Single fiber surface enhanced Raman scattering probe

Abstract

Raman spectroscopy is a time honored technique for identifying molecular structures. In surface enhanced Raman scattering close proximity of the sample to so-called “hot spots” in a rough metallic surface enhances the Raman signal strength enormously. For in vivo applications an optical fiber in a narrow probe is desirable to minimize invasiveness. Unfortunately, in a long fiber to the spectrometer Raman scattering within the fiber masks the signal from the specimen. Systems are available which avoid this problem by using one fiber to transmit the exciting light, additional fibers to collect the scattered Raman light, and metallic nanoparticles disbursed within the specimen. Unfortunately, the Raman signal is up to thousands of times smaller than for a single fiber. In addition, variation in the dispersion of the nanoparticles makes comparisons between sites problematical. The authors have retained the advantages of a single fiber by coupling a short length to the spectrometer via a 1 m long air path in an articulated mirrored arm. The fiber is inside a 0.5 mm ID stainless steel needle and has gold nanoparticles glued to its end. Representative spectra were obtained from various biological tissues, and distinct differences between cancerous and benign mouse colon cells were observed.