Conformational Changes in Calcium‐Sensor Proteins under Molecular Crowding Conditions

Fundamental components of signaling pathways are switch modes in key proteins that control start, duration, and ending of diverse signal transduction events. A large group of switch proteins are Ca²⁺ sensors, which undergo conformational changes in response to oscillating intracellular Ca²⁺ concentrations. Here we use dynamic light scattering and a recently developed approach based on surface plasmon resonance to compare the protein dynamics of a diverse set of prototypical Ca²⁺‐binding proteins including calmodulin, troponin C, recoverin, and guanylate cyclase‐activating protein. Surface plasmon resonance biosensor technology allows monitoring conformational changes under molecular crowding conditions, yielding for each Ca²⁺‐sensor protein a fingerprint profile that reflects different hydrodynamic properties under changing Ca²⁺ conditions and is extremely sensitive to even fine alterations induced by point mutations. We see, for example, a correlation between surface plasmon resonance, dynamic light scattering, and size‐exclusion chromatography data. Thus, changes in protein conformation correlate not only with the hydrodynamic size, but also with a rearrangement of the protein hydration shell and a change of the dielectric constant of water or of the protein–water interface. Our study provides insight into how rather small signaling proteins that have very similar three‐dimensional folding patterns differ in their Ca²⁺‐occupied functional state under crowding conditions.     

Silver Nanoparticle Thin Films with Nanocavities for Surface‐Enhanced Raman Scattering

The formation of nanometer‐sized gaps between silver nanoparticles is critically important for optimal enhancement in surface‐enhanced Raman scattering (SERS). A simple approach is developed to generate nanometer‐sized cavities in a silver nanoparticle thin film for use as a SERS substrate with extremely high enhancement. In this method, a submicroliter volume of concentrated silver colloidal suspension stabilized with cetyltrimethylammonium bromide (CTAB) is spotted on hydrophobic glass surfaces prepared by the exposure of the glass to dichloromethysilane vapors. The use of a hydrophobic surface helps the formation of a more uniform silver nanoparticle thin film, and CTAB acts as a molecular spacer to keep the silver nanoparticles at a distance. A series of CTAB concentrations is investigated to optimize the interparticle distance and aggregation status. The silver nanoparticle thin films prepared on regular and hydrophobic surfaces are compared. Rhodamine 6G is used as a probe to characterize the thin films as SERS substrates. SERS enhancement without the contribution of the resonance of the thin film prepared on the hydrophobic surface is calculated as 2×10⁷ for rhodamine 6G, which is about one order of magnitude greater than that of the silver nanoparticle aggregates prepared with CTAB on regular glass surfaces and two orders of magnitude greater than that of the silver nanoparticle aggregates prepared without CTAB on regular glass surfaces. A hydrophobic surface and the presence of CTAB have an increased effect on the charge‐transfer component of the SERS enhancement mechanism. The limit of detection for rhodamine 6G is estimated as 1.0×10^?8 M . Scanning electron microscopy and atomic force microscopy are used for the characterization of the prepared substrate.     

Ag Nanowire‐Ag Nanoparticle Hybrids for the Highly Enhanced Fluorescene Detection of Protoporphyrin IX Based on Surface Plasmon‐Enhanced Fluorescence

In this study, we developed an approach to fabricate novel 1D Ag NWs‐Ag NPs hybrid substrate for enhanced fluorescene detection of protoporphyrin IX (PpIX) based on surface plasmon‐enhanced fluorescence. The Ag NWs‐Ag NPs hybrid was synthesized by combining the hydrothermal method and self‐assembly method with the asisstance of polyvinylpyrrolidone (PVP). When the Ag NWs‐Ag NPs hybrid was deposited on the glass substrate and employed as active substrate to detect PpIX, the fluorescence intensity of PpIX was enhanced greatly due to the coupling effect of localized surface plasmon‐localized surface plasmon (LSP‐LSP) and localized surface plasmon‐surface plasmon propagation (LSP‐SPP) which induced great enhancement of the electromagnetic field. Furthermore, the enhancement effect was approximately linear when the concentration of PpIX was ranged from 1×10^?7 mol/L to 2×10^?5 mol/L, and the photobleaching phenomenon of PpIX was reduced greatly, indicating that the fabricated Ag NWs‐Ag NPs hybrid substrate had well performance for PpIX imaging. This work provides an effective approach to prepare highly sensitive and stable fluorescence enhancement substrate, and has great potential application in fluorescence imaging.     

Influence of grain orientation on zinc enrichment and surface morphology of an Al?Zn alloy

Zinc is an important alloying element in the 7000 series aluminium alloys. It is also an element that may enrich near the alloy surface during treatments of aluminium alloys by processes such as electropolishing, alkaline anodic etching and alkaline etching. The enrichment may occur since the change in Gibbs free energy per equivalent for formation of ZnO is less negative than that for formation of Al₂O₃. The enriched alloying element is present in an alloy layer up to ～5 nm thick located immediately beneath the alloy/film interface. In the present study, the dependence of the enrichment of zinc on the grain orientation of the alloy is investigated for a solid solution Al‐1.1at.%Zn alloy. The enrichment of the zinc is developed by alkaline etching of the alloy. The grain orientation is determined by electron backscattering diffraction, with enrichments quantified on selected grains by Rutherford backscattering spectroscopy and medium energy ion scattering. The morphologies of the surfaces of the etched grains are characterised by scanning electron microscopy and atomic force microscopy. The findings reveal that the zinc enrichment ranges from 1.7 × 10¹⁵ atoms/cm² to 3.9 × 10¹⁵ atoms/cm², with the greatest enrichment occurring on a grain of (100) orientation, while differing surface topographical textures are developed on the various grains. Copyright © 2009 John Wiley & Sons, Ltd.     

The First Demonstration of the Gyroid in a Polyoxometalate‐Based Open Framework with High Proton Conductivity

The fabrication of extended open frameworks with crystalline ordering on the atomic level by following peculiar mathematical geometry (e.g. Möbius band, Klein bottle, periodic minimal surfaces, etc.) is challenging, but extremely beneficial for discovering non‐trivial structure‐dependent properties. In light of this, we herein report the first polyoxometalate‐based open framework (POM‐OF) that definitely lies on the gyroid (G)‐minimal surface, which was constructed by a rare pair of chiral POM enantiomers and zinc ions. Due to the presence of the proton carriers (i.e., water, Na⁺, [(Bu)₄N]⁺, etc.) in the resultant gyroidal channels, with pore dimensions on the order of the quasi‐mesoporous scale, this compound shows a high proton conductivity of 1.04×10^?2 S cm^?1 at a relative humidity of 75 % (80 °C), and also exhibits enormous potential in the application of electrochemical catalysis.     

Photografting as a versatile,localizable, and single‐step surface functionalization of silica‐based monoliths dedicated to microscale separation techniques

In this work, we developed a surface functionalization way of silica monoliths with a rapid, simple, versatile, and localizable photografting step. The elaboration of a photoreactive layer at the surface of monoliths was first optimized. The functionalization with [γ‐(methacryloyloxy)propyl]trimethoxysilane at 80°C in a hydro‐organic solution containing triethylamine as catalyst allows reachng the highest density of methacrylate photoactive moieties on silica surfaces. These methacrylate reactive surfaces were subsequently photografted within few minutes with acrylate monomers bearing alkyl chains (C₁₂ and C₁₈). The photografting efficiency was determined by monitoring the retentive properties of monoliths in the RP mode. The retention factors are of the same order of magnitude as highly retentive columns obtained by modification of silica surface with long‐alkyl chain silanes or by thermal polymerization of long‐alkyl chain monomers. It was also verified that such grafting neither impaired the efficiency of the monolithic stationary phase (H_min = 6–8 μm in nano‐LC) nor its permeability (about 6 × 10^?14 m²). Further, it was also demonstrated that photografting is localizable in nonmasked defined areas. Results obtained in anion‐exchange chromatography after photopolymerization of [2‐(methacryloyloxy)ethyl]trimethylammonium chloride are presented as well to demonstrate the versatility of the developed approach.     

Real‐Space Observation of Atomic Site‐Specific Electronic Properties of a Pt Nanoisland/Au(111) Bimetallic Surface by Tip‐Enhanced Raman Spectroscopy

Resolving atomic site‐specific electronic properties and correlated substrate–molecule interactions is challenging in real space. Now, mapping of sub‐10 nm sized Pt nanoislands on a Au(111) surface was achieved by tip‐enhanced Raman spectroscopy, using the distinct Raman fingerprints of adsorbed 4‐chlorophenyl isocyanide molecules. A spatial resolution better than 2.5 nm allows the electronic properties of the terrace, step edge, kink, and corner sites with varying coordination environments to be resolved in real space in one Pt nanoisland. Calculations suggest that low‐coordinate atomic sites have a higher d‐band electronic profile and thus stronger metal–molecule interactions, leading to the observed blue‐shift of Raman frequency of the N≡C bond of adsorbed molecules. An experimental and theoretical study on Pt(111) and mono‐ and bi‐atomic layer Pt nanoislands on a Au(111) surface reveals the bimetallic effect that weakens with the increasing number of deposited Pt adlayer.     

XPS survey spectra simulation of nano‐structured surfaces

We have developed a software tool for the generation of survey spectra in X‐ray photoelectron spectroscopy (GOSSIP) to simulate wide spectra in the range 200–1500 eV from nano‐structured surfaces. It is based on linear combination of delta layers spectra with the atomic spectra of the elements or compounds of the surface to be simulated. The set of delta layers to reproduce any model is a 200‐file database of thin layers regularly buried up to a depth of 40 nm and has been generated with QUASES^™. The atomic spectra that constitute a second database have themselves been determined with QUASES^™ from experimental spectra of the elements or compounds in pure form. The principle of GOSSIP is described. Then the generation process is validated by comparison with experimental data for simple rectangular in‐depth distribution of elements. Copyright © 2009 John Wiley & Sons, Ltd.     

Multifunctional Tricarbazolo Triazolophane Macrocycles: One‐Pot Preparation,Anion Binding,and Hierarchical Self‐Organization of Multilayers

Programming the synthesis and self‐assembly of molecules is a compelling strategy for the bottom‐up fabrication of ordered materials. To this end, shape‐persistent macrocycles were designed with alternating carbazoles and triazoles to program a one‐pot synthesis and to bind large anions. The macrocycles bind anions that were once considered too weak to be coordinated, such as PF₆^?, with surprisingly high affinities (β₂=10¹¹ M ^?2 in 80:20 chloroform/methanol) and positive cooperativity, α=(4 K₂/K₁)=1200. We also discovered that the macrocycles assemble into ultrathin films of hierarchically ordered tubes on graphite surfaces. The remarkable surface‐templated self‐assembly properties, as was observed by using scanning tunneling microscopy, are attributed to the complementary pairing of alternating triazoles and carbazoles inscribed into both the co‐facial and edge‐sharing seams that exist between shape‐persistent macrocycles. The multilayer assembly is also consistent with the high degree of molecular self‐association observed in solution, with self‐association constants of K=300 000 M ^?1 (chloroform/methanol 80:20). Scanning tunneling microscopy data also showed that surface assemblies readily sequester iodide anions from solution, modulating their assembly. This multifunctional macrocycle provides a foundation for materials composed of hierarchically organized and nanotubular self‐assemblies.     

Influence of compaction and surface roughness on low‐energy ion scattering signals

Investigation of the surface composition of powders often requires compaction. To study the effect of compaction on surface analysis, samples have been compacted at various pressures ranging from 0 Pa (i.e. no compaction) up to 2000 MPa (2 × 10⁴ kg cm^?2) Low‐energy ion scattering (LEIS) was used to determine the composition of the outermost atomic surface layer. Using scanning electron microscopy, changes in the morphology due to compaction have been detected in the SiO₂ test samples. The LEIS yield of a compacted silica powder is found to be independent of the applied pressure during compaction between 2 MPa and 2000 MPa (2 × 10⁴ kg cm^?2). Analysis of a submonolayer of Ta₂O₅ on a silica support shows that the composition of the outermost atomic layer is not changed after compaction up to a pressure of at least 300 MPa. When compaction is applied, the absolute LEIS yield appears to be independent of the specific surface area of silica supports in the range 50–380 m² g^?1. A minor difference in LEIS signals is observed between compacted silica supports and flat quartz samples. In order to determine the surface roughness factor independently, and to study the material dependence of the surface roughness factor, angle‐dependent LEIS measurements have been carried out on oxidized silicon, gallium and gold surfaces. The results on the oxidized silicon confirm the small influence of surface roughness for silica particles, whereas measurements on the more closely packed metallic gallium and gold surfaces indicate a significant surface roughness effect. Copyright © 2004 John Wiley & Sons, Ltd.     

Changes in the surface morphology induced by 1.0‐MeV Au ion bombardment of Ti and Ti‐6Al‐4V

The effects of surface sputtering by 1.0‐MeV Au ion implantation in commercially pure Ti and its alloy Ti‐6Al‐4V have been studied. These materials are associated with applications in orthopaedic implants. There are few studies that try to explain the ion implantation process of Au in these materials when considering the effects generated on the surface by sputtering, especially at energies of the order of MeV. Discs of these materials were mirror polished and then implanted with 1.0‐MeV Au ions for 4.7 × 10¹⁷ ions/cm² at 45° incident angle with respect to the surface. Part of the eroded material was deposited simultaneously on glass slides to determine their spatial distribution. These discs and the slides were analysed by Rutherford backscattering spectroscopy (RBS), scanning electron microscopy (SEM), optical microscopy and atomic force microscopy. The implanted materials show the initial production of surface ripples that evolve into banded structures. Copyright © 2014 John Wiley & Sons, Ltd.     

Dramatic Fluorescence Enhancement of Bare Carbon Dots through Facile Reduction Chemistry

Reduction of bare carbon dots (CDs) in aqueous NaBH₄ solution is a facile and effective approach to enhance their fluorescence without any surface coverage. CDs are treated with dilute aqueous NaBH₄ solutions, enhancing their quantum yields (QYs) successfully from 1.6 % to 16 % which is comparable to semiconductive QDs in aqueous environments. If pristine CDs are treated hydrothermally prior to reduction by NaBH₄, QYs reach 40.5 %. This value is among the highest QYs reported for bare CDs in the literature. The approach to enhance fluorescence through chemical reduction is generally applicable to other kinds of CDs synthesized by various methods. Alteration of the chemical structure of the CDs by NaBH₄‐reduction is analyzed by ¹³C NMR, X‐ray photoelectron spectroscopy (XPS) and Raman spectroscopy, which demonstrate that the carbonyl group content is decreased after NaBH₄‐reduction, whereas the number of sp³‐type carbon defects is increased. The valence‐band maxima (VBM) near the surface related to the surface energy bands of the CDs are estimated by XPS. VBM data show a semiconducting layer on the surface of the CDs, and the VBM of the CDs decrease with increasing NaBH₄‐reduction time. The layered graphite structures in the cores of the CDs are clearly observed by transmission electron microscopy (TEM). CDs could perhaps be regarded as semiconductive surface defect layers formed by chemical erosion over conductive graphite cores. Chemical reduction by NaBH₄ changes the surface‐energy bands of the CDs, thus, enhances their fluorescence. The fluorescence properties of aqueous NaBH₄‐reduced CDs are also studied for possible biological applications.     

Formation of Superoxo Species by Interaction of O2 with Na Atoms Deposited on MgO Powders: A Combined Continuous‐Wave EPR (CW‐EPR), Hyperfine Sublevel Correlation (HYSCORE) and DFT Study

The formation of O₂^? radical anions by contact of O₂ molecules with a Na pre‐covered MgO surface is studied by a combined EPR and quantum chemical approach. Na atoms deposited on polycrystalline MgO samples are brought into contact with O₂. The typical EPR signal of isolated Na atoms disappears when the reaction with O₂ takes place and new paramagnetic species are observed, which are attributed to different surface‐stabilised O₂^? radicals. Hyperfine sublevel correlation (HYSCORE) spectroscopy allows the superhyperfine interaction tensor of O₂^?Na⁺ species to be determined, demonstrating the direct coordination of the O₂^? adsorbate to surface Na⁺ cations. DFT calculations enable the structural details of the formed species to be determined. Matrix‐isolated alkali superoxides are used as a standard to enable comparison of the formed species, revealing important and unexpected contributions of the MgO matrix in determining the electronic structure of the surface‐stabilised Na⁺? O₂^? complexes.     

Nanowire Transistor‐Based Ultrasensitive Virus Detection with Reversible Surface Functionalization

We have applied a reusable silicon nanowire field‐effect transistor (SiNW‐FET) as a biosensor to conduct ultrasensitive detection of H5N2 avian influenza virus (AIV) in very dilute solution. The reversible surface functionalization of SiNW‐FET was made possible using a disulfide linker. In the surface functionalization, 3‐mercaptopropyltrimethoxysilane (MPTMS) was first modified on the SiNW‐FET (referred to as MPTMS/SiNW‐FET), with subsequent dithiothreitol washing to reduce any possible disulfide bonding between the thiol groups of MPTMS. Subsequently, receptor molecules could be immobilized on the MPTMS/SiNW‐FET by the formation of a disulfide bond. The success of the reversible surface functionalization was verified with fluorescence examination and electrical measurements. A surface topograph of the SiNW‐FET biosensor modified with a monoclonal antibody against H5N2 virus (referred to as mAb_H5/SiNW‐FET) after detecting approximately 10^?17 M H5N2 AIVs was scanned by atomic force microscopy to demonstrate that the SiNW‐FET is capable of detecting very few H5N2 AIV particles.     

Structure and properties of some novel fluoroelastomer/clay nanocomposites with special reference to their interaction

In the present work, rubber/clay nanocomposites were prepared by a solution mixing process using fluoroelastomers and different nanoclays (namely, Cloisite NA+, Cloisite 10A, Cloisite 20A, and Cloisite 30B). Fluoroelastomers having different microstructure and viscosity (Viton B‐50, Viton B‐600, Viton A‐200, and VTR‐8550) were used. Characterization of the nanocomposites was done by using X‐ray diffraction and atomic force microscopy. The mechanical and dynamic mechanical properties were studied. The surface energy of the clays and the elastomer was also measured. Even with the addition of only 4 phr of clay in Viton B‐50, tensile strength and modulus improved by 30–96% and 80–134%, respectively, depending on the nature of the nanoclays. Exfoliation was observed with both the unmodified and the modified clays at low loading in all the fluoroelastomers. Best properties were observed with the unmodified clay. All the grades of fluororubber followed the same trend. The increment (19%) in storage modulus was also higher in the case of the unmodified clay filled Viton B‐50 system. The results were explained with the help of thermodynamics, surface energies, and swelling studies. The difference in surface energy, Δγ, between the rubber and the unmodified clay was lower. The work of adhesion (67.63 mJ/m²) between Viton B‐50 and Cloisite NA+ was also higher than that (51.42 mJ/m²) between Viton B‐50 and Cloisite 20A. Negative ΔH_S value for the unmodified clay‐filled system thermodynamically favored the formation of the nanocomposite as compared to the modified clay filled samples where ΔH_S is positive or zero. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 162‐176, 2006     

Summary of ISO/TC 201 Standard: XIX ISO 17331:2004—Surface chemical analysis—Chemical methods for the collection of elements from the surface of silicon‐wafer working reference materials and their determination by total‐reflection x‐ray fluorescence (TXRF) spectroscopy

This international standard specifies chemical methods for the collection of iron and/or nickel from the surface of silicon‐wafer working reference materials by the vapour‐phase decomposition method or the direct acid droplet decomposition method. The determination of the elements collected may be carried out by total‐reflection x‐ray fluorescence spectroscopy, as well as by graphite‐furnace atomic absorption spectroscopy or inductively coupled plasma mass spectroscopy. This international standard applies to iron and/or nickel atomic surface densities from 6 × 10⁹ to 5 × 10¹¹ atoms cm^?2. Copyright © 2005 John Wiley & Sons, Ltd.     

Kinetic Analysis of the Interaction between Nonsteroidal Anti-inflammatory Drugs and Cyclooxygenase-2Using Wavelength Modulation Surface Plasmon Resonance

A surface plasmon resonance (SPR) biosensor based on wavelength modulation technology was developed and validated for the kinetic analysis of the interactions between two nonsteroidal anti‐inflammatory drugs (NSAIDs) and cyclooxygenase‐2 (COX‐2). After the effect of different concentration COX‐2 on the binding capacity of the SPR biosensor surface was studied, the COX‐2 was immobilized covalently onto the biosensor surface using a standard amine coupling method. The affinity constants for indomethacin, ketoprofen binding to COX‐2 are 7.5×10³ L/mol and 9.25×10³ L/mol, respectively. The biosensor surface can be regenerated after being rinsed with 0.01 mol/L NaOH, and the biosensor can be used repeatedly. These indicated that the wavelength modulation SPR biosensor has the potential application in the fields of pharmacokinetics, pharmacodynamics and drug discovery.     

Patterning of cells on a PVC film surface functionalized by ion irradiation

Micropatterns of cells on a poly(vinyl chloride) (PVC) film surface were created by using ion irradiation. A PVC film was irradiated with H⁺ ions through a pattern mask in order to create patterns of the hydrophilic/hydrophobic regions on the PVC surface. The effect of ion irradiation on the surface properties of the PVC film was characterized by using Fourier transform‐infrared spectroscopy (FT‐IR), water contact angle measurement, and X‐ray photoelectron spectroscopy (XPS). The results revealed that the chemical environment of the PVC film surface was effectively changed by ion irradiation due to dehydrochlorination and oxidation. The in vitro cell culture on the patterned PVC film surface showed selective adhesion and proliferation of the cells on the ion‐irradiated regions. Well‐defined 50 µm patterns of the cells were obtained on the PVC film surface irradiated to 1 × 10¹⁵ ions/cm². Copyright © 2009 John Wiley & Sons, Ltd.     

Formation Mechanism of a Silane‐PVA/PVAc Complex Film on a Glass Fiber Surface

Mechanical properties of glass fiber reinforced composite materials are affected by fiber sizing. A complex film formation, based on a silane film and PVA/PVAc (polyvinyl alcohol/polyvinyl acetate) microspheres on a glass fiber surface is determined at 1) the nanoscale by using atomic force microscopy (AFM), and 2) the macroscale by using the zeta potential. Silane groups strongly bind through the Si? O? Si bond to the glass surface, which provides the attachment mechanism as a coupling agent. The silane groups form islands, a homogeneous film, as well as empty sites. The average roughness of the silanized surface is 6.5 nm, whereas it is only 0.6 nm for the non‐silanized surface. The silane film vertically penetrates in a honeycomb fashion from the glass surface through the deposited PVA/PVAc microspheres to form a hexagonal close pack structure. The silane film not only penetrates, but also deforms the PVA/PVAc microspheres from the spherical shape in a dispersion to a ellipsoidal shape on the surface with average dimensions of 300/600 nm. The surface area value S_a represents an area of PVA/PVAc microspheres that are not affected by the silane penetration. The areas are found to be 0.2, 0.08, and 0.03 μm² if the ellipsoid sizes are 320/570, 300/610, and 270/620 nm for silane concentrations of 0, 3.8, and 7.2 μg mL^?1, respectively. The silane film also moves PVA/PVAc microspheres in the process of complex film formation, from the low silane concentration areas to the complex film area providing enough silane groups to stabilize the structure. The values for the residual silane honeycomb structure heights (H_a) are 6.5, 7, and 12 nm for silane concentrations of 3.8, 7.2, and 14.3 μg mL^?1, respectively. The pH‐dependent zeta‐potential results suggest a specific role of the silane groups with effects on the glass fiber surface and also on the PVA/PVAc microspheres. The non‐silanized glass fiber surface and the silane film have similar zeta potentials ranging from ?64 to ?12 mV at pH’s of 10.5 and 3, respectively. The zeta potentials for the PVA/PVAc microspheres on the glass fiber surface and within the silane film significantly decrease and range from ?25 to ?5 mV. The shapes of the pH‐dependent zeta potentials are different in the cases of silane groups over a pH range from 7 to 4. A triple‐layer model is used to fit the non‐silanized glass surface and the silane film. The value of the surface‐site density for Γ_Xglass and Γ_Xsilane, in which X denotes the Al? O? Si group, differs by a factor of 10^?4, which suggests an effective coupling of the silane film. A soft‐layer model is used to fit the silane‐PVA/PVAc complex film, which is approximated as four layers. Such a simplification and compensation of the microsphere shape gives an approximation of the relevant widths of the layers as the follows: 1) the layer of the silane groups makes up 10 % of the total length (27 nm), 2) the layer of the first PVA shell contributes 30 % to the total length (81 nm), 3) the layer of the PVAc core contributes 30 % to the total length (81 nm), and finally 4) the layer of the second PVA shell provides 30 % of the total length (81 nm). The coverage simulation resulted in a value of 0.4, which corresponds with the assumption of low‐order coverage, and is supported by the AFM scans. Correlating the results of the AFM scans, and the zeta potentials sheds some light on the formation mechanism of the silane‐PVA/PVAc complex film.     

A Highly Sensitive Electrochemiluminescence Choline Biosensor Based on Poly(aniline‐luminol‐hemin) Nanocomposites

Poly(aniline‐luminol‐hemin) nanocomposites are prepared on an electrode surface through electropolymerization, and a highly sensitive electrochemiluminescence (ECL) biosensor for choline is developed based on the poly(aniline‐luminol‐hemin) nanocomposites and an enzyme catalyzed reaction of choline oxidase (CHOD). The obtained nanocomposites are characterized by scanning electron microscopy (SEM), atomic absorption spectrometry (AAS) and ECL. The results indicate that hemin can be incorporated into the poly(aniline‐luminol) nanocomposites using the facile electropolymerization method, and the poly(aniline‐luminol‐hemin) nanocomposites are rod shaped porous nanostructure. Moreover, the poly(aniline‐luminol‐hemin) nanocomposites exhibit higher ECL intensity than poly(aniline‐luminol) nanocomposites in alkaline media due to the catalytic effect of hemin on the ECL of the polymerized luminol and the electron transfer ability of hemin in the nanocomposites. CHOD is immobilized on the surface of the poly(aniline‐luminol‐hemin) nanocomposites modified electrode with glutaraldehyde, and the ECL biosensor based on poly(aniline‐luminol‐hemin)/CHOD exhibits a wider linear range for the choline detection. The enhanced ECL signals are linear with the logarithm of concentration of choline over the range of 1.0×10^?11～1.0×10^?7 mol L^?1 with a low detection limit of 1.2×10^?12 mol L^?1. Moreover, the proposed biosensor is successfully applied to the detection of choline in milk.