Surface-Enhanced Femtosecond Stimulated Raman Spectroscopy

Abstract

Surface-enhanced Raman spectroscopy (SERS) and femtosecond stimulated Raman spectroscopy (FSRS) have revolutionized the Raman spectroscopy field. SERS provides spectroscopic detection of single molecules, and FSRS enables the acquisition of Raman spectra on the ultrafast time scale of molecular motion. Here, we present the first successful combination of these two techniques, demonstrating surface-enhanced femtosecond stimulated Raman spectroscopy (SE-FSRS) using gold nanoantennas with embedded reporter molecules. Using a picosecond Raman and femtosecond probe pulse, the time- and ensemble-averaged enhancement factor is estimated to be in the range of 10(4)-10(6). We report the line shapes, power dependence, and magnitude of the SE-FSRS signal and discuss contributions to sample degradation on the minute time scale. With these first successful proof-of-principle experiments, time-resolved SE-FSRS techniques can now be rationally attempted with the goals of investigating the dynamics of plasmonic materials as well as examining the contributions of environmental heterogeneities by probing more homogeneous molecular subsets.

First demonstration of surface enhanced-stimulated Raman spectroscopy (SE-SRS) using low-power CW sources

“…We were able to achieve SE-SRS using power densities that are orders of magnitude smaller than Frontiera et al 4 -our pump beam peak power was 0.01 W cm À2 versus 0.1 W cm À2 for theirs, while their probe beam was 10 W cm À2 versus 0.004 W cm À2 for ours. Since it is assumed that only dimers contribute to the signal, and they comprise 10% of the sample, one can detect dimer-only concentrations as low as 6 pM.…”

“…2) the same characteristics as the spontaneous Raman signal, without a dispersive response as seen by Frontiera et al 4 In particular, the 1205 cm À1 mode is the most prominent in the SERS spectra, and has been assigned by Zhuang et al 5 to the symmetric stretching of C-C and bending vibrations of pyridl C-N bonds. The SRL is proportional to the pump and Stokes power, as expected.…”

Tip-enhanced Raman spectroscopy: From concepts to practical applications

“…As a result, particular molecular systems are expected to be more stable than others under pulsed irradiation. Changes in the fine structure of the probe are also possible in analogy to previous studies on plasmonic colloids and surfaces, [26,33] and preferred probe geometries and compositions may be discerned.…”

“…The Van Duyne group pioneered surface-enhanced FSRS (SE-FSRS), [26] demonstrating ~10 4 to 10 6 signal enhancement using Au nanoantennas. Further work illustrated that Fano-like couplings between molecule and plasmon cause dispersive lineshapes in SE-FSRS.…”

Surface enhanced hyper Raman scattering (SEHRS) and its applications

“…4,5 Apart from a so-called chemical contribution, the enormous enhancements were attributed mostly to the highly confined local optical fields of the nanostructures, 6,7 arising from resonances of their localized surface plasmons (oscillations of the conductive electrons relative to the metal nuclei) with both incident and Raman scattered light. 8 In general, all incoherent and also coherent optical effects can benefit from enhanced local optical fields, among them several other vibrational spectroscopies, such as IR absorption, 9 hyper Raman scattering (HRS), 10,11 coherent anti-Stokes Raman scattering (CARS), 12,13 femtosecond stimulated Raman scattering (fs SRS), 14 and second hyper Raman scattering. 15 This led to the development of several related surface enhanced spectroscopic methods.…”