Surface-Enhanced Raman and Surface-Enhanced Hyper-Raman Scattering of Thiol-Functionalized Carotene

Abstract

A thiol-modified carotene, 7′-apo-7′-(4-mercaptomethylphenyl)-β-carotene, was used to obtain nonresonant surface-enhanced Raman scattering (SERS) spectra of carotene at an excitation wavelength of 1064 nm, which were compared with resonant SERS spectra at an excitation wavelength of 532 nm. These spectra and surface-enhanced hyper-Raman scattering (SEHRS) spectra of the functionalized carotene were compared with the spectra of nonmodified β-carotene. Using SERS, normal Raman, and SEHRS spectra, all obtained for the resonant case, the interaction of the carotene molecules with silver nanoparticles, as well as the influence of the resonance enhancement and the SERS enhancement on the spectra, were investigated. The interaction with the silver surface occurs for both functionalized and nonfunctionalized β-carotene, but only the stronger functionalization-induced interaction enables the acquisition of nonresonant SERS spectra of β-carotene at low concentrations. The resonant SEHRS and SERS spectra are very similar. Nevertheless, the SEHRS spectra contain additional bands of infrared-active modes of carotene. Increased contributions from bands that experience low resonance enhancement point to a strong interaction between silver nanoparticles and electronic levels of the molecules, thereby giving rise to a decrease in the resonance enhancement in SERS and SEHRS.

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“…The spectra of pristine SWNHs and SWNH‐ICGs showed a D band at 1341 cm −1 and a G band at 1572 cm −1 . In the spectrum of SWNH‐ICGs, the ICG on the surface of the SWNHs shows double peaks at 1258 and 1294 cm −1 attributable to protruding methyl groups, [56] and the strong Raman signal from 1483 to 1643 cm −1 can be assigned to the C=C stretching of polyene chains and benzene rings . Owing to overlap of the peaks of SWNHs and ICG in the spectrum of the SWNH‐ICG nanohybrids, the intensity of the G band at around 1572 cm −1 is significantly increased.…”

Surface enhanced hyper Raman scattering (SEHRS) and its applications

“…44,45,83,86 Experiments using one individual wavelength were also reported using more compact, turn-key mode-locked Nd:YAG lasers with pulse durations of a few picoseconds (1-10 ps) with relatively high peak powers. 17,20,[22][23][24]64,70,82,85 Excitation of SEHRS in the near infrared can also be combined with excitation of one-photon SERS in the near infrared in the identical sample. 22,44,64 In spite of their relatively low peak intensities, tunable synchronously pumped optical parametric oscillators (OPOs) with signals between 0.72 and 0.99 mm or with idler pulses from 1.15 up to 2 mm can provide possibilities for excitation of SEHRS.…”

“…85 The functionalization of carotene, which leads to a stronger interaction with the silver surface gave the possibility of obtaining non-resonant SERS spectra in solution at low concentration. The SEHRS spectra (Fig.…”

“…9A) spectra is reported, since the interaction with the silver surface lowers the symmetry of the adsorbed molecules. 85 The strong contribution by resonance enhancement is obvious in several reports comparing HRS with resonant SEHRS spectra, for example for CV 86 and R6G. 66,86 Fig.…”

“…9C) were used to study the interaction with silver nanoparticles. 85 It was discussed that the interaction with the silver surface occurs via the p-electrons of the polyene chain for both functionalized and non-functionalized b-carotene, but only the stronger, functionalization induced interaction enables the acquisition of non-resonant SERS spectra of b-carotene at low concentrations (Fig. 9C).…”