10 research outputs found
Raman Spectroscopy as an Assay to Disentangle Zinc Oxide Carbon Nanotube Composites for Optimized Uric Acid Detection
Refluxed zinc oxide (ZnO) nanoparticles (NPs) were prepared and attached to carboxylic acid functionalized multi-walled carbon nanotubes (COOH-MWNTs) via sonication. Practical optimization of electrocatalysts using sonication to disentangle a carbon nanotube composite for monitoring uric acid (UA) is shown. Monitoring UA is important for the management of medical disorders. Selection of sonication time is a crucial step in producing the desired composite. We report, for the first time, the practical use of Raman spectroscopy to tune the sonication involved in tethering ZnO NPs to the multi-walled carbon nanotube (MWNT) surface. Maximum current for detecting UA, using chronoamperometry and cyclic voltammetry, correlated with the highest sp2-hybridized carbon signal, as seen in the integrated Raman G band peak areas denoting maximum COOH-MWNT disentanglement. An array of ZnO/COOH-MWNT composites were prepared ranging from 60 to 240 min sonication times. Optimum sonication (150 min) corresponded with both maximum measured current and MWNT disentanglement. The sensor was able to quantitatively and selectively measure UA at clinically relevant concentrations (100⁻900 μM) with rapid current response time (< 5 s)
Morphology of hydrothermally synthesized ZnO nanoparticles tethered to carbon nanotubes affects electrocatalytic activity for H 2 O 2 detection
We describe the synthesis of zinc oxide (ZnO) nanoparticles and demonstrate their attachment to multiwalled carbon tubes, resulting in a composite with a unique synergistic effect. Morphology and size of ZnO nanostructures were controlled using hydrothermal synthesis, varying the hydrothermal treatment temperature, prior to attachment to carboxylic acid functionalized multi-walled carbon nanotubes for sensing applications. A strong dependence of electrocatalytic activity on nanosized ZnO shape was shown. High activity for H2O2 reduction was achieved when nanocomposite precursors with a roughly semi-spherical morphology (no needle-like particles present) formed at 90 °C. A 2.4-fold increase in cyclic voltammetry current accompanied by decrease in overpotential from the composites made from the nanosized, needle-like-free ZnO shapes was observed as compared to those composites produced from needle-like shaped ZnO. Electrocatalytic activity varied with pH, maximizing at pH 7.4. A stable, linear response for H2O2 concentrations was observed in the 1 “20 mM concentration range
Strong Exciton–Plasmon Coupling in Silver Nanowire Nanocavities
The
interaction between plasmonic and excitonic systems and the
formation of hybridized states is an area of intense interest due
to the potential to create exotic light-matter states. We report herein
coupling between the leaky surface plasmon polariton (SPP) modes of
single Ag nanowires and excitons of a cyanine dye (TDBC) in an open
nanocavity. Silver nanowires were spin-cast onto glass coverslips,
and the wavevector of the leaky SPP mode was measured by back focal
plane (BFP) microscopy. Performing these measurements at different
wavelengths allows the generation of dispersion curves, which show
avoided crossings after deposition of a concentrated TDBC–PVA
film. The Rabi splitting frequencies (Ω) determined from the
dispersion curves vary between nanowires, with a maximum value of
Ω = 390 ± 80 meV. The experiments also show an increase
in attenuation of the SPP mode in the avoided crossing region. The
ability to measure attenuation for the hybrid exciton-SPP states is
a powerful aspect of these single nanowire experiments because this
quantity is not readily available from ensemble experiments
Brillouin Oscillations from Single Au Nanoplate Opto-Acoustic Transducers
Brillouin
oscillations, which are GHz frequency waves that arise
from the interaction of light with acoustic waves, are experiencing
increasing applications in biology and materials science. They provide
information about the speed of sound and refractive index of the material
they propagate in, and have recently been used in imaging applications.
In the current study, Brillouin oscillations are observed through
ultrafast transient reflectivity measurements using chemically synthesized
Au nanoplates as opto-acoustic transducers. The Au nanoplates are
semitransparent, which allows the Brillouin oscillations to be observed
from material on both sides of the plate. The measured frequencies
are consistent with the values expected from the speeds of sound in
the different materials, however, the attenuation constants are much
larger than those reported in previous studies. The increased damping
is attributed to diffraction of the acoustic wave as it propagates
away from the excitation region. This effect is more significant for
experiments with high numerical aperture objectives. These results
are important for understanding the relationship between frequency
and spatial resolution in Brillouin oscillation microscopy
Surface Plasmon Polariton Interference in Gold Nanoplates
Transient
absorption microscopy (TAM) measurements have been used
to study the optical properties of surface plasmon polariton (SPP)
modes in gold nanoplates on a glass substrate. For thin gold nanoplates,
the TAM images show an oscillation in the signal across the plate
due to interference between the “bound” and “leaky”
SPP modes. The wavelength of the interference pattern is given by
λ = 2π/Δ<i>k</i>, where Δ<i>k</i> is the difference between the wavevectors for the bound
and leaky modes and is sensitive to the dielectric constant of the
material above the gold nanoplate. Back focal plane imaging was also
used to measure the wavevector of the leaky mode, which, in combination
with the Δ<i>k</i> information from the TAM images,
enabled the bound mode wavevector to be determined. These experiments
represent the first far-field optical measurement of the wavevector
for the bound mode in metal nanostructures
Morphology of Hydrothermally Synthesized ZnO Nanoparticles Tethered to Carbon Nanotubes Affects Electrocatalytic Activity For Hâ‚‚Oâ‚‚ Detection
We describe the synthesis of zinc oxide (ZnO) nanoparticles and demonstrate their attachment to multiwalled carbon tubes, resulting in a composite with a unique synergistic effect. Morphology and size of ZnO nanostructures were controlled using hydrothermal synthesis, varying the hydrothermal treatment temperature, prior to attachment to carboxylic acid functionalized multi-walled carbon nanotubes for sensing applications. A strong dependence of electrocatalytic activity on nanosized ZnO shape was shown. High activity for H2O2 reduction was achieved when nanocomposite precursors with a roughly semi-spherical morphology (no needle-like particles present) formed at 90 °C. A 2.4-fold increase in cyclic voltammetry current accompanied by decrease in overpotential from the composites made from the nanosized, needle-like-free ZnO shapes was observed as compared to those composites produced from needle-like shaped ZnO. Electrocatalytic activity varied with pH, maximizing at pH 7.4. A stable, linear response for H 2O2 concentrations was observed in the 1-20 mM concentration range