Zhang, Xin: Electrochemical and Photochemical Functionalization of Au and Si Surfaces by Grafting of Diazonium and Azide Compounds. , Humboldt-Universität zu Berlin, 2011
Abstract:
In this work, various strategies for the functionalization of Au- and Si-surfaces for immobilization of biomolecules by maleimido groups have been developed, assembled and tested with cysteine-modified peptides. The electrochemical functionalization with diazonium compounds and UV-photochemical processing with azide aryls have been used to modify the surfaces with respect to COOH, NH2, and especially maleimido groups. The direct electrochemical deposition of maleimidobenzene led to an ultra thin layer with a thickness of about 1 ML after the 1st potential scan and approximately 2.3 ML after the 15th scan, whereas the layer thickness for carboxybenzene and aminobenzene was 3.8 (12.8) and 2.3 (19.0), respectively. The analysis of the flown electrical charge during the deposition and the change in mass (as measured by EQCM) yielded a grafting efficiency between 20 and 70 %, what is mainly due to sterical hindrance and mesomeric effects of the functional groups. IR spectroscopic investigations showed that the amidation reaction on the COOH- modified surface is very slow and is finished after about 2 days at room temperature, whereas the reaction time in solution is typically 4–8 hours. This behaviour points to a strong sterical hindrance due to the functional surface molecules which have low rotational probability. The mechanism of the photolysis of azide compounds is complex. In this study, however, a mixture of three different compounds on the surfaces (benzene ring with functional group, azepine variant and polyazipine) was observed after UV-light illumination of the azide aryls dissolved in acetonitrile. Nevertheless, the expected functional groups (-COOH, -NH2 and -maleimide) were on the surfaces. All of the individual steps were investigated by infrared ellipsometry and the surface species were characterized by their vibrational modes. For some selected samples, XPS was used to investigate the interface substrate/functional group in detail with respect Si-C and Si-N surface bonds. The real-time recognition process of an antibody with the cysteine-modified functional surface groups was demonstrated with FIA-QCM and electrical measurements, what proved the possibility for a quantitative sensing technique based on such modified functional surfaces.