\nu $$ ν 3 PO43− sub-component is obscured by the 1033 cm−1 Phenylalanine peak, while the ~ 1076 cm−1$$\nu $$ ν 3 PO43− sub-component is masked by the $$\nu $$ ν 1 CO32− band. With $$\nu $$ ν 1 PO43− peak broadening, $$\nu $$ ν 2 PO43− integral area increases exponentially and individual peaks comprising the $$\nu $$ ν 4 PO43− band merge together. Therefore, $$\nu $$ ν 2 PO43− and $$\nu $$ ν 4 PO43− band profiles are sensitive to changes in mineral crystallinity.