个人简介

B.A. (1999), Dartmouth College Ph.D. (2005), Stanford University Postdoctoral Researcher (2005-2007), Northwestern University

研究领域

Analytical Chemistry; Physical Chemistry

The Willets lab is interested in understanding the complex interaction between organic molecules and noble metal nanoparticles (~20-200 nm in size) with applications in sensing, spectroscopy, and electrochemistry. Noble metal nanoparticles support localized surface plasmons, which are the light-driven collective oscillation of electrons in these materials. Localized surface plasmons give noble metal nanoparticles their characteristic colors (such that silver and gold nanoparticles can be red, green, blue, etc), but also lead to significant electromagnetic field enhancements at the surface of the nanoparticles. Molecules located in these enhanced electromagnetic fields experience significant increases in their spectroscopic signatures, including fluorescence, Raman and IR absorption. Unfortunately, both the molecules and the nanoparticles are smaller than the resolution of optical microscopes, which are limited by the diffraction limit of light. This means that we cannot directly image these light-matter interactions using standard far-field optical microscopy. The Willets lab is using a variety of optical techniques to defeat the diffraction limit and image these interactions directly, including point spread function fitting using 2-D Gaussian and dipole emission models coupled with active control of the emission state of a single molecule through approaches such as ground state depletion (GSD) microscopy or electrochemical control. These techniques are used in conjunction with structural characterization methods like atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) to better understand the underlying structure-function relationships in these molecular plasmonic systems.

近期论文

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A.L. Weisman, K.H. DuBay, K.A. Willets, R.A. Friesner. “A First-Principles Polarized Raman Method for Determining Whether a Uniform Region of a Sample is Crystalline or Isotropic.” J. Chem. Phys. In revision. K. Marchuk and K.A. Willets. “Localized surface plasmons and hot electrons.” Chemical Physics. Invited Perspective. 2014. DOI: 10.1016/j.chemphys.2014.10.016 K.A. Willets. “Super-resolution imaging of SERS hot spots.” Invited tutorial review, Chem. Soc. Rev., 43(11), 3854-3864 (2014). A.J. Wilson and K.A. Willets. “ Visualizing site-specific redox potentials on the surface of plasmonic nanoparticles with super-localization SERS microscopy.” Nano Lett. 14, 939-945 (2014). K.L. Blythe, E.J. Titus and K.A. Willets. “Triplet-state mediated super-resolution imaging of fluorophore-labeled gold nanorods.” ChemPhysChem (Invited contribution to special themed issue on super-resolution imaging and nanophotonics), 15, 784-793 (2014). K.A. Willets. “Plasmon point spread functions: how do we model plasmon-mediated emission processes?” Invited perspective, Frontiers of Physics, 9, 3-16 (2014). E.J. Titus and K.A. Willets. “Super-localization surface-enhanced Raman scattering microscopy: comparing point spread function models in the ensemble and single molecule limits.” ACS Nano, 7, 8284-8294 (2013). E.J. Titus and K.A. Willets. “Accuracy of super-localization imaging using Gaussian and dipole emission point-spread functions for modeling gold nanorod luminescence.” ACS Nano, 7, 6258-6267 (2013). K.A. Willets. “New tools for investigating electromagnetic hot spots in single-molecule surface enhanced Raman scattering ,” Invited review, ChemPhysChem, 14, 3186-3195 (2013). K.A. Willets. “Super-resolution imaging of interactions between molecules and plasmonic nanostructures,” Invited perspective, Phys. Chem. Chem. Phys. (Special themed issue on Plasmonics and Spectroscopy) 15, 5345-5354 (2013). A.J. Wilson and K.A. Willets. “Surface-enhanced Raman scattering (SERS) imaging using noble metal nanoparticles,” Invited focus article, WIRES Nanomedicine and Nanobiotechnology. 5, 180-189 (2013). E.J. Titus and K.A. Willets, “Applying super-resolution imaging techniques to problems in SERS,” Invited book chapter, Frontiers of Surface-Enhanced Raman Scattering: Single-Nanoparticles and Single Cells” (Eds. Yukihiro Ozaki, Katrin Kneipp, and Ricardo Aroca) from John Wiley & Sons, Chichester, UK. K.L. Blythe, K.M. Mayer, M.L. Weber, K.A. Willets. “Ground state depletion microscopy for imaging interactions between gold nanowires and fluorophore-labeled ligands.” Invited article. Phys. Chem. Chem. Phys. 15, 4136-4145 (2013). E.J. Titus, M.L. Weber, S.M. Stranahan, K.A. Willets. “Super-resolution SERS imaging beyond the single-molecule limit: an isotope-edited approach.” Nano Lett. 12, 5103-5110 (2012). B. Cannon, A. Campos, Z. Lewitz, K.A. Willets, R. Russell. “Zeptomole detection of DNA nanoparticles by single-molecule fluorescence with magnetic field-directed localization.” Anal. Biochem. 431, 40-47 (2012). K.A. Willets. “Probing local electromagnetic field enhancements on the surface of plasmonic nanoparticles.” Invited review, Prog. Surf. Sci. 87, 209–220 (2012). M.L. Weber, K.A. Willets. “Nanoscale studies of plasmonic hot spots using super-resolution optical imaging.” Invited review, MRS Bulletin, 37, 745-751 (2012). K.A. Koen, M.L. Weber, K.M. Mayer, E. Fernandez, K.A. Willets. “Spectrally-resolved polarization anisotropy of single plasmonic nanoparticles excited by total internal reflection.” J. Phys. Chem. C. 116, 16198−16206 (2012). J.C. Heckel, A.L. Weisman, S.T. Schneebeli, M.L. Hall, L.J. Sherry, S.M. Stranahan, K.H. Dubay, R.A. Friesner, K.A. Willets. “Polarized Raman spectroscopy of oligothiophene crystals to determine unit cell orientation.” J. Phys. Chem. A. 116, 6804–6816 (2012). K.A. Willets, S.M. Stranahan, M.L. Weber. “Shedding light on surface-enhanced Raman scattering hot spots through single molecule super-resolution imaging.” J. Phys. Chem. Lett. 3, 1286-1294 (2012). Journal cover art.