topics in (nano) biotechnology self-assembly 10th june 2003

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).