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LbL MEMS andProtein Structures Annie Cheng Rajesh KumarGroup: 203-2 Sections: 3.10 and 3.11
LbL MEMS • LbL electrostatic self-assembly strategy • Multi-layer composition • Material of choice was cationic PDAC and anionic clay sheets • Actuation realized by magnetic over-layer of iron oxide magnetic nanocrystals deposited on surface • Created array of clay-polymer-magnetite ultra-thin cantilevers • Each cantilever anchored to a silicon substrate • Moves in response to an external magnetic field
LbL Lithography Steps • Spin-coat positive resist on a silicon wafer • Create channel using photo lithography • Expose all areas with UV except cantilever areas • LbL deposit polymer-clay-magnetic nanocrystal multilayer • Remove the UV exposed resist with developer • Remove unexposed resist with acetone • Result is free standing cantilevers
Application • Self-assembled cantilever arrays have wide range of: • Composition • Size • Shapes • Applications • Sensors (chemical) • Actuators • Incorporation of intact and functioning biological molecules and assemblies into synthetic materials
Optical images of the cantilever before and after applying a magnetic field
Trapping Active Proteins • Enzymes and DNA • bear multiple charged groups • can be deposited in a polyelectrolyte multilayer • can be layered with the retention of function • molecules are bound only by charged groups on the outside of the molecule
Trapping Active Proteins • Electrostatic LbL • has been used to form multilayers containing P450 (enzyme that converts olefins to epoxides) • can fit other substrates in the enzyme's cavity like benzene and styrene (toxic) • we call this enzymatic non-specificity + Olefin Ozin and Arsenault, Royal Society of Chemistry, 2005.
PAMAM/Hb Multilayer • LbL G4 polyamidoamine (PAMAM) with heme protein • Heme protein can be Hb, Mb, Cat • Polyelectrolyte thin film layers can be self-assembled by LbL adsorption of oppositely charged segments • Dip in alternate protein solutions until desired bilayer number reached • Control of film thickness Shen and Hu, Beijing Normal University, 2005.
Structure and Properties of PAMAM 4th generation (G4) 3rd generation (G3)
Effects of pH • Self-assembly depends fundamentally on pH of system • Different isoelectric points (pI) for proteins • pH 9.0 vs. pH 5.0 - self-assemble in both cases of opposite charge and like charge, respectively • pH 5.0 - contribution of Asp and Glu • Opposite charged species favoured but NOT required
Electroactivity • Film thickness plays role in determining electroactivity • Films closest to electrodes are most electroactive • Successive layers become less and less electroactive • Distance between Hb and electrode is crucial for effective electron exchange
Further Applications • electrochemical bioreactors • biosensors • non-specific catalysis