50 research outputs found
Construction of Bimetallic MetalāOrganic Frameworks with the Nanosheet-Assembled Hierarchical Hollow Structure for CO<sub>2</sub> Fixation
Incorporating secondary metal nodes with functionality
into organic
ligand nodes to form a bimetallic metalāorganic frameworks
(MOFs) would facilitate an enhancement in properties and broaden applied
areas of MOFs. Hierarchical tubular Cu/Zn-MOF-74 assembled by nanosheet
arrays is synthesized at ambient temperature and pressure by phase
transformation of Cu-based precursor MOF in immersion solution with
Zn2+. The content of Zn in Cu/Zn-MOF-74 can be controlled
by adjusting the concentration of Zn2+ in immersion solution,
and it can reach a maximum of 36.4%. Moreover, the catalytic activity
toward cycloaddition of CO2 with styrene oxide of Cu/Zn-MOF-74
is improved significantly compared with that of monometallic Cu-MOF-74.
Meanwhile, the advanced hierarchical tubular structure contributing
to enhancement in catalytic activity enables Cu/Zn-MOF-74 to present
higher conversion toward this cycloaddition of CO2 than
traditional rod-like Cu/Zn-MOF-74. This templated synthesis would
provide an opportunity for designing various bimetallic MOFs or MOF-based
compounds with improved performances in multiple applications
Plasmon-Controlled FoĢrster Resonance Energy Transfer
The localized plasmons of metal nanocrystals have been
widely utilized
to control a variety of optical signals, such as Raman, fluorescence,
and circular dichroism, from proximal dye molecules. We show, on the
single-particle level, that the FoĢrster resonance energy transfer
between two different fluorophores can be modulated by adjacent plasmonic
nanocrystals. The donor and acceptor fluorophore molecules are embedded
in a mesostructured silica shell that is uniformly coated on AuāAg
coreāshell nanocrystals. The longitudinal plasmon wavelengths
of the coreāshell metal nanocrystals are synthetically tailored
by varying the aspect ratio. Comparison of the scattering and fluorescence
spectra taken from the different hybrid nanostructures indicates that
the energy transfer efficiency can be controlled by the plasmon wavelength.
When the plasmon peak overlaps with the emission peak of the donor,
the energy transfer channel is turned off. When the plasmon peak is
red-shifted to be in between the emission peak of the donor and the
absorption peak of the acceptor or right at the intrinsic emission
peak of the acceptor, the energy transfer channel is turned on
Photothermal DNA Release from Laser-Tweezed Individual Gold Nanomotors Driven by Photon Angular Momentum
Gold
nanoparticles offer a unique possibility for contact-free
bioanalysis and actuation with high spatial resolution that increases
their potential for bioapplications such as affinity-based biosensing,
drug delivery, and cancer treatment. Here we demonstrate an ultrasensitive
optomechanical method for probing and releasing DNA cargo from individual
gold nanoparticles trapped and manipulated by laser tweezers. Single
nanorods are operated as rotational nanomotors, driven and controlled
by circularly polarized laser light in aqueous solution. By rotational
dynamics analysis, we resolve differences in the thickness of adsorbed
ultrathin molecular layers, including different DNA conformations,
with nanometer resolution. We then utilize photothermal heating to
release DNA from single nanomotors while measuring the temperature-dependent
kinetics and activation energy of the DNA melting process. The method
opens new possibilities for optomechanical quantification and application
of thermally induced molecular transitions in strongly confined geometries,
such as inside microfluidic devices and single cells
Anaerobic biodegradation of spiramycin I and characterization of its new metabolites
<p>Activated sludge was used to treat the wastewater containing spiramycin I. Three new metabolites were isolated and identified, which produced by oxidation of C6-aldehyde, hydrolysis of C5-mycaminose-mycarose and macrolactone ring-open reaction of spiramycin I in anaerobic digestion. And their antimicrobial activities were inactivated. Our results indicated that anaerobic biodegradation metabolites of spiramycin I could not induce bacterial resistance in environment.</p
Mass-Based Photothermal Comparison Among Gold Nanocrystals, PbS Nanocrystals, Organic Dyes, and Carbon Black
Gold nanocrystals have attractive plasmon-enabled photothermal
conversion properties, which have been widely employed for photothermal
therapy and solar energy harvesting. For practical applications, the
mass-normalized photothermal conversion performance is often desired
to be known for Au nanocrystals with different shapes and sizes and
for different nanomaterials. We study the photothermal conversion
performances of differently shaped and sized Au nanocrystals and compare
them with those of PbS nanocrystals, carbon black, and organic dyes
at the same mass concentrations. Both the mass-normalized extinction
cross section and the photothermal conversion efficiency of Au nanocrystals
decrease as their size is increased. The photothermal conversion performance
of carbon black is comparable to that of relatively small Au nanocrystals,
while the photothermal conversion performance of organic dyes and
PbS nanocrystals is inferior to that of Au nanocrystals. Our results
are useful for the design of Au nanocrystals and the choice of nanomaterials
for photothermal applications
Gold Nanorod Rotary Motors Driven by Resonant Light Scattering
Efficient and robust artificial nanomotors could provide a variety of exciting possibilities for applications in physics, biology and chemistry, including nanoelectromechanical systems, biochemical sensing, and drug delivery. However, the application of current man-made nanomotors is limited by their sophisticated fabrication techniques, low mechanical output power and severe environmental requirements, making their performance far below that of natural biomotors. Here we show that single-crystal gold nanorods can be rotated extremely fast in aqueous solutions through optical torques dominated by plasmonic resonant scattering of circularly polarized laser light with power as low as a few mW. The nanorods are trapped in 2D against a glass surface, and their rotational dynamics is highly dependent on their surface plasmon resonance properties. They can be kept continuously rotating for hours with limited photothermal side effects and they can be applied for detection of molecular binding with high sensitivity. Because of their biocompatibility, mechanical and thermal stability, and record rotation speeds reaching up to 42 kHz (2.5 million revolutions per minute), these rotary nanomotors could advance technologies to meet a wide range of future nanomechanical and biomedical needs in fields such as nanorobotics, nanosurgery, DNA manipulation and nano/microfluidic flow control
Correlating the Plasmonic and Structural Evolutions during the Sulfidation of Silver Nanocubes
Ag/Ag<sub>2</sub>S hybrid nanostructures have recently received much attention, because of their synthetically tunable plasmonic properties and enhanced chemical stability. Sulfidation of pregrown Ag nanocrystals is a facile process for making Ag/Ag<sub>2</sub>S nanostructures. Understanding the sulfidation process can help in finely controlling the compositional and structural parameters and in turn tailoring the plasmonic properties. Herein we report on our study of the structural and plasmonic evolutions during the sulfidation process of Ag nanocubes, which is carried out at both the ensemble and single-particle levels. Ensemble extinction measurements show that sulfidation first causes the disappearance of the high-order triakontadipolar plasmon modes, which have electric charges located on the sharp vertices and edges of Ag nanocubes, suggesting that sulfidation starts at the vertices of Ag nanocubes. As sulfidation goes on, the dipolar plasmon peak gradually red-shifts, with its intensity first decreasing and then increasing. Electron microscopy characterizations reveal that sulfidation progresses from the outer region to the center of Ag nanocubes. The cubic shape is maintained throughout the sulfidation process, with the edge length being increased gradually. Single-particle scattering measurements show that the dipolar plasmon peak red-shifts and decreases in intensity during sulfidation. An additional scattering peak appears at a shorter wavelength at the late stage of sulfidation. The difference in the sulfidation behavior between ensemble and single-particle measurements is understood with electrodynamic simulations. During ensemble measurements, the Ag core is increasingly truncated, and it becomes a nanosphere eventually. Sulfidation stops at an intermediate stage. During single-particle measurements, Ag nanocubes are completely transformed into Ag<sub>2</sub>S, leading to the observation of the shorter-wavelength scattering peak
Probing Photothermal Effects on Optically Trapped Gold Nanorods by Simultaneous Plasmon Spectroscopy and Brownian Dynamics Analysis
Plasmonic
gold nanorods are prime candidates for a variety of biomedical,
spectroscopy, data storage, and sensing applications. It was recently
shown that gold nanorods optically trapped by a focused circularly
polarized laser beam can function as extremely efficient nanoscopic
rotary motors. The system holds promise for applications ranging from
nanofluidic flow control and nanorobotics to biomolecular actuation
and analysis. However, to fully exploit this potential, one needs
to be able to control and understand heating effects associated with
laser trapping. We investigated photothermal heating of individual
rotating gold nanorods by simultaneously probing their localized surface
plasmon resonance spectrum and rotational Brownian dynamics over extended
periods of time. The data reveal an extremely slow nanoparticle reshaping
process, involving migration of the order of a few hundred atoms per
minute, for moderate laser powers and a trapping wavelength close
to plasmon resonance. The plasmon spectroscopy and Brownian analysis
allows for separate temperature estimates based on the refractive
index and the viscosity of the water surrounding a trapped nanorod.
We show that both measurements yield similar effective temperatures,
which correspond to the actual temperature at a distance of the order
10ā15 nm from the particle surface. Our results shed light
on photothermal processes on the nanoscale and will be useful in evaluating
the applicability and performance of nanorod motors and optically
heated nanoparticles for a variety of applications
Depositional characteristics of the northern South China Sea in response to the evolution of the Pearl River
<p>Geochemical data from South China Sea sedimentary rocks show the effects of both source composition and depositional environments.
This enables us to link tectonic trends with erosion in the Pearl River region since <em>c.</em> 32 Ma. In particular, a shift in the geochemistry appears to signal a response to a well-recorded regional tectonic event
at <em>c.</em> 23ā25 Ma, probably corresponding to a jump in the seafloor spreading axis from the west to the SW within the South China
Sea. This may correlate with the uplift of the West Yunnan Plateau and possibly also the eastern Tibetan Plateau. Clay mineralogy,
sandāmud ratio, and major and rare earth element concentrations, also varied in response to the environment in the drainage
areas of the palaeo-Pearl River. By comparing data from the modern sources and the sedimentary record from the northern South
China Sea, especially the erosionātransportationādeposition patterns, three groups of index minerals (Ati, GZi, ZTR), as well
as rare earth elements can be recognized. These are used to characterize the Pearl River from the east to the west, representing
three different parent rock sources. The evolution of the palaeo-Pearl River can be tracked by variations of heavy minerals
and key elements that are indicative of provenance.
</p
Supplement 1: Brownian fluctuations of an optically rotated nanorod
Supplement 1 Originally published in Optica on 20 July 2017 (optica-4-7-746