The Supramolecular Nano‐Materials Group
Ligand coated metal nanoparticles and quantum dots
Francesco StellacciDepartment of Materials Science
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Outline
• Self-Assembled Monolayers
• SAM coated nanomaterials
• Mixed SAM coated nanomaterials
• Quantum dots
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Thiolated Monolayers on Gold
Sδ- - Auδ+ 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
2 * RS - Au
RS - SR + Au - Au (surface)
dodecane solution
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Metal Nanoparticles Synthesis
Metal Salt (AuHCl4) + HS
Reducing Agent (NaBH4)+HS
Ligand exchange reaction*
Direct mixed ligands reaction**
A. C. Templeton, M. P. Wuelfing and R. W. Murray, Accounts Chem. Res. 2000, 33, 27F. Stellacci, et al. Adv. Mat. 2002, 14, 194
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Characterizing Metal Nanoparticles
2.7 nm
3 nm
TEM shows atoms in the core STM shows ligands in the shell
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Au (111)
STM Height Image of OT/MPA Mixed Monolayer on Au(111)
Mixed SelfMixed Self--Assembled MonolayersAssembled Monolayers
5 nm
Randomly distributed domains of OT form in a surrounding matrix of MPA
MPA
OT
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.
SHCOOH SH
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Ordered Domains on NPs
Hydrophobic/Hydrophilic Ripples Form by Spontaneous Self-Assembly
SH
MPA
OT
SHCOOH
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Hydrophobic/Hydrophilic Ripples
Hydrophobic Region:
Methyl Terminated Molecules
Hydrophilic Region:
Carboxylic Acid Terminated Molecules
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Solid interdigitated state
Solid de-interdigitated state
ΔHde-int
Particle Particle InterdigitationInterdigitation
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XX--Ray DiffractionRay Diffraction
2:1 OT:MPA Au np(5:1 Au:ligand)
2:1 OT:MPA (Ag np) (2:1 Au:ligand)
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Phase Separation on NanoparticlesPhase Separation on Nanoparticles
OT:MPA
OT:MUA
SH NH2SH NH2
Hexanethiol: p-Aminothiophenol
SH OH
O
SH
SH
Ag core
SH
OT:Mercaptohexanol
SHOH
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Ripple Spacing in OT:MPA System
Morphology ranges from discretely packed domains to defect rich ripples to perfect ripples.
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Solubility and Morphology
0
1
2
3
4
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
MPA / (OT+MPA)
Solu
bilit
y
RipplesDomains Domains
Perfect OrderingDefect-Rich Defect-Rich
Note: Solubility Decreases with Increasing %MPA due to Morphology
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Ripple Spacing in OT:MPA System
Morphology ranges from discretely packed domains to defect rich ripples to perfect ripples.
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Surface Chemistry Modification
Highly soluble in Toluene
Highly soluble in Ethanol
HS
HS OH
O
HS
O
OH
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Protein Nonspecific AbsorptionProteins can assume a few possible conformations as determined by molecular structure
Hydrophilic regionHydrophobic region
1) Maximizes exposure of hydrophobic region
2) Minimizes exposure ofhydrophobic region
Hydrophilic Surface Hydrophobic Surface
Surface composed of Hydrophilic/Hydrophobic Domains
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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 frustratedand cannot adsorb to nanoparticle surface.
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Cytochrome C: a large Protein
Extensive Adsorption of Protein onto Monolayer
Protein24 h
No Adsorption of Protein
3.6 x 3.6 x 13.7 nm
Protein24 h
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Lysozyme: a small Protein
4.5 x 3.0 x 3.0 nm
Protein24 h
Protein24 h
Extensive Adsorption of Protein onto Monolayer
No Adsorption of Protein
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Curvature EffectsCurvature Effects
Increasing Curvature
Flat Au (111) on Mica
OT:MPA Mixed Monolayers formed on surfaces of varying curvatures
Au on Si, with 20 nm hemispheres
Au film with Au crystals ~ 10 nm
Au film with Au crystals ~ 4 nm
10 nm 10 nm 5 nm 5 nm
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Synthesis and Conformation
Nanoparticles obtained via the two-step method
Nanoparticles obtained via the one-step method
Metal Salt (AuHCl4) +
NaBH4
HS SH COOH
(AuSR)n
Metal Salt (AuHCl4) + HS
NaBH4
SH COOH
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Kinetic Effect
Au thermally evaporated on Si
SAM formed in the absence of(AuSR)n SAM formed in the presence of (AuSR)n
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