Single Molecule Tip-Enhanced Raman Spectroscopy with Silver Tips

Abstract

We present single molecule tip-enhanced resonance Raman spectra from brilliant cresyl blue (BCB) submonolayers adsorbed on a planar Au surface with Ag tips. A gap of 1 nm between a Ag tip and the Au substrate was employed to create a highly enhanced electric field and to generate Raman scattering from an area of ∼100 nm 2 . Three lines of evidence are presented to prove the single molecule sensitivity of our experiments: (1) Extremely diluted samples were used. Estimations show that at most a few molecules were excited by the Ag tip. (2) Spectroscopic fluctuations, including intensity fluctuations, frequency shifts, and line shape changes were observed. A histogram analysis of the intensity fluctuations of two different BCB coverages was carried out. The results clearly show the features of single molecule behavior. (3) Discrete signal losses also were observed. This is because of photochemical processes involving single molecules. Besides BCB, which shows a strong resonant absorption at 633 nm (the wavelength of the excitation laser), a self-assembled monolayer of benzenethiol, which does not strongly absorb at 633 nm, was studied. Good quality spectra were recorded with a short exposure time (10 s) and time-dependent spectral changes were also observed.

Review of near-field optics and superlenses for sub-diffraction-limited nano-imaging

“…Leveraging the increased Raman scattered light output of SERS with the highly localized field enhancement of apertureless SNOM, it is possible to create sub-diffraction-limited spectroscopic images with TERS that provide sufficient light output for detection. [145][146][147][148][149][150][151][152][153][154][155][156][157][158][159][160] …”

Surface-enhanced Raman spectroscopy at single-molecule scale and its implications in biology

“…They claimed that they can attain SM sensitivity because the Raman band from brilliant cresyl blue shows fluctuations in intensity and to a minor extent also in frequency [83,86], which is a possible indicator for SM behaviour as discussed in §2 (the characteristics of SM-SERS). Another popular dye used for SM-TERS study is malachite green isothiocyanate [58,87,88], which has a strong adsorption band centred around the excitation line at 632.8 nm and exhibits strong fluorescence as reported by Domke et al [89].…”

Combined Antenna and Localized Plasmon Resonance in Raman Scattering from Random Arrays of Silver-Coated, Vertically Aligned Multiwalled Carbon Nanotubes

“…39 Also, in a study of the distribution of localized site Raman enhancements on nanostructured Ag substrates it was found that over 50% of the Raman signal originated from less than 1% of the molecules. 9 Clearly, it takes only a very small percentage of hot-spot area to make a substantive difference to the average SERS EF.…”