Label-free diagnostics and cancer surgery Raman spectra guidance for the human colon at different excitation wavelengths.

Raman spectroscopy and imaging are highly structure-sensitive methods that allow the characterization of biological samples with minimal impact. In this paper, Raman spectra and imaging of noncancerous and cancerous human colon tissue samples were measured at different excitation wavelengths: 355, 532, and 785 nm. Intra-patient variability in the analyzed spectra showed colon sample heterogeneity for both noncancerous and cancerous human sample types. The lowest inter-patient variability of Raman spectra was observed for the fingerprint region of noncancerous samples for the 532 nm excitation laser line. The bands of principal biochemical constituents (proteins, lipids, nucleic acids) predominate in VIS and NIR-Raman spectra (excitation: 532, 785 nm), with the special role of the bands of intrinsic tissue chromophores-carotenoids for VIS excitation due to resonance enhancement. At 355 nm excitation, high autofluorescence of colon tissues were observed. Our studies proved high potential of Raman spectroscopy and Raman imaging in differentiation of noncancerous and cancerous human colon tissues and that the wavelengths 532 and 785 nm offer wide possibilities for the detection of human colon tissue pathology for ex vivo and in vivo measurements and prevail over 355 nm excitation.