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?