Thermoresponsive polymeric hydrogels anchored at gold surfaces and used as matrix for enzymes

Marianna Gniadek ,  Marcin Karbarz ,  Zbigniew Stojek 

Warsaw University, Faculty of Chemistry, Pasteura 1, Warszawa 02-093, Poland

Abstract
We have focused our attention on polymeric hydrogels that are cross-linked polymer networks filled with water. The content of water in hydrogels may be higher than 95%. Some of these polymers can exist in two different states: swollen and collapsed (shrunken). The transition from one state to another is called the volume phase transition. This transition is a response to the changes in such conditions as temperature [1] and pH [2]. When a hydrogel in a swollen state undergoes the volume phase transition, water is removed from the polymeric network.

The unique structure and environmental sensitivity of the polymeric gels make them useful in various applications including, drug delivery systems, separation techniques, and construction of sensors. In the development of such applications the knowledge of the internal structure and the mobility of the molecules and ions in these materials and the influence of the environmental conditions on these properties is very useful. The electroanalytical methods offer a fast, inexpensive and accurate approach to such examinations [3].

The discontinuous change in the volume of the gels examined by us occurs when temperature exceeds 34 0C. The first step was to anchor a thin film of NIPA {cross-linked poly(N-isopropylacrylamide)} hydrogel to the surface of a gold electrode. To achieve this, the surface of the electrode, before the polymerization process, was treated with dimetyl-vinyletoxysilane. The schematic structure of the NIPA polymer linked with the electrode through the dimetyl-vinyletoxysilane is shown in the figure. Then we attempted to examine the volume phase transition of the gels in the attached state and to find out whether the adhesion of the layer to gold is strong enough not to permit the peeling of the polymer layer during the shrinking process. For these examinations we have employed various electroanalytical and optical methods. The shrinking behaviour the NIPA hydrogel attached to the gold surface was compared with that of a free, grown in a capillary, gel sample. The anchoring of thin layers of NIPA hydrogel was apparently successful.

The electrode with the anchored gel appeared to be a good matrix for immobilization of the enzymes. Some tests with glucose oxydase and laccase have been made. The enzymes introduced to the matrix during its polymerization growth did not loose their activity. This was confirmed electrochemically and spectrometrically.

[1] X. Z. Zhang , J. T. Zhang, R. X. Zhuo, C. C. Chu,. J. Chem. Phys., 43 (2002) 4823.
[2] K. Ogawa, A. Nakayama, E. Kokufuta, Langmuir, 19 (2003) 3178.
[3] W. Hyk, M. Karbarz, Z. Stojek, M. Ciszkowska, J. Phys. Chem. B, 108 (2004) 846.

 

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Presentation: Short communication at SMCBS'2005 Workshop, by Marianna Gniadek
See On-line Journal of SMCBS'2005 Workshop

Submitted: 2005-07-31 16:36
Revised:   2009-06-07 00:44