We present the characterization of the direct electron transfer and the catalytic activity  of sulfite oxidase in a hybrid biosensor for sulfite detection, consisting of a combination of ultrafine gold nanoparticles and enzyme.

The human sulfite oxidase (hSOx) is a molybdenum and heme containing protein. It catalyzes the oxidation of sulfite to sulphate releasing the electrons to an external acceptor. The natural electron acceptor, cytochrome c, may be used to transfer electrons to an electrode [1]  or may be replaced by a chemically modified electrode [2]. On positively charged surfaces the electron transfer proceeds through the heme domain of sulfite oxidase. In order to increase the efficiency of the bioelectrocatalysis we introduced nanoparticles.   A hybrid system with an Au-electrode, self assembled alkyl thiol derivatives, polyethylene imine capped nanoparticles and sulfite oxidase has been created. The nanoparticles had a core size of about 6 ± 2 nm nm and a hydrodynamic diameter of 9 ± 1 nm.

Electrochemical as well as UV-vis and SERRS characterization of the system will be presented.
[1] Spricigo R., Dronov R., Rajagopalan K. V., Lisdat F., Leimkühler S., Scheller F. W., Wollenberger U. Soft Matter, 2008, 4, 972.

[2] Sezer M., Spricigo R., Utesch T., Millo D., Leimkühler S., Mroginski M. A., Wollenberger U., Hildebrandt P., Weidinger I. M. Phys Chem Chem Phys., 2010, 12, 7894-7903.

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1. Enhancing heterogeneous electron transfer between enzymes and electrodes
2. Surface modification of gold electrodes for a switchable biosensor