Characterization of human breast biopsy specimens with near-IR Raman spectroscopy.

Breast biopsy samples were examined with Raman spectroscopy with laser wavelengths ranging from 406 to 830 nm. A combination of a single-stage spectrograph, band reject filter, and CCD detector permitted low laser powers and minimal risk of sample radiation damage. Spectra of formalin-fixed human tissue revealed Raman features for lipids and carotenoids. The best defined lipid features were observed for 782- and 830-nm laser excitation, while carotenoid features were strongest in the 488-515-nm range due to resonance enhancement. Comparison of the spectra with those of fatty acid esters revealed that the major lipid component is a derivative of oleic acid. Lipid and carotenoid Raman bands were superimposed on a luminescent background which was less prominent at longer laser wavelengths. A compact, portable, diode laser spectrometer was tested in a clinical setting with fiber optic sampling. The results indicate that substantial biochemical information is available from near-IR Raman spectroscopy and the technique may have clinical applications.