Layer-by-layer assembly of multilayer films composed of avidin and biotin-labeled antibody for immunosensing

Protein multilayers composed of avidin and biotin-labeled antibody (bio-Ab) were prepared on gold surface by layer-by-layer assembly technology using the high specific binding constant (K-a: approximate to 10(15) M-1) between avidin and biotin. The assembly process of the multilayer films was monitored by using real-time BIA technique based on surface plasmon resonance (SPR). The multilayer films were also characterized by electrochemical impedance spectroscopy (EIS) and reflection absorption Fourier transform infrared spectroscopy (FTIR). The results indicate that the growth of the multilayer is uniform. From response of SPR for each layer, the stoichiometry S for the interaction between avidin and bio-Ab is calculated to be 0.37 in the multilayer whereas 0.82 in the first layer. The protein mass concentration for each layer was also obtained. The schematic figure for the multilayer assembly was proposed according to the layer mass, concentration and S value. The utility of the mutilayer films for immunosensing has been investigated via their subsequent interaction with hIgG. The binding ability of the multilayer increased for one to three layers of antibody, and then reach saturation after the fourth layer. These layer-by-layer constructed antibody multilayers enhance the binding ability than covalently immobilized monolayer antibody. This technology can be also used for construction of other thin films for immunosensing and biosensor.

Chitosan mediated assembly of gold nanoparticles multilayer

We initiate a systematic exploration of a natural polymer, chitosan, as a structural material for designing functional layers on electrode surfaces in this work. Au colloid films are organized on chitosan layer by adsorption. We have successfully constructed a multilayer An nanoparticle assembly through electrostatic interactions on chitosan functionalized quartz substrates by the alternate treatment of the substrate with solution of citrate-stabilized gold nanoparticles (negatively charged) and chitosan solution (positively charged). The resulting substrates were characterized by UV-Vis spectrometry, atomic force microscopy (AFM), and electrochemical impedance spectroscopy (EIS) measurements. These assemblies of colloid An multilayer are highly stable, and can be kept for a long time in distilled water, only being removed by scratching or extreme electrochemical conditions.

DNA-templated assembly and electropolymerization of aniline on gold surface

Biomolecule template gives new opportunities for the fabrication of novel materials with special features. Here we report a route to the formation of DNA-polyaniline (PAn) complex, using immobilized DNA as a template. A gold electrode was first modified with monolayer of 2-aminoethanethiol by self-assembly. Thereafter, by simply immersing the gold electrode into DNA solution, DNA molecules can be attached onto the gold surface, followed by the DNA-templated assembly and electropolymerization of protonated aniline. The electrostatic interactions between DNA and aniline can keep the aniline monomers aligning along the DNA strands. Investigations by surface plasmon resonance (SPR), electrochemistry and reflection absorption UV/Vis-Near IR spectroscopy substantially convince that PAn can be electrochemically grown around DNA template on gold surface. This work may be provides fundamental aspects for building PAn nanowires with DNA as template on solid surface if DNA molecules can be individually separated and stretched.

Self-assembly of star block copolymers by dynamic density functional theory

The dynamic mean-field density functional method, driven from the generalized time-dependent Ginzburg-Landau equation, was applied to the mesoscopic dynamics of the multi-arms star block copolymer melts in two-dimensional lattice model. The implicit Gaussian density functional expression of a multi-arms star block copolymer chain for the intrinsic chemical potentials was constructed for the first time. Extension of this calculation strategy to more complex systems, such as hyperbranched copolymer or dendrimer, should be straightforward. The original application of this method to 3-arms block copolymer melts in our present works led to some novel ordered microphase patterns, such as hexagonal (HEX) honeycomb lattice, core-shell HEX lattice, knitting pattern, etc. The observed core-shell HEX lattice ordered structure is qualitatively in agreement with the experiment of Thomas [Macromolecules 31, 5272 (1998)].

Assembly of the transition metal substituted polyoxometalates ZnW11M(H2O)O-39(n-) (M = Mn, Cu, Fe, Co, Cr, Ni, Zn) on 4-aminobenzoic acid modified glassy carbon electrode and their electrochemical study

Through layer-by-layer assembly, a series of undecatungstozincates monosubstituted by first-row transition metals, ZnW11M(H2O)O-39(n-) (M=Cr, Mn, Fe, Co, Ni, Cu. or Zn) were first successfully immobilized on a 4-aminobenzoic acid modified glassy carbon electrode surface. The electrochemical behaviors of these polyoxometalates were investigated. They exhibit some special properties in the films different from those in homogeneous aqueous solution. The Cu-centered reaction mechanism in the ZnW11Cu multilayer film was described. The electrocatalytic behaviors of these multilayer film electrodes to the reduction of H2O2 and BrO3- were comparatively studied.

Determination of the interfacial acidity of the functional alkanethiols self-assembly membrane by capacitance measurement

The acid-base equilibrium of self-assembly monolayer(SAM) of mercaptopropionic acid on gold electrode was studied by capacitance titration. The change of capacitance was due to protonation and deprotonation of the modified electrode surface. This method can be used to measure pH value in solution and capacitance of solid/liquid on SAMs surface synchronously. The shift of pK(a) was observed during the experiment as previous reports. The factors that affect the capacitance measurement were discussed in detail.

Possibility of design of nanodevices by confined macromolecular self-assembly

Computer simulation has revealed that dual nanostructures for the development of nanodevices as nanowires, optical nanofibres and nanobatteries be obtained by the self-assembly of block copolymers confined geometry. The formation of individual nanostructures depends on the structures of block copolymers the confinement geometry and the interactions block copolymers and the boundary of the confinement geometry. In order to obtain individual nanostructures experimentally, attention needs to be paid to the manufacture of the confinement geometry and the design of the interactions between block copolymers and the boundary of the confinement geometry, The recently developed lithography technique should make experiments successful.

Synthesis of tetra-iron substituted sandwich-type pentadecatungstodiarsenate and its multilayers on glassy carbon electrode by self-assembly with electrocatalytic properties

A novel sandwich-type compound, Na-12 [Fe-4 (H2O)(2) (As2W15O56)(2)] . 38H(2)O (denoted as Fe(4)AS(4)W(30)) was synthesized. The compound was well characterized by means of IR, UV-Vis, W-138 NMR and elemental analyses. Redox electrochemistry of the compound has been studied in acid buffer solutions using cyclic voltammetry(CV). The compound containing multilayer films has been fabricated on the 4-aminobenzoic acid(4-ABA) modified glassy carbon electrode(GCE) surface by alternate deposition with a quaternized poly (4-vinylpyridine) partially completed with [Os(bpy)(2)Cl](2+/-) (denoted as QPVP-Os). CV, X-ray photoelectron spectroscopy (XPS) and UV-Vis spectroscopy were used to characterize the asprepared multilayer films. It is proved that the multilayer films are uniform and stable. The electrocatalytic activities of the multilayer films were investigated on the reduction of two substrates of important analytical interest, NO2- and H2O2.

Multilayer assembly of Bis-Keggin-type heteropoly compound on chemically modified glassy carbon electrode and its electrocatalysis

Through layer-by-layer assembly, the bis-Keggin-type heteropolyanion K10H3 [Nd(SiMo7W4O39)(2)] XH2O was successfully immobilized on a glassy carbon electrode surface grafted covalently by 4-aminobenzoic acid. The electrochemical behavior of the heteropolyanion was investigated. Cyclic voltammetry proved the uniform growth of the film. However, the characteristic redox peaks of the heteropolyanion in the film were deformed with increasing of the number of the multilayer film. The effect of pH on the redox behaviors of [Nd(SiMo7W4)(2)](13-) in the film was discussed. The multilayer film electrodes have excellent electrocatalytic activities to the reduction of BrO3-, HNO2 and H2O2.

Layer-by-layer assembly of multilayer films composed of streptavidin and biotinylated antibody by real-time biomolecular interaction analysis

Layer-by-layer assembly of multilayer films of streptavidin and biotinylated antibody was completed on the streptavidin coated surface. Real-time biomolecular interaction analysis (BIA) based on surface plasmon resonance technique was used to monitor the multilayer assembly in solution continuously. The results indicate that the uniform multilayer film can be fabricated successfully based on the strong interaction between streptavidin and biotin. The mean surface mass concentration of each adsorption layer is 1. 32 ng/mm(2) for biotinylated antibody, 2. 93 ng/mm(2) for streptavidin, according to the correlation of SPR response with surface concentration.

Layer-by-layer assembly of multilayer films consisting of silicotungstate and a cationic redox polymer on 4-aminobenzoic acid modified glassy carbon electrode and their electrocatalytic effects

A novel 4-aminobenzoic acid (4-ABA) monolayer film is formed on glassy carbon electrode (GCE) by amino cation radical method. Silicotungstic heteropolyanion (SiW12O404-, denoted as SiW12)-containing multilayer films have been fabricated on the 4-ABA modified GCE surface by alternate deposition with a quaternized poly(4-vinylpyridine) partially complexed with [Os(bpy)(2)Cl](2+/+) (denoted as QPVP-Os). Cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS) and X-ray reflectivity (XR) have been used to characterise the as-prepared multilayer films. It is proved that the multilayer films are uniform and stable. The average thickness for a bilayer of QPVP-Os/SiW12 in the multilayer film is 30.2 Angstrom. The electrocatalytic activities of the multilayer films have been investigated on the reduction of three substrates of important analytical interests, HNO2, BrO3- and H2O2. Especially, the influence of layer number of the multilayer films on the electrocatalytic reduction of HNO2 has been investigated in detail. (C) 2000 Elsevier Science B.V. All rights reserved.

Assembly of alternating polycation and DNA multilayer films by electrostatic layer-by-layer adsorption

The assembly of alternating DNA and positively charged poly(dimethyldiallylammonium chloride) (PDDA) multilayer films by electrostatic layer-by-layer adsorption has been studied. The real-time surface plasmon resonance (BIAcore) technique was used to characterize and monitor the formation of multilayer films in solution in real time continuously. Electrochemical impedance spectroscopy (EIS) and UV-vis absorbance measurements were also used to study the film assembly, and linear film growth was observed. All the results indicate that the uniform multilayer can be obtained on the poly(ethylenimine)- (PEI-) coated substrate surface. The kinetics of the adsorption of DNA on PDDA surface was also studied by the real-time BIAcore technique; the observed rate constant was calculated using a Langmuir model (k(obs) = (1.28 +/- 0.08) x 10(-2) s(-1).