The  Supramolecular  Nano‐Materials  Group

Ligand coated metal nanoparticles and quantum dots

Francesco StellacciDepartment of Materials Science

and Engineeringfrstella@mit.edu

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Outline

• Self-Assembled Monolayers

• SAM coated nanomaterials

• Mixed SAM coated nanomaterials

• Quantum dots

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Self-Assembly

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Protein Self-Assembly

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Molecular Self-Assembly

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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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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

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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Core Effect

3 nm

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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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Evolution of Surface MorphologyEvolution of Surface Morphology

OT:MPA 10:1DT:MPA 2:1

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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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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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