1. Gold and Silver Nanoparticles
Discovering Mixtures
Gold and Silver Nanoparticles

2. How Big is a Nanometer? Which is measured with a nanometer?
1 meter (m): Doorway ~2 meters high
1 millimeter (mm): Thickness of a dime
1 micrometer (mm): Size of a bacterium
1 nanometer (nm): Diameter of DNA ~2 nm

3. Gold vs. Silver What do you know about gold?
What do you know about silver?
All pieces of gold large enough to see behave the same.
This similar behavior is the result of the physical and chemical properties of the substance. However, these properties are “bulk” properties, properties that are present when the sample is large. Most of the atoms are on the inside of the substance. These atoms determine how the substance will behave.
If the sample is small, very small - on the order of nanometers - then the interactions occurring on the surface of the substance become much more important and we see the results of these surface interactions rather then the bulk interactions. There are much fewer atoms inside the substance compared to those on the outside. The atoms on the surface determine how the substance will behave. The behavior – or properties – of the substance change.

4. Making Gold and Silver
How big are the particles of gold and silver we will make?
We can get an idea by looking at three properties.
Settling
Tyndall effect
Filtering

5. Settling Settle out Remain dispersed See particles on bottom
Large particles (more than 1000 nm)
Remain dispersed
Never see particles on bottom
Smaller particles (less than 1000 nm)
May be clear or cloudy

6. Tyndall Effect Tyndall effect is based on light
scattering when it hits the
particles in the mixture.
Tyndall effect – light scattered
by particles
See line of light
Particles larger than 1 nm
No Tyndall effect – light passes without scattering
No line
Particles less than 1 nm
Tyndall Effect
No Tyndall Effect

7. Classifying Mixtures Doesn’t Settle No Light Scattering Doesn’t Settle
Settling
Tyndall effect
Size
Solution
Less than 1 nm
Colloid
1 to 1000 nm
Suspension
More than 1000 nm
Doesn’t Settle
No Light Scattering
Doesn’t Settle
Light Scattering
Settles
Light Scattering

8. Solutions
Particles in a solution are so small that they do not settle — the movement of molecules is enough to keep them dispersed.
Light passes through these objects without scattering

9. Colloids
Colloidal particles are so small they do not settle — the movement of molecules is enough to keep them dispersed.
Light scatters when passing through.

10. Suspensions
Particles in a suspension are large enough that they will settle. Gravity will overcome the movement of molecules.
Light scatters when passing through.

11. Making Gold and Silver
Groups of four
Follow directions on handout

12. Size Estimate
Use settling and the Tyndall effect to get a size range for the particles of gold and silver.
Settling
Tyndall Effect

13. Get Closer Size Estimate
Filter nanoparticles through a 20 nm filter to see if they will pass through or not.
What would you predict if the particles are larger than 20 nm?
What would you predict if the particles are smaller than 20 nm?

14. Early Nanotechnologists
Medieval glass artists unknowingly became nanotechnologists when they made a color of stained glass by mixing tiny amounts of gold into hot liquid glass.
The gold nanoparticles in the stained glass interact with light in a way that produces a rich color.
One of the rich colors found in the stain glass in several famous medieval churches is due to very small gold particles. Although they didn’t know it, these artists were actually nanotechnologists creating very small pieces of gold.

15. Using Gold Nanoparticles
Gold nanoparticles are currently manufactured for targeted delivery of biomolecules and drugs to selected cells.
Trials are underway using this method to treat cancer cells in mice.
The drug appears to accumulate in the tumor but not in the healthy cells.