TOPICS IN (NANO) BIOTECHNOLOGY Self-assembly 10th June 2003

Nano Chemistry? AtomsMoleculesMacromolecules Protein, DNA.. Cells m m10 -6 m1 m Nano Bottom up building-up of structures!

Self-Assembly Carries out many of the difficult steps in nanofabrication - atomic-level modification of structure, using highly developed techniques of synthetic chemistry Inspiration from a wealth of examples in biology - Proteins, DNA, cell-membrane etc. Target structure is thermodynamically stable - structures are relatively defect-free and self-healing Understanding is still at a very elementary level - ”molecular shape” - Enthalpy vs. Entropy - nature of non-covalent forces

Self-Assembled Monolayers (SAMs)

Can exploit mixed SAMs to develop tailor designed materials with gradient of wettability, charge, polarity etc. Mixed Self-Assembled Monolayers (SAMs)

Self-Assembled Monolayers (SAMs)

Amphiphiles

Amphiphiles Micelles form at CMC - this can be modelled and easily controlled They can form direct or reverse micelles depending on solvent nature

Amphiphiles on Water Micelles, liposomes and other self-assembled structures WATER Hydrophobic tail Hydrophilic head

Water Air Hydrophobic groups Conjugated -electron system Hydrophilic groups  -stacking of adjacent polymers Air Water Air Space filling model A. B.C. J. Am. Chem.Soc. 120, P. 7643,(1998)

Langmuir-Blodgett Compression isotherm 1. Spreading 3. Transfer 2. Compression

Langmuir-Blodgett

Metal Nanoparticles -Link between the well-established fields of solid- state and atomic physics (”Clusters, condensed matter in embryonic form”) -how many atoms before bulk? -large surface/volume ratio (negligible in bulk) -electronic quantum number n. Dispersion relation E(n) is composed of a sequence of electronic levels (like atoms and molecules) -Growth spiral (Magic numbers) Mackay icosahedra 1, 13, 55, 147, 309, 561 etc.

3-7 nm S S Au S S S S S S S S S = C n H 2n+1 S x x X = OH, DNA, OPV etc. Ligand Stabilized Gold Nanoparticles

Ligand ExchangeLigand Exchange Ligand Mobility ++ Ligand Stabilized Gold Nanoparticles

Potential Applications of Monolayer Protected Nanoparticles Materials Science Nanoscale Electronics Electrooptics Photography Electronic Inks Molecular Machines Optical Filters and Switches Decorative Applications Thin FIlms Chemical Platforms Catalysis Chemical Sensors Nano-Reactors Biological Sciences Bio-Sensing Drug Delivery Therapeutics Microscopy Labels

Superstructures Collective properties Site energies, interparticle coupling strength, lattice dimensions Control of superstructure, 2D nanoarrays (Nanoalloys)

DNA + Gold Nanoparticles - Molecular Recognition -Mirkin et al.: Nature, 1996, 382, 607

1.4 nm 6 nm agglomerated The change in the optical properties of the solutions reflects the differences in the mean free path of the free electrons in the metal particles.

Layer-by-Layer and a couple by Katakis…. Spatial control - many publications by Frank Caruso

Branched DNA Halliday junction contains four DNA strands bound together to form double helical arms flanking a branch point Take synthetic DNA with programmed sticky ends and they will self assemble into desired structure

DNA as a scaffold Can be used to assemble nanoelectronic components, or for example to position biological macromolecules so as to study their structure by X- ray crystalllography

Dendrimers Dendros = tree Monodisperse polymers of specified size and weight Spherical shapes with a well-defined interior and exterior Discovered in early 1980s by Donald Tomalia

Dendrimers In the divergent methods, dendrimer grows outwards from a multifunctional core molecule In the convergent approach, the dendrimer is constructed stepwise, starting from the end groups and progressing inwards.

Dendrimers Application in biosensors, bioreactors, biocatalysis, drug delivery, diagnostics, MRI imaging, gene therapy...

Homework Select one method of self-assembly each and describe it and find an application (one page maximum).