topics in (nano) biotechnology self-assembly 10th june 2003
TRANSCRIPT
TOPICS IN (NANO) BIOTECHNOLOGY
Self-assembly
10th June 2003
Nano Chemistry?Nano Chemistry?
Atoms Molecules MacromoleculesProtein, DNA..
Cells
10-9 m10-10 m 10-6 m 1 mNano
Bottom up building-up of structures!
Self-AssemblySelf-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)Self-Assembled Monolayers (SAMs)
Self-Assembled Monolayers (SAMs)Self-Assembled Monolayers (SAMs)
Self-Assembled Monolayers (SAMs)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)Mixed Self-Assembled Monolayers (SAMs)
Self-Assembled Monolayers (SAMs)Self-Assembled Monolayers (SAMs)
AmphiphilesAmphiphiles
AmphiphilesAmphiphiles
Micelles form at CMC - this can be modelled and easily controlled
They can form direct or reverse micelles depending on solvent nature
Amphiphiles on WaterAmphiphiles on Water
Micelles, liposomes and other self-assembled structures
WATER
Hydrophobic tailHydrophilic head
S
S
O
O
O
S
S
O
O
O
S
S
O
O
O
S
S
O
O
O
n
Water
Air
O
O
O
O
O
O
Hydrophobic groups
Conjugated -electron system
Hydrophilic groups
-stacking of adjacent polymers
Air
WaterWater
Air
Space filling model
A.
B. C.
J. Am. Chem.Soc. 120, P. 7643,(1998)
Langmuir-BlodgettLangmuir-Blodgett
0 1000 2000
0
10
20
30
40
50
(m
N/m
)
Area (Å2/cluster)
Compression isotherm
1. Spreading
3. Transfer
2. Compression
Langmuir-BlodgettLangmuir-Blodgett
Metal NanoparticlesMetal 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
n
p
pN1
2 )210(1
1, 13, 55, 147, 309, 561 etc.
3-7 nm
SS
AuS
S
SSS
S
SS
S = CnH2n+1S
x
x X = OH, DNA, OPV etc.
Ligand Stabilized Gold NanoparticlesLigand Stabilized Gold Nanoparticles
• Ligand ExchangeLigand Exchange
Ligand MobilityLigand Mobility
+ +
Ligand Stabilized Gold NanoparticlesLigand Stabilized Gold Nanoparticles
Potential Applications ofPotential Applications ofMonolayer Protected NanoparticlesMonolayer 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
SuperstructuresSuperstructures
Collective properties Site energies, interparticle coupling strength, lattice dimensionsControl of superstructure, 2D nanoarrays(Nanoalloys)
DNA + Gold NanoparticlesDNA + Gold Nanoparticles- Molecular Recognition- 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-LayerLayer-by-Layer
+ + + + + + +
--
+ +
- - - - - - - - -
+ + ++ +
+ + + + ++ +
- - - - -
+ + + + + + +
--
+ +
- - - - - - - - -
+ + ++ +
+ + + + ++ +
- - - - -
and a couple by Katakis….
Spatial control - many publications by Frank Caruso
Branched DNABranched 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 scaffoldDNA 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
DendrimersDendrimers
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
DendrimersDendrimers
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.
DendrimersDendrimers
Application in biosensors, bioreactors, biocatalysis, drug delivery, diagnostics, MRI imaging, gene therapy...
HomeworkHomework
Select one method of self-assembly each and describe it and find an application (one page maximum).