BIOTEST

Material:
- Nanoparticles of gold
- Watch glass
- Distilled water
- Water with sugar
- NaCl

Procedure: 
We need to know that the nanoparticles of gold change their color when we change the aggregation.
- Take the watch glasses with nanoparticles.
- In the first one put distilled water (don't change the color).
- In the second one put water with sugar (don't change the color).
- In the third one put NaCl (the color change).

Question: 
Why change the color when we put NaCl?
Because the nanoparticles of gold do the aggregation (recombination of the nanoparticles).