Ligand coated metal nanoparticles and quantum dots Supramolecular Nano‐Materials Group Ligand coated metal nanoparticles and quantum dots Francesco Stellacci Department of Materials

The  Supramolecular  Nano‐Materials  Group

Ligand coated metal nanoparticles and quantum dots

Francesco StellacciDepartment of Materials Science

and [email protected]

S u N M a G

Outline

• Self-Assembled Monolayers

• SAM coated nanomaterials

• Mixed SAM coated nanomaterials

• Quantum dots

S u N M a G

Self-Assembly

S u N M a G

Protein Self-Assembly

S u N M a G

Molecular Self-Assembly

S u N M a G

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

S u N M a G

Molecular Self-Assembly

S u N M a G

Commensurate vs. Incommensurate

S u N M a G

Wetting Properties

S u N M a G

Wetting Properties II

S u N M a G

Etch Pits and Defects

S u N M a G

Phase Separation

S u N M a G

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

S u N M a G

Characterizing Metal Nanoparticles

2.7 nm

3 nm

TEM shows atoms in the core STM shows ligands in the shell

S u N M a G

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

S u N M a G

Ordered Domains on NPs

Hydrophobic/Hydrophilic Ripples Form by Spontaneous Self-Assembly

SH

MPA

OT

SHCOOH

S u N M a G

Hydrophobic/Hydrophilic Ripples

Hydrophobic Region:

Methyl Terminated Molecules

Hydrophilic Region:

Carboxylic Acid Terminated Molecules

S u N M a G

Solid interdigitated state

Solid de-interdigitated state

ΔHde-int

Particle Particle InterdigitationInterdigitation

S u N M a G

XX--Ray DiffractionRay Diffraction

2:1 OT:MPA Au np(5:1 Au:ligand)

2:1 OT:MPA (Ag np) (2:1 Au:ligand)

S u N M a G

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

S u N M a G

Core Effect

3 nm

S u N M a G

Ripple Spacing in OT:MPA System

Morphology ranges from discretely packed domains to defect rich ripples to perfect ripples.

S u N M a G

Evolution of Surface MorphologyEvolution of Surface Morphology

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

S u N M a G

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

S u N M a G

Ripple Spacing in OT:MPA System

Morphology ranges from discretely packed domains to defect rich ripples to perfect ripples.

S u N M a G

Surface Chemistry Modification

Highly soluble in Toluene

Highly soluble in Ethanol

HS

HS OH

O

HS

O

OH

S u N M a G

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

S u N M a G

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.

S u N M a G

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

S u N M a G

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

S u N M a G

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

S u N M a G

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

S u N M a G

Kinetic Effect

Au thermally evaporated on Si

SAM formed in the absence of(AuSR)n SAM formed in the presence of (AuSR)n

S u N M a G

Other Monolayers

S u N M a G

Other Monolayers II

S u N M a G

S u N M a G

Size Control

S u N M a G

Optical Properties

S u N M a G

Artificial Atoms

S u N M a G