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Modification of Self-Assembled Monolayers and Hydrogel Nanomembranes by Ultraviolet Light

Yan, Rui

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Custom design of organic and biological surfaces and soft matter lithography are important issues of modern nanotechnology and physical chemistry of interfaces. An important tool in this regard is ultraviolet (UV) light which can be used for controlled modification and patterning of organic and biological surfaces. In this context, the effect of UV light on alkanethiolate (AT) self-assembled monolayers (SAMs) on gold substrates was studied, with a particular emphasis on its wavelength dependence. The experiments were first performed for the most basic system of non-substituted AT SAMs which exhibited qualitatively similar photooxidation behavior at UV wavelength variation from 254 to 375 nm but a strong decrease of the photooxidation cross-section with increasing wavelength. Based on these results, the possibility of UV-promoted exchange reaction (UVPER) with non-substituted AT SAMs as the primary matrix and azide-substituted ATs as substituents was tested and successfully realized, resulting in the fabrication of mixed SAMs with variable density of the azide tail groups, capable of the subsequent click reaction with various kinds of molecules and functional moieties with alkynyl group. Such a click reaction with several representative substituents was demonstrated. Further, the above approach was extended to oligo(ethylen glycole) substituted AT SAMs serving as protein repelling primary matrix. Combining UVPER and the subsequent click reaction with a biotin-bearing substituent, biorepulsive templates with controlled density of the docking sites for the specific adsorption of biotin-complementary proteins such as avidin and streptavidin were prepared and successfully tested regarding their non-specific and specific protein affinity. This approach was extended to UV lithography, resulting in preparation of custom-designed, gradient protein-adhesion patterns. Finally, based on the results for the OEG-AT SAMs, the effect of UV light on protein-repelling poly(ethylen glycole) (PEG) nanomembranes was studied. It was demonstrated that UV irradiation induces extensive desorption of the PEG material, without photooxidation or other noticeable changes in the chemical composition, biorepelling behavior and hydrogel properties of the residual membrane. This opens a new way of 3D patterning of all-PEG materials, potentially useful for nanofabrication and biotechnology.

Item Type: Dissertation
Supervisor: Zharnikov, Prof. (apl.) Dr. Michael
Date of thesis defense: 4 November 2016
Date Deposited: 08 Nov 2016 08:38
Date: 2016
Faculties / Institutes: Fakultät für Chemie und Geowissenschaften > Institute of Physical Chemistry
Subjects: 540 Chemistry and allied sciences
660 Chemical engineering
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