The redox protein cytochrome c (CytC) assembles into electroactive multilayers on gold electrodes. For this purpose desoxyribonucleic acid (DNA) can be utilized as a negatively charged building block. This system can act as a basic construct for the establishment of analytical signal chains when redox enzymes are coupled to these layered assemblies.

One redox enzyme with particular promise is PQQ-GDH, which has an isoelectric point similar to CytC and thus should embed easily. The reaction between CytC and PQQ-GDH has been well investigated when both molecules are in solution: spectrophotometrical- and cyclovoltammetric (CV) analysis show, that PQQ-GDH is able to reduce CytC efficiently. But the reaction between these molecules when both are immobilized on electrodes is a real challenge.

Here we study the electron transfer reaction between PQQ-GDH and CytC with different arrangements. Thus we first assemble a monolayer of CytC on a thiol-modified gold wire electrode. We then place the electrode in a solution of PQQ-GDH. CV-measurements show that a catalytic current occurs in the presence of the substrate (glucose). Next, we investigate the situation when both molecules are immobilized. We use the layer-by-layer deposition technique to assemble a multilayer electrode of CytC, with a terminal layer of PQQ-GDH: (CytC/DNA)n/PQQ-GDH. We find, that a catalytic current flows when glucose is present, proving that inter-protein communication occurs with both surface-fixed components.

This bi-protein multilayer system is sensitive to glucose and the response can be tuned in a certain range by increasing the number of protein layers deposited on the electrode.

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1. Electrochemical observation of the thermally induced phase transition for a switchable polymer immobilised onto gold electrodes
2. Arranging proteins in electro-active multilayer architectures