Surface Modification and Characterization of Polycarbonate Microdevices for Capture of Circulating Biomarkers, Both in Vitro and in Vivo

Herein, we report the fabrication, characterization, and testing of a polymer microprojection array, for the direct and selective capture of circulating biomarkers from the skin of live mice. First, we modified polycarbonate wafers using an electrophilic aromatic substitution reaction with nitric acid to insert aromatic nitro-groups into the benzene rings, followed by treatment with sodium borohydride to reduce the nitro-groups to primary amines. Initial characterization by ultraviolet–visible (UV–vis) spectroscopy suggested that increasing acid concentration led to increased depth of material modification and that this was associated with decreased surface hardness and slight changes in surface roughness. Chemical analysis with X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance fourier transform infrared (ATR-FT-IR) spectroscopy showed nitrogen species present at the surface for all acid concentrations used, but subsurface nitrogen species were only observed at acid concentrations >35%. The nitrogen species were identified as a mixture of nitro, imine, and amine groups, and following reduction, there was sufficient amounts of primary amine groups for covalent attachment of a polyethylene glycol antifouling layer and protein capture probes, as determined by colorimetric and radiometric assays. Finally, the modification scheme was applied to polycarbonate microprojection arrays, and we show that these devices achieve flank skin penetration depths and biomarker yields comparable with our previously reported gold-coated silicon arrays, with very low nonspecific binding even in 10% mouse serum (in vitro) or directly in mouse skin (in vivo). This study is the first demonstration showing the potential utility of polymer microprojections in immunodiagnostics applications

A Surfactant-Free Strategy for Synthesizing and Processing Intermetallic Platinum-Based Nanoparticle Catalysts

Using Pt₃Fe nanoparticles as an example, a surfactant-free Np-KCl matrix method (Np stands for nanoparticle) is developed for the synthesis of nanoparticles with controlled size and structure. In this method, the Np-KCl assembly is formed in a one-pot reduction in THF at room temperature. KCl is an insoluble byproduct of the reaction and serves as a matrix that traps the nanoparticles to avoid particle agglomeration and to control the coalescence of nanoparticles during thermal annealing up to 600 °C. By varying the molar ratio of metal precursors and KCl, as well as the time and temperature of annealing, the final particle sizes and crystalline order can be independently controlled. After thermal processing, nanoparticles were released from the KCl matrix and transferred in an ethylene glycol–water solution to support materials forming a uniform Np-support assembly. A detailed study of the synthesis of ordered intermetallic Pt₃Fe nanoparticles with an average diameter of 4 nm, using this Np-KCl method, is provided as an example of a generally applicable method. This surfactant-free strategy has been extended to the synthesis of other bi- and trimetallic nanoparticles of Pt-transition metals

Defining Crystalline/Amorphous Phases of Nanoparticles through X‑ray Absorption Spectroscopy and X‑ray Diffraction: The Case of Nickel Phosphide

In this study we elucidate the structural distinctions between amorphous and crystalline Ni₂P nanoparticles synthesized using tri-<i>n</i>-octylphosphine (TOP), through X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), and inductively coupled plasma (ICP). We determine the differences in their chemical and atomic structure, which have not been previously reported, yet are essential for understanding their potential as nanocatalysts. These structural characteristics are related to the corresponding nanoparticle magnetic properties analyzed by performing magnetic measurements. XAS results reveal a significant P concentration in the amorphous nanoparticle sample – placing the stoichiometry close to Ni₂P – despite XRD results that show only fcc Ni contributions. By comparing the long-range structural order from XRD to the short-range radial structure from EXAFS we conclude that both techniques are necessary to obtain a complete structural picture of amorphous and crystalline nanoparticle phases due to the limitations of XRD amorphous characterization. We find that phases are amorphous with respect to XRD when their offsets (deviations) from bulk interatomic distances have a standard deviation as high as ∼4.82. Phases with lower standard deviation (e.g., ≲1.22), however, are detectable as crystalline through XRD. The possible presence of amorphous phases should be considered when using XRD alone for nanoparticle characterization. This is particularly important when highly reactive reagents such as TOP are used in synthesis. By characterizing amorphous nickel phosphide nanoparticles that have a comparable stoichiometry to Ni₂P, we confirm that TOP serves as a highly effective phosphorus source, even at temperatures as low as 230 °C. Unintended amorphous structure domains may significantly affect nanoparticle properties, and in turn, their functionality

MOF-Derived Bimetallic Pd–Co Alkaline ORR Electrocatalysts

The development of highly active, durable, and low-cost electrocatalysts for the oxygen reduction reaction (ORR) has been of paramount importance for advancing and commercializing fuel cell technologies. Here, we report on a novel family of Pd–Co binary alloys (PdxCo, x = 1–6) embedded in bimetallic organic framework (BMOF)-derived polyhedral carbon supports. BMOF-derived Pd3Co, annealed at 300–400 °C, exhibited the most promising ORR activity among the family of materials studied, with a half-wave potential (E1/2) of 0.977 V vs RHE and a mass activity of 0.86 mA/μgPd in 1 M KOH, both values being superior to those of commercial Pd/C electrocatalysts. Moreover, it maintained robust durability after 20,000 potential cycles with a minimal degradation in E1/2 of 10 mV. The enhanced performance and stability are ascribed to the uniform elemental distribution of Pd and Co and the Co-containing N-doped carbon (Co–N–C) structures. In anion exchange membrane fuel cell (AEMFC) tests, the peak power density of the cell employing a BMOF-derived Pd3Co cathode reached 1.1 W/cm2 at an ultralow Pd loading of 0.04 mgPd/cm2. Strategies developed herein provide promising insights into the rational design and synthesis of highly active and durable ORR electrocatalysts for alkaline fuel cells

Reaction Kinetics of Germanium Nanowire Growth on Inductively Heated Copper Surfaces

This article describes the chemical kinetics of germanium nanowire growth on inductively heated copper surfaces using diphenylgermane as a precursor. Inductive heating of metal surfaces presents a simple, rapid, and contact-free method to activate the direct growth of nanowires on metal surfaces. We show the main effects of synthesis temperature, duration, precursor concentration on the morphology, and loading of the nanowire film. We describe the complex interplay of precursor degradation, nucleation, and growth in context of a multistep reaction mechanism. We studied the temporal evolution of nanowire loading and morphology to develop a kinetic model, which predicts critical thresholds that define the onset of sequential axial and radial nanowire growth modes. These results may be used to commercially scale a nanowire growth process

Capture of the Circulating <i>Plasmodium falciparum</i> Biomarker HRP2 in a Multiplexed Format, via a Wearable Skin Patch

Herein we demonstrate the use of a wearable device that can selectively capture two distinct circulating protein biomarkers (recombinant P. falciparum r<i>Pf</i>HRP2 and total IgG) from the intradermal fluid of live mice <i>in situ</i>, for subsequent detection <i>in vitro</i>. The device comprises a microprojection array that, when applied to the skin, penetrates the outer skin layers to interface directly with intradermal fluid. Because of the complexity of the biological fluid being sampled, we investigated the effects of solution conditions on the attachment of capture antibodies, to optimize the assay detection limit both <i>in vitro</i> and on live mice. For detection of the target antigen diluted in 20% serum, immobilization conditions favoring high antibody surface density (low pH, low ionic strength) resulted in 100-fold greater sensitivity in comparison to standard conditions, yielding a detection limit equivalent to the plate enzyme-linked immunosorbent assay (ELISA). We also show that blocking the device surface to reduce nonspecific adsorption of target analyte and host proteins does not significantly change sensitivity. After injecting mice with r<i>Pf</i>HRP2 via the tail vein, we compared analyte levels in both plasma and skin biopsies (cross-sectional area same as the microprojection array), observing that skin samples contained the equivalent of ∼8 μL of analyte-containing plasma. We then applied the arrays to mice, showing that surfaces coated with a high density of antibodies captured a significant amount of the r<i>Pf</i>HRP2 target while the standard surface showed no capture in comparison to the negative control. Next, we applied a triplex device to both control and r<i>Pf</i>HRP2-treated mice, simultaneously capturing r<i>Pf</i>HRP2 and total IgG (as a positive control for skin penetration) in comparison to a negative control device. We conclude that such devices can be used to capture clinically relevant, circulating protein biomarkers of infectious disease via the skin, with potential applications as a minimally invasive and lab-free biomarker detection platform

Facile Synthesis of Carbon-Supported Pd–Co Core–Shell Nanoparticles as Oxygen Reduction Electrocatalysts and Their Enhanced Activity and Stability with Monolayer Pt Decoration

The rational synthesis of active, durable, and low-cost catalysts is of particular interest to fuel cell applications. Here, we describe a facile method for the preparation of Pd-rich Pd_<i>x</i>Co alloy nanoparticles supported on carbon, using an adsorbate-induced surface segregation effect. The electronic properties of Pd were modulated by alloying with different amounts of Co, which affects the oxygen reduction reaction (ORR) activity. The electrocatalytic activity of the Pd₃Co@Pd/C nanoparticles for the ORR was enhanced by spontaneously depositing a nominal monolayer of Pt. The activities of the different catalysts for the ORR could be correlated with the oxygen adsorption energy and the d-band center of the catalyst surface, as calculated using density functional theory, which is in agreement with previous theoretical studies. The materials synthesized herein are promising cathode catalysts for fuel cell applications and the facile synthesis method could be readily adapted to other catalyst systems, facilitating screening of high efficiency catalysts

Three-Dimensional Tracking and Visualization of Hundreds of Pt−Co Fuel Cell Nanocatalysts During Electrochemical Aging

We present an electron tomography method that allows for the identification of hundreds of electrocatalyst nanoparticles with one-to-one correspondence before and after electrochemical aging. This method allows us to track, in three-dimensions, the trajectories and morphologies of each Pt−Co nanocatalyst on a fuel cell carbon support. In conjunction with the use of atomic-scale electron energy loss spectroscopic imaging, our experiment enables the correlation of performance degradation of the catalyst with changes in particle/interparticle morphologies, particle−support interactions, and the near-surface chemical composition. We found that aging of the catalysts under normal fuel cell operating conditions (potential scans from +0.6 to +1.0 V for 30 000 cycles) gives rise to coarsening of the nanoparticles, mainly through coalescence, which in turn leads to the loss of performance. The observed coalescence events were found to be the result of nanoparticle migration on the carbon support during potential cycling. This method provides detailed insights into how nanocatalyst degradation occurs in proton exchange membrane fuel cells (PEMFCs) and suggests that minimization of particle movement can potentially slow down the coarsening of the particles and the corresponding performance degradation

Nanoscale Imaging of Lithium Ion Distribution During In Situ Operation of Battery Electrode and Electrolyte

A major challenge in the development of new battery materials is understanding their fundamental mechanisms of operation and degradation. Their microscopically inhomogeneous nature calls for characterization tools that provide operando and localized information from individual grains and particles. Here, we describe an approach that enables imaging the nanoscale distribution of ions during electrochemical charging of a battery in a transmission electron microscope liquid flow cell. We use valence energy-loss spectroscopy to track both solvated and intercalated ions, with electronic structure fingerprints of the solvated ions identified using an ab initio nonlinear response theory. Equipped with the new electrochemical cell holder, nanoscale spectroscopy and theory, we have been able to determine the lithiation state of a LiFePO₄ electrode and surrounding aqueous electrolyte in real time with nanoscale resolution during electrochemical charge and discharge. We follow lithium transfer between electrode and electrolyte and image charging dynamics in the cathode. We observe competing delithiation mechanisms such as core–shell and anisotropic growth occurring in parallel for different particles under the same conditions. This technique represents a general approach for the operando nanoscale imaging of electrochemically active ions in the electrode and electrolyte in a wide range of electrical energy storage systems

Systematic Optimization of Battery Materials: Key Parameter Optimization for the Scalable Synthesis of Uniform, High-Energy, and High Stability LiNi_0.6Mn_0.2Co_0.2O₂ Cathode Material for Lithium-Ion Batteries

Ni-rich LiNi_<i>x</i>Mn_<i>y</i>Co_{1‑<i>x</i>‑<i>y</i>}O₂ (<i>x</i> > 0.5) (NMC) materials have attracted a great deal of interest as promising cathode candidates for Li-ion batteries due to their low cost and high energy density. However, several issues, including sensitivity to moisture, difficulty in reproducibly preparing well-controlled morphology particles and, poor cyclability, have hindered their large scale deployment; especially for electric vehicle (EV) applications. In this work, we have developed a uniform, highly stable, high-energy density, Ni-rich LiNi_0.6Mn_0.2Co_0.2O₂ cathode material by systematically optimizing synthesis parameters, including pH, stirring rate, and calcination temperature. The particles exhibit a spherical morphology and uniform size distribution, with a well-defined structure and homogeneous transition-metal distribution, owing to the well-controlled synthesis parameters. The material exhibited superior electrochemical properties, when compared to a commercial sample, with an initial discharge capacity of 205 mAh/g at 0.1 C. It also exhibited a remarkable rate capability with discharge capacities of 157 mAh/g and 137 mAh/g at 10 and 20 C, respectively, as well as high tolerance to air and moisture. In order to demonstrate incorporation into a commercial scale EV, a large-scale 4.7 Ah LiNi_0.6Mn_0.2Co_0.2O₂ Al-full pouch cell with a high cathode loading of 21.6 mg/cm², paired with a graphite anode, was fabricated. It exhibited exceptional cyclability with a capacity retention of 96% after 500 cycles at room temperature. This material, which was obtained by a fully optimized scalable synthesis, delivered combined performance metrics that are among the best for NMC materials reported to date