This paper reports a new low cost technique for fabricating Surface Enhanced Raman Spectroscopy substrates. A Gold (Au) nano-metallic structure for surface enhancement is created by depositing Au nanoparticles on a Multi-wall Carbon Nanotube layer previously deposited on the etched Aluminum foil. A low cost, simple method is used to deposit the nanotubes. Huge enhancements have been observed in both in vitro and in vivo measurements.

A needle probe has been developed to obtain surface enhanced Raman scattering data from within a solid specimen located remotely from the spectrometer. It produces the high signal strength of a single mode optical fiber but with a negligible fiber induced background. The observed Raman signal strength is comparable to that obtained with a microscope objective of the same numerical aperture in a conventional spectrometer arrangement and many times larger than that of probes using two fibers.

Conventional Raman scattering is a well-known technique for detecting and identifying complex molecular samples. In surface enhanced Raman scattering, a nanorough metallic surface close to the sample enormously enhances the Raman signal. In previous work, the metallic surface was a thin layer of gold deposited on a rough transparent epoxy substrate. The advantage of the clear substrate was that the Raman signal could be obtained by passing light through the substrate, on to opaque samples simply placed against its surface. In this work, a commercially available Raman spectrometer was coupled to a distant probe. Raman signals were obtained from the surface, and from the interior, of a solid specimen located more than 1 m away from the spectrometer. The practical advantage of this arrangement is that it opens up surface enhanced Raman spectrometry to a clinical environment, with a patient simply sitting or lying near the spectrometer.

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.

Raman Spectroscopy is a well-known method for identifying molecules by their spectroscopic “fingerprint”. In Surface Enhanced Raman Scattering (SERS), the presence of nanometallic surfaces in contact with the molecules enormously enhances the spectroscopic signal. Raman enhancing surfaces are often fabricated lithographically or chemically, but the throughput is low and the equipment is expensive. In this work a SERS layer was formed by the self-assembly of silver nanospheres from a hexane suspension onto an imprinted thermoplastic sheet (PET). In addition, the SERS layer was transferred and securely bonded to other surfaces. This is an important attribute for probes into solid specimen. Raman spectra were obtained with Rhodamine 6G (R6G) solution concentrations ranging from 1 mm to 1 nm. The methods described here produced robust and sensitive SERS surfaces with inexpensive equipment, readily available materials, and with no chemical or lithographic steps. These may be critical concerns to laboratories faced with diminishing funding resources.