There are many, many ways to measure big forces in the macroscopic things we can see and touch. There are ways to measures forces between atoms in small numbers. In between, there’s a gap.
Now, two research groups have a way there, at the scale of the biting force of the roundworm Caenorhabditis elegans. It’s tiny, with only 959 body cells, nearly a third as nerve cells. It’s famous for studies that led to four Nobel Prizes. Fine, but how hard can it bite?
Piezoelectric materials that report a voltage on being squeezed are too large; the atomic force microscope can’t handle an object so big relative to atoms, and moving, as well. Jennifer Dionne at Stanford and P. James Schuck at Columbia got their groups to coat tiny nanoparticles ‘doped’ with several metals in the rare earths such as thulium.
A special property is that the metal ions can absorb invisible (to us) infrared light, then hang onto the energy for a time sufficient to collect enough to pool that energy and emit red or green light. Moving the ions together a tiny bit with a “smooshing” force makes a big difference in when and how much light is emitted. Voila: C. elegans fed the nanoparticle bites with 80 Mpa of pressure. That’s 80 times more than you and I can do. Bite to light! I call those measurements incredibly clever.
This has been an outreach activity of the Las Cruces Academy, viewable at GreatSchools.org
Source: Physics Today, online, 12 Feb., https://doi.org/10.1063/pt.olhq.pbhu
Image: Wikipedia, Creative Commons
