TOPICS IN (NANO) BIOTECHNOLOGY Self-assembly 19th January, 2007

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-Assembly the classic ’bottom-up’ approaches idea could be to throw everything together and wait for the structures to self assemble still very much a research topic and true application is a long way off self assembled monolayers on gold and silicon, nanoparticle self assembly, supported lipid bilayers, nanoparticle films, ligand directed assembly etc.

Self-Assembly

Self-Assembled Monolayers

Langmuir Blodgett Films of Lipids

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

Langmuir-Blodgett

Langmuir-Blodgett

Self-assembled monolayers on gold

Gold Self-Assembled Monolayers (SAMs)

Self-assembled monolayers on silicon

Si Self-Assembled Monolayers (SAMs)

Thermal Stability of SAMs

Self-Assembled Monolayers (SAMs)

Polycation/polyanion self assembly

Electrostatic self assembly

Electrostatic self assembly – protein multilayers

Electrostatic self assembly – nanoparticles

Nanoparticle self assembly

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

Nanoparticle Films

Ligand Directed Assembly Bifunctional ligand nanoparticle substrate + +

Natan, M. J.; et. al. Chem. Mater. 2000, 12, Tapping mode AFM (1mm x 1mm) of HSCH 2 CH 2 OH linked Au colloid multilayers: (A) monolayer; (B) 3 Au treatments; (C) 5 Au treatments; (D) 7 Au treatments; (E) 11 Au treatments. Monolayer formed by adsorption of Au particles on 3- mercaptopropyltrimethoxysilane derivatized SiO 2 surface Multilayers constructed by immersion in a 5mM solution of 2-mercaptoethanol for 10 min. followed by immersion in Au particle solution for 40 – 60 min. Ligand Directed Assembly

Electrostatic Assembly Polycationic polymer Very stable in most solvents Control inter-layer spacing Conductive, semiconductive, or insulating Shipway, A.N.; Katz, E.; Willner, I. CHEMPHYSCHM. 2000, 1,

Convective Self Assembly Definition : Particles are allowed to freely diffuse. As the solvent evaporates, particles crystallize in a hexagonally close-packed array. Optimize : Particle concentration Particle/Substrate charge Evaporation Top View Colvin, V.L.; et. al. J. Am. Chem. Soc. 1999, 121,

Photolithography Patterning Typically pattern the capture monolayer followed by particle adsorption Few examples of patterning after nanoparticle deposition SEM images showing lithographically defined patterned nanoparticle films with combination of spin-coating driven self-assembly of nanoparticles, interferometric lithography (IL) and reactive ion etching (RIE): (a)photoresist pattern above blanket nanoparticle layer; (b)nanoparticle pattern after etching and photoresist removal; (c)photoresist pattern; (d)nanoparticle pattern after etching and photoresist removal; (e)-(f) 2D isolated discs.

Photolithography Patterned Nanoparticles SEM image of Au nanoparticles adsorbed onto a patterned (3- mercaptopropyl)- trimethoxysilane monolayer on SiO 2 coated Silicon wafer. AFM image (80 mm x 80 mm) of a three-layer coating of nanoparticles followed by photopatterning.

Electron Beam Lithography Typically: –coat substrate with polymer film –write pattern with e - beam –dissolve exposed polymer –evaporate metal into “holes” Somorjai, G. A.; et. al. J. Chem. Phys. 2000, 113(13),

Images of Nanoparticle Arrays formed by Electron Beam Lithography AFM and SEM of Pt nanoparticle array. Particles are 40nm in diameter and spaced 150nm apart. Spin-coat PMMA on Si(100) wafer with 5nm thick SiO 2 on surface. Beam current: 600pA Accelerating Voltage: 100dV Beam diameter: 8nm Exposure time: 0.6  s at each site Pt deposition: 15 nm by e - beam evaporation

Nanosphere Lithography Hulteen, J.C.; Van Duyne, R.P. J. Vac. Sci. Technol. A 1995, 13(3), (A)Representation of a single-layer nanopshere mask formed by convective self assembly. (B)Illustration of the exposed sites on the substrate with single-layer mask (C)AFM image (1.7mm x 1.7mm) of Ag deposited on mica with a mask of 264nm diameter nanoparticles. Mask preparation: Spin coat 267 nm polystyrene nanoparticles at 3600 rpm. Deposition: Ag vapor deposition Mask removal: sonicate 1-4 min. in CH 2 Cl 2

Microcontact Printing PDMS stamp to “ink” a capture monolayer on a substrate followed by nanoparticle adsorption PDMS stamp to “ink” the nanoparticles directly onto the substrate Shipway, A.N.; Katz, E.; Willner, I. CHEMPHYSCHM. 2000, 1, Side View Top View

AFM of Microcontact Patterned Nanoparticle Array Natan, M. J.; et. al. Chem. Mater. 2000, 12, AFM scan (10  m x 10  m) of microcontact printed Au surfaces. HOOC(CH 2 ) 15 SH is initially stamped on substrate. The surface is then exposed to 1.0 mM 2-mercaptoethylamie followed by exposure to a 17nM solution of 12nm Au nanoparticles.

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