Gold Nanoparticle-Based Mediatorless Biosensor Prepared on Microporous Electrode

A mediatorless biosensor was fabricated with a double‐sided microporous gold electrode by successively immobilizing a mixed self‐assembled monolayer (SAM) comprising carboxylic‐acid‐ and thiol‐terminated thiolate (dl‐thiorphan and 1,8‐octanedithiol), glucose oxidase (GOx) and finally gold nanoparticle (Au NP) on one working side. The double‐sided microporous gold electrodes were formed by plasma sputtering of gold on a porous nylon substrate, yielding a face‐to‐face type two‐electrode electrochemical cell. While the straight chain molecule 1,8‐octanedithiol forms a dense insulating monolayer, the side armed dl‐thiorphan forms a low density layer for the diffusion of redox couples to the electrode surface. The mixed SAM not only provided the linking functional groups for both enzyme and Au NP but also resulted in the appropriately spaced monolayer for direct electron tansfer (ET) process from the center of the redox enzyme to the electrode surface. After covalently immobilizing GOx onto the carboxylic‐acid‐terminated monolayer, Au NP was easily immobilized to both enzyme and nearby thiols by simple dispensing of the colloidal gold solution. It was observed that the resulting amperometric biosensor exhibited quantitatively the same response to glucose in the presence and in the absence of dissolved oxygen, which evidence that the Au NPs immobilized on and around the GOx promote direct ET from the enzymes to the electrode, assuming the role of a common redox mediator.