Detecting the poisons on frogs nondestructively

For researchers studying the chemical defenses of poison frogs, taking samples of the frogs’ skin poses serious ethical questions. The small amphibians are protected species, and sampling techniques cause stress to the animals or require euthanasia. But now, scientists have developed a way to sample the skins of frogs without harming them: by using a mass spectrometry pen (ACS Meas. Sci. Au 2022, DOI: 10.1021/acsmeasuresciau.2c00035).

Analytical chemist Livia Eberlin of the University of Texas at Austin originally developed the instrument, called the MasSpec Pen, to help surgeons distinguish healthy human tissues from cancerous ones during operations. The sampler uses a drop of water to pick up molecules from the surface of tissues and feeds the drop into an attached mass spectrometer for near-instant identification. Eberlin founded a start-up to develop that diagnostic application, but she also kept looking for other possible uses for the technology. “I love chemical analysis of all sorts,” she says, “especially of complex samples.”

The application to chemical ecology came about in 2014, when Eberlin met biologist Lauren O’Connell of Stanford University, and the two became close friends. O’Connell studies how poison frogs metabolize and sequester alkaloids to use them as chemical defenses. So the pair wondered if Eberlin’s pen could help O’Connell understand the chemicals produced by the tiny critters. Graduate student Anna Krieger modified the system for the frogs by making the tip of the MasSpec Pen large enough to cover glands on the animals’ backs and by adding ethanol to the solvent to help pick up the lipophilic alkaloids.

Bibiana Rojas of the University of Vienna, who researches chemical defenses in amphibians, says the nondestructive technique is “game-changing” and a massive ethical improvement over other methods. Because researchers don’t have to euthanize the animals, the method makes all sorts of new experiments possible, she says. The researchers demonstrated this by following how the chemicals of a single animal changed over time, something which would have previously required sacrificing multiple animals.

The only caveat is that the equipment must be used in the lab. Eberlin’s team is working on combining the MasSpec Pen with portable mass spectrometers to allow scientists to take this type of analysis into the field. O’Connell says that’s important not just for her but also for enabling her local collaborators to do more field research of their own. Meanwhile, other biologists have already contacted Eberlin, wondering if the equipment could also help their research on different animals and plants.

“I’m just happy that Livia wanted to do this crazy project with me,” O’Connell says. “It’s been really fun to collaborate with a friend.”