Untersuchung von Wechselwirkungen zwischen mikrostrukturierten Enzymen mittels elektrochemischer Rastermikroskopie (SECM)

Wechselwirkungen zwischen lateral mikrostrukturierten Enzymen sind für die Entwicklung von Biosensoren von Bedeutung. Die elektrochemische Rastermikroskopie (SECM) eignet sich sowohl zur Strukturierung als auch zur lokalen Reaktivitätscharakterisierung von Oberflächen: Mittels lokaler elektrochemischer Desorption im Direktmodus des SECM können Strukturen in vorhandene selbstorganisierte Alkanthiolatmonolagen (SAM) auf Gold geschrieben werden. Diese Monolagen können sowohl flächig abgeschieden als auch durch Microcontactprinting (µCP) strukturiert aufgebracht sein. In diesen freigelegten Strukturen läßt sich ein z.B. mit S-Acetylthioessigsäure-N-hydroxysuccinimidylester (SATA) SH-funktionalisierte Enzyme kovalent immobilisieren. Verbunden mit der Möglichkeit, eine Goldoberfläche mittels µCP großflächig zu mikrostrukturieren und anschliessend an die verbleibenden freien Goldflächen über ein aminofunktionalisiertes Thiol ein Enzym (z.B. Meerrettich Peroxidase, HRP) kovalent zu koppeln, ergibt sich ein einfacher Weg zu lateral mikrostrukturierten Anordnungen von Enzymen. In den vorgestellten Experimenten wurden die Enzyme Glucoseoxidase (GOD) und Meerettich Peroxidase (HRP) verwendet. Zur Untersuchung der enzymatischen Aktivität eignet sich besonders der Generator-Kollektor-Modus des SECM. Je nach Wahl der experimentellen Parameter kann die Aktivität eines einzelnen Enzyms in der Mikrostruktur bzw. die Aktivität von HRP in Abhängigkeit der der GOD sichtbar gemacht werden. Solche Anordnungen sind geeignet zur Unterdrückung von Interferenzen in miniaturisierten Multienzym-Mikrostrukturen

Controlling the supramolecular assembly of redox active dendrimers at molecular printboards by scanning electrochemical microscopy

Redox-active ferrocenyl (Fc)-functionalized poly(propylenimine) (PPI) dendrimers solubilized in aqueous media by complexation of the Fc end groups with β-cyclodextrin (βCD) were immobilized at monolayers of βCD on glass (“molecular printboards”) via multiple host−guest interactions. The directed immobilization of the third-generation dendrimer−βCD assembly G3-PPI−(Fc)16−(βCD)16 at the printboard was achieved by supramolecular microcontact printing. The redox activity of the patterned dendrimers was mapped by scanning electrochemical microscopy (SECM) in the positive feedback mode using [IrCl6]3- as a mediator. Local oxidation of the Fc−dendrimers by the microelectrode-generated [IrCl6]2- resulted in an effective removal of the Fc−dendrimers from the host surface since the oxidation of Fc to the oxidized form (Fc+) leads to a concomitant loss of affinity for βCD. Thus, SECM provided a way not only to image the surface, but also to control the binding of the Fc-terminated dendrimers at the molecular printboard. Additionally, the electrochemical desorption process could be monitored in time as the dendrimer patterns were gradually erased upon multiple scan

Highly stable, reactive and ultrapure nanoporous metallic films

Nanoporous metals possess unique properties attributed to their high surface area and interconnected nanoscale ligaments. They are mostly fabricated by wet synthetic methods involving solution-based dealloying processes whose purity is compromised by residual amounts of the less noble metal. Here, we demonstrate a novel dry synthesis method to produce nanoporous metals, which is based on the plasma treatment of metal nanoparticles formed by physical vapor deposition. Our approach is general and can be applied to many metals including non-noble ones. The resultant nanoporous metallic films are impurity-free and possess highly curved ligaments and nanopores. The metal films are remarkably robust with many catalytically active sites, which is highly promising for electrocatalytic applications.Comment: 40 pages (including 13 pages of supplementary information), 5 figures, submitte

Soft Microelectrode Linear Array for Scanning Electrochemical Microscopy

A linear array of eight individual addressable microelectrodes has been developed in order to perform highthroughput scanning electrochemical microscopy (SECM) imaging of large sample areas in contact regime. Similar to previous reports, the soft microelectrode array was fabricated by ablating microchannels on a polyethylene terephthalate (PET) film and filling them with carbon ink. Improvements have been achieved by using a 5 μm thick Parylene coating that allows for smaller working distances, as the probe was mounted with the Parylene coating facing the sample surface. Additionally, the application of a SECM holder allows scanning in contact regime with a tilted probe, reducing the topographic effects and assuring the probe bending direction. The main advantage of the soft microelectrode array is the considerable decrease in the experimental time needed for imaging large sample areas. Additionally, soft microelectrode arrays are very stable and can be used several times, since the electrode surface can be regenerated by blade cutting. Cyclic voltammograms and approach curves were recorded in order to assess the electrochemical properties of the device. An SECM image of a gold on glass chip was obtained with high resolution and sensitivity, proving the feasibility of soft microelectrode arrays to detect localized surface activity. Finite element method (FEM) simulations were performed in order to establish the effect of diffusion layer overlapping between neighboring electrodes on the respective approach curves

Seeing Big with Scanning Electrochemical Microscopy

Specialized microelectrode probes fabricated in a soft polymer film now make it possible to use scanning electrochemical microscopy to image the reactivity of large, corrugated, tilted, and dry surfaces