Single-Molecule Surface-Enhanced Raman Spectroscopy of Nonresonant Molecules

Abstract

Single-molecule surface-enhanced Raman scattering (SERS) detection of nonresonant molecules is demonstrated experimentally using the bianalyte SERS method. To this end, bianalyte SERS is performed at 633 nm excitation using the nonresonant molecule 1,2-di-(4-pyridyl)-ethylene (BPE) in combination with a benzotriazole derivative as a partner. The results are then extended to the even more challenging case of a small nonresonant molecule, adenine, using an isotopically substituted adenine as bianalyte SERS partners. In addition, SERS cross sections of single-molecule events are quantified, thus providing estimates of the enhancement factors needed to see them. It turns out that an enhancement factor on the order of approximately 5 x 10(9) was sufficient for single-molecule detection of BPE, while maximum enhancement factors of approximately 5 x 10(10) were observed in extreme cases. In the case of adenine, single-molecule detection was only possible in the rare cases with enhancement factors of approximately 10(11). This study constitutes a quantitative fundamental test into the lowest detection limits (in terms of differential cross sections) for single-molecule SERS.

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

“…These values are among the smallest values for molecules (except perhaps for N 2 and alkane molecules, which have s Raman B10 À 31 and 10 À 32 cm 2 sr À 1 , respectively, at NIR excitations 38,41 SECARS experimental setup. A sample-scanning nonlinear optical microscope was constructed for the single-particle SECARS measurements ( Supplementary Fig.…”

“…We then examined whether SECARS obtained using this approach could achieve single-molecule sensitivity for small molecules, which would require 38 an enhancement factor of B10 10 -10 11 . A polarization-sensitive CARS geometry 39 (with a polarization analyser oriented to transmit y-polarized light placed before the detector) was used to suppress B99% of the essentially x-polarized 22 background FWM signal, with the quadrumer dimensions slightly modified to reduce the unpolarized background two-photon luminescence ( Supplementary Fig.…”

“…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.…”

Surface-Enhanced Raman Scattering: Metal Nanostructures Coated With Langmuir-Blodgett Films

“…In 2006 Kalkan and Fonash reported SMD of fluorescein using SERS and Ag surfaces activated by laser 129 . Zhang et al 130 announced in 2009 SMD using SERS for azo dyes (related to human carcinogen) adsorbed on Ag particle aggregates in colloid, while Blackie et al 131 applied the bianalyte approach to detect adenine through SERS. The theoretical framework for the phenomenology and statistics of SERS signals from single molecules in the presence of the electromagnetic hot spots was put forward by Le Ru et al 132 , which could account for various experimental manifestations of the effect reported in the literature.…”

Culture‐Free Detection of Crop Pathogens at the Single‐Cell Level by Micro‐Raman Spectroscopy

“…Moreover, confocal micro‐Raman spectroscopy provides high spatial resolution and allows the differentiation of bacterial cells at the micrometric scale 13. In particular, surface‐enhanced Raman scattering spectroscopy is able to enhance the signal by 11 orders of magnitude, which is sufficient for single‐molecule detection 14. Therefore, micro‐Raman spectroscopy has been utilized to monitor bacterial development, probe cellular stress response, analyze functions of microbial communities, and detect clinically relevant bacteria in laboratory settings 11, 12, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24.…”