Design and Fabrication of a Low-Cost, Portable, Battery-Operated Surface Enhanced Raman Scattering (SERS) Optical Device

Abstract

Raman Spectroscopy is a time-honored, non-invasive method for analyzing and identifying the molecular composition of materials. However, unenhanced Raman Spectroscopy has extremely low sensitivity which limits its sensing capability. SERS brings rough nano-metallic surfaces in contact with the material molecules to enormously enhance the Raman signals. The sensitivity of SERS can be exploited in probe applications where the spectrometer needs to be brought near the specimen. For example, a long optical fiber coupled to a SERS device can be used to characterize and identify easy-to-reach cancerous tissues in organisms. Unfortunately, background signals in a long fiber can easily mask any signal returning from the end of the probe. A classical solution is to inject nanoparticles and use multiple optical fibers (one to deliver the excitation light and one or more to return the scattered Raman light). However, the coupling between the fibers is poor, reducing the signal strength, and reproducibility between locations, and removal of the injected nanoparticles present difficulties. This work intends to address those challenges by designing and fabricating a low-cost handheld SERS device. The development of this SERS device is broadly split into (a) fabrication of a probe suitable low-cost SERS substrate (b) design and fabrication of the handheld SERS device optics. The method used for the fabrication and characterization of the SERS layer low-cost substrate involved sandpaper imprint patterning of silver nanoparticles. This was accomplished at low cost with inexpensive equipment, readily available materials, and with no chemical or lithographic steps. The handheld SERS optics incorporated a solid-state laser, diffractive optics, the low-cost SERS substrate at one end of a GRIN lens, and a short-tube pathway to the Raman spectrometer. The response of the optical system and imprinted SERS layer was tested to obtain the Raman spectrum from 1nmol to 1mmol Rhodamine 6G suspension. This yielded good Raman scattering results. The developed device was made with a SERS substrate fabrication method which is a low-cost alternative and with no lithography or chemical synthesis. This SERS portable design is also suitable for bio-probes or remote sampling without the disadvantages associated with injected clouds substrates and multiple collection fiber systems.