Quantitative evaluation of blinking in surface enhanced resonance Raman scattering and fluorescence by electromagnetic mechanism

Abstract

We analyze blinking in surface enhanced resonance Raman scattering (SERRS) and surface enhanced fluorescence (SEF) of rhodamine 6G molecules as intensity and spectral instability by electromagnetic (EM) mechanism. We find that irradiation of intense NIR laser pulses induces blinking in SERRS and SEF. Thanks to the finding, we systematically analyze SERRS and SEF from stable to unstable using single Ag nanoparticle (NP) dimers. The analysis reveals two physical insights into blinking as follows. (1) The intensity instability is inversely proportional to the enhancement factors of decay rate of molecules. The estimation using the proportionality suggests that separation of the molecules from Ag NP surfaces is several angstroms. (2) The spectral instability is induced by blueshifts in EM enhancement factors, which have spectral shapes similar to the plasmon resonance. This analysis provides us with a quantitative picture for intensity and spectral instability in SERRS and SEF within the framework of EM mechanism.

Recent Progress on Plasmon-Enhanced Fluorescence

“…Here From Equation (5), the fluorescence enhanced effect shows a balance between several processes including the increase of excitation rate by the local EM field, a radiative decay rate enhancement by SPCE, and quenched effect due to the nonradiative energy transfer from the fluorophore center to the metallic substrate, all of which critically depend on the distance between the fluorophore center and the metallic substrate [26].…”

One-dimensional plasmonic hotspots located between silver nanowire dimers evaluated by surface-enhanced resonance Raman scattering

“…13 For example, a single molecule SERRS observation is usually interrupted or terminated by desorption and carbonization of molecules at the hotspots. 6,13,14 Thus, it is important to increase the volume of the hotspots to reduce the instability and improve the investigations of the phenomena.…”

“…The strength of the SEF spectra compared to the SERRS spectra means small SEF quenching rates, pointing to a relatively large distance between the dye molecules and metal surfaces compared with that for NP dimers. 6 Note that the quenching rates are determined by the energy transfer from electronically excited molecules to metal surfaces. 24 The similarity between the SEF and conventional fluorescence implies that the plasmon resonance is too broad to cause spectral modulation in the SERRS and SEF spectra.…”

Recent progress and frontiers in the electromagnetic mechanism of surface-enhanced Raman scattering

“…(2)) was also examined by several experiments pertaining to the SERS effects, e.g., the refractive index dependence of the SERS spectra and the relationships between SERS and surfaceenhanced hyper Raman scattering (SEHRS), and has been confirmed as qualitatively correct [36][37][38]. However, in the studies of the SERS blinking, some limitations and problems of the EM mechanism were also discovered [33]. In Section 2.3, we introduce the problems and limitations in EM mechanism.…”

“…A detailed description of the twofold EM mechanism is provided herein, in Section 2.2. Note that a quantitative analysis of the blinking in SERS and surface-enhanced fluorescence (SEF) indicates that the two-fold EM mechanism is intrinsically correct [33].…”