“…[1][2][3] Among these analytical techniques, Raman spectroscopy is one of powerful and versatile techniques, as this approach is non-labelling, non-destructive to living tissues / cells, and less influenced by water. As Raman data of a biological tissue is usually complicated and large, techniques for spectral pre-treatments 4,5 and advanced spectral analytical methods, such as principal component analysis (PCA) and non-negative matrix factorization (NMF), 6,7 have been developed and applied.…”