Ag Nanocrystal Junctions as the Site for Surface-Enhanced Raman Scattering of Single Rhodamine 6G Molecules

Abstract

Atomic force microscopy (AFM) measurements show that the Ag nanoparticles that yield surface-enhanced Raman scattering (SERS) of single molecules of Rhodamine (R6G) are all compact aggregates consisting of a minimum of two individual particles. Comparison of 514.5 and 632.8 nm excitation shows that the single molecule R6G signal is significantly higher when the excitation wavelength is resonant with the absorption band of R6G and suggests that the Raman excitation spectrum follows the absorption profile for R6G. We have also observed an interesting superlinear power dependence of the SERS signal. On average, by increasing the incident power by 2 orders of magnitude and decreasing the integration time by the same factor to maintain constant fluence, increases of 4 to 6 times were observed in the SERS intensity. We discuss these results in terms of model where the R6G molecule that yields single molecule SERS signals is located at the junction of two Ag nanoparticles. We have also modeled the system using molecular resonance Raman theory to provide further insight into the enhancement mechanism.

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“…10). This result is roughly consistent with recent SERS data, which showed the presence of intense signals that appeared to be located between clusters of particles [20,21]. Emission spectra were collected from eight selected regions of varying brightness.…”

“…Our findings show no enhancement in fluorescence emission after chloride dipping, which is consistent with MEF being a through-space phenomenon as compared to SERS, which conversely is thought to be a contact (or near contact) interaction with a metallic surface [20,21].…”

Controllable Cobalt Oxide/Au Hierarchically Nanostructured Electrode for Nonenzymatic Glucose Sensing

“…These structures, which are typically made of spherical silica cores surrounded by a layer of noble metal aggregates, have variation in size, shape and surface morphology due to the random nature of aggregation [64,65]. The polydispersity found within a given ensemble of shells will lead to a broadening of the extinction line width [66].…”

“…Following incubation, the bioconjugated and cell bound HGNs were exposed to NIR laser with 32 W/cm 2 power output for 5 min. Release of DOX was monitored by 64 Cu radiolabeling. In evaluating post-treatment for cytotoxicity, mice treated with free DOX suffered the greatest toxicity, with 3/5 subjects dying during the course of treatment from vacuolar cardiomyopathy.…”

“…The highly localized EM field of the metal, due to SPR, is known to enhance the Raman signal by 5-10 orders of magnitude [273][274][275][276]. Aggregation of metal nanoparticles can also be employed to produce significant SERS enhancement through the generation of hot spots which result from EM coupling between particles in near field proximity to one another [56,64,182,198,277,278].…”