5 research outputs found
Long-Range Plasmophore Rulers
Using on-wire lithography, we studied
the emission properties of
nanostructures made of a polythiophene disk separated by fixed nanoscopic
distances from a plasmonic gold nanorod. The intense plasmonic field
generated by the nanorod modifies the shape of the polythiophene emission
spectrum, and the strong distance dependence of this modulation forms
the basis for a new type of “plasmophore ruler”. Simulations
using the discrete dipole approximation (DDA) quantitatively support
our experimental results. Importantly, this plasmophore ruler is independent
of signal intensity and is effective up to 100 nm, which is more than
two times larger than any reported value for rulers based on photoluminescence
processes
A Postsynthetic Modification of II–VI Semiconductor Nanoparticles to Create Tb<sup>3+</sup> and Eu<sup>3+</sup> Luminophores
We
describe a novel method for creating luminescent lanthanide-containing
nanoparticles in which the lanthanide cations are sensitized by the
semiconductor nanoparticle’s electronic excitation. In contrast
to previous strategies, this new approach creates such materials by
addition of external salt to a solution of fully formed nanoparticles.
We demonstrate this postsynthetic modification for the lanthanide
luminescence sensitization of two visible emitting lanthanides (Ln),
Tb<sup>3+</sup> and Eu<sup>3+</sup> ions, through ZnS nanoparticles
in which the cations were added postsynthetically as external Ln(NO<sub>3</sub>)<sub>3</sub>·<i>x</i>H<sub>2</sub>O salt to
solutions of ZnS nanoparticles. The postsynthetically treated ZnS
nanoparticle systems display Tb<sup>3+</sup> and Eu<sup>3+</sup> luminescence
intensities that are comparable to those of doped Zn(Ln)S nanoparticles,
which we reported previously (<i>J. Phys. Chem. A</i>, <b>2011</b>, <i>115</i>, 4031–4041). A comparison
with the synthetically doped systems is used to contrast the spatial
distribution of the lanthanide ions, bulk versus surface localized.
The postsynthetic strategy described in this work is fundamentally
different from the synthetic incorporation (doping) approach and offers
a rapid and less synthetically demanding protocol for Tb<sup>3+</sup>:ZnS and Eu<sup>3+</sup>:ZnS luminophores, thereby facilitating their
use in a broad range of applications
Modulating the Bond Strength of DNA–Nanoparticle Superlattices
A method
is introduced for modulating the bond strength in DNA–programmable
nanoparticle (NP) superlattice crystals. This method utilizes noncovalent
interactions between a family of [Ru(dipyrido[2,3-<i>a</i>:3′,2′-<i>c</i>]phenazine)(N–N)<sub>2</sub>]<sup>2+</sup>-based small molecule intercalators and DNA
duplexes to postsynthetically modify DNA–NP superlattices.
This dramatically increases the strength of the DNA bonds that hold
the nanoparticles together, thereby making the superlattices more
resistant to thermal degradation. In this work, we systematically
investigate the relationship between the structure of the intercalator
and its binding affinity for DNA duplexes and determine how this translates
to the increased thermal stability of the intercalated superlattices.
We find that intercalator charge and steric profile serve as handles
that give us a wide range of tunability and control over DNA–NP
bond strength, with the resulting crystal lattices retaining their
structure at temperatures more than 50 °C above what nonintercalated
structures can withstand. This allows us to subject DNA–NP
superlattice crystals to conditions under which they would normally
melt, enabling the construction of a core–shell (gold NP-quantum
dot NP) superlattice crystal
Boron-Dipyrromethene-Functionalized Hemilabile Ligands as “Turn-On” Fluorescent Probes for Coordination Changes in Weak-Link Approach Complexes
Herein we report
a new class of hemilabile ligands with boron-dipyrromethene (Bodipy)
fluorophores that, when complexed to Pt(II), can signal changes in
coordination mode through changes in their fluorescence. The ligands
consist of phosphino-amine or phosphino-thioether coordinating moieties
linked to the Bodipy’s meso carbon via a phenylene spacer.
Interestingly, this new class of ligands can be used to signal both
ligand displacement and chelation reactions in a fluorescence “turn-on”
fashion through the choice of weakly binding heteroatom in the hemilabile
moiety, generating up to 10-fold fluorescence intensity increases.
The Pt(II) center influences the Bodipy emission efficiency by regulating
photoinduced electron transfer between the fluorophore and its meso
substituent. The rates at which the excited Bodipy-species generate
singlet oxygen upon excitation suggest that the heavy Pt(II) center
also influences Bodipy’s emission efficiency by affecting intersystem
crossing from the Bodipy excited singlet to excited triplet states.
This signaling strategy provides a quantitative read-out for changes
in coordination mode and potentially will enable the design of new
molecular systems for sensing and signal amplification
OWL-Based Nanomasks for Preparing Graphene Ribbons with Sub-10 nm Gaps
We report a simple and highly efficient method for creating
graphene
nanostructures with gaps that can be controlled on the sub-10 nm length
scale by utilizing etch masks comprised of electrochemically synthesized
multisegmented metal nanowires. This method involves depositing striped
nanowires with Au and Ni segments on a graphene-coated substrate,
chemically etching the Ni segments, and using a reactive ion etch
to remove the graphene not protected by the remaining Au segments.
Graphene nanoribbons with gaps as small as 6 nm are fabricated and
characterized with atomic force microscopy, scanning electron microscopy,
and Raman spectroscopy. The high level of control afforded by electrochemical
synthesis of the nanowires allows us to specify the dimensions of
the nanoribbon, as well as the number, location, and size of nanogaps
within the nanoribbon. In addition, the generality of this technique
is demonstrated by creating silicon nanostructures with nanogaps