Gold

Module Outcomes

Image: British museum

Module Outcomes• Have an awareness of origins/history of gold as a

precious metal and its use in medieval times• Have an understanding of bulk properties of gold

(including metallic structure)• An awareness that properties of gold change at the

nanoscale• Understand how gold nanoparticles are produced in a

school laboratory• Define a colloidal solution

• Explain why gold has different colours in stained glass windows (in terms of size and shape of nanoparticles)

• Have an appreciation of how gold nanoparticles are being used in medical applications.

Gold Is Valuable

• Gold is a soft metal usually alloyed in jewellery to give it more strength, and the term carat describes the amount of gold present (24 carats is pure gold)

• Gold for jewellery can be given a range of hues depending on the metal with which it is alloyed (white, red, blue, green etc.)

• Jewellery consumes around 75% of all gold produced.

Use in Jewellery

Images top to bottom: Steve Evans @ flickr, jamesgroup @ stock.xchng

Gold Is ValuableOther uses

• Metallic gold is applied as a thin film on the windows of large buildings to reflect the heat of the Sun's rays

• Gold electroplating is used in the electronic industry to protect their copper components and improve their solder ability.

Activity 1What do we know about gold?

• Describe the bulk properties of gold

• Where is gold positioned on the periodic table? To which group does it belong?

• Using a box of oranges and a bag of smarties describe the metallic structure of gold.Images top to bottom: José Luis Sánchez Mesa @ flickr, Craig Jewell @ stock.xchng

Understanding The Properties of Gold

Properties of Metals

• lustrous–they have a shiny surface when polished• Malleable–they can be hammered, bent or rolled into any

desired shape• Ductile–they can be drawn out into wires • good conductors of heat and electricity• generally have high densities• have a range of melting points but most are quite high• are often hard and tough with high tensile strength,

meaning that they offer high resistance to the stresses of being stretched or drawn out and therefore

• do not easily break.

Understanding The Properties of Gold

Gold

• Gold is metallic, with a yellow colour when in a mass

• It is a good conductor of heat and electricity

• It is inert-unaffected by air and most reagents

• It is the most malleable and ductile metal

• Extensively used in jewellery.

Image: © Dorling Kindersley

Understanding The Properties of Gold

Metallic Structures• The Metallic bonding in gold

may be compared to an orange stall

• The oranges represent the fixed, closely packed cations in the lattice

• Electrons (represented by the smarties) may be found moving freely in the spaces between the oranges – this is why gold is a good conductor.

Image: © Dorling Kindersley

Understanding The Properties of Gold

So that’s bulk gold, BUT…Are the properties of gold the same at the nanoscale?

Experiment 1 Making Gold Nanoparticles

Watch Video 1 and then conduct the experiment.

Image: Courtesy RMIT and St.Helena

What Is Colloidal Gold?• Colloidal gold is nanoparticles of pure gold

suspended in water or a solution. The particles are approx a few nanometers in diameter (approx 10 to 50 nm)

• These particles are so small they can only be seen by the most powerful electron microscopes available today

• If you shine a laser beam through the colloidal solution the particles will scatter light.

What Is A Nanoparticle?A nanoparticle is an entity with a width of a few nanometers to a few hundred, containing tens to thousands of atoms.

Image: Schatz Group, Northwestern University

Calculating The Size Of The Nanoparticles

Images: Schatz Group, Northwestern University

Watch Video 2 on calculating the size of nanoparticles.

1. List and briefly explain the three methods used to determine the size of gold nanoparticles

2. Which method is the most accurate?

Gold Has Been Around For Ages

Image: Courtesy F. Calati

• Medieval artisans were the first nanotechnologists

• They made stained glass by mixing gold chloride into molten glass

• They created tiny gold spheres, which absorbed and reflected sunlight in a way that produces a variety of colors

• They knew that by putting varying, tiny amounts of gold and silver in the glass, they could produce the effects found in stained-glass windows.

The Lycurgus Cup

Image: British museum

The Lycurgus Cup made by the Romans dates to the fourth century AD. One of the very unusual features of the Cup is its colour.

When viewed in reflected light, (in daylight) it appears green.

When a light is shone into the cup and transmitted through the glass, it appears red.Optional Research activity: Dichroic glass was used to make this cup, find out what property this glass has.

Size & Shape Determines Colour

Images: Dr. Chad A. Mirkin, Northwestern University

Gold particles in glass25 nm — red reflected50 nm — green reflected100 nm — orange reflected

Colour

Optional Research activity: Surface Plasmon Effect

• Nanoparticles often have unexpected visible properties because they are small enough to scatter visible light rather than absorb it

• Gold nanoparticles appear deep red to black in solution. In fact a whole range of colours can be observed depending on the size of the gold nanoparticles

• The distance between particles also effects colour. Surface plasmon resonance is the term used by nanotechnologists to describe this effect.

5nm clusters of Gold

Bulk Gold Vs Nano Gold

• Is shiny • Always gold in colour• Is inert• Conducts electricity

Bulk Gold

• Vary in appearance depending on size and shape of cluster

• Are never gold in colour• Are found in a range of colours• Are very good catalysts • Are not “metals” but are semiconductors.

Gold Particles

Bulk & Nano

Bulk & Nano

Reflection Of Light

Reflection Of Light

What If?…you could use gold to detect

meningococcal infection before it progressed too far?

Image: Courtesy of Meningococcal Education, meningococcal.org

You Can!

Image: Courtesy of Nanotechnology Victoria Pty Ltd

Victorian nanotechnology venture Quintain NS is working on a meningococcal diagnostic test that uses gold nanoparticles.The test allows for detection of meningococcal disease in less than fifteen minutes compared to the current tests which can take up to 48 hours.

Using Nanogold in Diagnosis

Image: Courtesy Bridge8/Flinders University

1. What happens when salt is added to the red gold nanoparticles?

2. What does the animation demonstrate?

Watch Video 3 on the coupling of gold nanoparticles

Why All The Fuss Over Nanogold?

• They offer promise in medicine.• For sensitive diagnostic tests and novel treatments in

the detection of Alzheimer’s disease by finding a protein in spinal fluid

• Nanobullets that heat up and kill cancer cells

• They offer promise in computing/electronics/printing

• In data storage where gold nanoparticles will be used to increase the speed at which data can be written

• Nanogold Conductive Inks.

Revision1. What is a gold nanoparticle?2. What are the traditional ways for

synthesizing gold nanoparticles?3. How do you determine the size of a

gold nanoparticle?4. Why are gold nanoparticles so

important in medical research?