TOPICS IN (NANO) BIOTECHNOLOGY Self-assembly

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

2. 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

3. 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.

4. Self-Assembly

5. Self-Assembled Monolayers

7. Langmuir Blodgett Films of Lipids

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

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

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

11. Langmuir-Blodgett

12. Langmuir-Blodgett

14. Langmuir-Blodgett

15. Self-assembled monolayers on gold

16. Gold Self-Assembled Monolayers (SAMs)

17. Gold Self-Assembled Monolayers (SAMs)

18. Gold Self-Assembled Monolayers (SAMs)

19. Self-assembled monolayers on silicon

20. Si Self-Assembled Monolayers (SAMs)

21. Si Self-Assembled Monolayers (SAMs)

22. Thermal Stability of SAMs

23. Self-Assembled Monolayers (SAMs)

24. Polycation/polyanion self assembly

25. Electrostatic self assembly

26. Electrostatic self assembly

27. Electrostatic self assembly

28. Electrostatic self assembly

29. Electrostatic self assembly – protein multilayers

30. Electrostatic self assembly – protein multilayers

31. Electrostatic self assembly – protein multilayers

32. Electrostatic self assembly – nanoparticles

33. Electrostatic self assembly – nanoparticles

34. Nanoparticle self assembly

35. x S S S S S Au S S S S S = CnH2n+1S S x X = OH, DNA, OPV etc. 3-7 nm Ligand Stabilized Gold Nanoparticles

36. Nanoparticle Films

37. Ligand Directed Assembly nanoparticle + substrate Bifunctional ligand +

38. Ligand Directed Assembly • Monolayer formed by adsorption of Au particles on 3-mercaptopropyltrimethoxysilane derivatized SiO2 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. Tapping mode AFM (1mm x 1mm) of HSCH2CH2OH linked Au colloid multilayers: (A) monolayer; (B) 3 Au treatments; (C) 5 Au treatments; (D) 7 Au treatments; (E) 11 Au treatments. Natan, M. J.; et. al. Chem. Mater. 2000, 12, 2869-2881

39. - - - - + + + + - - - - - - - - - - - - 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, 18-52.

40. 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, 11630-11637.

41. 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): • photoresist pattern above blanket nanoparticle layer; • nanoparticle pattern after etching and photoresist removal; • photoresist pattern; • nanoparticle pattern after etching and photoresist removal; • (e)-(f) 2D isolated discs.

42. Photolithography Patterned Nanoparticles SEM image of Au nanoparticles adsorbed onto a patterned (3-mercaptopropyl)-trimethoxysilane monolayer on SiO2 coated Silicon wafer. AFM image (80 mm x 80 mm) of a three-layer coating of nanoparticles followed by photopatterning.

43. 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), 5432-5438.

44. Images of Nanoparticle Arrays formed by Electron Beam Lithography Spin-coat PMMA on Si(100) wafer with 5nm thick SiO2 on surface. Beam current: 600pA Accelerating Voltage: 100dV Beam diameter: 8nm Exposure time: 0.6ms at each site Pt deposition: 15 nm by e- beam evaporation AFM and SEM of Pt nanoparticle array. Particles are 40nm in diameter and spaced 150nm apart.

45. Nanosphere Lithography • Representation of a single-layer nanopshere mask formed by convective self assembly. • Illustration of the exposed sites on the substrate with single-layer mask • 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 CH2Cl2 Hulteen, J.C.; Van Duyne, R.P. J. Vac. Sci. Technol. A1995, 13(3), 1553-1558.

46. Side View Top View 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, 18-52.

47. AFM of Microcontact Patterned Nanoparticle Array AFM scan (10mm x 10mm) of microcontact printed Au surfaces. HOOC(CH2)15SH 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. Natan, M. J.; et. al. Chem. Mater. 2000, 12, 2869-2881

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