Switching on cell adhesion with microelectrodes.
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Cell Adhesion↗
Biomedical subjects
Chuan Zhao
Publications and source records attributed to Chuan Zhao.
Modeling steady-state experiments with a scanning electrochemical microscope involving several independent diffusing species using the boundary element method.
The BEM algorithm developed earlier for steady-state experiments in the scanning electrochemical microscopy (SECM) feedback mode has been expanded to allow for the treatment of more than one independently diffusing species. This allows the treatment of substrate-generation/tip-collection SECM experiments. The simulations revealed the interrelation of sample layout, local kinetics, imaging conditions, and the quality of the obtained SECM images. Resolution in the SECM SG/TC images has been evaluated, and it depends on several factors. For most practical situations, the resolution is limited by the diffusion profiles of the sample. When a dissolved compound is converted at the sample (e.g., oxygen reduction or enzymatic reaction at the sample), the working distance should be significantly larger than in SECM feedback experiments (ca. 3 r(T) for RG = 5) in order to avoid diffusional shielding of the active regions on the sample by the UME body. The resolution ability also depends on the kinetics of the active regions. The best resolution can be expected if all the active regions cause the same flux. In one simulated example, which might mimic a possible scenario of a low-density protein array, considerable compromises in the resolving power, were noted when the flux from two neighboring spots differs by more than a factor of 2.
Algorithms↗
Photoelectrochemical kinetics of eosin y-sensitized zinc oxide films investigated by scanning electrochemical microscopy.
Eosin Y is used as a sensitizer for nanoporous zinc oxide films for prospective applications in photoelectrochemical solar cells. The kinetics of the reduction of the intermittently formed photo-oxidized dye molecules by iodide ions in the electrolyte phase was investigated by using the feedback mode of scanning electrochemical microscopy (SECM). The bulk solution phase contained triiodide as electron transfer mediator, from which the ultramicroelectrode-generated iodide ions acted as electron donors for photo-oxidized Eosin Y molecules (D(+) (ads)) at the zinc oxide sample. Effective rate constants for the dye regeneration could be extracted from the SECM approach curves. The effective rate constants at different triiodide concentrations could be related to the rate constant for the reaction of the dissolved donor with photo-oxidized Eosin Y bound to ZnO, as well as to the overall rate of the photosensitization process. For the reaction D(+) (ads) + 1.5 I(-)-->D(ads) + 0.5 I(3) (-) a rate constant of k(ox) = (1.4+/-0.8)x10(8) cm(9/2) mol(-3/2) s(-1) was determined.
Journal Article↗
Scanning electrochemical microscopy for detection of biosensor and biochip surfaces with immobilized pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase as enzyme label.
Scanning electrochemical microscopy (SECM) was applied to study quinoprotein-based biosensor or biochip. A typical quinoprotein, pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase (GDH), was taken as example. Feedback mode and generation collection (GC) mode in SECM have been explored in imaging the catalytic activity of GDH on microscopic magnetic bead domains. Biotinylated GDH was immobilized by using streptavidin-coated paramagnetic microbeads, which were deposited as microspot on a hydrophobic surface. Ferrocenemethanol and ferricyanide were used as electron mediators for feedback and GC detection, respectively. Enzymatic catalysis was further studied quantitatively using the theory developed for SECM.
Biosensing Techniques↗
An SECM detection scheme with improved sensitivity and lateral resolution: detection of galactosidase activity with signal amplification by glucose dehydrogenase.
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Electrochemistry↗
Scanning electrochemical microscopy of quinoprotein glucose dehydrogenase.
The activity of immobilized glucose dehydrogenase (GDH), a typical PQQ-dependent quinoprotein, was studied qualitatively and quantitatively by scanning electrochemical microscopy (SECM). PQQ-dependent GDH is of interest because of its high activity and independence of dissolved oxygen in catalyzing the transfer of electrons from glucose to an electron mediator. Biotinylated glucose dehydrogenase was bound to streptavidin-coated paramagnetic beads (surface concentration > or = 1.8 x 10(-11) mol cm(-2)) which were deposited as microscopic microspots on a hydrophobic surface. The catalytic activity of immobilized GDH was mapped in SECM feedback mode and generation-collection mode using ferrocenemethanol, ferrocenecarboxylic acid, p-aminophenol, and ferricyanide as electron mediators, respectively. The apparent steady-state kinetics of catalysis were measured under conditions of high d-glucose concentration using the theory developed for the SECM feedback and generation collection (GC) modes. In feedback mode, curves of the kinetically controlled substrate current against normalized distance were plotted, and it was found that GDH catalysis follows pseudo-first-order kinetics. In GC mode detection, the catalysis follows zero-order kinetics in the presence of high concentration of both substrates for GDH. The turnover rate obtained for immobilized GDH is lower than that of native GDH but much higher than that generally observed for glucose oxidase.
Electrochemistry↗
Determination of total phenols in environmental wastewater by flow-injection analysis with a biamperometric detector.
A flow injection (FI) method with a biamperometric detector, based on the biamperometry for an irreversible redox couple, is described for the determination of phenols in environmental wastewater. The method relies on coupling of the oxidation of phenols at one platinum-wire electrode with the reduction of MnO4- at another platinum wire electrode to enable biamperometric detection with an applied potential difference of 0 V. The linear dynamic range for the dependence of current on phenol concentration was from 1.0 x 10(-6) to 1.0 x 10(-4) mol L(-1), with a detection limit of 4.0 x 10(-7) mol L(-1) (signal-to-noise ratio, S/N=3). In comparison with the 4-aminoantipyrine (4-AAP) standard method and the 3-methyl-2-benzothiazoline hydrazone (MBTH) method the proposed method can be used to detect many para-substituted phenols that do not react with 4-AAP and MBTH, and response factors are higher for most of the phenols tested. The method, which is simple, economic, and rapid (180 samples h(-1)), has been applied to the analysis of four wastewater samples. The results obtained were compared with those from 4-AAP method. The recoveries obtained by adding phenol standards to samples ranged from 94.3 to 105.2% with a standard deviation of 3.6%.
Electrochemistry↗