TITLE:
Chemical Enhancement of the Surface Enhanced Raman Scattering Signals of Anilines via Their Ortho-Substituents
AUTHORS:
Rachel A. Davies, Ngee S. Chong, Beng Guat Ooi
KEYWORDS:
SERS; Raman; Enhancement Factors; Aniline Derivatives; Ortho-Substituent; Nanoparticle; TEM Characterization
JOURNAL NAME:
Optics and Photonics Journal,
Vol.3 No.5A,
September
18,
2013
ABSTRACT:
While Raman spectroscopy is a useful method for
analyzing many organic compounds, it is limited by relatively low sensitivity.
Therefore, Surface Enhanced Raman Spectroscopy (SERS) based on the adsorption
of organic analytes onto gold or silver nanostructures has been used to enhance
the signal of chemicals presented at very low concentrations. Although the
plasmonic effect of SERS has been shown to play a large role in
signal enhancement, the significance of the chemical effect due to the analyte
chemisorption on the gold or silver surface is less well understood. In this
study, the role of aniline substituents is examined by probing the SERS intensities
of various anilines in silver and gold colloids using a Raman spectrometer with
an excitation wavelength of 785 nm. The SERS enhancement factors and detection
limits for aniline and its mono- and di-substituted ortho derivatives are determined and compared. Both the steric requirements
of chemisorption and the inductive effects of electron-withdrawal due to the
substituents affect the signal intensities of various vibrational
modes of the amino group and the aromatic ring. The degree of enhancement is
also related to the methods for preparing the silver and gold colloids, which
are characterized by probing the nanoparticle morphology and its degree of
aggregation using transmission electron microscopy (TEM).