The Supramolecular Nano‐Materials Group
Ligand coated metal nanoparticles and
quantum dots
Francesco Stellacci
Department of Materials Science
and Engineering
frstella@mit.edu
Outline
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• Self-Assembled Monolayers
• SAM coated nanomaterials
• Mixed SAM coated nanomaterials
• Quantum dots
Self-Assembly
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Protein Self-Assembly
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Molecular Self-Assembly
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Thiolated Monolayers on Gold
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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
Molecular Self-Assembly
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Commensurate vs. Incommensurate
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Wetting Properties
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Wetting Properties II
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Etch Pits and Defects
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Phase Separation
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Metal Nanoparticles Synthesis
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Metal Salt (AuHCl4) +
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HS
+
Reducing Agent (NaBH4)
HS
Direct mixed
ligands reaction**
F. Stellacci, et al. Adv. Mat. 2002, 14, 194
Ligand exchange
reaction*
A. C. Templeton, M. P. Wuelfing and R. W. Mu rray, Accounts Chem. Res. 2000, 33, 27
Characterizing Metal Nanoparticles
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3 nm
TEM shows atoms in the core
2.7 nm
STM shows ligands in the shell
Mixed Self-Assembled Monolayers
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Au (111)
Randomly distributed
domains of OT form in a
surrounding matrix of MPA
MPA
HS
COOH
HS
5 nm
STM Height Image of OT/MPA Mixed Monolayer on Au(111)
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.
Ordered Domains on NPs
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Hydrophobic/
Hydrophilic Ripples Form
by Spontaneous SelfAssembly
HS
COOH
MPA
HS
OT
Hydrophobic/Hydrophilic Ripples
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Hydrophilic Region:
Carboxylic Acid
Terminated Molecules
Hydrophobic Region:
Methyl Terminated
Molecules
Particle Interdigitation
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Solid interdigitated state
ΔHde-int
Solid de-interdigitated state
X-Ray Diffraction
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2:1 OT:MPA Au np
(5:1 Au:ligand)
2:1 OT:MPA (Ag np)
(2:1 Au:ligand)
G
Phase Separation on Nanoparticles
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HS
HS
NH 2
Hexanethiol: p-Aminothiophenol
Ag core
OT:MPA
O
HS
OH
HS
OH
OT:MUA
OT:Mercaptohexanol
HS
HS
Core Effect
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3 nm
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Ripple Spacing in OT:MPA System
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Morphology ranges from discretely packed domains
to defect rich ripples to perfect ripples.
Evolution of Surface Morphology
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DT:MPA 2:1
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OT:MPA 10:1
Solubility and Morphology
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4
Domains
Ripples
Defect-Rich
Domains
Perfect Ordering
Defect-Rich
Solubility
3
2
1
0
0.1
0.2
0.3
0.4
0.5
0
MPA / (OT+MPA)
Note: Solubility Decreases with
Increasing %MPA due to Morphology
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0.8
Ripple Spacing in OT:MPA System
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Morphology ranges from discretely packed domains
to defect rich ripples to perfect ripples.
Surface Chemistry Modification
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OH
O
HS
HS
OH
O
Highly soluble in Toluene
Highly soluble in Ethanol
Protein Nonspecific Absorption
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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
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Size of hydrophobic/hydrophilic
regions of protein are greater
than size scale of ligand
domains on the nanoparticles.
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Proteins are conformationally frustrated
and cannot adsorb to nanoparticle surface.
Cytochrome C: a large Protein
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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
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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
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OT:MPA Mixed Monolayers formed on surfaces of varying curvatures
Increasing Curvature
10 nm
Flat Au (111)
on Mica
10 nm
Au on Si, with
20 nm
hemispheres
5 nm
Au film with
Au crystals
~ 10 nm
5 nm
Au film with
Au crystals
~ 4 nm
Synthesis and Conformation
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HS
(AuSR)n
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Metal Salt (AuHCl4) + HS
Metal Salt (AuHCl4)
+
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COOH
NaBH4
NaBH4
HS
Nanoparticles obtained via
the two-step method
COOH
Nanoparticles obtained via
the one-step method
Kinetic Effect
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Au thermally evaporated on Si
SAM formed in the absence of
(AuSR)n
SAM formed in the presence of (AuSR)n
Other Monolayers
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Other Monolayers II
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Size Control
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Optical Properties
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Artificial Atoms
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