Determination of the distance dependence and experimental effects for modified SERS substrates based on self-assembled monolayers formed using alkanethiols

Modified SERS (surface-enhanced Raman scattering) substrates are based on s elf-assembled monolayers (SAMs) formed from compounds such as alkanethiols. Chain lengths ranging from ethanethiol to octadecanethiol were used to inv estigate properties of modified SERS substrates. These properties include d etermining the magnitude of the SERS electromagnetic enhancement, developin g a sensitivity factor for detecting aromatic compounds, and evaluating SER S substrates for performance characteristics such as stability and solvent effects. A SERS electromagnetic enhancement was determined to be 2.1 x 10(3 ) for detecting aromatic compounds. The effects of experimental conditions on the SERS detection process were addressed. SERS sensitivity was shown to be highly dependent upon a correlation between the SERS interfacial distan ce dependence and a hydrophobic effect exhibited by the alkyl chain of the thiol. The distance dependence was more significant than the hydrophobic ef fect for detecting aromatic compounds. For comparison to the electromagneti c enhancement, a SERS sensitivity factor was determined for detecting benze ne in wafer and in organic solvents. Experimental stability issues, such as solvent and laser exposure, were shown to affect the sensitivity of modifi ed SERS substrates. 1-Propanethiol exhibited the strongest sensitivity and stability; under all solvent and experimental conditions.