Bionanoengineering with DNA

show/hide words to know

Bottom-up approach: the development of complex structures from simple and small building blocks...more

Self-assembly: an automatic process in which a molecule or molecules rearrange to form a more complex structure...more

Self-assembly force: an outside energy that allows a molecule or molecules to shift into a more complex structure...more

Nanoscale Forces

Image showing someone trying to hold a magnet down, but it is repulsed away from another magnet.

Parts of molecules can act like magnets, attracting or repelling different parts of molecules. Image by Pieter Kuiper.

You pick up a magnet in each hand and hold them so the bottom of each is facing the other. You move them closer. As you try to push the magnets together, you can feel a force pushing them apart instead. These magnets have two different sides, with different poles. Similar poles will repel each other, but if you flip one over, so that a north and south pole are close to one another, the magnets pull together and connect.

One of the forces that controls the assembly of nanostructures is very similar. Electrostatic forces are the attractive/repulsive forces when parts of the molecules act like magnets. Many molecules used in bionanotechnology are charged (either positively or negatively). These types of forces are important when designing a structure.

Like Oil and Water

The other forces involved are called hydrophobic forces. Hydrophobic force is the attraction between two “fatty” molecules or parts of a molecule. You can try this at home: take a glass of water, and add a few drops of oil to it. Move the water around very gently and, after a while, you should find that most of the oil drops have gathered into one or two larger floating oil drops. What is happening here?

Close up image of oil droplets staying separated from water

Droplets of oil floating together on water. Oil and water don't mix. Click to enlarge.

Well, fatty molecules don’t like to interact with water. (Have you ever heard the term “like oil and water”? They don’t mix.) Because the fatty molecules want to get away from water, when they encounter other fatty molecules, they will come together to form a fatty “pocket”. This lets more of the fatty molecules get farther away from the water.

This hydrophobic force or effect is one of the main driving forces for self-assembly. The hydrophobic effect allows the self-assembled structure to be at its most stable state. The most stable state of a biomolecules is usually a position in which the molecule is the most “relaxed.” This means there isn’t stress or strain on the bonds within the molecule, trying to get it to change shape. So, it can hold that state easily, making it stable.

To build at a nanoscale, you need to understand electrostatic and hydrophobic forces in detail. With this knowledge, you can better predict the self-assembly of structures.

Day gecko image by Anrita1705 via Pixabay.

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Bibliographic details:

  • Article: Nanoscale Forces
  • Author(s): Julio Bernal, Tara MacCulloch
  • Publisher: Arizona State University School of Life Sciences Ask A Biologist
  • Site name: ASU - Ask A Biologist
  • Date published: February 4, 2020
  • Date accessed: June 12, 2024
  • Link:

APA Style

Julio Bernal, Tara MacCulloch. (2020, February 04). Nanoscale Forces. ASU - Ask A Biologist. Retrieved June 12, 2024 from

American Psychological Association. For more info, see

Chicago Manual of Style

Julio Bernal, Tara MacCulloch. "Nanoscale Forces". ASU - Ask A Biologist. 04 February, 2020.

MLA 2017 Style

Julio Bernal, Tara MacCulloch. "Nanoscale Forces". ASU - Ask A Biologist. 04 Feb 2020. ASU - Ask A Biologist, Web. 12 Jun 2024.

Modern Language Association, 7th Ed. For more info, see
Gecko crawling on tree
Sometimes small forces can have big effects. Very tiny forces are responsible for this gecko being able to walk on walls and ceilings.

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