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Surface-enhanced optical phenomena

Ever since an experimental observation (1974) of large Raman scattering cross sections from pyridine molecules adsorbed onto silver electrodes, there have been considerable efforts to understand and produce materials demonstrating “surface-enhancement.” Metallic, nanostructured substrates have the ability to generate intense optical fields localized to subwavelength regions that are orders of magnitude larger than the incident optical fields. These enhanced fields can amplify certain optical effects, such as Raman scattering, fluorescence, harmonic generation, and four-wave mixing. We are working on developing different types of surfaces that enhance these processes, for applications in molecular sensing and spectroscopy.
Nonlinear plasmonics: SERS hot spot isolation and enhanced laser cell transfection, at UCLA IEEE photonics society seminar, University of California, Los Angeles (Westwood, CA), Thursday, February 4, 2010:
talk_1554.pdf
Surface-enhanced Raman scattering (SERS) is one of the most sensitive molecular spectroscopy techniques currently available. Using SERS, it is possible to obtain vibrational spectra from chemical quantities as small as a single molecule. However, it is challenging to have molecules of interest adsorb specifically to a substrate’s “hot spots,” or regions of largest electromagnetic enhancement. I will describe a nonlinear optical technique that masks SERS substrates such that only hot spots are available as molecular adsorption sites. Using this approach, we have demonstrated a 27-fold... Read more about Nonlinear plasmonics: SERS hot spot isolation and enhanced laser cell transfection
Plasmon-enhanced ultrafast laser cell transfection, at Photonics West 2011 (San Francisco, CA), Sunday, January 23, 2011:
talk_1700.pdf
We present a method for transfecting biological cells using ultrafast plasmons excited on large areas of bio-compatible, nano-pyramid substrates. This technique does not employ any potentially toxic chemical transfection reagents or metallic nanoparticles. Leveraging the field enhancement supported by these pyramidal plasmonic nanostructures, we generate localized, transient pores in the membranes of large numbers of cells at a rate of approximately 10^4 per second. Diffusion through these pores enables the delivery of functional short interfering RNA (siRNA) molecules into the cells. We... Read more about Plasmon-enhanced ultrafast laser cell transfection
Nonlinear plasmonics: SERS hot spot isolation and enhanced laser cell transfection, at Stanford University (Stanford, CA), Tuesday, January 26, 2010:
talk_1553.pdf
Surface-enhanced Raman scattering (SERS) is one of the most sensitive molecular spectroscopy techniques currently available. Using SERS, it is possible to obtain vibrational spectra from chemical quantities as small as a single molecule. However, it is challenging to have molecules of interest adsorb specifically to a substrate’s “hot spots,” or regions of largest electromagnetic enhancement. I will describe a nonlinear optical technique that masks SERS substrates such that only hot spots are available as molecular adsorption sites. Using this approach, we have demonstrated a 27-fold... Read more about Nonlinear plasmonics: SERS hot spot isolation and enhanced laser cell transfection
Nonlinear plasmonics: SERS hot spot isolation and enhanced laser cell transfection, at Northwestern University (Evanston, IL), Thursday, February 25, 2010
Surface-enhanced Raman scattering (SERS) is one of the most sensitive molecular spectroscopy techniques currently available. Using SERS, it is possible to obtain vibrational spectra from chemical quantities as small as a single molecule. However, it is challenging to have molecules of interest adsorb specifically to a substrate’s “hot spots,” or regions of largest electromagnetic enhancement. I will describe a nonlinear optical technique that masks SERS substrates such that only hot spots are available as molecular adsorption sites. Using this approach, we have demonstrated a 27-fold... Read more about Nonlinear plasmonics: SERS hot spot isolation and enhanced laser cell transfection
Isolating surface-enhanced Raman scattering hot spots using surface-enhanced multiphoton lithography, at Photonics West 2010 (San Francisco, CA), Monday, January 25, 2010:
talk_1552.pdf
We present a method for improving femtomole-level trace detection (10^9 molecules) using large-area surface-enhanced Raman scattering (SERS) substrates. Using multiphoton-induced exposure of a commercial photoresist, we physically limit the available molecular adsorption sites to only the electromagnetic “hot spots” on the substrate. This process prevents molecules from adsorbing to sites of weak SERS enhancement, while permitting adsorption to sites of extraordinary SERS enhancement. For a randomly adsorbed submonolayer of benzenethiol molecules the average Raman scattering cross section of... Read more about Isolating surface-enhanced Raman scattering hot spots using surface-enhanced multiphoton lithography
E. D. Diebold, N. H. Mack, S. K. Doorn, and E. Mazur. 2009. “Femtosecond laser-nanostructured substrates for surface-enhanced Raman scattering.” Langmuir, 25, Pp. 1790–1794. Publisher's VersionAbstract
We present a new type of surface-enhanced Raman scattering (SERS) substrate that exhibits extremely large and uniform cross-section enhancements over a macroscopic (greater than 25 mm2) area. The substrates are fabricated using a femtosecond laser nanostructuring process, followed by thermal deposition of silver. SERS signals from adsorbed molecules show a spatially uniform enhancement factor of approximately 107. Spectroscopic characterization of these substrates suggests their potential for use in few or single-molecule Raman spectroscopy.
E. D. Diebold, P. Peng, and E. Mazur. 2010. “Surface-enhanced Raman scattering hot spot isolation using surface-enhanced multiphoton lithography.” In . Photonics West. Publisher's VersionAbstract
In this Manuscript, we present the fabrication and spectroscopic characterization of a large-area surfaceenhanced Raman scattering (SERS) substrate, as well as a method for improving femtomole-level trace detection (109 molecules) using this substrate. Using multiphoton-induced exposure of a commercial photoresist, we physically limit the available molecular adsorption sites to only the electromagnetic "hot spots" on the substrate. This process prevents molecules from adsorbing to sites of weak SERS enhancement, while permitting adsorption to sites of extraordinary SERS enhancement. For a randomly adsorbed submonolayer of benzenethiol molecules the average Raman scattering cross-section of the processed sample is 27 times larger than that of an unprocessed SERS substrate.
R. Olivares-Amaya, D. Rappoport, P. Muñoz, P. Peng, E. Mazur, and A. n. Aspuru-Guzik. 2012. “Can Mixed-Metal Surfaces Provide an Additional Enhancement to SERS?” J. Phys. Chem., 116, Pp. 15568–15575. Publisher's VersionAbstract
We explore the chemical contribution to surface-enhanced Raman scattering (SERS) in mixed-metal substrates, both experimentally and by computer simulation. These substrates are composed of a chemically active, transition- metal overlayer deposited on an effective SERS substrate. We report improved analytical enhancement factors obtained by using a small surface coverage of palladium or platinum over nanostructured silver substrates. Theoretical predictions of the chemical contribution to the surface enhancement using density functional theory support the experimental results. In addition, these approaches show that the increased enhancement is due not only to an increase in surface coverage of the analyte but also to a higher Raman scattering cross section per molecule. The additional chemical enhancement in mixed-metal SERS substrates correlates with the binding energy of the analyte on the surface and includes both static and dynamical effects. SERS using mixed-metal substrates has the potential to improve sensing for a large group of analyte molecules and to aid the development of chemically specific SERS-based sensors.
E. D. Diebold, P. Peng, and E. Mazur. 2009. “Isolating surface-enhanced Raman scattering hot spots using multiphoton lithography.” J. Am. Chem. Soc., 131, Pp. 16356–16357. Publisher's VersionAbstract
We present a method for improving femtomole-level trace detection (10^9 molecules) using large-area surface-enhanced Raman scattering (SERS) substrates. Using multiphoton-induced exposure of a commercial photoresist, we physically limit the available molecular adsorption sites to only the electromagnetic hot spots on the substrate. This process prevents molecules from adsorbing to sites of weak SERS enhancement, while permitting adsorption to sites of extraordinary SERS enhancement. For a randomly adsorbed submonolayer of benzenethiol molecules the average Raman scattering cross section of the processed sample is 27 times larger than that of an unprocessed SERS substrate.
E. D. Diebold. 2010. “Plasmon-enhanced nonlinear optics for applications in sensing and biology”. Publisher's VersionAbstract
In this thesis, we present the results of three experiments that combine techniques from the elds of ultrafast nonlinear optics and plasmonics, with the aim of developing tools for improved surface-enhanced Raman spectroscopy and biological cell transfection. We fi rst describe the use of femtosecond laser pulses to generate large areas of a nanostructured silicon surface which is used as a new type of substrate for surface-enhanced Raman scattering (SERS). We perform spectroscopic characterization of this substrate and nd its Raman cross-section enhancement factor to be on the order of 10^7. This large, spatially-uniform, and reproducible enhancement factor is nearly constant across the near-infrared spectral region. In a second experiment, we develop a technique to spatially isolate the \hot spots" on SERS substrates. This technique leverages the plasmonic near eld enhancement of metallic nanostructures to preferentially expose a commercial photoresist using femtosecond laser pulses. By isolating the hot spots, analyte molecules adsorb only to the regions of largest electromagnetic enhancement. Compared to an unprocessed substrate covered with a sub-monolayer of benzenethiol molecules, a processed substrate shows a 27-fold im- provement in its average Raman cross-section enhancement factor. Finally, we present a proof-of-principle experiment which demonstrates high-throughput ultrafast laser transfection of biological cells using large-area plasmonic substrates. Utilizing the fi eld localization properties of a substrate fabricated using photolithography, wet etching, and template stripping, we demonstrate the introduction of silence RNA (siRNA) molecules into cells with an efficiency of approximately 50% after exposure to femtosecond laser pulses.