Chemical Enhancement of the Surface Enhanced Raman Scattering Signals of Anilines via Their Ortho-Substituents

Rachel A. Davies, Ngee S. Chong, Beng Guat Ooi

Department of Chemistry, Middle Tennessee State University, Murfreesboro, USA.

DOI: 10.4236/opj.2013.35A003                

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).

Keywords

SERS; Raman; Enhancement Factors; Aniline Derivatives; Ortho-Substituent; Nanoparticle; TEM Characterization

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	G. C. Schatz, M. A. Young and R. P. Van Duyne, “Electromagnetic Mechanism of SERS,” Topics in Applied Physics, Vol. 103, 2006, pp. 19-46. doi:10.1007/3-540-33567-6_2
[2]	A. M. Michaels, M. Nirmal and L. E. Brus, “Surface Enhanced Raman Spectroscopy of Individual Rhodamine 6G Molecules on Large Ag Nanocrystals,” Journal of the American Chemical Society, Vol. 121, No. 43, 1999, pp. 9932-9939. doi:10.1021/ja992128q
[3]	Y. Fan and S. Q. Man, “SERS Study of Malachite Green on Silver Nanocaps Arrays,” Advanced Materials Research, Vol. 418-420, 2012, pp. 8-12. doi:10.4028/www.scientific.net/AMR.418-420.8
[4]	Y. Ikezawa, H. Saito, K. Matsui and G. Toda, “A Study of the Competitive Adsorption of Pyridine and Monosubstituted Pyridines on a Silver Electrode by the SERS Method,” Surface Science, Vol. 176, No. 3, 1986, pp. 603-609. doi:10.1016/0039-6028(86)90058-0
[5]	T. Tanaka, A. Nakajim, A. Watanabe, T. Ohno and Y. Ozaki, “Surface-Enhanced Raman Scattering Spectroscopy and Density Functional Theory Calculation Studies on Adsorption of o-, m-, and p-Nitroaniline on Silver and Gold Colloid,” Journal of Molecular Structure, Vol. 661-662, 2003, pp. 437-449.
[6]	M. A. Palafox, J. L. Nunez and M. Gil, “Accurate Scaling of the Vibrational Spectra of Aniline and Several Derivatives,” Journal of Molecular Structure (Theochem), Vol. 593, No. 1-3, 2002, pp. 101-131. doi:10.1016/S0166-1280(02)00319-6
[7]	H. Park, S. B. Lee, K. Kim and M. S. Kim, “Surface-Enhanced Raman Scattering of p-Aminobenzoic Acid at Ag Electrode,” Journal of Physical Chemistry, Vol. 94, No. 19, 1990, pp. 7576-7580. doi:10.1021/j100382a049
[8]	D. Li, D-W. Li, J. D. Fossey and Y. Long, “Portable Surface-Enhanced Raman Scattering Sensor for Rapid Detection of Aniline and Phenol Derivatives by On-Site Electrostatic Preconcentration,” Analytical Chemistry, Vol. 82, No. 22, 2010, pp. 9299-9305. doi:10.1021/ac101812x
[9]	N. Leopold and B. Lendl, “A New Method for fast Preparation of Highly Surface-Enhanced Raman Scattering (SERS) Active Silver Colloids at Room Temperature by Reduction of Silver Nitrate with Hydroxylamine Hydrochloride,” Journal of Physical Chemistry B, Vol. 107, No. 24, 2003, pp. 5723-5727. doi:10.1021/jp027460u
[10]	J. P. Xie, J. Y. Lee and D. I. C. Wang, “Seedless, Surfactantless, High-Yield Synthesis of Branched Gold Nanocrystals in HEPES Buffer Solution,” Chemistry of Materials, Vol. 19, No. 11, 2007, pp. 2823-2830. doi:10.1021/cm0700100
[11]	L.-B. Zhao, R. Huang, M.-X. Bai, D.-Y. Wu and Z.-Q. Tian, “Effect of Aromatic Amine-Metal Interaction on Surface Vibrational Raman Spectroscopy of Adsorbed Molecules Investigated by Density Functional Theory,” The Journal of Physical Chemistry, Vol. 115, No. 10, 2011, pp. 4174-4183.
[12]	N. S. Chong, K. A. Smith, S. Setti and B. G. Ooi, “Application of Gold and Silver Colloidal Nanoparticles for the Surface-Enhanced Raman Spectrometric Analysis of Melamine and 4-Aminobiphenyl,” International Journal of Environmental Technology and Management, Vol. 16, No. 1/2, 2013, pp. 3-20. doi:10.1504/IJETM.2013.050681
[13]	L.-B. Zhao, Y.-F. Huang, X.-M. Liu, J. R. Anema, D.-Y. Wu, B. Ren and Z.-Q. Tian, “A DFT Study on Photoinduced Surface Catalytic Coupling Reactions on Nanostructured Silver: Selective Formation of Azobenzene Derivatives from para-Substituted Nitrobenzene and Aniline,” Physical Chemistry Chemical Physics, Vol. 14, 2012, pp. 12919-12929. doi:10.1039/c2cp41502j
[14]	K. A. Smith, N. S. Chong, K. Donthula and B. G. Ooi, “Influence of the Structural Characteristic of Silver and Gold Nanoparticles on the Surface-Enhancement Factors of the Raman Signals from Aromatic Amines,” Nano-Formulation, Series 336, 2012, pp. 121-132.
[15]	J. T. Hugall, J. J. Baumberg and S. Mahajan, “Disentangling the Peak and Background Signals in Surface-Enhanced Raman Scattering,” Journal of Physical Chemistry C, Vol. 116, No. 10, 2012, pp. 6184-6190. doi:10.1021/jp3002977
[16]	L. Lipping, A. Kutt, K. Kaupmees, I. Koppel, P. Burk, I. Leito and I. A. Koppel, “Acidity of Anilines: Calculations vs. Experiment,” Journal of Physical Chemistry A, Vol. 115, No. 37, 2011, pp. 10335-10344. doi:10.1021/jp204064q
[17]	K. C. Gross and P. G. Seybold, “Substituent Effects on the Physical Properties and pKa of Aniline,” International Journal of Quantum Chemistry, Vol. 80, No. 4-5, 2000, pp. 1107-1115. doi:10.1002/1097-461X(2000)80:4/5<1107::AID-QUA60>3.0.CO;2-T
[18]	E. N. Esenturk and A. R. H. Walker, “Surface-Enhanced Raman Scattering Spectroscopy via Gold Nanostars” Journal of Raman Spectroscopy, Vol. 40, No. 1, 2009, pp. 86-91. doi:10.1002/jrs.2084
[19]	C. G. Khoury and T. Vo-Dinh, “Gold Nanostars for Surface-Enhanced Raman Scattering: Synthesis, Characterization and Optimization” Journal of Physical Chemistry C, Vol. 112, No. 48, 2008, pp. 18849-18859.
[20]	Q. Su, X. Ma, J. Dong, C. Jiang and W. Qian “A Reproducible SERS Substrate Based on Electrostatically Assisted APTES-Functionalized Surface-Assembly of Gold Nanostars,” ACS Applied Materials & Interfaces, Vol. 3, No. 6, 2011, pp 1873-1879. doi:10.1021/am200057f