Super-resolution imaging of plasmonic nanostructures
Ligand binding at the nano-bio interface
We are interested in understanding how ligands bind to the surface of single plasmonic nanoparticles. By combining fluorophore-labeled ligands with super-resolution imaging, we are able to reconstruct images of the nanoparticle shape, while also revealing heterogeneity in the positions of the ligands bound to the surface. We also find evidence of coupling between the molecular emission and the plasmon modes of the nanoparticle, which impacts the accuracy of the reconstructed images. We currently collaborate with leading theorists to understand the impact of these plasmon coupling effects.
Representative publications (click here for the complete list): |
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- K. L. Blythe and K.A. Willets. “Super-resolution imaging of fluorophore-labeled DNA bound to gold nanoparticles: a single molecule, single particle approach.” Invited feature article. J. Phys. Chem. C. 120, 803 (2016).
- K.L. Blythe, E.J. Titus, K.A. Willets. “The effects of tuning fluorophore density, identity, and spacing on reconstructed images in super-resolution imaging of fluorophore-labeled gold nanorods.” J. Phys. Chem. C. 119, 28099 (2015).
Local temperature effects on single nanostructures
Plasmon excitation leads to local heating at the surface of single nanoparticles, which can affect the behavior of molecules interacting with the nanoparticle surface. We have used super-resolution imaging techniques to show thermally-mediated restructuring of surface-bound ligands and are now working to expand this technique to provide quantitative nanothermometry measurements on single nanoparticles.
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Representative publications:
- X. Cheng, T.P. Anthony, C.A. West, Z. Hu, V. Sundaresan, A.J. McLeod, D.J. Masiello, K.A. Willets. “Plasmon heating promotes ligand reorganization on single gold nanorods." J. Phys. Chem. Lett. 10, 1394 (2019).
- U. Bhattacharjee, C. West, S.A. Hosseini Jebeli, H.J. Goldwyn, X-T Kong, Z. Hu, E.K. Beutler, W-S Chang, K.A. Willets, S. Link, D.J. Masiello. “Active far-field control of the thermal near-field via plasmon hybridization.” ACS Nano. DOI: 10.1021/acsnano.9b04968. (2019).
Surface-enhanced Raman scattering (SERS) hot spots
Junctions between adjacent plasmonic nanoparticles lead to large regions of electromagnetic field enhancements, known as "hot spots." We use super-resolution imaging to correlate the position and SERS intensity of single molecules diffusing on the nanoparticle surface to map out these hot spots with <10 nm spatial resolution. We then use correlated electron microscopy to match the maps of the hot spots with specific geometric features of the nanoparticles. We have extended this technique to studing electrochemical reactions on single nanoparticle electrode surfaces.
Representative publications (click here for the complete list): |
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- K.A. Willets. “Super-resolution imaging of SERS hot spots.” Invited tutorial review, Chem. Soc. Rev., 43, 3854 (2014).
- S. M. Stranahan, K.A. Willets. “Super-resolution optical imaging of single-molecule SERS hot spots.” Nano Lett. 10, 3777 (2010).
Optical point spread function fitting
Plasmon-coupled emission generates unique optical point spread functions that tell us about the geometry of the hot spot or orientation of an anisotropic nanoparticle. We analyze these point spread functions to understand how the position of molecules near the plasmonic nanostructure surface impacts the surface-enhanced emission properties or to gain structural and spectroscopic insight into single nanoparticle emitters.
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Representative publications (click here for the complete list):
- K.A. Willets. “Plasmon point spread functions: how do we model plasmon-mediated emission processes?” Invited perspective, Frontiers of Physics, 9, 3 (2014).
- P.B. Joshi, T.P. Anthony, A.J. Wilson, K.A. Willets. “Imaging out-of-plane polarized emission patterns on gap mode SERS substrates: from high molecular coverage to the single molecule regime.” Faraday Discussions. 205, 245 (2017).
