Subscribe for 33¢ / day

Q: How many molecules are in a cubic inch?

— Will, 7, Arboretum Elementary School, Waunakee

A: Molecules are formed by atoms bonding together, and there are many different types of molecules that you interact with every day. For example, water and sugar are both molecules.

Each molecule has a different size, so that determines how many would fit in a cubic inch of space. One cubic inch of water contains about 5x10^23 molecules. That means a five followed by 23 zeros. If you were looking at a cubic inch of sugar, that would contain 5x10^22 molecules, so a bit less than water but still a very large number of molecules.

Imagine the thickness of a strand of hair. If you were to lay water molecules across the thickness, you could fit about 1 million molecules. That’s how small molecules are.

Researchers can use microscopes and other techniques to look at a single molecule at a time. Single-molecule research can be powerful because you can see the differences between molecule A and molecule B and compare how different molecules are behaving.

Scientists can use fluorescence to do this work. A fluorescent molecule called a fluorophore is attached to the molecule being studied. You can think of the fluorophore as a flashlight.

A laser is required to essentially “turn on the flashlight” — turn on the fluorophore — so it emits the light. This helps illuminate the molecule that scientists are interested in so they can see it under a microscope.

Katie Lupo is a graduate researcher in the Goldsmith Group in the University of Wisconsin-Madison department of chemistry.