Table 2 Summary of simple ratiometric values used in the work, their molecular sources and depth behavior.
Ratiometric indicator | Molecular source | Depth behavior | Related values |
|---|---|---|---|
Fl-FP (Raman-normalized fluorescence) | Melanin and protein oxidation products in the epidermis and dermal fluorophores | Stepwise increase near the basal layer | – |
\(\frac{{I}_{1244}}{{I}_{1298}}\) | Collagen in the papillary dermis | Stepwise increase near the dermal–epidermal junction | Non-negative matrix factorization component 3 (Fig. 4C) |
\(\frac{{I}_{1412}}{{I}_{1620}}\) | Natural Moisturizing Factor in the stratum corneum | Localization and monotonous decrease in the stratum corneum | Non-negative matrix factorization component 4 (Fig. 4D) |
\(\frac{{I}_{1540}}{{I}_{1655}}\) | Melanin in the epidermis | Local maximum near the basal layer | Spectral decomposition amplitudes and (Fig. 2) and non-negative matrix factorization component 2 (Fig. 4B) |
