The Supramolecular Nano Materials Group Ligand coated metal nanoparticles and quantum dots Francesco Stellacci Department of Materials Science and Engineering frstella@mit.edu
Outline Self-Assembled Monolayers SAM coated nanomaterials Mixed SAM coated nanomaterials Quantum dots
Self-Assembly
Protein Self-Assembly
Molecular Self-Assembly
Thiolated Monolayers on Gold S δ- -Au δ+ bond energy = 1.34 ev However, 2 S - Au bonds are not much stronger than one S - S disulfide bond and one Au - Au metallic bond A monolayer in solution therefore develops an equilibrium dodecane solution 2 * RS - Au RS -SR + Au -Au (surface)
Molecular Self-Assembly
Commensurate vs. Incommensurate
Wetting Properties
Wetting Properties II
Etch Pits and Defects
Phase Separation
Metal Nanoparticles Synthesis Metal Salt (AuHCl 4 ) + HS HS + Reducing Agent (NaBH 4 ) Direct mixed ligands reaction ** Ligand exchange reaction * F. Stellacci, et al. Adv. Mat. 2002, 14, 194 A. C. Templeton, M. P. Wuelfing and R. W. Murray, Accounts Chem. Res. 2000, 33, 27
Characterizing Metal Nanoparticles 3 nm TEM shows atoms in the core STM shows ligands in the shell 2.7 nm
Mixed Self-Assembled Monolayers Au (111) MPA Randomly distributed domains of OT form in a surrounding matrix of MPA HS COOH HS 5 nm OT STM Height Image of OT/MPA Mixed Monolayer on Au(111) R. Smith, S. Reed, P. Lewis, J. Monnell, R. Clegg, K. Kelly, L. Bumm, J. Huthison, P. Weiss. J. Phys. Chem. B 2001, 105, 1119-1122.
Ordered Domains on NPs Hydrophobic/ Hydrophilic Ripples Form by Spontaneous Self- Assembly HS HS MPA COOH OT
Hydrophobic/Hydrophilic Ripples Hydrophilic Region: Carboxylic Acid Terminated Molecules Hydrophobic Region: Methyl Terminated Molecules
Particle Interdigitation Solid interdigitated state ΔH de-int Solid de-interdigitated state
X-Ray Diffraction 2:1 OT:MPA Au np (5:1 Au:ligand) 2:1 OT:MPA (Ag np) (2:1 Au:ligand)
Phase Separation on Nanoparticles HS H S NH 2 Hexanethiol: p-aminothiophenol Ag core OT:MPA O HS OH HS OH OT:Mercaptohexanol OT:MUA HS HS
Core Effect 3 nm
Ripple Spacing in OT:MPA System Morphology ranges from discretely packed domains to defect rich ripples to perfect ripples.
Evolution of Surface Morphology DT:MPA 2:1 OT:MPA 10:1
Solubility and Morphology 4 Domains Ripples Domains 3 Defect-Rich Perfect Ordering Defect-Rich Solubility 2 1 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Note: Solubility Decreases with Increasing %MPA due to Morphology MPA / (OT+MPA)
Ripple Spacing in OT:MPA System Morphology ranges from discretely packed domains to defect rich ripples to perfect ripples.
Surface Chemistry Modification HS OH O HS HS OH O Highly soluble in Toluene Highly soluble in Ethanol
Protein Nonspecific Absorption Proteins can assume a few possible conformations as determined by molecular structure 1) Maximizes exposure of hydrophobic region 2) Minimizes exposure of hydrophobic region Hydrophilic region Hydrophobic region Hydrophilic Surface Hydrophobic Surface Surface composed of Hydrophilic/Hydrophobic Domains
The Nano Lotus Leaf Effect Size of hydrophobic/hydrophilic regions of protein are greater than size scale of ligand domains on the nanoparticles. Proteins are conformationally frustrated and cannot adsorb to nanoparticle surface.
Cytochrome C: a large Protein Protein 24 h Extensive Adsorption of Protein onto Monolayer 3.6 x 3.6 x 13.7 nm Protein 24 h No Adsorption of Protein
Lysozyme: a small Protein Protein 24 h Extensive Adsorption of Protein onto Monolayer 4.5 x 3.0 x 3.0 nm Protein 24 h No Adsorption of Protein
Curvature Effects OT:MPA Mixed Monolayers formed on surfaces of varying curvatures Increasing Curvature 10 nm 10 nm 5 nm 5 nm Flat Au (111) on Mica Au on Si, with 20 nm hemispheres Au film with Au crystals ~ 10 nm Au film with Au crystals ~ 4 nm
Synthesis and Conformation Metal Salt (AuHCl 4 ) + Metal Salt (AuHCl 4 ) + HS HS HS COOH NaBH 4 (AuSR) n NaBH 4 HS COOH Nanoparticles obtained via the two-step method Nanoparticles obtained via the one-step method
Kinetic Effect Au thermally evaporated on Si SAM formed in the absence of (AuSR) n SAM formed in the presence of (AuSR) n
Other Monolayers
Other Monolayers II
Size Control
Optical Properties
Artificial Atoms