A Frequency Domain Existence Proof of Single-Molecule Surface-Enhanced Raman Spectroscopy

Abstract

The existence of single-molecule surface-enhanced Raman spectroscopy (SMSERS) is proven by employing a frequency-domain approach. This is demonstrated using two isotopologues of Rhodamine 6G that offer unique vibrational signatures. When an average of one molecule was adsorbed per silver nanoparticle, only one isotopologue was typically observed under dry N2 environment. Additionally, the distribution of vibrational frequencies hidden under the ensemble average is revealed by examining the single-molecule spectra. Correlation with transmission electron microscopy reveals that SMSERS active aggregates are composed of multiple randomly sized and shaped nanoparticles. At higher coverage and in a humid environment, adsorbate interchange was detected. Using 2D cross correlation, vibrational modes from different isotopologues were anti-correlated, indicating that the dynamic behavior was from multiple molecules competing for a single hot spot. This allows hot-spot diffusion to be directly observed without analyzing the peak intensity fluctuations.

Coherent anti-Stokes Raman scattering with single-molecule sensitivity using a plasmonic Fano resonance

“…Surfaceenhanced Raman scattering (SERS) [1][2][3] has advanced to the detection limit of individual resonant molecules when the molecule is closely associated with the nanoscale junction between chemically fabricated nanoparticles [4][5][6][7][8][9][10][11][12] . Here two enhancement mechanisms are at play: the enhanced Raman cross-section of a molecule when the excitation laser is resonant with an electronic excitation of the molecule; and the extremely large local electromagnetic (EM) field enhancement generated by optically exciting the collective plasmon mode of the two closely adjacent nanoparticles.…”

“…8 and Supplementary Note 4). We used the bi-analyte method 7,10 , where p-MA and adenine (both Raman cross-sections B10 À 30 cm 2 sr À 1 in air for NIR excitation 38,40 ) have clearly distinguishable Raman spectra allowing for the unequivocal identification of each molecule. A mixed solution of equal concentrations (100 nM) of the two molecules was dropcasted onto multiple (49) quadrumers for SECARS.…”

Silica-coated dimers of silver nanospheres as surface-enhanced Raman scattering tags for imaging cancer cells

“…SERS signals were collected by point mapping 24 Â 24 mm areas, with 2.0 mm steps, and l ex ¼ 514 nm, t ¼ 10 s and P laser ¼ 2 mW for each point measurement. The intensities of SERS peak at 1588 cm 21 were chosen for generating SERS mapping image with user-defined Matlab (MathWorks) programs. ORIGINLAB software (Northampton, MA, USA) was used for SERS spectra baseline correction.…”

“…To quantitatively compare the SERS enhancements between these tags, we used the peak at 1588 cm 21 (the strongest band in the 4-MBA spectra) to calculate the SERS EF for Figure 3. SERS spectra recorded from individual SERS tags supported on glass slides: (a) dimer tags, (b) sphere tags and (c) cube tags.…”

“…intensified E-fields located at the junctions between nanoparticles [20][21][22][23]. In this regard, different types of coupled nanoparticles have been prepared for the use of fabricating highly sensitive SERS tags [24][25][26][27][28][29].…”