Surface‐ and Resonance‐Enhanced Micro‐Raman Spectroscopy of Xanthene Dyes: From the Ensemble to Single Molecules

Vosgröne, T.; Meixner, A. J.

doi:10.1002/cphc.200400395

Cited by 112 publications

(91 citation statements)

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“…As shown in the lowest part of Scheme 1, the XN dyes used in this study have a planar xanthene skeleton with a phenyl ring that is perpendicular to the skeleton. The strong electric dipole transition moment (500-600 nm) of the XN dye is parallel to the long axis of the xanthene skeleton, 47,48 as shown by the arrow. The phenyl ring is able to swivel around the phenyl-xanthene bond, and the carboxyl/carboxyl-ester group can swing around the carbon-carbon bond.…”

Section: /40mentioning

confidence: 99%

pH-Responsive Switchable Aggregation Phenomena of Xanthene Dyes Adsorbed on Tungsten(VI) Oxide Colloid Surface

Adachi

Watanabe

Yamazaki

2014

Ind. Eng. Chem. Res.

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The surface interactions between xanthene (XN) dyes, including rhodamine B, rhodamine 3B, rhodamine 19, rhodamine 6G, rhodamine 110, and rhodamine 123, and tungsten(VI) oxide (WO 3 ) colloid particles were investigated. These XN dyes were strongly adsorbed as monolayer onto the WO 3 surface via the electrostatic interaction between their peripheral cationic amino-substituents and negatively surfacecharged WO 3 colloid particles, and most of ones adsorbed eventually formed the stable π-stacked dimers.The geometry of dimers formed on the WO 3 colloid surface is discussed on the molecular exciton theory framework. Cationic XN dyes formed the approximately ideal face-to-face H-dimers on the WO 3 colloid surface, whereas zwitterionic ones had a higher tendency to form the oblique J-dimers. Additionally, we have experimentally demonstrated the possibility of pH-induced switching between H-and J-aggregation modes of the XN dye's dimers formed on the WO 3 colloid surface. The findings lead to a better understanding of organic dye's adsorption/aggregation behaviors on the metal oxide surface.

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Section: /40mentioning

confidence: 99%

pH-Responsive Switchable Aggregation Phenomena of Xanthene Dyes Adsorbed on Tungsten(VI) Oxide Colloid Surface

Adachi

Watanabe

Yamazaki

2014

Ind. Eng. Chem. Res.

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“…[3,8] However, it is difficult to determine how much of the enhancement is due to field effects, because conventional resonance Raman intensities are difficult to measure directly on resonance.…”

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Resonance Raman Cross‐Sections and Vibronic Analysis of Rhodamine 6G from Broadband Stimulated Raman Spectroscopy

2008

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Surface-enhanced resonance Raman spectroscopy (SERRS) [1] is a powerful technique for obtaining vibrational spectra of fluorescent molecules on metal surfaces. Raman scattering is strongly enhanced by two mechanisms:[2] 1) molecular resonance occurs when the probe laser lies within the molecular electronic absorption, 2) electromagnetic or chemical enhancement occurs due to interaction with the metal surface. The combination of these effects results in a 10 14 -10 15 -fold enhancement in scattering, enabling single-molecule SERRS spectroscopy.[3] However, due to the lack of resonance Raman (RR) spectra of fluorophores used in SERRS, the enhancement contributions from resonance and surface effects are difficult to separate and quantify. Although Raman techniques such as picosecond RR spectroscopy using Kerr gating [4] and coherent anti-Stokes Raman scattering (CARS) [5] are capable of rejecting fluorescence, these techniques are not ideal. Kerr-gated RR yields poor collection efficiency, while CARS has more complex lineshapes resulting in spectra that are more difficult to analyze. In contrast, the recently developed femtosecond stimulated Raman spectroscopy (FSRS) enables us to acquire and quantify RR cross-sections even in the presence of strong fluorescence.[6] Here we exploit this fluorescence rejection capability of FSRS to obtain a RR spectrum of the highly fluorescent dye rhodamine 6G (R6G) and quantify its resonance Raman scattering cross-sections. This result allows an estimate of the magnitude of surface and resonance enhancements in SERRS.Recent progress has advanced SERRS technology to the single-molecule detection limit.[3] SERRS experiments performed at wavelengths close to the absorption maximum of R6G resulted in a Raman cross-section of 10 À14 cm 2 molecule À1 .[3] Comparable or higher enhancements were reported for molecules adsorbed on colloidal silver or gold clusters in SERS experiments performed at near-infrared excitation: however, the anomalous enhancements may be due to the presence of colloidal clusters where the concentration of adsorbed molecules is higher.[7] Therefore, SERRS experiments with excitation wavelengths close to the absorption maximum are the most direct way of achieving optimal sensitivity for single molecule detection. [3,8] However, it is difficult to determine how much of the enhancement is due to field effects, because conventional resonance Raman intensities are difficult to measure directly on resonance.FSRS is a powerful new structural probe of chemical and biological systems in both steady-state and time-resolved studies.[9] Following a femtosecond actinic pulse, the simultaneous interaction of a 800 nm narrow-bandwidth picosecond Raman pump and a broadband femtosecond continuum Raman probe leads to the production of sharp vibrational gain features on top of the dispersed probe envelope. These gain features constitute the broadband stimulated Raman spectrum (SRS). FSRS has been successfully used to study a variety of chemical reaction dynamics-such as the first s...

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“…In general, SM SERS literature reports spectra that are clearly characteristic for the investigated molecule and thus allow identification of the adsorbed species, also at any time during serial acquisition. [6][7][8][9][10][11][12][13] Surface diffusion may indeed account for intensity fluctuations in SERS, where a rough surface provides a variety of different adsorption sites or hot spots for the molecule. 6,12 Changes in the band positions which have been observed in SM SERS studies include a narrowing or splitting of bands 11 and slight shifts of ± 2-5 cm −1 of band positions (which by far exceeds the resolution of the instrument of 25 cm −1 employed by Neacsu et al).…”

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“…the whole spectrum shifts slightly! 11,12 Adding SM spectra (i.e. averaging over a time series) must lead to a spectrum which is similar to an "ensemble" spectrum, a spatial average over many molecules, for example, an adsorbate monolayer.…”

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Comment on “Scanning-probe Raman spectroscopy with single-molecule sensitivity”

Domke

Pettinger

2007

Phys. Rev. B

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We reinterpret the scanning-probe Raman spectra shown in the above paper [C.C. Neacsu et al., Phys. Rev. B 73, 193406 (2006)] and compare it to a variety of single-molecule surface-enhanced Raman (SER) studies. The observed blinking behaviour and spectral features must be attributed to carbon contaminations rather than to Malachite Green (MG) single molecules, because, under the given experimental conditions, the extremely high field enhancement of 5 x 10 9 will inevitably lead to a quick (photo)decomposition of the adsorbate.PACS numbers: 68.37. Uv, 33.20.Fb In a recent paper, 1 Neacsu et al. present an AFMtip-enhanced Raman (TER) study on Malachite Green (MG) at gold films. They analyze near-field (tip approx. 5 nm above sample surface) and far-field (tip several 100 nm above sample surface) spectra of a Au surface covered with MG at low adsorbate concentration in correlation with a DFT calculation as well as of the clean Au surface. In a time series of 100 AFM-TER spectra (1 s integration time per spectrum) for a submonolayer MG surface coverage, spectral diffusion is observed and interpreted as characteristic single-molecule (SM) behaviour due to "random surface diffusion of MG in and out of the near-field-confined surface area under the tip, facilitated by the thin most likely liquid water layer on the gold surface". A Raman enhancement of up to 5 x 10 9 is derived from comparison of tip-enhanced versus far-field response of the same surface monolayer.Figures 2b and 2c in Ref. 1 show a near-field (tip approached) and a far-field (no tip) spectrum of MG on Au, respectively. The far-field spectrum exhibits the typical Raman features of MG which can be ssigned according to Lueck et al. 2 ) and a DFT calculation (Fig. 2c in Ref. 1), but the near-field spectrum does not resemble neither the far-field nor the DFT spectrum.The authors state that "the pronounced spectral difference between the tip-enhanced and the far-field response resembles the observation frequently made in SERS" (surface-enhanced Raman spectroscopy) and claim that "this characteristical difference is the result of the strong optical field localization, and related to different selection rules for the tip-scattered response, akin to SERS". Different selection rules cannot be held responsible for the so remarkable differences between near-field and farfield spectra presented by Neacsu et al. Note in this context that SER as well as TER spectra usually strongly resemble the far-field spectra of the investigated species in the band positions, in a way that the unambiguous identification of the molecule is always possible. In fact, a comparison of the Raman bands found in literature for MG in water (far-field, Ref. 2) and MG on silver colloids (near-field, Ref.3) does not reveal any band displacements larger than ± 3 cm −1 , and also the relative band intensities are similar. Variations in band intensities may occur according to surface selection rules (changes in the polarizability perpendicularly to the surface, i.e. parallel to the incident...

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Surface‐ and Resonance‐Enhanced Micro‐Raman Spectroscopy of Xanthene Dyes: From the Ensemble to Single Molecules

Cited by 112 publications

References 50 publications

pH-Responsive Switchable Aggregation Phenomena of Xanthene Dyes Adsorbed on Tungsten(VI) Oxide Colloid Surface

pH-Responsive Switchable Aggregation Phenomena of Xanthene Dyes Adsorbed on Tungsten(VI) Oxide Colloid Surface

Resonance Raman Cross‐Sections and Vibronic Analysis of Rhodamine 6G from Broadband Stimulated Raman Spectroscopy

Comment on “Scanning-probe Raman spectroscopy with single-molecule sensitivity”

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