WFU Physics Colloquium

TITLE: Comparison of Tumor and Healthy Tissues using Raman Spectroscopy

SPEAKER: Professor Jeff Naeini,

TIME: Thursday Oct. 22, 2009 at 4:00 PM

PLACE: Room 101 in Olin Physical Laboratory

Raman spectroscopy or the inelastic scattering of light by vibrational excitations is a well-known technique for molecular identification and has been extensively used in chemistry, physics, biology, and medicine. Conventional Raman scattering is useful for studying vibrational levels in molecules, but the low conversion efficiency of pump-photons into shifted-photons (Stokes for down-shifted and anti-Stokes for up-shifted in frequency) makes measurements rather lengthy.

Since the first demonstration of coherent anti-Stokes Raman scattering (CARS) by Terhune and Maker, coherent Raman proved to be a superior spectroscopic technique for characterizing gases, liquids, and solids. In CARS one coherently excites the vibrational levels using two beams, a pump beam and a Stokes-shifted beam, which greatly enhance the probability of Raman scattering for a probe beam and hence resulting in much faster measurements.

We have carried out conventional Raman scattering and CARS measurements of tumor and healthy tissues. We have quantitatively compared tumor and healthy tissue spectra using the intensity-ratio of the peaks at 1300 cm^-1 and 860cm^-1. Using the conventional Raman spectra, we have found this ratio to increase from 0.37±0.01 in healthy tissue to 0.51±0.01 in the malignant tissue. This result is consistent with the increase in the ratio of the nucleus-to-cytoplasm, a criterion that pathologists use to mark infiltrating carcinoma.

We have obtained consistent spectra (peak frequencies) using both Raman techniques and successfully confirmed the stronger lines in the tumor tissues by using coherent Raman spectroscopy. We have shown that coherent Raman, CARS in particular, can be used in a backscattering configuration to obtain the Raman spectra with higher sensitivity (improved by 6 orders of magnitude).