Surface Enhanced Raman Scattering (SERS) Substrates and Probes

Abstract

Raman spectroscopy is a well-known technique for complex molecular detection. In Raman spectrometry, laser beam is focused on a sample to generate a unique "fingerprint" of the molecule. The Raman signal is very weak. To overcome this problem nano rough metallic substrates are fabricated to enhance the signal strength. In clinical applications, remote contact and minimally invasive probes inside the specimen are needed. This research work is divided in: (1) development of Surface Enhanced Raman Scattering (SERS) substrate using gold coated etched aluminum foil, (2) development of the SERS probe using the aluminum based substrate with a single optical fiber and GRIN lens connected to the Raman spectrometer by an articulate arm, (3) differentiation of the cancerous and benign colon of a mouse, (4) development of a SERS substrate using gold-coated Multi-wall Carbon Nanotube (MWCNT) on etched aluminum, and (5) development of another SERS substrate using gold-coated etched silicon wafer. A low cost clinical probe is developed by using an optical fiber, a gradient-index (GRIN) lens, and a SERS substrate for molecular imaging to detect biological specimens. A low-cost SERS substrate is fabricated from aluminum foil covered with 20nm of gold. The optical fiber connected to a GRIN lens is inside a 0.5mm diameter stainless steel needle. The nano-rough metallic substrate is glued to the end of the fiber by a thin layer of epoxy. Different concentrations of gelatins and various biological tissues have been detected by this probe connected with a 1m long air path in an articulate arm. Previous work manufactured probes with long single fiber and two short fibers. This needle probe successfully overcomes the problems associated with them. The observed Raman signal is comparable to the signal produced by a microscope objective of the same numerical aperture. To obtain a highly sensitive SERS substrate, a rough nano-metallic structure is developed by sputtering gold nano particles on the MWCNT laden etched aluminum foil. Another SERS substrate is fabricated by depositing gold nano particles on the smooth side of the silicon wafer after thinning it down from 420µm to 120µm for the development of clinical probes in future.