Facile Chemical Approach to ZnO Submicrometer Particles with Controllable Morphologies

We have developed a simple wet-chemistry approach to fabricating ZnO submicrometer particles with unique morphologies including rings, bowls, hemispheres, and disks. The size and morphology of the particles can be conveniently tailored by varying the concentrations of the zinc precursor. The reaction temperature, pH, and concentration of ammonia are also found to play critical roles in directing the formation of these particle morphologies. These submicrometer particles exhibit strong white-light emission upon UV excitation as a result of the presence of surface defect states resulting from the fabrication method and synthesis conditions

Surface-Enhanced Raman Spectroscopy of DNA

We report a method for obtaining highly reproducible surface-enhanced Raman spectroscopy (SERS) of single and double-stranded thiolated DNA oligomers. Following a protocol that relaxes the DNA into an extended conformation, SERS spectra of DNA oligonucleotides are found to be extremely similar, strongly dominated by the Stokes modes of adenine. A spectral correlation function analysis useful for assessing reproducibility and for quantifying the highly complex changes corresponding to modifications in molecular conformation of the adsorbate molecules is introduced. This approach is used to monitor the interaction of DNA with cisplatin, a chemotherapy agent in widespread use

Cu Nanoshells: Effects of Interband Transitions on the Nanoparticle Plasmon Resonance

The optical properties of metals arise both from optical excitation of interband transitions and their collective electronic, or plasmon, response. Here, we examine the optical properties of Cu, whose strong interband transitions dominate its optical response in the visible region of the spectrum, in a nanoshell geometry. This nanostructure permits the geometrical tuning of the nanoparticle plasmon energy relative to the onset of interband transitions in the metal. Spectral overlap of the interband transitions of Cu with the nanoshell plasmon resonance results in a striking double-peaked plasmon resonance, a unique phenomenon previously unobserved in other noble or coinage metal nanostructures

Controlled Texturing Modifies the Surface Topography and Plasmonic Properties of Au Nanoshells

We report a facile and controllable method for the postfabrication texturing of the surface topography of Au nanoshells based on site-selective chemical etching of the polycrystalline Au nanoshell surface by a bifunctional alkanethiol molecule, cysteamine. This nanoscale surface texturing process systematically introduces dramatic changes to the plasmonic properties of the Au nanoshells. The modification of the plasmon resonant properties of nanoshells as a function of increased surface roughness was examined experimentally and modeled theoretically using three-dimensional finite difference time domain (FDTD) simulations

Direct Optical Detection of Aptamer Conformational Changes Induced by Target Molecules

Aptamers are single-stranded DNA/RNA oligomers that fold into three-dimensional conformations in the presence of specific molecular targets. Surface-enhanced Raman spectroscopy (SERS) of thiol-bound DNA aptamer self-assembled monolayers on Au nanoshell surfaces provides a direct, label-free detection method for the interaction of DNA aptamers with target molecules. A spectral cross-correlation function, Γ, is shown to be a useful metric to quantify complex changes in the SERS spectra resulting from conformational changes in the aptamer induced by target analytes. While the pristine, unexposed anti-PDGF (PDGF = platelet-derived growth factor) aptamer yields highly reproducible spectra with Γ = 0.91 ± 0.01, following incubation with PDGF, the reproducibility of the SERS spectra is dramatically reduced, yielding Γ =0.67 ± 0.02. This approach also allows us to discriminate the response of a cocaine aptamer to its target from its weaker response to nonspecific analyte molecules