Nanoparticle technique gauges bite force in tiny C. elegans worms

A team of materials scientists, physicists, mechanical engineers, and molecular physiologists at Stanford University have developed a nanoparticle technique that can be used to measure force dynamics inside a living creature, such as Caenorhabditis elegans worms biting their food.

In their paper published in the journal Nature, the group describes how they used infrared radiation to excite luminescent nanocrystals in a way that allowed the energy levels of cells inside a C. elegans worm to be measured.

Andries Meijerink, with Utrecht University, has published a News & Views piece in the same journal issue, outlining the work done by the team in California.

As Meijerink notes, being able to measure forces inside living creatures could go a long way toward a better understanding of internal molecular processes. Such efforts have thus far been stymied by the need for remote sensing over variable ranges and scales. In this new study, the research team has found a way around such problems, and they have measured the force of the muscles inside the digestive tract of C. elegans.

The work built on prior research that showed that light from luminescent molecules can be used for remote sensing if the emission spectrum is impacted by certain physical changes, such as in temperature or pressure. They embedded erbium and ytterbium nanocrystals in tiny polystyrene spheres approximately the size of bacteria and then fed them to C. elegans worms. The size of the spheres allowed them to pass through the worm’s digestive system until they met a structure known as the grinder, that, like its name suggests, grinds up the food the worm eats.

The grinder, the researchers note, is operated by tensing and releasing underlying muscles. The spheres introduced by the researchers made their way into such muscles. The researchers then monitored the nanocrystals via a tiny fluorescence-reading microscope as the grinder was activated.

This allowed the team to measure changes to the luminescent molecular spectra as the worm applied its grinder. They were then able to use such changes to calculate how much energy was being used by the worm’s grinder muscle. They found the biting force to be approximately 10 µN.

The research team concludes by suggesting that their work shows that it is possible to measure force dynamics inside living creatures, which they suggest could lead to new approaches to studying internal biological processes.

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