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The spatial resolution of optical microscopes is bounded by the diffraction limit of light, which has two key implications: (1) the shape and size of objects smaller than the wavelength of light cannot be observed optically and (2) objects spaced by less than roughly half the wavelength of light cannot be uniquely identified. This mismatch between the size of species that we are interested in (from molecules to nanoparticles, <500 nm) and the spatial resolution of our microscope (>500 nm) presents an imaging challenge that can be addressed through super-resolution imaging.
Center-of-mass tracking
Center-of-mass tracking
We fit diffraction-limited emission/scattering from a single entity to a model function (such as a 2-D Gaussian) and track how its center-of-mass changes over time due to diffusion or changes in its shape/size.
Stochastic fluctuations
Stochastic fluctuations
When multiple emitters/scatters are present in the same diffraction limited spot, we rely on stochastic fluctuations in intensity, so we can localize one molecule at a time. This strategy allows us to build up images and reconstruct information that is otherwise hidden by the diffraction limit.
Representative publications
Representative publications
K.A. Willets. “Super-resolution surface-enhanced Raman scattering: perspectives on the past, present and future.” ACS Nano. 18, 27824 (2024).
P.A. Reinhardt, A.P. Crawford, C.A. West, G. Delong, S. Link, D.J. Masiello, K.A. Willets. “Towards Quantitative Nanothermometry Using Single-Molecule Counting.” J. Phys. Chem. B. 125, 12197 (2021).
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).
V. Sundaresan, J.W. Monaghan, K.A. Willets. “Monitoring Simultaneous Electrochemical Reactions with Single Particle Imaging.” Invited contribution to a special themed issue on Single Entity Electrochemistry. ChemElectroChem. 5, 3052 (2018).
V. Sundaresan, J.W. Monaghan, K.A. Willets. "Visualizing the Effect of Partial Oxide Formation on Single Silver Nanoparticle Electrodissolution." J. Phys. Chem. C. 122, 3138 (2018). ACS Editors’ Choice.
V. Sundaresan, K. Marchuk, Y. Yu, E.J. Titus, A.J. Wilson, C.M. Armstrong, B. Zhang, K.A. Willets. “Visualizing and Calculating Tip-Substrate Distance in Nanoscale Scanning Electrochemical Microscopy Using 3-Dimensional Super-Resolution Optical Imaging.” Anal. Chem. 89, 922 (2017).
Y. Yu, V. Sundaresan, S. Bandyopadhyay, Y. Zhang, M.A. Edwards, K. McKelvey, H.S. White, K.A. Willets. “Three-Dimensional Super-Resolution Imaging of Single Nanoparticles Delivered by Pipettes.” ACS Nano. 11, 10529 (2017).
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).
K.L. Blythe, E.J. Titus, K.A. Willets. “Comparing the accuracy of reconstructed image size in super-resolution imaging of fluorophore-labeled gold nanorods using different fit models.” J. Phys. Chem. C. 119, 19333 (2015).
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).
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