Surface-Enhanced Raman Scattering of 4-Aminobenzenethiol in Ag Sol: Relative Intensity of a₁- and b₂-Type Bands Invariant against Aggregation of Ag Nanoparticles

Abstract

4-Aminobenzenthiol (4-ABT) is an unusual molecule, showing variable surface-enhanced Raman scattering (SERS) spectra depending upon measurement conditions. In an effort to reduce ambiguity and add clarity, we have thus conducted an ultraviolet-visible (UV-vis) extinction measurement, along with Raman scattering measurement, after adding 4-ABT into aqueous Ag sol. Upon the addition of 4-ABT, the surface plasmon absorption band of Ag at 410 nm gradually diminished and, concomitantly, a weak and broad band developed at longer wavelengths, obviously because of the aggregation of Ag nanoparticles. At the same time, the Raman scattering peaks of 4-ABT varied in intensity as the Ag particles proceeded to form aggregates. A close examination revealed that the peak intensity of the ring 7a band of 4-ABT, a typical a(1) vibrational mode, could be correlated with the UV-vis extinction of the Ag sol measured at the excitation laser wavelength. In a separate Raman measurement conducted using sedimented Ag colloidal particles, 4-ABT was found not to be subjected to any surface-induced photoreaction, implying that all of the observable Raman peaks were, in fact, solely due to 4-ABT on Ag. The intensities of the b(2)-type bands, such as the ring 3, 9b, and 19b modes of 4-ABT, were then analyzed and found to be invariant with respect to the 7a band, irrespective of the extent of Ag aggregation as far as at a fixed excitation wavelength. The intensity ratio of the b(2)-type/7a bands would then reflect the extent of the chemical enhancement that was involved in the SERS of 4-ABT in aggregated Ag sol.

Spectroelectrochemical Study of the Photoinduced Catalytic Formation of 4,4′-Dimercaptoazobenzene from 4-Aminobenzenethiol Adsorbed on Nanostructured Copper

“…Since then, many papers have been published, and the three strongly enhanced Raman peaks have been widely considered as an experimental evidence of a chemical mechanism of SERS. [20][21][28][29][30][31] Alternatively, it has been also proposed, based on the spectral similarity of 4-ABT and 4,4'-dimercaptoazobenzene (4,4'-DMAB) adsorbed on Ag, that these bands correspond to N=N stretching (a g symmetric vibrational modes) of 4,4'-DMAB produced from 4-ABT via a photocatalytic coupling reaction. 24,32 Recently, similar SERS spectra have been obtained when 4-ABT was adsorbed on nanostructured Pt substrates.…”

Intense Raman scattering on hybrid Au/Ag nanoplatforms for the distinction of MMP-9-digested collagen type-I fiber detection

“…5 (a) and (b), strong Raman bands appear, which are attributed to the b 2 -type bands of 4-ABT (as listed in Table S4), in particular for sample N_6 (i.e, 4-ABT-coated Ag NPs on S_3fibAu_NR). The most intense Raman shift appeared at 1586 cm À 1 , which is assigned to the ring C-C stretching modes (Abdelsalam, 2009;Cao and Che, 2014;Kim et al, 2012Kim et al, , 2011aKim et al, , 2011bShao et al, 2014;Uetsuki et al, 2010), most probably due to a strong electronic charge transfer between 4-ABT-coated Ag NPs and Ag NCsfibAu_NR at the small gaps, as shown in Fig. 4(d-ii) and (d-iii) (Abdelsalam, 2009;Cao and Che, 2014;Kim et al, 2012Kim et al, , 2011aKim et al, , 2011bShao et al, 2014;Uetsuki et al, 2010).…”

“…CV peak at 1618 cm À 1 was used as index for relation of relative Raman intensities with respect to Au or Ag NCs on fibAu_NR. chemistry of Ag (relatively dark) caused by 4-ABT (Kim et al, 2011a(Kim et al, , 2011b. In Fig.…”

Different behaviors in the transformation of PATP adsorbed on Ag or Au nanoparticles investigated by surface-enhanced Raman spectroscopy – A study of the effects from laser energy and annealing

“…It that the so-called ''b 2 modes'' signal is actually from the a g modes of DMAB as a product of the laser-induced chemical transformation of PATP, considering the traditional metal-to-adsorbate charge transfer mechanism [16][17][18][19][20][21] could not explain the laser power dependent behavior of ''b 2 modes''. Furthermore, several works have pointed out that in addition to surface plasmon resonance (SPR), the adsorbed triplet oxygen molecule ( 3 O 2 ) is also crucial for the chemical transformation of PATP to DMAB [5,10].…”