1,720,986 research outputs found
Multilayered assembly of dendrimers with enzymes on gold: Thickness-controlled biosensing interface
No full textA new approach to construct a multilayered enzyme film on the Au surface for use as a biosensing interface is described, The film was prepared by alternate layer-by-layer depositions of G4 poly(amidoamine) dendrimers and periodate-oxidized glucose oxidase (GOx), The cyclic voltammograms obtained from the Au electrodes modified with the GOx/dendrimer multilayers revealed that bioelectrocatalytic response is directly correlated to the number of deposited bilayers, that is, to the amount of active enzyme immobilized on the Au electrode surface. From the analysis of voltammetric signals, the coverage of active enzyme per GOx/dendrimer bilayer during the multilayer-forming steps was estimated, which demonstrates that the multilayer is constructed in a spatially ordered manner. Also, with the ellipsometric measurements, a linear increment of the film thickness was registered, supporting the formation of the proposed multilayered structure. The E5D5 electrode showed the sensitivity of 14.7 mu A.mM(-1) glucose.cm(-2) and remained stable over 20 days under day-by-day calibrations. The proposed method is simple and would be applicable to the constructions of thickness- and sensitivity-controllable biosensing interfaces composed of multienzymes as well as a single enzyme
Bioelectrocatalyzed signal amplification for affinity interactions at chemically modified electrodes
No full textA comparative study was performed to evaluate the signal amplification strategies in electrochemical affinity sensing, which included the direct electron transfer and diffusible-group mediated electron transfer between label enzymes that were specifically bound to target proteins and chemically modified electrode surfaces. As a platform surface for affinity recognition reactions, a double functionalized poly(amidoamine) dendrimer monolayer that was modified with ferrocene and biotin groups was constructed on a gold surface. With the chemically modified electrode, a model affinity sensing with avidin was investigated. The advantages of adopting the diffusible-group mediated signaling strategy were demonstrated in terms of signal sensitivity and stability
Affinity biosensor for avidin using a double functionalized dendrimer monolayer on a gold electrode
No full textWe have developed an affinity biosensor system based on avidin-biotin interaction on a gold electrode. As the building block of an affinity-sensing monolayer, a fourth-generation (G4) poly(amidoamine) dendrimer having partial ferrocenyl-tethered surface groups was prepared and used. The unmodified surface amine groups from dendrimers were functionalized with biotinamidocaproate, and the biotinylated and electroactive dendritic monolayer was constructed on a gold electrode for the affinity-sensing surface interacting with avidin. An electrochemical signal from the affinity biosensor was generated by free glucose oxidase in electrolyte, depending on the degree of coverage of the sensing surface with avidin. The sensor signal decreased correlatively with increasing avidin concentration and approached a minimum level when the sensing surface was fully covered with avidin. The detection limit of avidin was about 4.5 pM, and the sensor signal was linear ranging from 1.5 pM to 10 nM under optimized conditions. From the kinetic analysis using the biotinylated glucose oxidase, an active enzyme coverage of 2.5 x 10(-12) mol/cm(2) on the avidin-pretreated surface was registered, which demonstrates the formation of a spatially ordered and compact protein layer on the derivatized electrode surface. (C) 2000 Academic Press
In situ biochemical reduction of interference in an amperometric biosensor with a novel heterobilayer configuration of polypyrrole glucose oxidase horseradish peroxidase
No full textA novel heterobilayer configuration for in situ biochemical reduction of interference in the amperometric glucose biosensor is described. The heterobilayer biosensor was constructed by electrochemical formation of a polypyrrole film in the presence of horseradish peroxidase (HRP) on top of an immobilized glucose oxidase (GO) film. In the heterobilayer configuration, electro-oxidizible compounds such as ascorbate, urate and acetaminophen, which severely interfere with the amperometric detection, were oxidized by the catalytic reaction of horseradish peroxidase before reaching the electrode surface. As a source of hydrogen peroxide required for the preoxidation of interferents, a portion of diffusing-away hydrogen peroxide produced by glucose oxidase, was utilized without any external supply. Preparation conditions for the heterobilayer biosensor were optimized in terms of sensitivity for glucose and the reduction of interference. The biosensor showed a good suppression of interference and a negligible deviation (less than 5%) in the amperometric detection, especially when the glucose concentration was higher than 50 mM
Reversible affinity interactions of antibody molecules at functionalized dendrimer monolayer: affinity-sensing surface with reusability
No full textWe described reversible affinity interactions of antibody molecules at a chemically functionalized electrode surface for a repeatedly renewable affinity-biosensing interface. Underlying biofunctionalizable monolayers were constructed with poly(amidoamine) dendrimers, whose surface chain-end groups were double-functionalized with biotinyl ligand and ferrocenyl groups for biospecific recognition and electron transfer reactions, respectively. Functionalized monolayers on gold electrodes provide platform surfaces for biospecific recognition reaction with monoclonal anti-biotin antibody molecules. Bound antibody molecules were dissociated from the surface via displacement reaction by the addition of free biotin in solution, enabling the affinity surface to be renewed and repeatedly utilized. Tracking of the association/dissociation reaction cycles were performed by registering the bioelectrocatalytic currents at the electrode using glucose oxidase (GOx) as a signal generator and ferrocenyl-tethered dendrimer (Fc-D) as an electron transferring mediator in electrolyte. Shielding of the affinity surface by biospecifically bound antibody molecules caused hindrance in electron transfer, resulting in reduced signal from cyclic voltammetry. By the displacement reaction using free biotin, bound antibody molecules were dissociated from the surface and the bioelectrocatalytic signal was restored. With the affinity surfaces constructed in this work, continuous association/dissociation reactions have been successfully accomplished, providing a possibility of reusable affinity biosensing inter-face. (C) 2002 Elsevier Science B.V. All rights reserved
Electrocatalytic signal amplification of PNA-modified DNA sensing surface with negatively charged mediators
No full textEnzyme-catalyzed signal amplification for electrochemical DNA detection with a PNA-modified electrode
No full textPatterning biological molecules onto poly(amidoamine) dendrimer on gold and glass
No full textPatterning of biological molecules was attempted on both gold and glass using fourth generation (G4) poly(amidoamine) (PAMAM) dendrimer as an interfacing layer between solid surfaces and biomolecules. As for the patterning of avidin and anti-biotin antibody on gold, PAMAM dendrimers representing amine functionalities were firstly printed onto the 11-mercaptoundecanoic acid SAM by microcontact printing, followed by biotinylation, and reacted with fluorescence-labeled avidin or anti-biotin antibody. Fluorescence microscopic analysis revealed that the patterns of avidin and anti-biotin antibody were well constructed with the resolution of <2mum. The PAMAM dendrimers were also printed onto aldehyde-activated slide glass and reacted directly with anti-BSA antibodies, which had been oxidized with sodium periodate. As a result, distinct patterns of the anti-BSA antibodies were also obtained with a comparable edge resolution to that of avidin patterns on gold. These results clearly show that PAMAM dendrimers can be adopted as an interfacing layer for the patterning of biological molecules on solid surfaces with micrometer resolution
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