Construction of layer-by-layer self-assemblies of glucose oxidase and cationic polyelectrolyte onto glassy carbon electrodes and electrochemical study of the redox-mediated enzymatic activity

Build-up of enzyme–polyelectrolyte multilayer onto glassy carbon (GC) surfaces by electrostatic self-assembling method has been investigated. In order to functionalize GC surface by a starting negatively charged layer, two approaches have been carried out: (i) covalent linkage of phenyl acetic acid through electroreduction of 4-phenylacetic diazonium salt (GCA surface), and (ii) formation of a glucose oxidase (GOD) monolayer through an affinity reaction between a GOD conjugated antibody and a previously adsorbed antigen monolayer (GCB surface). GCA and GCB surfaces have been modified by a precursor film (PF) composed of one layer of poly(styrenesulfonate) (PSS) sandwiched between two layers of poly(dimethyldiallylammonium) (PDDA), which improves the further assembling of enzymes. GOD, used as a model enzyme, has been self-assembled with PDDA onto these GC/PF surfaces. Enzymatic activity of immobilized GOD has been electrochemically assessed layer-by-layer during the build-up of (GOD–PDDA)n multilayers. Cyclic voltammetry (CV) performed in the presence of excess glucose and using ferrocene derivatives as artificial redox mediators allowed to quantify the amount of electrically wired enzyme on the basis of kinetic models reported in literature. By using three mediators bearing different electrical charges we conclude that electrostatic interactions between the redox mediator and enzyme microenvironment play a key role in determining the rate of enzyme active site