Size-Dependent Properties How do the properties of gold change at the nanoscale?

Properties of a Material A property describes how a material acts under certain conditions Types of properties Optical (e.g. color, transparency) Electrical (e.g. conductivity) Physical (e.g. hardness, melting point) Chemical (e.g. reactivity, reaction rates) Properties are usually measured by looking at large (~1023) aggregations of atoms or molecules

Optical Properties of Gold Bulk gold appears yellow in color Nanosized gold appears red in color The particles are so small that electrons are not free to move about as in bulk gold. Because this movement is restricted, the particles react differently with light. “Bulk” gold looks yellow 12 nanometer gold particles look red

Optical Properties of Gold

Quantum Effects Classical mechanical models that we use to understand matter at the macroscale break down for… The very small (nanoscale) The very fast (near the speed of light) Quantum mechanics better describes phenomena that classical physics cannot, like… The colors of nanogold The probability (instead of certainty) of where an electron will be found Macrogold Nanogold

Objectives You will: Make gold nanoparticles Determine the color of the nanoparticles Determine the size of the nanoparticles Describe what they will do in the lab. We will walk them through the processes they need to follow to achieve these goals.

Changing the spacing of gold The distance between the gold nanoparticles changes by adding a salt. Notice the color change

SEM picture of colloidal gold

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.

Using colloidal gold Gold nanoparticles are currently manufactured for targeted delivery of biomolecules and drugs to selected cells. The drug appears to accumulate in the tumor but not in the healthy cells.