LbL MEMS andProtein Structures
Annie ChengRajesh Kumar
Group: 203-2Sections: 3.10 and 3.11
LbL MEMS
• LbL electrostatic self-assembly strategyo Multi-layer composition
• Material of choice was cationic PDAC and anionic clay sheetso Actuation realized by magnetic over-layer of iron
oxide magnetic nanocrystals deposited on surface
• Created array of clay-polymer-magnetite ultra-thin cantileverso Each cantilever anchored to a silicon substrateo 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 Compositiono 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 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
Questions?
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