Image: Researchers deploy microscope in a sea-ice sackhole for microbe analysis. [Kelsey Ammondson]

Researchers have developed a holographic microscope to image microbes that thrive in extreme environments, and perhaps even on other planets.

Jay Nadeau from Caltech, US , and colleagues have already captured images and reconstructed videos of bacteria and algae that live in sea-ice brine, in Greenland.

The team now hopes the device will be taken on future search-for-extra-terrestrial-life missions to Mars and beyond.

"Our overarching hypothesis is that motility is a good biosignature," says Nadeau. "We suspect that if we send back videos of bacteria swimming, that is going to be a better proof of life than pretty much anything else."

Nadeau is part of a group of optical engineers, microbiologists and astrobiologists from the 'Motility' group at Caltech , that, in their words: 'want to convince the world that the best way to study bacteria is to watch them swim'.

A motile bacterium (small cell) travels in the wake of a larger eukaryote in this recording taken directly in sea ice brine. [Jay Nadeau/Caltech]

Digital holography uses an array detector to record the optical interference fringes reflected from an object, in order to reconstruct a 3D image.

The latest device, an off-axis digital holography microscope, is based on a robust, stable and compact twin-beam optical set-up with fewer elements that traditional digital holography microscopes.

As the researchers point out, all optics are mounted within commercially available lens tube assemblies to ensure the system is affordable but also mechanically stiff.

Initial tests, within a laboratory freezer, indicated the instrument could resolve motility in single cells at sub-micrometer resolution, down to temperatures of -15°C, at which point motility stopped.

Meanwhile field-testing at Nuuk, in Greenland, proved a success with videos reconstructed from images of bacteria and algae that live in the sea-ice brine.

"Nobody had ever looked at sea-ice organisms immediately after collection like we did," says Nadeau's colleague, Stephanie Rider from Caltech. "Who knows how much samples have been warmed up and cooled down by the time someone studies them?"

Capturing images of microbe motility, from cells only microns in size [Nadeau/Caltech]

Researchers are now developing the microscope's sample chamber further, and hope to scale down the entire device.

They also believe the microscope is an ideal candidate for inclusion on a lander going to Mars, Jupiter's moon Europa or Saturn's moon Enceladus.