Surface-Enhanced Raman Spectroscopy of Self-Assembled Monolayers:  Sandwich Architecture and Nanoparticle Shape Dependence

Abstract

Surface enhanced Raman scattering (SERS) spectra of 4-mercaptobenzoic acid (4-MBA) self-assembled monolayers (SAMs) on gold substrates is presented for SAMs onto which gold nanoparticles of various shapes have been electrostatically immobilized. SERS spectra of 4-MBA SAMs are enhanced in the presence of immobilized gold nanocrystals by a factor of 10(7)-10(9) relative to 4-MBA in solution. Large enhancement factors are a likely result of plasmon coupling between the nanoparticles (localized surface plasmon) and the smooth gold substrate (surface plasmon polariton), creating large localized electromagnetic fields at their interface, where 4-MBA molecules reside in this sandwich architecture. Moreover, enhancement factors depend on nanoparticle shape and vary by a factor of 10(2). This SERS geometry offers large surface enhancements for molecules adsorbed onto planar substrates and could be quite useful for determining chemical information for poor Raman scatterers from assays on 2-D substrates.

Surface enhanced Raman scattering of p-aminothiophenol self-assembled monolayers in sandwich structure fabricated on glass

“…33,37,[53][54][55][56] The EF was defined as EF = I SERS /N ads I bulk /N bulk , where I SERS stands for the intensity of a vibrational mode in the SERS spectrum of p-ATP and I bulk for the intensity of the same vibrational mode in the Raman spectrum from the solution phase or solid sample. Both of these intensities can be directly obtained from the experiment.…”

“…N ads is the number of surface adsorbed p-ATP molecules within the laser spot. This value can be obtained according to the method proposed by Orendorff et al,33 which is…”

“…Recently, Orendorff et al fabricated a sandwich architecture of a smooth macroscopic Au substrate, 4-mercaptobenzoic acid Self-assembled monolayers ͑SAMs͒, and Au NPs with various shapes. 33 Large enhancement factors ͑10 7 -10 9 ͒ were obtained on the SERS spectra of 4-mercaptobenzoic acid ͑4-MBA͒ SAMs and were considered to be derived mainly from the electromagnetic coupling of LSP-SPP between the nanosized Au particles and the smooth Au substrate. On the other hand, Kim and co-workers have systematically reported that a SERS spectrum could be obtained for p-ATP adsorbed onto macroscopically smooth Au and Cu surfaces by assembling nanosized Ag and Au particles thereon.…”

Evaluation of Thiol Raman Activities and pKa Values Using Internally Referenced Raman-Based pH Titration

“…[8][9][10][11][12][13] Biological thiols like glutathione and cysteine have multiple functions in vital biological processes in humans, animals and plants. [14][15][16][17] One key indicator of thiol reactivity is its pKa value.…”

Facile Method for Constructing Metallic Nanoarrays on a Solid Surface

“…Gold nanospheres, immobilized on top of 1-mercaptobenzoic acid monolayers, yielded a SERS enhancement factor of 10 7 , while other anisotropic shapes had enhancement factors of 10 8 to 10 9 . 91 Our highly anisotropic metallic nanoarrays therefore serve as highly localized light fields for enhancing SERS. In addition to SERS, surface enhanced fluorescence has also been reported for molecules near the surfaces of MNPs.…”