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Surfaces, Interfaces, and Catalysis; Physical Properties of Nanomaterials and Materials
Plasmon Heating Promotes Ligand Reorganization on Single Gold Nanorods Xiaoyu Cheng, Taryn Patrice Anthony, Claire A. West, Zhongwei Hu, Vignesh Sundaresan, Aaron James McLeod, David J. Masiello, and Katherine A. Willets J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.9b00079 • Publication Date (Web): 06 Mar 2019 Downloaded from http://pubs.acs.org on March 12, 2019
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The Journal of Physical Chemistry Letters
Plasmon Heating Promotes Ligand Reorganization on Single Gold Nanorods Xiaoyu Cheng†#¶, Taryn P. Anthony†#, Claire A. West‡, Zhongwei Hu‡, Vignesh Sundaresan#, Aaron J. McLeod#, David J. Masiello‡, Katherine A. Willets*#
#Department
of Chemistry, Temple University, Philadelphia, Pennsylvania, United States, 19122
‡Department
of Chemistry, University of Washington, Seattle, Washington, United
States 98195
¶Present
address: National Engineering Research Center for Optical Instruments, State Key
Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou, 310058, China
†These
authors contributed equally to this work.
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*Corresponding
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The Journal of Physical Chemistry Letters
ABSTRACT
Single-molecule
fluorescence
microscopy
is
used
to
follow
dynamic
ligand
reorganization on the surface of single plasmonic gold nanorods. Fluorescently-labeled DNA is attached to gold nanorods via a gold-thiol bond using a low pH loading method. No fluorescence activity is initially observed from the fluorescent labels on the nanorod surface, which we attribute to a collapsed geometry of DNA on the metal. Upon several minutes of laser illumination, a marked increase in fluorescence activity was observed, suggesting that the ligand shell reorganizes from a collapsed, quenched geometry to an upright, ordered geometry. The ligand reorganization is facilitated by plasmon-mediated photothermal heating, as verified by controls using an external heat source and simulated by coupled optical and heat diffusion modeling. Using super-resolution image reconstruction, we observe spatial variations in where ligand reorganization occurs at the single particle level. The results suggest the possibility of non-uniform plasmonic heating, which would be hidden with traditional ensemble-averaged measurements.
TOC GRAPHIC
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The Journal of Physical Chemistry Letters
Plasmonic nanostructures exhibit unique optical features due to their ability to support localized
surface
plasmon
resonances
(LSPR),
in
which
resonant
incident
electromagnetic radiation drives the surface conduction electrons to oscillate in phase.1 Excitation at the LSPR generates significantly enhanced photon scattering (both intrinsic Rayleigh scattering from the nanostructure as well as Raman scattering from nearby analytes), photothermal heating, and hot charge carriers, all of which make plasmonic nanostructures promising for a range of applications, including optoelectronic devices, (bio)sensors, nanotherapeutics, and photothermal agents.2-3 For many of these applications, it is typically necessary to functionalize the nanoparticle surfaces with organic ligands, which impart biocompatibility and target selectivity, and allow delivery of therapeutic agents.2, 4-5 During the past two decades, remarkable progress has been made on optimizing surface modification strategies, allowing construction of increasingly more sophisticated nano-interfaces to reach molecular degrees of controls.6-9 On the other hand, far less is known on how exactly ligands organize and behave on nanoparticle surfaces due to challenges in characterization, especially at the single particle level where both electron and optical microscopy methods have limited contrast
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and/or spatial resolution.9-12 That said, single entity measurements are crucial, because they enable rare events and heterogeneity within the sample to be studied, which are usually buried within the ensemble.13 For instance, there is evidence to show that a single protein can initiate nanoparticle aggregation14 and a single molecule interaction can dominate plasmonic sensor responses.15 The need for developing new characterization methods to study the ligand-particle interface at both the single molecule and single particle level has become increasingly evident. We have previously shown that localization-based super-resolution imaging can address this challenge by localizing the position of single ligand molecules attached to the surface of individual plasmonic gold nanorods (AuNRs), hence probing the ligandparticle interface with single molecule sensitivity and
