Home About us Contact
|
Home About us Contact | ||
|
|
||
Glucose Detection (glucose + detection)
Selected AbstractsBiosensor Based on Self-Assembling Glucose Oxidase and Dendrimer-Encapsulated Pt Nanoparticles on Carbon Nanotubes for Glucose DetectionELECTROANALYSIS, Issue 6 2007Lihuan Xu Abstract A novel amperometric glucose biosensor based on layer-by-layer (LbL) electrostatic adsorption of glucose oxidase (GOx) and dendrimer-encapsulated Pt nanoparticles (Pt-DENs) on multiwalled carbon nanotubes (CNTs) was described. Anionic GOx was immobilized on the negatively charged CNTs surface by alternatively assembling a cationic Pt-DENs layer and an anionic GOx layer. Transmission electron microscopy images and ,-potentials proved the formation of layer-by-layer nanostructures on carboxyl-functionalized CNTs. LbL technique provided a favorable microenvironment to keep the bioactivity of GOx and prevent enzyme molecule leakage. The excellent electrocatalytic activity of CNTs and Pt-DENs toward H2O2 and special three-dimensional structure of the enzyme electrode resulted in good characteristics such as a low detection limit of 2.5,,M, a wide linear range of 5,,M,0.65,mM, a short response time (within 5,s), and high sensitivity (30.64,,A mM,1,cm,2) and stability (80% remains after 30 days). [source] Electrochemically Induced Formation of Surface-Attached Temperature-Responsive Hydrogels.ELECTROANALYSIS, Issue 9 2010Amperometric Glucose Sensors with Tunable Sensor Characteristics Abstract Employing thermally responsive hydrogels, the design of an amperometric glucose sensor is proposed. The properties of the biosensor can be modulated upon changing the temperature. Homo- and copolymers of N -isopropylacrylamide (NIPAm) and oligo(ethylene glycol) methacrylate (OEGMA) were prepared by electrochemically induced polymerization thus yielding surface-attached hydrogels. The growth of the films as well as the change in the film thickness in dependence from the temperature were investigated by means of an electrochemical quartz crystal microbalance (EQCM). The layer thickness in the dry state ranged from 20 to 120,nm. The lower critical solution temperature (LCST) of the hydrogel increases with increasing content of the more hydrophilic OEGMA. Hence, the swelling in aqueous electrolyte is composition dependent and can be adjusted by selecting a specific NIPAm to OEGMA ratio. All homo- and copolymer films showed good biocompatibility and no fouling could be observed during exposing the surfaces to human serum albumin. For amperometric glucose detection, glucose oxidase was entrapped in the films during electrochemically-induced polymerization. Both the apparent Michaelis constant (K and the apparent maximum current (i as determined by amperometry could be adjusted both by the film composition as well as the operation temperature. [source] The role of hexose transport and phosphorylation in cAMP signalling in the yeast Saccharomyces cerevisiaeFEMS YEAST RESEARCH, Issue 1 2001Filip Rolland Abstract Glucose-induced cAMP signalling in Saccharomyces cerevisiae requires extracellular glucose detection via the Gpr1-Gpa2 G-protein coupled receptor system and intracellular glucose-sensing that depends on glucose uptake and phosphorylation. The glucose uptake requirement can be fulfilled by any glucose carrier including the Gal2 permease or by intracellular hydrolysis of maltose. Hence, the glucose carriers do not seem to play a regulatory role in cAMP signalling. Also the glucose carrier homologues, Snf3 and Rgt2, are not required for glucose-induced cAMP synthesis. Although no further metabolism beyond glucose phosphorylation is required, neither Glu6P nor ATP appears to act as metabolic trigger for cAMP signalling. This indicates that a regulatory function may be associated with the hexose kinases. Consistently, intracellular acidification, another known trigger of cAMP synthesis, can bypass the glucose uptake requirement but not the absence of a functional hexose kinase. This may indicate that intracellular acidification can boost a downstream effect that amplifies the residual signal transmitted via the hexose kinases when glucose uptake is too low. [source] Surface-enhanced Raman sensors: early history and the development of sensors for quantitative biowarfare agent and glucose detectionJOURNAL OF RAMAN SPECTROSCOPY, Issue 6-7 2005Christy L. Haynes Abstract Surface-enhanced Raman spectroscopy (SERS) is a powerful technique for the sensitive and selective detection of low-concentration analytes. This paper includes a discussion of the early history of SERS, the concepts that must be appreciated to optimize the intensity of SERS and the development of SERS-based sensors. In order to achieve the lowest limits of detection, both the relationship between surface nanostructure and laser excitation wavelength, as well as the analyte/surface binding chemistry, must be carefully optimized. This work exploits the highly tunable nature of nanoparticle optical properties to establish the first set of optimization conditions. The SERS enhancement factor, EFSERS, is optimized when the energy of the localized surface plasmon resonance (LSPR) lies between the energy of the excitation wavelength and the energy of the vibrational band of interest. With the narrow LSPRs used in this work, it is straightforward to achieve EFSERS , 108. These optimization conditions were exploited to develop SERS-based sensors for two important target molecules: a Bacillus anthracis biomarker and glucose in a serum protein mixture. Using these optimized film-over-nanosphere surfaces, an inexpensive, portable Raman spectrometer was used successfully to detect the infectious dose of Bacillus subtilis spores with only a 5-s data collection. The biomarker used to detect the Bacillus subtilis spores binds irreversibly to SERS substrates, whereas other important biomolecules, such as glucose, do not have any measurable binding affinity to a bare silver surface. To overcome this difficulty, a biocompatible partition layer was self-assembled on the SERS substrate before exposure to the analyte solution. Using the partition layer approach to concentrate glucose near the SERS-active substrate, physiological glucose concentrations can be detected even in the presence of interfering serum proteins. Copyright © 2005 John Wiley & Sons, Ltd. [source] Fabrication of poly(ethylene glycol)-based hydrogels entrapping enzyme-immobilized silica nanoparticlesPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 7 2010Eunji Jang Abstract In this study, we immobilized enzymes by combining covalent surface immobilization and hydrogel entrapment. A model enzyme, glucose oxidase (GOX), was first covalently immobilized on the surface of silica nanoparticles (SNPs) via 3-aminopropyltriethoxysilane (APTES), and the resultant SNP-immobilized enzyme was physically entrapped within photopolymerized hydrogels prepared from two different molecular weights (MWs) (575 and 8000,Da) of poly(ethylene glycol)(PEG). The hydrogel entrapment resulted in a decrease in reaction rate and an increase in apparent Km of SNP-immobilized GOX, but these negative effects could be minimized by using hydrogel with a higher MW PEG, which provides higher water content and larger mesh size. The catalytic rate of the PEG 8000 hydrogel was about ten times faster than that of the PEG 575 hydrogel because of enhanced mass transfer. Long-term stability test demonstrated that SNP-immobilized GOX entrapped within hydrogel maintained more than 60% of its initial activity after a week, whereas non-entrapped SNP-immobilized GOX and entrapped GOX without SNP immobilization maintained less than 20% of their initial activity. Incorporation of SNPs into hydrogel enhanced the mechanical strength of the hydrogel six-fold relative to bare hydrogels. Finally, a hydrogel microarray entrapping SNP-immobilized GOX was fabricated using photolithography and successfully used for quantitative glucose detection. Copyright © 2009 John Wiley & Sons, Ltd. [source] A Dual-Electrode Approach for Highly Selective Detection of Glucose Based on Diffusion Layer Theory: Experiments and SimulationCHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2005Kang Wang Dr. Abstract A dual-electrode configuration for the highly selective detection of glucose in the diffusion layer of the substrate electrode is presented. In this approach, a glassy carbon electrode (GCE, substrate) modified with a conductive layer of glucose oxidase/Nafion/graphite (GNG) was used to create an interference-free region in its diffusion layer by electrochemical depletion of interfering electroactive species. A Pt microelectrode (tip, 5 ,m in radius) was located in the diffusion layer of the GNG-modified GCE (GNG-G) with the help of scanning electrochemical microscopy. Consequently, the tip of the electrode could sense glucose selectively by detecting the amount of hydrogen peroxide (H2O2) formed from the oxidization of glucose on the glucose oxidase layer. The influences of parameters, including tip,substrate distance, substrate potential, and electrolyzing time, on the interference-removing efficiency of this dual-electrode approach have been investigated systematically. When the electrolyzing time was 30 s, the tip,substrate distance was 1.8,a (9.0 ,m) (where a is the radius of the tip electrode), the potentials of the tip and substrate electrodes were 0.7 V and 0.4 V, respectively, and a mixture of ascorbic acid (0.3,mM), uric acid (0.3,mM), and 4-acetaminophen (0.3,mM) had no influence on the glucose detection. In addition, the current,time responses of the tip electrode at different tip,substrate distances in a solution containing interfering species were numerically simulated. The results from the simulation are in good agreement with the experimental data. This research provides a concept of detection in the diffusion layer of a substrate electrode, as an interference-free region, for developing novel microelectrochemical devices. [source] | ||||||||||