Impedance Biosensing atop MoS2 Thin Films with Mo−S Bond Formation to Antibody Fragments Created by Disulphide Bond Reduction

Immobilization of antibody fragments to 3‐phenoxybenzoic acid (3‐PBA), which are created by disulphide bond (S?S) reduction with tris (2‐carboxyethyl) phosphine (TCEP), is reported atop MoS₂ and Cu‐doped MoS₂ thin films. MoS₂ and Cu‐doped MoS₂ thin films are electrodeposited using previously reported methods and tested for their ability to immobilize antibody fragments, before and after annealing in Ar at 500 °C for 3 h. This annealing procedure removes excess sulphur in the as‐deposited films, and creates coordinatively unsaturated Mo sites that are highly reactive towards sulphur, as previously reported for MoS₂ hydrodesulphurization catalysts. As demonstrated by electrochemical impedance spectroscopy (EIS) measurements, both annealed MoS₂ and Cu‐doped MoS₂ thin films adsorb antibody fragments through Mo?S bond formation, unlike the as‐deposited films. Impedance detection of 3‐PBA is reported utilizing antibody fragments bound to both materials, with a sensitivity of 2.7×10⁸ Ω cm² M^?1 and a detection limit of 2.5×10^?6 M atop MoS₂, and a sensitivity of 5.9×10⁸ Ω cm² M^?1 and a detection limit of 3.8×10^?6 M atop Cu‐doped MoS₂. The rms surface roughness obtained by atomic force microscopy (AFM) measurements atop annealed MoS₂ and Cu‐doped MoS₂ ranges from 60–140 nm, so the methods described herein are not limited to ultra‐smooth substrates.     

Effects of annealing on the surface structure of Ga‐isotope‐implanted single‐crystal ZnO

We studied the effects of Ga isotope implantation on surface structure using single‐crystal (0001) ZnO with an atomically flat surface. The surface morphology with steps and terraces was greatly changed by Ga implantation and post‐annealing: the step‐and‐terrace structure was suppressed by Ga implantation but a step‐and‐terrace structure appeared on the surface after post‐annealing at 900 °C for 4 min. The diffusion of Ga towards the surface through dislocation pipes at a density of up to 5 × 10⁸ cm^?2 was the dominant mechanism, and a significant amount of Ga moved from the implanted layer to the surface. The reaction between Ga and ZnO during post‐annealing appeared to improve sheet resistance and surface morphology. Copyright © 2005 John Wiley & Sons, Ltd.     

Effects of gold‐induced crystallization process on the structural and electrical properties of germanium thin films

Gold‐induced (Au‐) crystallization of amorphous germanium (α‐Ge) thin films was investigated by depositing Ge on aluminum‐doped zinc oxide and glass substrates through electron beam evaporation at room temperature. The influence of the postannealing temperatures on the structural properties of the Ge thin films was investigated by employing Raman spectra, X‐ray diffraction, and scanning electron microscopy. The Raman and X‐ray diffraction results indicated that the Au‐induced crystallization of the Ge films yielded crystallization at temperature as low as 300°C for 1 hour. The amount of crystallization fraction and the film quality were improved with increasing the postannealing temperatures. The scanning electron microscopy images show that Au clusters are found on the front surface of the Ge films after the films were annealed at 500°C for 1 hour. This suggests that Au atoms move toward the surface of Ge film during annealing. The effects of annealing temperatures on the electrical conductivity of Ge films were investigated through current‐voltage measurements. The room temperature conductivity was estimated as 0.54 and 0.73 Scm⁻¹ for annealed samples grown on aluminum‐doped zinc oxide and glass substrates, respectively. These findings could be very useful to realize inexpensive Ge‐based electronic and photovoltaic applications.     

Photo‐crosslinked fluorinated thin films from azido‐functionalized random copolymers

Random copolymers of styrene, p‐azidomethylstyrene and 1H,1H,2H,2H‐perfluorodecyl methacrylate were prepared in two steps involving nitroxide‐mediated radical copolymerization and azidation reaction and further characterized by ¹H and ¹⁹F NMR, size exclusion chromatography, differential scanning calorimetry, and thermal gravimetric analysis. Ultrathin films of these azidomethyl‐functionalized fluorinated random copolymers, with thicknesses ranging from 20 to 100 nm, were spin coated onto Si substrates and then crosslinked by ultraviolet irradiation resulting in smooth and insoluble crosslinked fluorinated polymer mats. The surface properties of the supported thin films were investigated by X‐ray photoelectron spectroscopy and water contact angle measurements. These tailored photo‐crosslinked coatings afford a versatile control and homogenization of the wetting properties of different organic and inorganic substrates. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3888–3895, 2010     

Matrix‐assisted laser ablation production of gold cluster ions from Au‐coated photonic crystals

A new strategy was explored to generate pure gold cluster ions, Au_n^+/?, from gold films deposited on solid substrates via a matrix‐assisted laser ablation technique. The gold films deposited on SiO₂‐particle‐assembled photonic crystals were demonstrated to be the most ideal compared with the films deposited on various glass slides. Dropped with a matrix of 2‐(4‐hydroxyphenylazo) benzoic acid and bombarded by nitrogen pulse laser (355 nm), they could release a series of Au_n⁺ with n more than 110 or Au_n^? with n more than 60 according to the data obtained by inline time‐of‐flight mass spectrometry. The gold‐deposited photonic crystal substrates could be stored at room temperature for at least 6 months. The method is hence steady and convenient in use. Copyright © 2012 John Wiley & Sons, Ltd.     

High‐Conductivity Two‐Dimensional Polyaniline Nanosheets Developed on Ice Surfaces

A new method to develop two‐dimensional PANI nanosheets using ice as a removable hard template is presented. Distinctly high current flows of 5.5 mA at 1 V and a high electrical conductivity of 35 S cm^?1 were obtained for the polyaniline (PANI) nanosheets, which marked a significant improvement from previously values on other PANIs reported over the past decades. These improved electrical properties of ice‐templated PANI nanosheets were attributed to the long‐range ordered edge‐on π‐stacking of the quinoid ring, ascribed to the ice surface‐assisted vertical growth of PANI. The unprecedented advantages of the ice‐templated PANI nanosheets are two‐fold. First, the PANI nanosheet can be easily transferred onto various types of substrates via float‐off from the ice surfaces. Second, PANI can be patterned into any shape using predetermined masks, and this is expected to facilitate the eventual convenient and inexpensive application of conducting polymers in versatile electronic device forms.     

In Situ Synthesis of Porous Carbons by Using Room‐Temperature,Atmospheric‐Pressure Dielectric Barrier Discharge Plasma as High‐Performance Adsorbents for Solid‐Phase Microextraction

A one‐step, template‐free method is described to synthesize porous carbons (PCs) in situ on a metal surface by using a room‐temperature, atmospheric‐pressure dielectric barrier discharge (DBD) plasma. This method not only features high efficiency, environmentally friendliness, and low cost and simple equipment, but also can conveniently realize large‐area synthesis of PCs by only changing the design of the DBD reactor. The synthesized PCs have a regulated nestlike morphology, and thus, provide a high specific surface area and high pore volume, which result in excellent adsorption properties. Its applicability was demonstrated by using a PC‐coated stainless‐steel fiber as a solid‐phase microextraction (SPME) fiber to preconcentrate polycyclic aromatic hydrocarbons (PAHs) prior to analysis by gas chromatography with flame ionization detection (GC‐FID). The results showed that the fiber exhibited excellent enrichment factors (4.1×10⁴ to 3.1×10⁵) toward all tested PAHs. Thus, the PC‐based SPME‐GC‐FID provides low limits of detection (2 to 20 ng L ^?1), good precision (<7.8 %), and good recoveries (80–115 %) for ultra‐sensitive determination of PAHs in real water samples. In addition, the PC‐coated fiber could be stable enough for more than 500 replicate extraction cycles.     

The Solid‐Phase Synthesis of an Fe‐N‐C Electrocatalyst for High‐Power Proton‐Exchange Membrane Fuel Cells

The environmentally friendly synthesis of highly active Fe‐N‐C electrocatalysts for proton‐exchange membrane fuel cells (PEMFCs) is desirable but remains challenging. A simple and scalable method is presented to fabricate Fe^II‐doped ZIF‐8, which can be further pyrolyzed into Fe‐N‐C with 3 wt % of Fe exclusively in Fe‐N₄ active moieties. Significantly, this Fe‐N‐C derived acidic PEMFC exhibits an unprecedented current density of 1.65 A cm^?2 at 0.6 V and the highest power density of 1.14 W cm^?2 compared with previously reported NPMCs. The excellent PEMFC performance can be attributed to the densely and atomically dispersed Fe‐N₄ active moieties on the small and uniform catalyst nanoparticles.     

Study in the effect of annealing on hydrogen retention properties of C‐90%SiC films

Carbon‐rich silicon carbide (C‐90%SiC) films as hydrogen barriers were deposited on the surface of stainless steel substrates with magnetron sputtering, and then bombarded by argon ion beam. In order to remove the argon atoms reserved during films preparation, some samples with the prepared C‐90%SiC films were thermally annealed for 30 min at 473, 673 and 873 K in vacuum, respectively. These samples together with the un‐annealed ones were then irradiated by a 5 keV hydrogen ion beam. SEM was used to investigate the surface micrograph of those films and SIMS was used to measure the mass spectra of positive species and the depth distribution of argon and hydrogen in the samples. A remarkable decrease in hydrogen intensity in the substrates with annealing indicates that annealing for removing argon can effectively improve hydrogen retention properties of the C‐90%SiC films. Copyright © 2008 John Wiley & Sons, Ltd.     

Template‐Free Supracolloidal Self‐Assembly of Atomically Precise Gold Nanoclusters: From 2D Colloidal Crystals to Spherical Capsids

We report supracolloidal self‐assembly of atomically precise and strictly monodisperse gold nanoclusters involving p‐mercaptobenzoic acid ligands (Au₁₀₂‐pMBA₄₄) under aqueous conditions into hexagonally packed monolayer‐thick two‐dimensional facetted colloidal crystals (thickness 2.7 nm) and their bending to closed shells leading to spherical capsids (d ca. 200 nm), as controlled by solvent conditions. The 2D colloidal assembly is driven in template‐free manner by the spontaneous patchiness of the pMBA ligands around the Au₁₀₂‐pMBA₄₄ nanoclusters preferably towards equatorial plane, thus promoting inter‐nanocluster hydrogen bonds and high packing to planar sheets. More generally, the findings encourage to explore atomically precise nanoclusters towards highly controlled colloidal self‐assemblies.     

Growth of c‐axis‐oriented aluminum nitride thin films onto different substrates and buffer layers

The growth of aluminum nitride thin films onto various substrates (glass, flexible polyimide, or silicon) and onto different buffer layers (Au, Nb, Cu, Ag, Co, Fe, NiFe, or IrMn) is reported. Samples grown on IrMn, Co, NiFe, Nb, or Au show smooth surfaces. This same smooth quality is observed in samples grown at a lower 200 °C temperature directly on glass, Si, or flexible polyimide. In applications where thin and smooth piezoelectric films are necessary, c‐axis‐oriented AlN can be grown onto a wide range of different surfaces: conducting, insulating, ferromagnetic, antiferromagnetic, or flexible. Copyright © 2014 John Wiley & Sons, Ltd.     

Surface‐Independent and Oriented Immobilization of Antibody via One‐Step Polydopamine/Protein G Coating: Application to Influenza Virus Immunoassay

For the construction of high‐performance biosensor, it is important to interface bioreceptors with the sensor surface densely and in the optimal orientation. Herein, a simple surface modification method that can optimally immobilize antibodies onto various kinds of surfaces is reported. For the surface modification, a mixture of polydopamine (PDA) and protein G was employed. PDA is a representative mussel‐inspired polymer, and protein G is an immunoglobulin‐binding protein that enables an antibody to have an optimal orientation. The surface characteristics of PDA/Protein G mixture‐coated substrates are analyzed and the PDA/protein G ratio is optimized to maximize the antibody binding efficiency. Moreover, the antibody‐immobilized substrates are applied to the detection of influenza viruses with the naked eye, providing a detection limit of 2.9 × 10³ pfu mL^‐1. Importantly, the several substrates (glass, SiO₂, Si, Al₂O₃, polyethylene terephthalate, polyethylene, polypropylene, and paper) can be modified by simple incubation with the mixture of PDA/protein G, and then the anti‐influenza A H1N1 antibodies can be immobilized on the substrates successfully. Regardless of the substrate, the influenza viruses are detectable after the sandwich immunoreaction and silver enhancement procedure. It is anticipated that the developed PDA/protein G coating method will extend the range of applicable materials for biosensing.     

Well‐Defined Dinuclear Gold Complexes for Preorganization‐Induced Selective Dual Gold Catalysis

The synthesis, reactivity, and potential of well‐defined dinuclear gold complexes as precursors for dual gold catalysis are explored. Using the preorganizing abilities of the ditopic PN^HP^iPr ( L^H ) ligand, dinuclear Au^I–Au^I complex 1 and mixed‐valent Au^I–Au^III complex 2 provide access to structurally characterized chlorido‐bridged cationic species 3 and 4 upon halide abstraction. For 2 , this transformation involves unprecedented two‐electron oxidation of the redox‐active ligand, generating a highly rigidified environment for the Au₂ core. Facile reaction with phenylacetylene affords the σ,π‐activated phenylacetylide complex 5 . When applied in the dual gold heterocycloaddition of a urea‐functionalized alkyne, well‐defined precatalyst 3 provides high regioselectivities for the anti‐Markovnikov product, even at low catalyst loadings, and outperforms common mononuclear Au^I systems. This proof‐of‐concept demonstrates the benefit of preorganization of two gold centers to enforce selective non‐classical σ,π‐activation with bifunctional substrates.     

Metal Enhanced Electrochemical Cyclooxygenase‐2 (COX‐2) Sensor for Biological Applications

Pain measurement is commonly required in biomedical and other emergency situations, yet there has been no pain biosensor reported in literature. Conventional approaches for pain measurement relies on Wong‐Baker face diagrams, which are grossly inadequate for situations involving children or unconscious people. We report a label‐free immunosensor for monitoring the pain biomarker cylooxygenase‐2 (COX‐2) in blood. The sensor is based on the concept of metal‐enhanced detection (MED). MED relies on the idea that the immobilization of underpotential deposition (upd) metallic films deposited either as a monolayer or electrostatically held onto a solid gold substrate could significantly amplify bimolecular recognition such as involving antigen‐antibody (Ab‐Ag) interactions. The surface bound Ab‐Ag complex insulates the electrode; causing a decrease in concentration‐dependent redox signals. A linear detection range of (3.64–3640.00)×10^?4 ng/mL was recorded with a detection limit of 0.25×10^?4 ng/mL, which was 4 orders of magnitude lower than that reported for ELISA for the same biomarker. The immunosensor exhibited selectivity of less than 6 % for potential interferents.     

Amine‐Functionalized Polyglycidyl Methacrylate Microsphere as a Unified Template for the Synthesis of Gold Nanoparticles and Single‐Crystal Gold Plates

Polyglycidyl methacrylate (PGMA) microspheres, crosslinked and surface‐functionalized by amine, can be used as a solid‐state template for the synthesis of gold (Au) crystals in the forms of either nanoparticles (NPs) or plates. It is discovered that the polymer microsphere acts as an internal template to cultivate Au NPs inside the microsphere or an external template to generate the single‐crystal plates depending on the critical concentration (C_cr) of gold ions. The ion–dipole interaction and the structure‐dependent solubility of gold induce two distinct gold nanostructures in the presence of the functionalized polymer microspheres. The catalytic activity and long‐term storage of the developed gold nanostructures that can be easily scaled‐up for mass production through the developed novel methodology is demonstrated.     

The Electrochemical Detection of Arsenic(III) at a Silver Electrode

A study of three electrode substrates namely gold, platinum and silver, for arsenic detection via anodic stripping voltammetry is reported. Hitherto it has been accepted that gold is the most suitable metallic surface for use in this context, as suggested by Forsberg and co‐workers (Forsberg, G.; O'Laughlin, J. W.; Megargle, R. G. Anal. Chem. 1975, 47, 1586.). We revisit these experiments and find that by switching from hydrochloric acid to nitric acid the oxidation of silver that had previously masked the arsenic stripping signal at this surface is shifted considerably enough to allow a clear, analytically reliable As(III) stripping signal to be detected. In contrast to silver and gold platinum is found to have poor performance as an electrode substrate for arsenic detection. Using ASV a LOD of 6.3×10^?7 M is found for As(III) detection at a silver electrode, similar to that which we have previously reported at a gold electrode (A. O. Simm, C. E. Banks and R. G. Compton. Electroanalysis, 2005, 17, 335.) The use of ultrasound was then investigated to further reduce the LOD, which was found to be 1.4×10^?8 M. Apart from reduced cost of silver it also has an added advantage over gold in that it has a higher hydrogen reduction overvoltage enabling a 100 mV more negative deposition potential to be used before the onset of hydrogen evolution when compared to a gold electrode.     

Facile fabrication of silver nanoparticles on silicon for surface‐enhanced infrared and Raman analysis

A facile and economic method to fabricate and immobilize silver nanoparticles on a thin Si wafer (AgNP/Si) is reported for an analytical template in ambient environment by surface‐enhanced infrared/Raman spectroscopy. The protocol involves immersion of the Si wafer in a solution containing silver nitrate and hydrofluoric acid. To screen appropriate conditions for preparing AgNP/Si for SEIRAS application, different combinations of AgNO₃ and HF solutions were examined with paranitrobenzoic acid (PNBA) used as the probe molecule in transmission measurements. These SEIRA‐active substrates were also promising for SERS application, as demonstrated with high quality SERS spectra of iron (III) protoporphyrin adlayer on AgNP/Si with a red excitation line. The AgNP/Si substrates prepared under different conditions were examined by SEM for qualitative correlation of enhancements with morphologies. Copyright © 2008 John Wiley & Sons, Ltd.     

Gold‐Catalysed Oxyarylation of Styrenes and Mono‐ and gem‐Disubstituted Olefins Facilitated by an Iodine(III) Oxidant

1‐Hydroxy‐1,2‐benziodoxol‐3(1H)‐one (IBA) is an efficient terminal oxidant for gold‐catalysed, three‐component oxyarylation reactions. The use of this iodine(III) reagent expands the scope of oxyarylation to include styrenes and gem‐disubstituted olefins, substrates that are incompatible with the previously reported Selectfluor‐based methodology. Diverse arylsilane coupling partners can be employed, and in benzotrifluoride, homocoupling is substantially reduced. In addition, the IBA‐derived co‐products can be recovered and recycled.     

Tunable Surface‐Enhanced Raman Scattering from High‐Density Gold Semishell Arrays with Controllable Dimensions

A convenient reproducible technique is reported for the fabrication of large‐area gold semishell arrays by mechanically pressing porous anodic alumina (PAA) stamps into gold/polymer bilayer structures that serve as robust and cost‐efficient surface‐enhanced Raman‐scattering (SERS) substrates. The surface structure can be tuned further to optimize the enhancement factor according to optional PAA fabrication parameters and imprinting pressures. Finite‐difference time‐domain calculations indicate that the structure may possess excellent SERS characteristics due to the high density and abundance of hot spots.     

Au-Ag template stripped pattern for scanning probe investigations of DNA arrays produced by dip pen nanolithography

We report on DNA arrays produced by dip pen nanolithography (DPN) on a novel Au-Ag micropatterned template stripped surface. DNA arrays have been investigated by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) showing that the patterned template stripped substrate enables easy retrieval of the DPN-functionalized zone with a standard optical microscope permitting multi-instrument and multitechnique local detection and analysis. Moreover the smooth surface of the Au squares ( approximately 5-10 A roughness) allows AFM/STM to be sensitive to the hybridization of the oligonucleotide array with label-free target DNA. Our Au-Ag substrates, combining the retrieving capabilities of the patterned surface with the smoothness of the template stripped technique, are candidates for the investigation of DPN nanostructures and for the development of label-free detection methods for DNA nanoarrays based on the use of scanning probes.