Finger probe array for topography-tolerant scanning electrochemical microscopy of extended samples.

Scanning electrochemical microscopy with soft microelectrode array probes has recently been used to enable reactivity imaging of extended areas and to compensate sample corrugation perpendicular to the scanning direction. Here, the use of a new type of microelectrode arrays is described in which each individual microelectrode can independently compensate corrugations of the sample surface. It consists of conventional Pt microelectrodes enclosed in an insulating glass sheath. The microelectrodes are individually fixed to a new holder system by magnetic forces. The concept was tested using a large 3D sample with heights up to 12 µm specially prepared by inkjet printing. The microelectrodes follow the topography in a constant working distance independently from each other while exerting low pressure on the surface.

Feedback mode SECM study of laccase and bilirubin oxidase immobilised in a sol-gel processed silicate film.

Thin silicate films with immobilised enzymes catalysing dioxygen reduction, i.e. laccase and bilirubin oxidase (BOD), were deposited on glass and poly(methyl 2-methylpropenoate) (Plexiglas) surfaces in a sol-gel process by sol drop evaporation. Scanning electrochemical microscopy (SECM) images and approach curves were recorded using hexacyanoferrate(iii) as mediator in the feedback mode. Confocal laser scanning microscopy (CLSM) images in the reflection mode showed larger film thickness close to the edge of the film and laccase aggregates within the film. SECM images obtained using different dioxygen concentrations showed that the film edge and laccase aggregates exhibit higher enzymatic activity towards dioxygen reduction. SECM current-distance curves enabled the determination of kinetic information at the particular regions of the samples after numerical fitting of model parameters. The heterogeneous first order rate constant at the film border was estimated to be ca. 19 times higher than the value obtained when approaching to the centre of the film. The reason of higher laccase surface concentration at the film edge is carefully discussed. For comparison of laccase and BOD activities, silicate spots of 50 microm diameter were deposited on a single Plexiglas sample and examined using SECM. BOD exhibits much higher activity especially at neutral pH.