Todd D Krauss

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Single-molecule fluorescence spectroscopy was used to determine the electronic properties of individual single-walled carbon nanotubes. Carbon nanotube structure was determined simultaneously from Raman spectroscopy. Fluorescence spectra from individual nanotubes with identical structures have different emission energies and linewidths that likely arise(More)
Semiconductor quantum dots (QDs) have been used in a simple fluorometric assay to detect single cells of the pathogenic Escherichia coli O157:H7 serotype. Composed of CdSe/ZnS core/shell QDs conjugated to streptavidin, this system exhibits 2 orders of magnitude more sensitivity than a similar assay using a common organic dye. Selectivity for this pathogenic(More)
Single-walled carbon nanotubes (SWNTs) have unique photophysical properties but low fluorescence efficiency. We have found significant increases in the fluorescence efficiency of individual DNA-wrapped SWNTs upon addition of reducing agents, including dithiothreitol, Trolox, and β-mercaptoethanol. Brightening was reversible upon removal of the reducing(More)
A simple and very sensitive method for determining refractive and absorptive nonlinearities based on spectral resolution of two-beam coupling is demonstrated. Nonlinear phase shifts as small as ~10(-6) rad and two-photon absorption coefficients as small as 10(-4) cm/GW are readily observed by use of this technique with nanojoule pulses from a mode-locked(More)
There is a keen interest in developing techniques for rapid genetic analysis that do not require labeling of an analyte. Here we demonstrate that fluorophore-tagged DNA hairpins attached to gold films can function as immobilized "molecular beacons". Two DNA hairpins incorporating portions of the Staphlococcus aureus FemA and mecR methicillin-resistance(More)
We have studied the self-assembling behavior of trioctylphosphine oxide (TOPO) on a highly oriented pyrolytic graphite surface. TOPO forms stripe-like structures in registry with the underlying graphite lattice. Using electrostatic force microscopy, we have also measured the charge, dipole, and dielectric constant of these monolayer films. The crystalline(More)
We report the observation of fluorescence from single PbS quantum dots (QDs) using confocal microscopy in an inert atmosphere. Single PbS QDs exhibit a narrowing of the fluorescence line width (relative to the ensemble) and fluorescence intermittency ("blinking"), consistent with the properties of other single QDs. However, single-particle line widths(More)
We demonstrate that Zn(II) porphyrin in Zn(II)cytochrome c (Zn cyt c) is a fluorescence resonance energy transfer (FRET) donor to an Alexa660 dye acceptor. The energy transfer efficiency is dependent on the distance between the two fluorophores as shown through protein denaturation studies of five Zn cyt c variants labeled with Alexa660 in different(More)
We find that giant surface-enhanced Raman scattering for adsorbates on silver surfaces is present only on surfaces that exhibit self-similar fractal topology as inferred from atomic force microscopy. The fractal character results in localizing the energy of incident photons to volumes of a few nanometers on a side, millions of times smaller than the(More)