LbL MEMS and Protein Structures Annie Cheng Rajesh Kumar Group: Sections: 3.10 and 3.11

LbL MEMS LbL electrostatic self-assembly strategy o Multi-layer composition Material of choice was cationic PDAC and anionic clay sheets o Actuation realized by magnetic over-layer of iron oxide magnetic nanocrystals deposited on surface Created array of clay-polymer-magnetite ultra-thin cantilevers o Each cantilever anchored to a silicon substrate o 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

LbL Lithography Steps

Application Self-assembled cantilever arrays have wide range of: o Composition o Size o Shapes Applications o Sensors (chemical) o Actuators o Incorporation of intact and functioning biological molecules and assemblies into synthetic materials

Structure of the LbL Magnetic Cantilevers

Optical images of the cantilever before and after applying a magnetic field

Trapping Active Proteins Enzymes and DNA o bear multiple charged groups o can be deposited in a polyelectrolyte multilayer o can be layered with the retention of function o molecules are bound only by charged groups on the outside of the molecule

Electrostatic LbL o has been used to form multilayers containing P450 (enzyme that converts olefins to epoxides) o can fit other substrates in the enzyme's cavity like benzene and styrene (toxic) o we call this enzymatic non-specificity Trapping Active Proteins + 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 self-assemble in both cases of opposite charge and like charge, respectively pH 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

Questions?