Co-reporter:James R. Matthews;Courtney M. Payne
Langmuir September 15, 2015 Volume 31(Issue 36) pp:9893-9900
Publication Date(Web):2017-2-22
DOI:10.1021/acs.langmuir.5b01203
Surface-enhanced Raman scattering (SERS) and localized surface plasmon resonance sensing (LSPR) have been applied for a detailed analysis of lipid bilayers at the surface of gold nanorods. The spatial dependence of surface enhancement and the optical effects of the lipid phase transition confirm the presence of a bilayer membrane structure. Deuterated lipids exchanged rapidly between the nanorod surface and lipid vesicles in solution, suggesting a loosely bound, natural membrane structure. However, at a low solution concentration of lipid vesicles, the lipids on the gold nanorod surface convert to a nonbilayer structure, which could impact biological applications of these nanomaterials.
Co-reporter:James R. Matthews, Cyna R. Shirazinejad, Grace A. Isakson, Steven M. E. Demers, and Jason H. Hafner
Nano Letters April 12, 2017 Volume 17(Issue 4) pp:2172-2172
Publication Date(Web):February 6, 2017
DOI:10.1021/acs.nanolett.6b04509
Gold nanostructures focus light to a molecular length scale at their surface, creating the possibility to visualize molecular structure. The high optical intensity leads to surface enhanced Raman scattering (SERS) from nearby molecules. SERS spectra contain information on molecular position and orientation relative to the surface but are difficult to interpret quantitatively. Here we describe a ratiometric analysis method that combines SERS and unenhanced Raman spectra with theoretical calculations of the optical field and molecular polarizability. When applied to the surfactant layer on gold nanorods, the alkane chain is found to be tilted 25° to the surface normal, which matches previous reports of the layer thickness. The analysis was also applied to fluid phase phospholipid bilayers that contain tryptophan on the surface of gold nanorods. The lipid double bond was found to be oriented normal to the bilayer and 13 Å from the nitrogen atom. Tryptophan was found to sit near the glycerol headgroup region with its indole ring 43° from the bilayer normal. This new method can determine specific interfacial structure under ambient conditions, with microscopic quantities of material, and without molecular labels.Keywords: lipid membrane; molecular structure; near field; plasmonics; Surface enhanced raman scattering (SERS); tryptophan;
Co-reporter:Courtney M. Payne, Dmitri E. Tsentalovich, Denise N. Benoit, Lindsey J. E. Anderson, Wenhua Guo, Vicki L. Colvin, Matteo Pasquali, and Jason H. Hafner
Chemistry of Materials 2014 Volume 26(Issue 6) pp:1999
Publication Date(Web):February 11, 2014
DOI:10.1021/cm402506e
Gold nanobelts were synthesized by the reduction of tetrachloroauric acid with ascorbic acid in the presence of the surfactants cetyltrimethylammonium bromide and sodium dodecylsulfate. The resulting structures have rectangular cross sectional dimensions that are tens of nanometers and lengths that are tens to hundreds of micrometers. We find that the nanobelt yield and resulting structures are very sensitive to temperature which is likely due to the transition of the surfactant solution from wormlike micelles to spherical micelles. The nanobelt crystal structure contains a mixture of face centered cubic and hexagonally close packed lattice phases that can be isolated and examined individually due to the unique nanobelt size and shape.
Co-reporter:Lindsey J. E. Anderson, Yu-Rong Zhen, Courtney M. Payne, Peter Nordlander, and Jason H. Hafner
Nano Letters 2013 Volume 13(Issue 12) pp:6256-6261
Publication Date(Web):November 8, 2013
DOI:10.1021/nl4037356
Plasmon propagation in thin plasmonic waveguides is strongly damped, making it difficult to study with diffraction-limited optics. Here we directly characterize plasmon propagation in gold nanobelts with incoherent light. The data indicate a short average propagation length of 0.94 μm but also reveal a weakly excited antisymmetric mode that has a propagation length greater than 10 μm with strong confinement of 2400 nm2. These results demonstrate that high confinement and long propagation length can be achieved with thin plasmonic structures.
Co-reporter:Subramanian Balamurugan;Kathryn M. Mayer;Seunghyun Lee;Steven A. Soper;David A. Spivak
Journal of Molecular Recognition 2013 Volume 26( Issue 9) pp:402-407
Publication Date(Web):
DOI:10.1002/jmr.2278
A localized surface plasmon resonance (LSPR) sensor surface was fabricated by the deposition of gold nanorods on a glass substrate and subsequent immobilization of the DNA aptamer, which specifically bind to thrombin. This LSPR aptamer sensor showed a response of 6-nm λmax shift for protein binding with the detection limit of at least 10 pM, indicating one of the highest sensitivities achieved for thrombin detection by optical extinction LSPR. We also tested the LSPR sensor fabricated using gold bipyramid, which showed higher refractive index sensitivity than the gold nanorods, but the overall response of gold bipyramid sensor appears to be 25% less than that of the gold nanorod substrate, despite the approximately twofold higher refractive index sensitivity. XPS analysis showed that this is due to the low surface density of aptamers on the gold bipyramid compared with gold nanorods. The low surface density of the aptamers on the gold bipyramid surface may be due to the effect of shape of the nanostructure on the kinetics of aptamer monolayer formation. The small size of aptamers relative to other bioreceptors is the key to achieving high sensitivity by biosensors on the basis of LSPR, demonstrated here for protein binding. The generality of aptamer sensors for protein detection using gold nanorod and gold nanobipyramid substrates is anticipated to have a large impact in the important development of sensors toward biomarkers, environmental toxins, and warfare agents. Copyright © 2013 John Wiley & Sons, Ltd.
Co-reporter:Courtney M. Payne, Lindsey J. E. Anderson, and Jason H. Hafner
The Journal of Physical Chemistry C 2013 Volume 117(Issue 9) pp:4734-4739
Publication Date(Web):January 27, 2013
DOI:10.1021/jp3080089
Gold nanobelts are elongated nanostructures that exhibit plasmon resonant scattering that is tunable with the cross-sectional aspect ratio. Their surfactant-directed chemical synthesis produces uniform nanobelts as well as similar, yet more complex, structures. Tapered gold nanobelts have a shift in their cross-sectional aspect ratio along their length and, therefore, a shift in plasmon resonance wavelength. The tapered nanobelts are shown to act as mesoscale plasmonic spectrometers to probe enhanced emission from nearby quantum dots. Nanobelts also form dimers, either because of bifurcation during growth or because of alignment during deposition, that run side by side with sub-10 nm gaps which create large volumes of electromagnetic enhancement for surface-enhanced Raman spectroscopy.
Co-reporter:Kathryn M. Mayer and Jason H. Hafner
Chemical Reviews 2011 Volume 111(Issue 6) pp:3828-3857
Publication Date(Web):June 8, 2011
DOI:10.1021/cr100313v
Co-reporter:Lindsey J. E. Anderson, Courtney M. Payne, Yu-Rong Zhen, Peter Nordlander, and Jason H. Hafner
Nano Letters 2011 Volume 11(Issue 11) pp:5034-5037
Publication Date(Web):October 5, 2011
DOI:10.1021/nl203085t
Plasmonic nanowires with sub-100-nm rectangular cross sections were found to exhibit a strong transverse plasmon peak at visible wavelengths. By correlating atomic force microscopy measurements of individual nanobelts with their dark-field scattering spectra, it is seen that the transverse peak tunes with cross-sectional aspect ratio. Simulations revealed that the scattering plasmonic modes are transverse antisymmetric excitations across the nanobelt width. Unlike larger diameter silver nanowires, these nanobelts exhibit sharp, tunable plasmon resonances similar to those of nanoparticles.
Co-reporter:Seunghyun Lee, Lindsey J. E. Anderson, Courtney M. Payne, and Jason H. Hafner
Langmuir 2011 Volume 27(Issue 24) pp:14748-14756
Publication Date(Web):October 3, 2011
DOI:10.1021/la202918n
Surface-enhanced Raman spectroscopy (SERS) of gold nanorods in cetyltrimethylammonium bromide solution has been used to analyze the interfacial surfactant structure based on the distance-dependent electromagnetic enhancement. The spectra were consistent with a surfactant bilayer oriented normal to the surface. As the surfactant concentration was reduced, a structural transition in the surfactant layer was observed through a sudden increase in the signal from the alkane chains. The structural transition was shown to influence the displacement of the surfactant layer by thiolated poly(ethylene glycol). The monodisperse and thoroughly characterized gold nanorod samples yield consistent enhancement factors that were compared to electromagnetic simulations.
Co-reporter:Lindsey J. E. Anderson, Kathryn M. Mayer, Robert D. Fraleigh, Yi Yang, Seunghyun Lee and Jason H. Hafner
The Journal of Physical Chemistry C 2010 Volume 114(Issue 25) pp:11127-11132
Publication Date(Web):June 9, 2010
DOI:10.1021/jp1040663
Dark field microspectroscopy is a powerful tool for studying plasmon resonances of noble metal nanoparticles and for developing their applications in sensing and imaging. Here we calibrate a dark field microspectrometer with measurements on gold nanospheres in a uniform dielectric medium to yield quantitative spectral scattering cross sections for elongated nanoparticle shapes. Gold bipyramids, 135 nm in length, were found to have a peak differential cross section of 1.2 × 10−16 m2. Measurements of a small ensemble of gold nanorods, 13 nm in diameter and 45 nm in length on average, were found to have a peak differential cross section of only 1 × 10−18 m2. For the smaller gold nanorods, approximate expressions for the total scattering cross section may be used to indicate their scattering signal in microscopy applications.
Co-reporter:Seunghyun Lee, Kathryn M. Mayer and Jason H. Hafner
Analytical Chemistry 2009 Volume 81(Issue 11) pp:4450
Publication Date(Web):May 5, 2009
DOI:10.1021/ac900276n
Gold nanoparticles bound to substrates exhibit localized surface plasmon resonance (LSPR) in their optical extinction spectra at visible and near-infrared wavelengths. The LSPR wavelength is sensitive to the surrounding refractive index, enabling a simple, label-free immunoassay when capture antibodies are bound to the nanoparticles. Gold bipyramids are nanoparticles with a penta-twinned crystal structure, which have a sharp LSPR because of their high monodispersity. Bipyramid substrates were found to have a refractive index sensitivity ranging from 288 to 381 nm/RIU (−0.62 to −0.68 eV/RIU), increasing with the nanoparticle size and aspect ratio. In an immunoassay, the bipyramid substrates yielded higher sensitivity than nanorods and nanospheres. An immunoassay sensitivity constant which depends on both the optical properties of the nanoparticle and conjugation chemistry was found to be KLSPR = 0.01 nm·μm2 for gold bipyramids.
Co-reporter:Colleen L. Nehl and Jason H. Hafner
Journal of Materials Chemistry A 2008 vol. 18(Issue 21) pp:2415-2419
Publication Date(Web):2008/02/11
DOI:10.1039/B714950F
Localized surface plasmon resonances in noble metal nanoparticles cause enhanced optical absorption and scattering that is tunable through the visible and near-infrared. Furthermore, these resonances create large local electric field enhancements at the nanoparticle surfaces, essentially focussing light at the nanometer scale. These properties suggest a range of applications, including biomedical imaging, therapeutics, and molecular sensing. Here we review some recent advances regarding shape-dependent optical properties of two specific nanoparticle geometries: gold nanorods and branched gold nanoparticles.
Co-reporter:Yi Yang, Kathryn M. Mayer, Jason H. Hafner
Biophysical Journal (15 March 2007) Volume 92(Issue 6) pp:
Publication Date(Web):15 March 2007
DOI:10.1529/biophysj.106.093328
The atomic force microscope (AFM) is sensitive to electric double layer interactions in electrolyte solutions, but provides only a qualitative view of interfacial electrostatics. We have fully characterized silicon nitride probe tips and other experimental parameters to allow a quantitative electrostatic analysis by AFM, and we have tested the validity of a simple analytical force expression through numerical simulations. As a test sample, we have measured the effective surface charge density of supported zwitterionic dioleoylphosphatidylcholine membranes with a variable fraction of anionic dioleoylphosphatidylserine. The resulting surface charge density and surface potential values are in quantitative agreement with those predicted by the Gouy-Chapman-Stern model of membrane charge regulation, but only when the numerical analysis is employed. In addition, we demonstrate that the AFM can detect double layer forces at a separation of several screening lengths, and that the probe only perturbs the membrane surface potential by <2%. Finally, we demonstrate 50-nm resolution electrostatic mapping on heterogeneous model membranes with the AFM. This novel combination of capabilities demonstrates that the AFM is a unique and powerful probe of membrane electrostatics.
Co-reporter:Yi Yang, Kathryn M. Mayer, Nissanka S. Wickremasinghe, Jason H. Hafner
Biophysical Journal (1 December 2008) Volume 95(Issue 11) pp:
Publication Date(Web):1 December 2008
DOI:10.1529/biophysj.108.136507
The electrostatic properties of biological membranes can be described by three parameters: the transmembrane potential, the membrane surface potential, and the membrane dipole potential. The first two are well characterized in terms of their magnitudes and biological effects. The dipole potential, however, is not well characterized. Various methods to measure the membrane dipole potential indirectly yield different values, and there is not even agreement on the source of the membrane dipole moment. This ambiguity impedes investigations into the biological effects of the membrane dipole moment, which should be substantial considering the large interfacial fields with which it is associated. Electrostatic analysis of phosphatidylcholine lipid membranes with the atomic force microscope reveals a repulsive force between the negatively charged probe tips and the zwitterionic lipids. This unexpected interaction has been analyzed quantitatively to reveal that the repulsion is due to a weak external field created by the internal membrane dipole potential. The analysis yields a dipole moment of 1.5 Debye per lipid with a dipole potential of +275 mV for supported phosphatidylcholine membranes. This new ability to quantitatively measure the membrane dipole moment in a noninvasive manner with nanometer scale spatial resolution will be useful in identifying the biological effects of the dipole potential.
Co-reporter:Colleen L. Nehl and Jason H. Hafner
Journal of Materials Chemistry A 2008 - vol. 18(Issue 21) pp:NaN2419-2419
Publication Date(Web):2008/02/11
DOI:10.1039/B714950F
Localized surface plasmon resonances in noble metal nanoparticles cause enhanced optical absorption and scattering that is tunable through the visible and near-infrared. Furthermore, these resonances create large local electric field enhancements at the nanoparticle surfaces, essentially focussing light at the nanometer scale. These properties suggest a range of applications, including biomedical imaging, therapeutics, and molecular sensing. Here we review some recent advances regarding shape-dependent optical properties of two specific nanoparticle geometries: gold nanorods and branched gold nanoparticles.
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