Dynamics of Nanoparticles (borrowing, as Nano often does, from

Macromolecular)

Techniques

Problems

Your career = Techniques X Problems

Tomas Hirschfeld: Most people work only on techniques, but not on finding problems. But remember, your career will be the vector cross product of techniques you learn and problems you choose.

This talk concerns

Why do we need dynamics for nanoparticle characterization?

1. Dynamics give us sizeMicroscopy does not always measure size well.Microscopy cannot follow rapid size/shape changes

well—e.g. self-assembly. Microscopy may alter the materials being studied. Small angle X-ray scattering and small angle

neutron scattering are slow, expensive, can damage samples, and sometimes have contrast issues.

2. Dynamics tells us basic informationStability of structures: scaffolds to slow the kT

problemInternal viscosity inside devices: how fast can

nanodevices work?

Dynamics Techniques

DLS = Dynamic light scattering FPR = Fluorescence photobleaching

recovery AUC = Analytical ultracentrifugation DOSY = Diffusion ordered NMR

spectroscopy (not this trip—takes too long to explain)

DLS = Dynamic Light Scattering

• If you look closely at light scattered by a sample, it fluctuates.

• Some of that is just DUST, a nuisance, but some fluctuations are interesting.

• The fluctuations represent how quickly the molecules are moving.

• This is tracked with a “correlation function”

Correlation Function

T

TT

dtttEtET

tEEtg ')'()'(2

1)()0()( lim

Where E(t) is the instantaneous electric field of the scattered light

E(t)

t’

t = 0

t =

<E 2>

0

Thus, correlationFunctions DECAYwith time!

Quick decay = fast mover = small particle

t

g (t )

Slow, big

Fast, small

= decay rate (Hz)

An exponential becomes a sigmoidal curve if you change the x-axis to

logarithmic.

Log( t )

g (t )

Slow, bigFast, small

comes from inflection point.

Dynamic Light ScatteringDynamic Light Scattering

Hv = q2Dtrans + 6Drot

LASER

VV HH

PMT

Hv Geometry Hv Geometry (Depolarized)(Depolarized)

Uv Geometry Uv Geometry (Polarized)(Polarized)

VV

Uv = q2Dtrans

o

nq

2/sin4

PMT

LASER

FPR = Fluorescence Photobleaching Recovery

• First, measure fluorescence: step F• Then photobleach (“erase”) some with

a bright flash of light: step P• Then observe recovery due to

diffusion: step R

The sample has to be fluorescently labeled. Destruction of the label must not damage the nanoparticle.

Fluorescence & Photobleaching

Blue input light

FluorescentSample

Green Detected

Light

Recovery of Fluorescence

Blue input light

FluorescentSample

With FluorescenceHole in Middle

Green Detected

LightSlowly Recovers

Modulation FPR Device Lanni & Ware, Rev. Sci. Instrum. 1982

*

*

*

*

AOM

M

M

D

RR

DM

OBJ

S

PMT

PA

SCOPE

TA/PVD

ARGON ION LASER

* = computer link

IF

X

c

5-10% bleach depth

Cue The Movie

The FPR contrast decay resembles DLS.

t

Contrast (t )

Slow, big

Fast, small

= decay rate (Hz)

AUC = Analytical Ultracentrifugation—a Good Way to Characterize Self-

assembled Species

Rotor (side perspective)Spins at up to 60,000 rpm

Sealed dual beam UV-Vis cell

Sedimentation: simple gravity + thermo

Fb

Fd

Fc

r

r = a; meniscus

r = b; bottom

40 45 50

0

1

2

Igor-Bricker sample

T=20.0oC24,000 RPM v

2=0.73 mL/g

Abs

orba

nce

r2/cm

2

)2

))(~1(exp()()(

222

2

RT

arvMacrc

SvedbergNobel PrizeChemistry, 1926

OK, so let’s look at 5 applications

1. Can we measure the viscosity in a nanoreactor? (DLS)

2. Can we watch a bio/nano particle change? (DLS & LS)

3. Nanotech needs scaffolds: will they stand still? (FPR)

4. Controlling self assembly. (DLS)5. Making a word using one of the most

fascinating of the new nano alphabets. (AUC)Some of this is published: See http://macro.lsu.edu/russo research articles link

ZADS = special form of DLSPTFE latex microrheology of

polyacrylamide gel

1E-6 1E-5 1E-4 1E-3 0.01 0.1 1 10

1.0

1.2

1.4

1.6

1.8

2.0

2470 s

1630 s

1340 s

1130 s

470 sg(

2)()

/sCamins & Russo, Langmuir, 4053, 1994See also: Piazza, Tong, Weitz

1

PTFE Particles

~ 250 nm

More ZADS

0 1000 2000 30000.0

0.2

0.4

0.6

0.8

1.0

Time/s

Fra

ctio

n F

roze

n b

y G

ela

tion

1

Seedlings

Sick Plants And close-up of mosaic pattern.

http://www.uct.ac.za/depts/mmi/stannard/linda.html

1

What we have been trying to do: rotation and translation of a TMV through “random coil” solutions.

Very hard to do right!

1. Cush et al. Macromolecules 1997.

2. Cush & Russo Macromolecules, 2004

(in press, probably December)

1

Drotation ~ -1 & Dtranslation ~ -1

Bottom line: TMV or nanoparticles can report the viscosity more or less accurately in a

small system.

100 1000 10000 100000 1000000 1E71

10

100

T

R

/

cP

Dextran MW

0.76 ± 0.01

(C)

1

“Virions are usually roughly spherical and about 200nm in diameter. The envelope contains rigid "spikes" of haemagglutinin and neuraminidase which form a characteristic halo of projections around negatively stained virus particles. “

Linda Stannard, of the Department of Medical Microbiology, University of Cape Town

http://web.uct.ac.za/depts/mmi/stannard/fluvirus.html

“The Flu” 2

0 2 4 6 8

2.6

2.8

3.0

3.2

3.4

3.6

3.8

4.0

4.2

4.4

4.6

4.8

5.0

5.2

5.4

= 45o

= 90o

From910921 ph 7.4 900 ± 30 Å From924935 ph 5 xxx min 1330 ± 30 Å From938949 ph 5 xxx min 1710 ± 50 Å

ln(I

/arb

itrar

y)

q2/1010cm2

Guinier plots. ILS vs. q2

pH 7.4 900 ÅpH 5 1330 ÅpH 5 later 1710 Å

2

Dynamics of Flu “opening up”: Addition of citric acid for pH change is shown by the line

at time 0.

-400 -200 0 200 400 600 800 1000 1200 14000

200

400

600

800

1000

1200

Rh

Rh /

Å

t /s

0

20

40

60

80

100

120

140

160

180

200

Intensity

Intensity/kcps

2

Sproing!!!

pH

2

Forms a reversible gel scaffold.

O

O

PSLG: poly(stearyl-L-glutamate)

3

Temperature-ramped modulation FPR

0 1000 2000 30000

1

2

3

4

Schmidtke et al.

Figure 6

scan1062

Melt at 30.9oC

2040 s

start ramp @ 0.3oC/min

Con

tras

t (A

C/D

C)

t (seconds)20 30 40 500

100

200

300

400

500

600

700

Schmidtke et al.Figure 7

combinehigh

DDSC

TRFPR: 30.7oC

DSC

DS

C (W

) or

DD

SC

+60

0 ( W

/ o C

)

T/ oC

20 30 40 50

1

2

AC

/DC

3

Everything can move, yet the structure remains.

Means that even though you have built a scaffold (for example, to grow artificial skin or hold a sensor or drug delivery nanomachine in place) and even though it may seem to hold its shape, you must be careful!

This kind of molecular view of gelation is not available from mechanical methods, such as rheology.

3

Observe Control of Self-assembly

Bolaform amphiphiles have a dumb-bell shape

hydrophilichydrophilic

hydrophobic

4

OH

OH

OH

NH

OH

OH

OHNH

OO

O

OH

OH

OH

NH OH

OH

OH

NH

OH

OH

OHNH

OO

O

OH

OH

OH

NH

Arborol example: [9]-10-[9]

9 watery hydroxyl groups

10 oily methylene groups

4

Arborol properties

• Dissolve in warm water.

• Gel on cooling—Why? How?

• Apparently, they are “real gels”

• Fibers inside the gels .

• Self-assembly • Reversible

4

Why do we care?

Self-assembling systemReversibleEasy to vary headgroup and core sizePossible applications in:• Porous media• Stationary phase for separations• Reversible, rigid rods dynamic liquid

crystals we can manipulate• Disease-inspired microfluidics—can we

simulate sickle cell anemia?

4

Dendrimer self-assembly challenges

• Can we control self-assembly? Synthesis!

• How would we know? Analysis!• What if we did? New Physics &

Materials!

Terminator

4

Self-assembly of [9]-12-[9] by DLS

Self-assembly of Dilute Arborols—Rh

0 1 2 3 4400

500

600

700

800

900

1000

1100

1200

1300

Rh/

(Å)

Number of Days

[9]-10-[9]only [9]-10-[9] plus [9]-6

Rh got from linear fit of gamma vs q2 of DLS data at five angles: 40, 50, 60, 70 and 90.

4

New problem: Hexaruthenium terpyridyl supramolecular structures

2 is the key monomer for

the supramolecule.

5 aids in Proof of structure.

Newkome et al.Angew.Chem.Int.Ed.1999, 38(24) 3717-21

5

Molecular snowflake by two methods

5

Data on supposed snowflake supports several scenarios, but self assembly

surely occurs

Same Data, Different Analysis0.5% (NMR conc.)

80% @ M=1340 M=325020% @ M=5600 + non-sedimenting stuff

0.006% (low!) M = 2600

5

Write the terpyridyl aggregate in shorthand form.

5

We see evidence of aggregation by SAXS, confirmed by DLS.

nStacked disks?

ContinueIn this wayto make aggregates of aggregates of aggregates etc.

Note that this alphabetretains symmetry similar tothe atomic alphabet

?

5

ConclusionsThe power of DLS, FPR and AUC has been

demonstrated.It was my purpose to familiarize you with

these tools….but maybe I accidentally showed you some good problems to study as well.

Maybe you can see a new vector cross product somewhere.

The terpyridyl ruthenium business is an example of a supramolecule; however, the proponents of supramolecular thinking have less influence than the nano people. So…it must be nano!