Surface Epitope Coverage Affects Binding Characteristics of Bisphenol-A Functionalized Nanoparticles in a Competitive Inhibition Assay

The biomolecule interface is a key element in immunosensor fabrication, which can greatly influence the sensor performance. This paper explores the effects of surface epitope coverage of small molecule functionalized nanoparticle on the apparent affinity (avidity) of antibody in a competitive inhibition assay using bisphenol-A (BPA) as a model target. An unconventional two-antibody competitive inhibition ELISA (ci-ELISA) using thiolated BPA modified gold nanoparticles (cysBPAv-AuNP) as a competing reagent was devised for this study. It was shown that the antibody complexation with cysBPAv-AuNPs required a minimum number of surface epitopes on the nanoparticle to form a sufficiently strong interaction and reliable detection. The binding of cysBPAv-AuNP to anti-BPA antibodies, for limited antibody binding sites, was enhanced by a greater number of epitope-modified nanoparticles (cysBPAv-AuNP) as well as with higher epitope coverage. Increasing the molar concentration of epitope present in an assay enhanced the binding between anti-BPA antibodies and cysBPAv-AuNP. This implies that, to increase the limit of detection of a competitive inhibition assay, a reduced molar concentration of epitope should be applied. This could be achieved by either lowering the epitope coverage on each cysBPAv-AuNP or the assay molar concentration of cysBPAv-AuNP or both of these factors

The rapid formation of functional monolayers on silicon under mild conditions

We report on an exceedingly mild chemical functionalization of hydrogen-terminated Si(100) with unactivated and unprotected bifunctional α,ω-dialkynes. Monolayer formation occurs rapidly in the dark, and at room temperature, from dilute solutions of an aromatic-conjugated acetylene. The method addresses the poor reactivity of p-type substrates under mild conditions. We suggest the importance of several factors, including an optimal orientation for electron transfer between the adsorbate and the Si surface, conjugation of the acetylenic function with a π-system, as well as the choice of a solvent system that favors electron transfer and screens Coulombic interactions between surface holes and electrons. The passivated Si(100) electrode is amenable to further functionalization and shown to be a viable model system for redox studies at non-oxide semiconductor electrodes in aqueous solutions

The Fabrication of stable gold nanoparticle-modified interfaces for electrochemistry

Forming stable gold nanoparticle (AuNP)-modified surface is important for a number of applications including sensing and electrocatalysis. Herein, tethering AuNPs to glassy carbon (GC) surfaces using surface bound diazonium salts is investigated as a strategy to produce stable AuNP surfaces. GC electrodes are first modified with 4-aminophenyl (GC-Ph-NH₂), and then the terminal amine groups are converted to diazonium groups by incubating the GC-Ph-NH₂ interface in NaNO₂ and HCl solution to form a 4-phenyl diazonium chloride-modified interface (GC-Ph-N₂⁺Cl⁻). Subsequently AuNPs are immobilized on the interface by electrochemical reduction to give a 4-phenyl AuNP-modified interface (GC-Ph-AuNP). For comparison, 4-aminophenyl AuNP- and 4-thiophenol AuNP-modified GC interfaces (GC-Ph-S-AuNP and GC-Ph-NH-AuNP), in which AuNPs are tethered to the surfaces by forming S–Au and NH–Au bond, respectively, were also prepared. Cyclic voltammetry, electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy are used to characterize these fabricated interfaces. The AuNP on GC-Ph-AuNP surfaces demonstrate good stability under sonication in Milli-Q water, during electrochemical treatment in 0.05 M H₂SO₄ solution, and over several weeks. By contrast, the GC-Ph-NH-AuNP and GC-Ph-S-AuNP surfaces showed significant particle losses under equivalent conditions.8 page(s

Cross-Linked Polymer Electrolytes for Li-Based Batteries: From Solid to Gel Electrolytes

International audienceWe report the preparation of solvent-free polymer electrolytes via a free radical copolymerization of methacrylate-based oligomers in the presence of LiTFSI. Properties of the electrolytes were then studied as a function of their compositions. Furthermore, the incorporation of a room temperature ionic liquid (RTIL) into the copolymer electrolyte to form a gel polymer electrolyte (GPE) is also reported. The high miscibility of the oligomers in the RTIL enables the preparation of the GPEs by a one-step method using the in situ free radical copolymerization. The GPEs have a dry aspect and are free-standing; they also exhibit an ionic conductivity close to 4 × 10–4 S cm–1 at 25 °C and to 1.45 × 10–3 S cm–1 at 65 °C. Furthermore, the GPEs have been used as electrolytes in a Li/Electrolyte/LiNi1/3Mn1/3Co1/3O2 battery. Specific capacities of 79 mAh g–1 and 118 mAh g–1 were reached at the C/5 and C/10 rate, respectively

Thin and Flexible Silicon Anode Based on Integrated Macroporous Silicon Film onto Electrodeposited Copper Current Collector

International audienceThe integration of a macroporous Si (pSi) layer on an electrodeposited Cu current collector is proposed as a facile, low-cost and industrial-scalable procedure to elaborate efficient new anode material for lithium-ion batteries. The preparation process consists of i) formation of macropores on a Si wafer by electrochemical etching, ii) chemical deposition of Cu NPs on microstructured Si, iii) electroplating of a thick continuous Cu film, and iv) peeling of pSi–Cu film. The anode device is flexible and presents a total thickness, comprising the current collector, of 25 μm. SEM characterization shows the partial integration of the copper film inside the Si porous structure. Electrochemical impedance spectroscopy measurements showed this architecture enhances the electrical contact between the Cu current collector and the pSi due to the optimized interface of the two materials. A specific capacity of 1360 mAh g−1 in EC/DMC LiPF6 1 M is achieved at low galvanostatic discharge current (0.2 A g−1). Even during cycling at a high current density of 1.8 A g−1, the macroporous silicon anode was stable, demonstrating a specific capacity of 750 mAh g−1 twice as large as graphite based anodes

Improved cycling performances of binder-free macroporous silicon Li-ion negative electrodes using room temperature ionic liquid electrolyte

International audienceThe present article describes the innovative combination of freestanding macroporous silicon layers on copper foil collectors androom temperature ionic, liquid1-propyl-1-methylpyrrolidinium bis(trifluosulfonyl)imide (Pyr13 FSI)-containing electrolyte(Pyr13 FSI mixed with 1 M LiTFSI) to produce highly stable negative electrodes for Li-ion batteries. A 20-μm-thickmacroporous silicon layer was synthesized by anodization in hydrofluoric acid (HF)-based electrolyte followed by the depositionof a thick and mechanically stable copper layer acting as current collector. After peeling-off the parent substrate, the freestandingmacroporous silicon layer was characterized as a negative electrode in a half-cell configuration. The electrode performances weredetermined under constant charge conditions (500, 750, and 1000 mA h g−1) and exhibited significantly higher stability for over1800 charge and discharge cycles in 1 M LiTFSI dissolved inPyr13 FSI

Effects of Surface Epitope Coverage on the Sensitivity of Displacement Assays that Employ Modified Nanoparticles: Using Bisphenol A as a Model Analyte

With the ever-increasing use of nanoparticles in immunosensors, a fundamental study on the effect of epitope density is presented herein, with a small molecule epitope, on the performance of the displacement assay format in an enzyme-linked immunosorbent assay (ELISA). Thiolated bisphenol A (BPA) functionalized gold nanoparticles (cysBPAv-AuNPs) and specific anti-BPA antibodies are employed for this purpose. It is shown that the displacement of cysBPAv-AuNPs bound to the immobilized antibodies was influenced by both the avidity of bound cysBPAv-AuNPs and the concentration of free BPA to displace it. The importance of surface epitope density was that it changed the number of epitopes in close proximity to the antibody-binding site. This then influenced the avidity of cysBPAv-AuNPs bound to the immobilized antibody. Furthermore, the molar epitope concentration in an assay appears to affect the degree of antibody binding site saturation. Controlling surface epitope density of the functionalized nanoparticles and molar epitope concentration in an assay leads to a decrease of the concentration of free BPA required to displace the bound cysBPAv-AuNP, and hence better assay performance with regards to the D50 value and dynamic range in the displacement assay

LiCoO2 with double porous structure obtained by electrospray deposition and its evaluation as an electrode for lithium-ion batteries

International audienceAn in-situ temperature-controlled Raman spectroscopy aided unique electrode fabrication technique has been developed for Li-ion battery applications, ensuring superior electrochemical quality of the multi-porous LiCoO2 films with higher stoichiometric purity of high temperature (HT)-LiCoO2 phase, by observing the structural changes during the fabrication process and thus confirming the transformation from the low temperature (LT)-LiCoO2 phase. This much desired simple process is not only free of any sort of binders or carbon additives but also works at atmospheric pressure, leading to a very simple deposition technique using a homemade and inexpensive set-up. Also, the time of depositions were varied and resultant films we investigated for their electrochemical performance. The high-resolution scanning electron microscope (SEM) observation has revealed not only a μm-size porous structure but also three-dimensional cross-link with 10 nm-level pores of the material, which ensured the much-desired porosity for high-performance cathodes

A Molecule with dual functionality 4-aminophenylmethylphosphonic acid : a comparison between layers formed on indium tin oxide by in situ generation of an aryl diazonium salt or by self-assembly of the phosphonic acid

4-Aminophenylmethylphosphonic acid was grafted on ITO surfaces by 1) electrochemical reductive adsorption of the corresponding aryl diazonium salt and 2) by self-assembly via the phosphonic acid moiety. The aryl diazonium salt derived surfaces are reasonably stable within a wide potential range from -600 mV to 600 mV compared to a very narrow stable range between -40 mV and 40 mV for the self-assembled layers. The different surface stabilities were assessed with a view to forming ITO-organic layer-gold nanoparticle (AuNPs) constructs. As expected the ITO-organic layer-AuNPs construct formed by electrochemical adsorption (ITO-Ph-AuNP) was significantly more stable than the construct formed by self-assembly of phosphonates (ITO-PO₃Ph-AuNPs).10 page(s

Novel glycerol assisted synthesis of polypyrrole nanospheres and its electrochemical properties

International audienc