Manfred Stamm

Nanostructured and functional polymer surfaces for control of biofunctionality

Previous and current research

The interaction of biomolecules in solution with a solid substrate is quite complex and turns out to determine in many cases the function of the interacting molecules in the particular environment. At the Leibniz Institut für Polymerforschung Dresden (IPF) we focus on the understanding and control of interfaces of polymers which also includes interfaces with biopolymers like proteins or polyelectrolytes. Thus for instance the adsorption of polyelectrolytes and proteins is studied onto differently functionalised surfaces, which may be charged or uncharged, soft or solid, rough or smooth ... In particular we have developed switchable and adaptive surfaces which can change their properties according to solvent, pH, salt or temperature. Gradient surfaces provide different properties at different locations. So the sample surface might be hydrophobic at the left and hydrophilic at the right side with continuously varying wetting behaviour in between. Such a gradient surface may be used for fast screening of protein adsorption, for the separation of liquids or for the control of protein movement at the surface. So we have a toolbox of polymer preparation techniques available, which have been demonstrated to allow control of biomolecules at surfaces.

Scanning probe techniques have been developed to high perfection and allow the visualisation of single molecules when those are adsorbed at a flat surface. In this way the molecules can be characterised at nanoscopic scale, but one can also manipulate and functionalise the single molecules at this level. This offers the possibility to generate nanodevices at ultimately small scale, working with tiny amounts of material. We have obtained for instance an electrically conducting nanowire which spans between two gold electrodes and which is based on a single polymer molecule attached to the electrodes. Synthetic polymers offer fascinating possibilities, since they can be produced with all sorts of functionalities and architectures. Even switching properties at molecular level have been demonstrated: a star-like polymer molecule can have its seven arms stretched away or collapsed in the core depending on environment (see figure).

In addition to dedicated surface chemistry a careful analysis of surface properties is important. The group is nicely equipped in that respect, and composition, structure, conductivity and many properties can be analysed at nanoscopic resolution.

AFM image of star-like polymer molecules adsorbed from toluene on a mica surface. The seven arms of PS are stretched under those conditions, while the seven PVP arms are collapsed in the centre. The situation is reversed after adsorption from acidic water. The size of each individual molecule is about 150nm.

Future prospects and goals

Our work aims at the understanding and control of the interaction of the biosystem with synthetic surfaces. One main project therefore deals with the preparation of model surfaces of well defined functionality, where different (bio-)molecules are investigated with respect to their adsorption and desorption behavior in different environment. This includes differently charged polyelectrolytes, but also model proteins in a systematic way. The use of gradient surfaces and fast screening techniques will help to come to some fundamental understanding. In a second project we want to use single molecules attached to the surface to act as sensors for adsorption of biomolecules utilising specific recognition processes. This requires functionalisation of molecules at nanoscopic level as well as the use of highly sensitive detection techniques. As a perspective we aim at the development of a sensor which provides single molecule sensitivity and selectivity at nanoscopic scale in a microfluidic cell.

Finally we want to control the movement of motor proteins on a synthetic surface utilising adjustable surface interaction and gradient surfaces.

About

Selected publications

P. Uhlmann, N. Houbenov, N. Brenner, K. Grundke, M. Stamm. In-situ Investigation of the Adsorption of Globular Model Proteins on Stimuli Responsive Binary Polyelectrolyte Brushes. Langmuir, Special Issue: "Stimuli Responsive Materials: Polymers, Colloids ans Multicomponent Systems", 23 (1), 57-64 (2007)

L. Ionov, A. Sidorenko, K.-J. Eichhorn, M. Stamm, Stimuli-Responsive Mixed Grafted Polymer Films with Gradually Changing Properties: Direct Determination of Chemical Composition, Langmuir, 21, 8711-8716 (2005)

L. Ionov, M. Stamm, S. Diez, Size Sorting of Protein Assemblies Using Polymeric Gradient Surfaces, Nano Letters, 5, 1910-1914 (2005)

P. Uhlmann, L. Ionov, N. Houbenov, M. Nitschke, K. Grundke, M. Motornov, S. Minko, M. Stamm, Sufrace functionalization by smart coatings: Stimuli-responsive binary polymer brushes, Progress in Organic Coatings, 55, 168-174 (2006)

V. Bocharova, A. Kiriy, H. Vinzelberg, I. Mönch, M. Stamm, Polypyrrole Nanowires Grown from Single Adsorbed Polyelectrolyte Molecules, Angewandte Chemie, 117, 6549-6552 (2005)

A. Kiriy, G. Gorodyska, S. Minko, C. Tsitsilianis, M. Stamm, Single Molecules and Associates of Heteroarm Star Copolymer Visualised by Atomic Force Microscopy, Macromolecules, 36, 8704 (2003)

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