(Invited) Trace Level Detections By Surface-Enhanced Raman Scattering

Abstract

The Raman signals of molecules attached on the very surface of noble metals nanostructures can be greatly enhanced due to the enhancement of the local electric field, by the localized surface plasmon resonance of the nanostructures incident by the laser beam. Therefore, one can make Raman scattering a powerful means in recognizing and quantifying molecules at trace levels. This, however, relies on the sensitivity, stability, etc., of the nanostructures which are used as the substrate surface-enhanced Raman scattering (SERS), and also, the methodologies to quantify the molecules, which are quite difficult even for normal Raman scattering.We report here, our attempts to design and fabricate silver nano rods as substrate for surface-enhanced Raman scattering, with very high sensitivity, thermal and chemical stability, excellent reusability, etc., by glancing angle deposition techniques with an e-bam system, and covering the surface of the silver nano rods completely by atomic layers deposition of Al2O3 with a thickness of ~ 1.0 nm. These nanorods could be thermally stable in morphology and performance as the SERS substrates up to higher than 400 oC, and chemically stable in harsh environments. These makes the covered Ag nanorods applicable in real environments as SERS substrates. based on the principle component analysis (PCA), we also developed qualitative and quantitative analysis methodologies to quantify chemicals or molecules in complex systems even at trace levels by SERS. Several examples will be shown for trace level analysis of real samples by surface-enahnced Raman scattering with the substrates we designed and fabricated and the approaches we established.