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 differenceoverexpression of ectophosphatasesbetween cancer and normal cells triggers the d-tyrosine phosphate decorated magnetic nanoparticles (Fe₃O₄-p­(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 Fe₃O₄-p­(d-Tyr) nanoparticles also selectively inhibit cancer cells in the coculture. As a general method to broadly target cancer cells without highly specific ligand–receptor 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_<i>x</i>Fe_3–<i>x</i>O₄ (M = Fe, Cu, Co, Mn) Nanoparticles and Their Electrocatalysis for Oxygen Reduction Reaction

Sub-10 nm nanoparticles (NPs) of M­(II)-substituted magnetite M_<i>x</i>Fe_3–<i>x</i>O₄ (M_<i>x</i>Fe_1–<i>x</i>O•Fe₂O₃) (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_<i>x</i>Fe_3–<i>x</i>O₄ NPs showed the M­(II)-dependent ORR catalytic activities with Mn_<i>x</i>Fe_3–<i>x</i>O₄ being the most active followed by Co_<i>x</i>Fe_3–<i>x</i>O₄, Cu_<i>x</i>Fe_3–<i>x</i>O₄, and Fe₃O₄. The ORR activity of the Mn_<i>x</i>Fe_3–<i>x</i>O₄ was further tuned by controlling <i>x</i> and MnFe₂O₄ NPs were found to be as efficient as the commercial Pt in catalyzing ORR. The MnFe₂O₄ NPs represent a new class of highly efficient non-Pt catalyst for ORR in alkaline media

<i>In Situ</i> X‑ray 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 Pt–Sn 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 Pt­(II) and Sn­(IV) precursors are used, in contrast to a typical simultaneous reduction mechanism, the PtSn NCs are formed through an initial reduction of Pt­(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 (∼280 °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/Fe₃O₄ NPs followed by temperature-controlled Fe etching in acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at ∼8 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 HClO₄ 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/cm² 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^–1) and mass activity (1949 A/g) than the NPs deposited on conventional carbon black (0.14 s^–1 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 SmCo₅ Matrix

We report a new strategy for stabilizing Fe nanoparticles (NPs) in the preparation of SmCo₅–Fe nanocomposites. We coat the presynthesized Fe NPs with SiO₂ and assemble the Fe/SiO₂ NPs with Sm–Co–OH to form a mixture. After reductive annealing at 850 °C in the presence of Ca, we obtain SmCo₅–Fe/SiO₂ composites. Following aqueous NaOH washing and compaction, we produced exchange-coupled SmCo₅–Fe 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_<i>x</i>Fe_3–<i>x</i>O₄ Nanocubes for Magnetic Recording

We report a facile synthesis of monodisperse ferrimagnetic Co_<i>x</i>Fe_3–<i>x</i>O₄ nanocubes (NCs) through thermal decomposition of Fe­(acac)₃ and Co­(acac)₂ (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_0.6Fe_2.4O₄ NCs showing a room temperature <i>H</i>_c of 1930 Oe. The ferrimagnetic NCs are self-assembled at the water–air 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 X‑ray 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 Pd–TOP (TOP: trioctylphosphine) complex via the “heat-up” 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 Pd–TOP complex but promote the formation of nuclei due to strong ligand–NP 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 ligand–NP 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-Fe₃O₄ 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 HClO₄ and hydrogen evolution reaction (HER) in 0.5 M H₂SO₄ with much enhanced activity (the most active fct-structured alloy NP catalyst ever reported) and stability (no obvious Fe loss and NP degradation after 20 000 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