Han Zeng

Direct Electrochemistry and Catalytic Function on Oxygen Reduction Reaction of Electrodes Based on Two Kinds of Magnetic Nano-particles with Immobilized Laccase Molecules

Synthesized carboxymethylated Chitosan coupled magnetic Fe3O4 nano-particles and phthaloyl Chitosan overlapped magnetic Fe3O4 nano-particles, were used as enzyme matrices to prepare two prototypes of Laccase-based electrodes. Dependences of structural and operating parameters on characteristics of spectrometry, aggregation status and catalysis for oxygen reduction reaction of surface anchored protein molecules, were investigated and compared by electrochemical means in combination with spectroscopy and transmission electron microscopy. Results from experiments revealed that the latter electrode displayed favorable catalytic effect in oxygen reduction reaction in the absence of mediator. Key factor in limiting the efficiency of catalysis was ascribed to the diffusion process of the substrate into the layer of nano-particles containing Laccase. While the former electrode only showed efficient catalytic effect in oxygen reduction reaction in the presence of electron mediator with rate determining step in mass-transferring of mediator.

Dependence of Catalytic Dynamics on Structural and Operational Parameters of Enzymatic Electrodes Based on Nano-composite

AbstractDependences of structural parameters and operational conditions on enzymatic catalysis of substrates (glucose and oxygen) for basal electrodes over-coated by composite consisting of nano-gold particle and polymer, were investigated systematically by the means of electrochemistry and spectrometry. Rate constants of steps involved in the whole catalytic cycle were estimated under the same dimension and were compared to confirm the limiting factor in the whole catalytic cycle. Results from experiments indicated that nano-gold particle surface anchored with aromatic ring as conductive support played the important role in achieving direct electron transfer between cofactors in redox protein molecules and electrical wired matrix. Complexations between components of nano-composite and redox sites within incorporated enzyme molecules acted as the paradoxical role in promoting the catalytic efficiency in the long term. Electrochemical conversion of substrates into product was identified to be the rate limiting step in the whole catalytic cycle for both enzyme based electrodes. Other parameters such as enzyme loading amounts in matrix, size of nano-particle and proportion of component in nano-composite only posed impact on magnitude of catalytic effect rather than the mechanism of catalysis.Graphical AbstractTransformation of substrate into product was ascribed to the limiting step in the whole catalysis for enzyme-based electrodes which resulted from great impact of interactions between enzyme carrier and redox protein on configuration of cofactors in enzyme molecules and binding ability to substrate for proteins.

Investigation in Mediated Heterogeneous Oxygen Reduction of Immobilized Laccase

AbstractDynamics of heterogeneous catalysis on oxygen reduction for Lac based electrode capped with a layer of Chitosan-multi-wall carbon nano-tubes complex in the presence of dissolved mediator, was investigated on the basis of precondition that the detainment of substrate and mediator could be neglected. Rates of steps involved in the whole catalytic cycle were determined by the means of UV–Vis spectroscopy, atomic adsorption spectroscopy, linear sweeping voltammetry and cyclic voltammetry in combination with rotating disk electrode technique. These kinetic parameters were normalized under the same dimension. Thus rate determining step was verified to be the diffusion of external mediator. Results also revealed the fact from analysis in changes of morphology and electric conductivity after protein incorporation into nano-composite that random adsorption of enzyme molecules on the conductive support resulted in the decrease in conductive area of nano-composite and hindered the direct electron transfer between active sites in enzyme molecules and conductive matrix. Non-oriented arrangement of protein molecules on the matrix also crippled the mechanical stability of nano-complex with enzyme resulting from weak interaction between incorporated protein molecules and carrier.Graphical AbstractCatalytic effect on dissolved oxygen reduction reaction for electrode which was over-coated by a layer of nano-complex with immobilized Laccase consisting of Chitosan and multi wall carbon nano-tubes, were found to be restrained by diffusion of electron relay.

Investigation on Electrochemical Behavior and Catalytic Function of Glassy Carbon Electrode on the Basis of Magnetic Nano-particle with Simultaneous Incorporation of Myoglobin and Electron Mediator

As-prepared magnetic nano-composite with Fe3O4 as core and carboxymethylated Chitosan as shell was proposed to act as matrix to co-immobilize electron relay and myoglobin by the means of chemical coupling. Subsequently Mb based bio-cathode was fabricated through the procedure of drop-casting in the presence of external magnet and was examined its performance in direct electron transferring and catalysis in electro-reduction of H2O2 with spectrometric and electro-chemical methods. Analysis in results indicated adjacent complexations between hetero-atoms in polymer and cofactors in enzyme/redox site of electron mediator would pose great impact on spectroscopic and electrochemical features of immobilized protein. These interactions would alter the path of electron shuttle and mechanism of catalysis.

Spectroscopic and Electrochemical Features of Glucose Oxidase Incorporation into Polyaniline-Cobaltous Oxalate Nano-complex

AbstractNano-complex as enzyme carrier was prepared via hybridization of nano-scale cobaltous oxalate with conductive polymer: polyaniline. Spectrometric means and electrochemical technique were proposed to explore the influence of interaction between nano-composite and redox protein on structural features, dynamics of electron shuttle and catalysis of immobilized enzyme. Results indicated that collaboration of π–π stacking effect as well as the complexation of metal ions in nano-composite with cofactors in enzyme molecule could lead to the firm linkage of glucose oxidase to the matrix of nano-composite. The ligation would cause orientated attachment of enzyme molecules onto the surface of nano-complex. Synergistic effect would not only enhance the enzyme loading capacity of carrier but also facilitate the direct electrochemistry of tethered enzyme molecules with intact structure and configuration of cofactor. However the complexation would cripple the enzymatic catalysis in electro-oxidation of glucose in spite of high affinity to glucose for glucose oxidase integration into nano-composite.Graphical AbstractCoordination of metal ions within nano-composite with cofactor of glucose oxidase (GOx) would lead to formation of composite with crippled emission fluorescence and hinder the electro-oxidation of glucose.