12 research outputs found
Enzymatic Transformation of Phosphate Decorated Magnetic Nanoparticles for Selectively Sorting and Inhibiting Cancer Cells
As
an important and necessary step of sampling biological specimens,
the separation of malignant cells from a mixed population of cells
usually requires sophisticated instruments and/or expensive reagents.
For health care in the developing regions, there is a need for an
inexpensive sampling method to capture tumor cells for rapid and accurate
diagnosis. Here we show that an underexplored generic differenceî¸overexpression
of ectophosphatasesî¸between cancer and normal cells triggers
the d-tyrosine phosphate decorated magnetic nanoparticles
(Fe<sub>3</sub>O<sub>4</sub>-pÂ(d-Tyr)) to adhere selectively
on cancer cells upon catalytic dephosphorylation, which enables magnetic
separation of cancer cells from mixed population of cells (e.g., cocultured
cancer cell (HeLa-GFP) and stromal cells (HS-5)). Moreover, the Fe<sub>3</sub>O<sub>4</sub>-pÂ(d-Tyr) nanoparticles also selectively
inhibit cancer cells in the coculture. As a general method to broadly
target cancer cells without highly specific ligandâreceptor
interactions (e.g., antibodies), the use of an enzymatic reaction
to spatiotemporally modulate the state of various nanostructures in
cellular environments will ultimately lead to the development of new
theranostic applications of nanomaterials
Monodisperse M<sub><i>x</i></sub>Fe<sub>3â<i>x</i></sub>O<sub>4</sub> (M = Fe, Cu, Co, Mn) Nanoparticles and Their Electrocatalysis for Oxygen Reduction Reaction
Sub-10 nm nanoparticles (NPs) of
MÂ(II)-substituted magnetite M<sub><i>x</i></sub>Fe<sub>3â<i>x</i></sub>O<sub>4</sub> (M<sub><i>x</i></sub>Fe<sub>1â<i>x</i></sub>Oâ˘Fe<sub>2</sub>O<sub>3</sub>) (M = Mn, Fe, Co, Cu)
were synthesized and studied as electrocatalysts for oxygen reduction
reaction (ORR) in 0.1 M KOH solution. Loaded on commercial carbon
support, these M<sub><i>x</i></sub>Fe<sub>3â<i>x</i></sub>O<sub>4</sub> NPs showed the MÂ(II)-dependent ORR
catalytic activities with Mn<sub><i>x</i></sub>Fe<sub>3â<i>x</i></sub>O<sub>4</sub> being the most active followed by Co<sub><i>x</i></sub>Fe<sub>3â<i>x</i></sub>O<sub>4</sub>, Cu<sub><i>x</i></sub>Fe<sub>3â<i>x</i></sub>O<sub>4</sub>, and Fe<sub>3</sub>O<sub>4</sub>. The ORR activity
of the Mn<sub><i>x</i></sub>Fe<sub>3â<i>x</i></sub>O<sub>4</sub> was further tuned by controlling <i>x</i> and MnFe<sub>2</sub>O<sub>4</sub> NPs were found to be as efficient
as the commercial Pt in catalyzing ORR. The MnFe<sub>2</sub>O<sub>4</sub> NPs represent a new class of highly efficient non-Pt catalyst
for ORR in alkaline media
<i>In Situ</i> Xâray Scattering Guides the Synthesis of Uniform PtSn Nanocrystals
Compared to monometallic nanocrystals
(NCs), bimetallic ones often
exhibit superior properties due to their wide tunability in structure
and composition. A detailed understanding of their synthesis at the
atomic scale provides crucial knowledge for their rational design.
Here, exploring the PtâSn bimetallic system as an example,
we study in detail the synthesis of PtSn NCs using <i>in situ</i> synchrotron X-ray scattering. We show that when PtÂ(II) and SnÂ(IV)
precursors are used, in contrast to a typical simultaneous reduction
mechanism, the PtSn NCs are formed through an initial reduction of
PtÂ(II) to form Pt NCs, followed by the chemical transformation from
Pt to PtSn. The kinetics derived from the <i>in situ</i> measurements shows fast diffusion of Sn into the Pt lattice accompanied
by reordering of these atoms into intermetallic PtSn structure within
300 s at the reaction temperature (âź280 °C). This crucial
mechanistic understanding enables the synthesis of well-defined PtSn
NCs with controlled structure and composition via a seed-mediated
approach. This type of <i>in situ</i> characterization can
be extended to other multicomponent nanostructures to advance their
rational synthesis for practical applications
Core/Shell Face-Centered Tetragonal FePd/Pd Nanoparticles as an Efficient Non-Pt Catalyst for the Oxygen Reduction Reaction
We report the synthesis of core/shell face-centered tetragonal (fct)-FePd/Pd nanoparticles (NPs) <i>via</i> reductive annealing of core/shell Pd/Fe<sub>3</sub>O<sub>4</sub> NPs followed by temperature-controlled Fe etching in acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at âź8 nm and Pd shell at 0.27, 0.65, or 0.81 nm), the fct-FePd/Pd-0.65 NPs are the most efficient catalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO<sub>4</sub> with Pt-like activity and durability. This enhanced ORR catalysis arises from the desired Pd lattice compression in the 0.65 nm Pd shell induced by the fct-FePd core. Our study offers a general approach to enhance Pd catalysis in acid for ORR
Stable Cobalt Nanoparticles and Their Monolayer Array as an Efficient Electrocatalyst for Oxygen Evolution Reaction
Monodisperse
cobalt (Co) nanoparticles (NPs) were synthesized and
stabilized against oxidation via reductive annealing at 600 °C.
The stable Co NPs are active for catalyzing the oxygen evolution reaction
(OER) in 0.1 M KOH, producing a current density of 10 mA/cm<sup>2</sup> at an overpotential of 0.39 V (1.62 V vs RHE, no <i>iR</i>-correction). Their catalysis is superior to the commercial Ir catalyst
in both activity and stability. These Co NPs are also assembled into
a monolayer array on the working electrode, allowing the detailed
study of their intrinsic OER activity. The Co NPs in the monolayer
array show 15 times higher turnover frequency (2.13 s<sup>â1</sup>) and mass activity (1949 A/g) than the NPs deposited on conventional
carbon black (0.14 s<sup>â1</sup> and 126 A/g, respectively)
at an overpotential of 0.4 V. These stable Co NPs are a promising
new class of noble-metal-free catalyst for water splitting
Stabilizing Fe Nanoparticles in the SmCo<sub>5</sub> Matrix
We
report a new strategy for stabilizing Fe nanoparticles (NPs)
in the preparation of SmCo<sub>5</sub>âFe nanocomposites. We
coat the presynthesized Fe NPs with SiO<sub>2</sub> and assemble the
Fe/SiO<sub>2</sub> NPs with SmâCoâOH to form a mixture.
After reductive annealing at 850 °C in the presence of Ca, we
obtain SmCo<sub>5</sub>âFe/SiO<sub>2</sub> composites. Following
aqueous NaOH washing and compaction, we produced exchange-coupled
SmCo<sub>5</sub>âFe nanocomposites with Fe NPs controlled at
12 nm. Our work demonstrates a successful strategy of stabilizing
high moment magnetic NPs in a hard magnetic matrix to produce a nanocomposite
with tunable magnetic properties
Systematic Identification of Promoters for Methane Oxidation Catalysts Using Size- and Composition-Controlled Pd-Based Bimetallic Nanocrystals
Promoters enhance the performance
of catalytic active phases by
increasing rates, stability, and/or selectivity. The process of identifying
promoters is in most cases empirical and relies on testing a broad
range of catalysts prepared with the random deposition of active and
promoter phases, typically with no fine control over their localization.
This issue is particularly relevant in supported bimetallic systems,
where two metals are codeposited onto high-surface area materials.
We here report the use of colloidal bimetallic nanocrystals to produce
catalysts where the active and promoter phases are colocalized to
a fine extent. This strategy enables a systematic approach to study
the promotional effects of several transition metals on palladium
catalysts for methane oxidation. In order to achieve these goals,
we demonstrate a single synthetic protocol to obtain uniform palladium-based
bimetallic nanocrystals (PdM, M = V, Mn, Fe, Co, Ni, Zn, Sn, and potentially
extendable to other metal combinations) with a wide variety of compositions
and sizes based on high-temperature thermal decomposition of readily
available precursors. Once the nanocrystals are supported onto oxide
materials, thermal treatments in air cause segregation of the base
metal oxide phase in close proximity to the Pd phase. We demonstrate
that some metals (Fe, Co, and Sn) inhibit the sintering of the active
Pd metal phase, while others (Ni and Zn) increase its intrinsic activity
compared to a monometallic Pd catalyst. This procedure can be generalized
to systematically investigate the promotional effects of metal and
metal oxide phases for a variety of active metal-promoter combinations
and catalytic reactions
Monolayer Assembly of Ferrimagnetic Co<sub><i>x</i></sub>Fe<sub>3â<i>x</i></sub>O<sub>4</sub> Nanocubes for Magnetic Recording
We
report a facile synthesis of monodisperse ferrimagnetic Co<sub><i>x</i></sub>Fe<sub>3â<i>x</i></sub>O<sub>4</sub> nanocubes (NCs) through thermal decomposition of FeÂ(acac)<sub>3</sub> and CoÂ(acac)<sub>2</sub> (acac = acetylacetonate) in the
presence of oleic acid and sodium oleate. The sizes of the NCs are
tuned from 10 to 60 nm, and their composition is optimized at <i>x</i> = 0.6 to show strong ferrimagnetism with the 20 nm Co<sub>0.6</sub>Fe<sub>2.4</sub>O<sub>4</sub> NCs showing a room temperature <i>H</i><sub>c</sub> of 1930 Oe. The ferrimagnetic NCs are self-assembled
at the waterâair interface into a large-area (in square centimeter)
monolayer array with a high packing density and (100) texture. The
20 nm NC array can be recorded at linear densities ranging from 254
to 31 kfci (thousand flux changes per inch). The work demonstrates
the great potential of solution-phase synthesis and self-assembly
of magnetic array for magnetic recording applications
Tuning Precursor Reactivity toward Nanometer-Size Control in Palladium Nanoparticles Studied by in Situ Small Angle Xâray Scattering
Synthesis of monodisperse
nanoparticles (NPs) with precisely controlled
size is critical for understanding their size-dependent properties.
Although significant synthetic developments have been achieved, it
is still challenging to synthesize well-defined NPs in a predictive
way due to a lack of in-depth mechanistic understanding of reaction
kinetics. Here we use synchrotron-based small-angle X-ray scattering
(SAXS) to monitor in situ the formation of palladium (Pd) NPs through
thermal decomposition of PdâTOP (TOP: trioctylphosphine) complex
via the âheat-upâ method. We systematically study the
effects of different ligands, including oleylamine, TOP, and oleic
acid, on the formation kinetics of Pd NPs. Through quantitative analysis
of the real-time SAXS data, we are able to obtain a detailed picture
of the size, size distribution, and concentration of Pd NPs during
the syntheses, and these results show that different ligands strongly
affect the precursor reactivity. We find that oleylamine does not
change the reactivity of the PdâTOP complex but promote the
formation of nuclei due to strong ligandâNP binding. On the
other hand, TOP and oleic acid substantially change the precursor
reactivity over more than an order of magnitude, which controls the
nucleation kinetics and determines the final particle size. A theoretical
model is used to demonstrate that the nucleation and growth kinetics
are dependent on both precursor reactivity and ligandâNP binding
affinity, thus providing a framework to explain the synthesis process
and the effect of the reaction conditions. Quantitative understanding
of the impacts of different ligands enables the successful synthesis
of a series of monodisperse Pd NPs in the broad size range from 3
to 11 nm with nanometer-size control, which serve as a model system
to study their size-dependent catalytic properties. The in situ SAXS
probing can be readily extended to other functional NPs to greatly
advance their synthetic design
New Approach to Fully Ordered fct-FePt Nanoparticles for Much Enhanced Electrocatalysis in Acid
Fully
ordered face-centered tetragonal (fct) FePt nanoparticles (NPs) are
synthesized by thermal annealing of the MgO-coated dumbbell-like FePt-Fe<sub>3</sub>O<sub>4</sub> NPs followed by acid washing to remove MgO.
These fct-FePt NPs show strong ferromagnetism with room temperature
coercivity reaching 33 kOe. They serve as a robust electrocatalyst
for the oxygen reduction reaction (ORR) in 0.1 M HClO<sub>4</sub> and
hydrogen evolution reaction (HER) in 0.5 M H<sub>2</sub>SO<sub>4</sub> with much enhanced activity (the most active fct-structured alloy
NP catalyst ever reported) and stability (no obvious Fe loss and NP
degradation after 20âŻ000 cycles between 0.6 and 1.0 V (vs RHE)).
Our work demonstrates a reliable approach to FePt NPs with much improved
fct-ordering and catalytic efficiency for ORR and HER