Concentration‐dependent surface‐enhanced Raman scattering and molecular dynamic study of dimethyl formamide

Abstract

A concentration-dependent Raman study of dimethyl formamide (DMF) in Ag nanocolloidal solution was carried out in order to observe the effect of concentration on the surface enhancement mechanism. The Raman spectra in the region 900-2200 cm −1 comprising four prominent Raman modes were measured experimentally and analyzed at five different concentrations: 1, 3, 5, 7, 10 mM, and in neat DMF. In order to find the possible configurations of DMF + Ag complexes, density functional theory (DFT) calculations were carried out taking one, three and five Ag atom clusters. The Raman spectra of unconjugated DMF, DMF + Ag and DMF + 3Ag complexes were calculated theoretically to assign the vibrational modes under consideration more accurately and to understand the wavenumber shift and change in intensity observed in experimental measurements. Water present in the colloidal solution may also conjugate with DMF and its complexes with Ag. In order to see the influence of water on the wavenumber shift and intensity changes, we have also obtained the optimized structures and Raman modes of DMF + water and DMF + water + Ag complexes. Good agreement between the experimental and theoretical wavenumber shifts has been obtained by using B3LYP functional theory and CEP-31G basis set for the DMF + Ag complex. The experimental results suggest that the SERS enhancement is concentration-dependent. The concentration-dependent linewidth shows the existence of the phenomena of motional narrowing and diffusion dynamics in the colloidal solution.

In-Situ Immobilization of Silver Nanoparticles on Self-Assembled Honeycomb-Patterned Films Enables Surface-Enhanced Raman Scattering (SERS) Substrates

“…This means a much larger possibility for R6G molecules to be located at the hot spots and a much closer distance between R6G and Ag NPs, leading to greater enhancement. Similar concentration dependence has been reported by other groups. , …”

“…Compared with SERS spectra reported by Hirai et al and Gupta et al, where 1375 and 1680 cm –1 because of the aromatic C–C stretching vibrations were found to be the strongest peaks, respectively, our spectra show that the peak at 614 cm –1 arising from C–C–C ring in-plane bending vibration (Table S1 of the Supporting Information) shows much stronger enhancement (Figure ) . It may be induced by the molecular orientation of analytes on the patterned substrates. , However, it is still unknown and needs further investigation. This special enhancement at Raman shift around 614 cm –1 will be helpful in the detection of analytes such as some kinds of pesticides and viruses with characteristic peaks in this range, for example, adenovirus …”

Probing Interaction between Individual Submonolayer Nanoislands and Bulk MoS2 Using Ambient TERS

“…This is expected from the well-known motional narrowing effect. 52 For close-packed molecules, the vibrational motion is restricted and the dephasing time is increased. The vibration will essentially occur at an averaged frequency.…”

“…Independent then from the adsorbate–substrate interaction, there is a narrowing of the peak position and the peak intensity distribution caused by the molecular–molecular interaction in the island. This is expected from the well-known motional narrowing effect . For close-packed molecules, the vibrational motion is restricted and the dephasing time is increased.…”

Recent advances in linear and nonlinear Raman spectroscopy II

“…The Au nanoparticles were conjugated with fluorescein isothiocyanate (which acts as the Raman probe) and goat anti-h-IgG (immunoglobulin) and the resultant particles were used for the detection of h-IgG. SERS and molecular dynamic study of dimethyl formamide in Ag nanocolloidal solution was carried out by Mishra et al 21 , in order to observe the effect of concentration on the surface enhancement mechanism. DFT calculations produced good agreement between experimental and theoretical data and the results suggested that the SERS enhancement is concentration-dependent.…”