Structure Formation, Melting and the

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Structure Formation, Melting and the Optical
Properties of Gold/DNA Nanocomposites
Sung Yong Park and David Stroud
Department of Physics, Ohio State University,
Columbus, OH 43210.
Work Supported by NSF DMR04-13395 and
DMR01-04987. Calculations carried out using
facilities of the Ohio Supercomputer Center
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1. Introduction
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DNA/Au nanoparticle colloids and linking strands
Linker DNA
Linker DNA
R. Elghanian, et. al., Science 277, 1078 (1997).
R. Jin, et. al, J. Am. Chem. Soc. 125, 1643
(2003).
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Recent Experiments
Particle-size dependence of Melting
Measured Melting Curves
DNA/Au
DNA only
Particle diameter
DNA only
DNA/Au
R.Elghanian, et. al., Science 277, 1078 (1997).
C.-H. Kiang, Physica A 321, 164 (2003).
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Recent Experiments Rebound Effect
R. Jin, et. al, J. Am. Chem. Soc. 125, 1643
(2003).
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2. Calculation of Optical Properties
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Maxwells Equations
Strategy Consider each particle as a single
dipole
Comparison DDA with more accurate method (89
13nm Au particle)
K.L. Kelly, et. al, CSE, (2001).
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3. Structure at low temperature
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Recipe for Reaction Limited Aggregations
1. Irrevesible process of bonding
2. Slow reaction (fractal dimension 2.1)
Cf. DLCA (lower fractal dimension)
At low T, this system satisfies these conditions.
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TEM Images of Linked DNA Gold Nanoparticles
Aggregate of 13 nm diameter DNA/gold
nanocomposites
Increased magnification image
http//www.chem.nwu.edu/mkngrp/view1.html
Comparison with fast process Gold-MUA
nanoparticles (mercaptoundecanoic acid)
Y. Kim, et. al, Nano Lett. 1, 165 (2001).
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Morphology dependence of extinction cross section
?
Experiment
Theory
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Comparison of size dependence of the extinction
cross section
RLCA cluster
Simple Cubic Cluster
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4. Melting Transition
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My strategy for explaining the results in
experiments

• Model the system as simply as possible

1. DNA hybridization

• Two-state model

• Multiple link per bond effect

2. Cluster configuration at given temperature T

• Bond percolation model

• Reaction limited cluster aggregation model

3. Calculation of Extinction Cross Section

• Discrete Dipole Approximation (Draine Flatau,
  1994)

• Dilute cluster limit

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1. DNA hybridization
Two State Model
probability that DNA pair remains hybidized is
Concentration of duplex
Total concentration of DNA
We treat p as static probability.
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Particle-size dependence of avg. no of DNA per
bond ltngt
1. DNA hybridization
multiple DNA per bond effect
Prob. that pair of Au particles have gt 1 DNA
links
Particle diameter
Temperature dependence of Peff
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My strategy for explaining the results in
experiments

• Model the system as simply as possible

1. DNA hybridization

• Two-state model

• Multiple link per bond effect

2. Cluster configuration at given temperature T

• Bond percolation model

• Reaction limited cluster aggregation model

3. Calculation of Extinction Cross Section

• Discrete Dipole Approximation (Draine Flatau,
  1994)

• Dilute cluster limit

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Schematics of melting for a regular square lattice
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Our model melting of a regular simple cubic
cluster
Bond percolation threshold
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My strategy for explaining the results in
experiments

• Model the system as simply as possible

1. DNA hybridization

• Two-state model

• Multiple link per bond effect

2. Cluster configuration at given temperature T

• Bond percolation model

• Reaction limited cluster aggregation model

3. Calculation of Extinction Cross Section

• Discrete Dipole Approximation (Draine Flatau,
  1994)

• Dilute cluster limit

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Calculation of extinction cross section
Using Discrete Dipole Approximation (DDA)
Dilute Cluster Limit
Temperature dependence of extinction cross
section at 520nm
DNA only
DNA only (higher concentration)
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D
Theory vs. Experiment
Temperature dependence of extinction cross
section at 520nm
DNA only
DNA/Au
DNA only
DNA only
DNA/Au
DNA only (higher concentration)
Theory
Experiment
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5. Effects of Restructuring
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If T increases, bonding becomes reversible. Thus
it becomes compact cluster.
Thus, the model to mimic this feature is needed.

• Bond percolation model

Reaction limited cluster aggregation model
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RLCA case
Radius of gyration
Slopefractal dimension 2.1
With RLCA BP
Long time 3.0
Short time2.1
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P0.9
N MC7000
N MC0
RLCA
N MC7000
MC70000
N MC70000