38 research outputs found
Layered Nanocomposites from Gold Nanoparticles for Neural Prosthetic Devices
Treatments of neurological diseases, diagnostics of brain
malfunctions,
and the realization of brainācomputer interfaces require ultrasmall
electrodes that are āinvisibleā to resident immune cells.
Functional electrodes smaller than 50 Ī¼m are impossible to produce
with traditional materials due to high interfacial impedance at the
characteristic frequency of neural activity and insufficient charge
storage capacity. The problem can be resolved by using gold nanoparticle
nanocomposites. Careful comparison indicates that layer-by-layer assembled
films from Au NPs provide more than 3-fold improvement in interfacial
impedance and 1 order of magnitude increase in charge storage capacity.
Prototypes of microelectrodes could be made using traditional photolithography.
Integration of unique nanocomposite materials with microfabrication
techniques opens the door for practical realization of the ultrasmall
implantable electrodes. Further improvement of electrical properties
is expected when using special shapes of gold nanoparticles
Anomalously Fast Diffusion of Targeted Carbon Nanotubes in Cellular Spheroids
Understanding transport of carbon nanotubes (CNTs) and other nanocarriers within tissues is essential for biomedical imaging and drug delivery using these carriers. Compared to traditional cell cultures in animal studies, three-dimensional tissue replicas approach the complexity of the actual organs and enable high temporal and spatial resolution of the carrier permeation. We investigated diffusional transport of CNTs in highly uniform spheroids of hepatocellular carcinoma and found that apparent diffusion coefficients of CNTs in these tissue replicas are anomalously high and comparable to diffusion rates of similarly charged molecules with molecular weights 10000Ć lower. Moreover, diffusivity of CNTs in tissues is enhanced after functionalization with transforming growth factor Ī²1. This unexpected trend contradicts predictions of the StokesāEinstein equation and previously obtained empirical dependences of diffusivity on molecular mass for permeants in gas, liquid, solid or gel. It is attributed to the planar diffusion (gliding) of CNTs along cellular membranes reducing effective dimensionality of diffusional space. These findings indicate that nanotubes and potentially similar nanostructures are capable of fast and deep permeation into the tissue, which is often difficult to realize with anticancer agents
Streptavidin Inhibits Self-Assembly of CdTe Nanoparticles
Nanoparticles (NPs) exhibit strong tendency to self-assemble.
It
is important to understand how the presence of other macromolecular
compounds, affects this ability. The interaction between standard
thiol-capped cadmium telluride (CdTe) NPs and streptavidin (STAV)īøthe
essential component of many NP applicationsīøwas examined at
different molar ratios and pH values. The central observation of this
study is that STAV strongly inhibits the self-assembly of CdTe NPs
into nanowires. The underlying mechanism of inhibition was attributed
to the formation of a STAV corona and surface layer that precludes
attachment of NPs to each other. Instead of nanowires, we observed
a spectrum of agglomerates containing both CdTe and STAV of different
geometries depending on the molar ratios of the reagents in NP synthesis
and pH values of the media
Nanoparticle Assemblies into Luminescent Dendrites in Shrinking Microdroplets
The
self-assembly of nanoparticles (NPs) is essential for emerging
dispersion-based energy-conscious
technologies. Of particular interest are micro- and macro-scale self-organizing
superstructures that can bridge 2D/3D processing scales. Here we report
the spontaneous assembly of CdTe NPs within an aqueous microdroplet
suspended in soybean oil. The gradual diffusion of the water into
the surrounding medium results in shrinking of the microdroplet, and
a concomitant formation of branched assemblies from CdTe NPs that
evolve in size from ā¼50 Ī¼m to ā¼1000 Ī¼m.
The fractal dimension of NP assemblies increases from ā¼1.7
to ā¼1.9 during the assembly process. We found that constituents
of the soybean oil enter the aqueous solution across the microdroplet
interface and affect NP assembly. The obtained NP dendrites can be
further altered morphologically by illumination with light that results
in the disassembly of the NP dendrites. The use of this microheterogeneous
dispersion platform with partially soluble hydrophilic and hydrophobic
solvents highlights the sensitivity of the NP assembly process to
environment and presents an opportunity to explore droplet-confined
NP assembly
Omnidispersible Hedgehog Particles with Multilayer Coatings for Multiplexed Biosensing
Hedgehog particles (HPs) replicating
the spiky geometry of pollen
grains revealed surprisingly high dispersion stability regardless
of whether their hydrophobicity/hydrophilicity matches that of the
media or not. This property designated as omnidispersibility is attributed
to the drastic reduction of van der Waals interactions between particles
coated with stiff nanoscale spikes as compared to particles of the
same dimensions with smooth surfaces. One may hypothesize but it remains
unknown, however, whether HPs modified with polymers or nanoparticles
(NPs) would retain this property. Surface modifications of the spikes
will expand the functionalities of HPs, making possible their utilization
as omnidispersible carriers. Here, we show that HPs carrying dense
conformal coatings made by layer-by-layer (LBL/LbL) assembly maintain
dispersion stability in environments of extreme polarity and ionic
strength. HPs, surface-modified by multilayers of polymers and gold
NPs, are capable of surface-enhanced Raman scattering (SERS) and overcome
the limited colloidal stability of other SERS probes. The agglomeration
resilience of HPs leads to a greater than one order of magnitude increase
of SERS intensity as compared to colloids with smooth surfaces and
enables simultaneous detection of several targets in complex media
with high ionic strength. Omnidispersible optically active colloids
open the door for rapid multiplexed SERS analysis in biological fluids
and other applications
Pseudonegative Thermal Expansion and the State of Water in Graphene Oxide Layered Assemblies
Unraveling the complex interplay between thermal properties and hydration is a part of understanding the fundamental properties of many soft materials and very essential for many applications. Here we show that graphene oxide (GO) demonstrates a highly negative thermal expansion (NTE) coefficient owing to unique thermohydration processes related with fast transport of water between the GO sheets, the amphiphilic nature of nanochannels, and close-to-zero intrinsic thermal expansion of GO. The humidity-dependent NTE of GO layered assemblies, or āpseudonegative thermal expansionā (PNTE), differs from that of other hygroscopic materials due to its relatively fast and highly reversible expansion/contraction cycles and occurrence at low humidity levels while bearing similarities to classic NTE. Thermal expansion of polyvinyl alcohol/GO composites is easily tunable with additional intricacy of thermohydration effects. PNTE combined with isotropy, nontoxicity, and mechanical robustness is an asset for applications of actuators, sensors, MEMS devices, and memory materials and crucial for developing methods of thermal/photopatterning of GO devices
Pushing the Limits: 3D Layer-by-Layer-Assembled Composites for Cathodes with 160 C Discharge Rates
Deficiencies of cathode materials severely limit cycling performance and discharge rates of Li batteries. The key problem is that cathode materials must combine multiple properties: high lithium ion intercalation capacity, electrical/ionic conductivity, porosity, and mechanical toughness. Some materials revealed promising characteristics in a subset of these properties, but attaining the entire set of often contrarian characteristics requires new methods of materials engineering. In this paper, we report high surface area 3D composite from reduced graphene oxide loaded with LiFePO<sub>4</sub> (LFP) nanoparticles made by layer-by-layer assembly (LBL). High electrical conductivity of the LBL composite is combined with high ionic conductivity, toughness, and low impedance. As a result of such materials properties, reversible lithium storage capacity and Coulombic efficiency were as high as 148 mA h g<sup>ā1</sup> and 99%, respectively, after 100 cycles at 1 C. Moreover, these composites enabled unusually high reversible chargeādischarge rates up to 160 C with a storage capacity of 56 mA h g<sup>ā1</sup>, exceeding those of known LFP-based cathodes, some of them by several times while retaining high content of active cathode material. The study demonstrates that LBL-assembled composites enable resolution of difficult materials engineering tasks
Shape-Dependent Biomimetic Inhibition of Enzyme by Nanoparticles and Their Antibacterial Activity
Enzyme inhibitors are ubiquitous in all living systems, and their biological inhibitory activity is strongly dependent on their molecular shape. Here, we show that small zinc oxide nanoparticles (ZnO NPs)īøpyramids, plates, and spheresīøpossess the ability to inhibit activity of a typical enzyme Ī²-galactosidase (GAL) in a biomimetic fashion. Enzyme inhibition by ZnO NPs is reversible and follows classical MichaelisāMenten kinetics with parameters strongly dependent on their geometry. Diverse spectroscopic, biochemical, and computational experimental data indicate that association of GAL with specific ZnO NP geometries interferes with conformational reorganization of the enzyme necessary for its catalytic activity. The strongest inhibition was observed for ZnO nanopyramids and compares favorably to that of the best natural GAL inhibitors while being resistant to proteases. Besides the fundamental significance of this biomimetic function of anisotropic NPs, their capacity to serve as degradation-resistant enzyme inhibitors is technologically attractive and is substantiated by strong shape-specific antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA), endemic for most hospitals in the world
Template-Free Hierarchical Self-Assembly of Iron Diselenide Nanoparticles into Mesoscale Hedgehogs
The
ability of semiconductor nanoparticles (NPs) to self-assemble
has been known for several decades. However, the limits of the geometrical
and functional complexity for the self-assembled nanostructures made
from simple often polydispersed NPs are still continuing to amaze
researchers. We report here the self-assembly of primary ā¼2ā4
nm FeSe<sub>2</sub> NPs with puck-like shapes into either (a) monocrystalline
nanosheets ā¼5.5 nm thick and ā¼1000 nm in lateral dimensions
or (b) mesoscale hedgehogs ā¼550 nm in diameter with spikes
of ā¼250 nm in length, and ā¼10ā15 nm in diameter,
the path of the assembly is determined by the concentration of dodecanethiol
(DT) in the reaction media. The nanosheets represent the constitutive
part of hedgehogs. They are rolled into scrolls and assembled around
a single core with distinct radial orientation forming nanoscale āneedlesā
approximately doubling its fractal dimension of these objects. The
core is assembled from primary NPs and nanoribbons. The size distribution
of the mesoscale hedgehogs can be as low as 3.8%, indicating a self-limited
mechanism of the assembly. Molecular dynamics simulation indicates
that the primary FeSe<sub>2</sub> particles have mobile edge atoms
and asymmetric basal surfaces. The top-bottom asymmetry of the puck-like
NPs originates from the Fe-rich/Se-rich stripes on the (011) surface
of the orthorhombic FeSe<sub>2</sub> crystal lattice, displaying 2.7
nm periodicity that is comparable to the lateral size of the primary
NPs. As the concentration of DT increases, the NPs bind to additional
metal sites, which increases the chemical and topographic asymmetry
and switches the assembly pathways from nanosheets to hedgehogs. These
results demonstrate that the self-assembly of NPs with non-biological
surface ligands and without any biological templates results in morphogenesis
of inorganic superstructures with complexity comparable to that of
biological assemblies, for instance mimivirus. The semiconductor nature
of FeSe<sub>2</sub> hedgehogs enables their utilizations in catalysis,
drug delivery, optics, and energy storage
Universal Synthesis of Single-Phase Pyrite FeS<sub>2</sub> Nanoparticles, Nanowires, and Nanosheets
Nanoscale pyrite FeS<sub>2</sub> is considered to be
one of few
potentially transformative materials for photovoltaics capable of
bridging the cost/performance gap of solar batteries. It also holds
promise for energy storage applications as the material for high-performance
cathodes. Despite prospects, the synthesis of FeS<sub>2</sub> nanostructures
and diversity of their geometries has been hardly studied. Moreover,
the state-of-the-art aqueous dispersions of nanoscale pyrite, which
have special significance for solar energetics, are particularly disappointing
due to low quality. There are no known methods to produce well-crystallized
nanoparticles and other geometries of nanoscale pyrite in water or
mixed aqueous solvents. Here, we describe a successful synthesis of
single-phase pyrite nanoparticles with a diameter of 2ā5 nm
in polar solvent and aqueous dispersions. The particles display high
uniformity and crystallographic purity. Moreover, the synthetic approach
developed for nanoparticles was proven to be quite universal and can
be modified to produce both nanowires and nanosheets, which also display
high crystallinity. The diameter of the pyrite nanowires was 80ā120
nm with the length exceeding 5 Ī¼m. The nanosheets displayed
lateral dimensions of 100ā200 nm with the thickness of 2 nm.
Availability of single-phase FeS<sub>2</sub> nanoscale aqueous dispersions
is expected to stimulate further studies of these materials in green
energy conversion technologies and drug delivery applications