The sol-gel process provides unique opportunity to produce hybrid materials combining simultaneously organic and inorganic properties in a single solid [1]. In addition, the porosity of such materials can be tuned and the shape of the solid can be adapted to the application, from monolith to particles and thin films. Sol-gel silica material also allows for the encapsulation of protein, bacteria and biological cells in an active form without preventing the diffusion of molecules (enzymatic substrate, nutriments, etc.) inside the porous gel network and provides a protective environment that allows a better resistance of the encapsulated biological object to harsh conditions (temperature, pH, etc.) and/or an improved long term stability [2].

This communication will show some examples of  hybrid sol-gel thin films for bioelectrochemical applications. Indeed, we recently investigated the co-immobilization in a single film of a NAD-dependant dehydrogenase (D-sorbitol, D-Glucose or L-Lactate dehydrogenase), the NAD⁺ cofactor and a suitable electrocatalytic system for allowing the safe detection-regeneration of the cofactor during the bioelectrocatalytic reactions [3-6].

We will see that such a complex layer can be successfully prepared with using the different possibilities offered by the sol-gel chemistry, i.e. the incorporation of polyelectrolytes, the co-condensation with chosen organoalkoxysilane and finally the processing for getting a thin film on the electrode surface. The method used to prepare the film, the evaporation of the starting sol (drop or spin-coating) or the electrochemically assisted deposition, affected strongly the bioelectrochemical response of the modified electrodes. These results will be discussed in a tentative to define the best strategy to be used according to the electrode to be modified (flat or porous electrodes) and the concerned application (biosensor, electroenzymatic synthesis, biobattery or biofuel cell).

[1] C. Sanchez ,L. Rozes, F. Ribot, C. Laberty-Robert, D. Grosso, C. Sassoye, C. Boissiere, L. Nicole, C. R. Chimie 2010, 13, 3.
[2] D. Avnir, T. Coradin, O. Lev, J. Livage, J. Mater. Chem. 2006, 16, 1013.
[3] Z. Wang, M. Etienne, G.-W. Kohring, A. Walcarius, Electroanalysis 2010, 22, 2092.
[4] A. Walcarius, R. Nasraoui, Z. Wang, F. Qu, V. Urbanova, M. Etienne, A. S. Demir, J. Gajdzik, R. Hempelmann, Bioelectrochem. 2011, 82, 46.
[5] Z. Wang, M. Etienne, G.-W. Kohring, Y. Bon-Saint-Côme, A. Kuhn, A. Walcarius, Electrochim. acta, in press.
[6] Z. Wang, M. Etienne, F. Quilès, G.-W. Kohring, A. Walcarius, submitted.

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2. Electrochemically Assisted Encapsulation of Bacteria in Sol-Gel Thin Films
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5. Electro-assisted generation of sol-gel thin films directed to electrochemical sensing
6. Shearforce-based distance control in scanning electrochemical microscopy
7. Heavy metal uptake and ion exchange properties of functionalized mesoporous silica materials