There's more than chemistry in detecting life on other planets. While most alien-hunting focuses on chemical signatures—and whether those chemicals detected on other planets match those most likely to add up to life—we should also be focusing on molecular movement. Vibrations. As argued in a recent paper, detecting mechanical motion is a capability already within our reach, yet one that goes untapped.
Biophysicist Sandor Kasas and colleagues at the École Polytechnique Fédérale de Lausanne in Switzerland have developed a new nanomotion detector with the capability for registering the slight, diminutive tremors of mechanical motion found in even the tiniest organisms in response to metabolic activity. Such sensors could be deployed very cheaply as a complement to current biochemical methods.
"Nanomechanical oscillators are extremely sensitive devices that are commonly used to measure very small deflections and forces in the order of the piconewton," Kasas writes in the Proceedings of the National Academy of Sciences. "These powerful and versatile sensors are capable of characterizing biological systems with unprecedented detail and time resolution and are nowadays used for several biological applications."
THE RESULT IS NOTHING LESS THAN A 'LIFE DETECTOR'
Kasas and his team had previously tested their nanosensor on various forms of bacteria. In a timespan of less than 30 minutes they were able to construct an individual bacteria strain's complete antibiogr am (basically a report giving the sensitivity of different sorts of bacteria to different sorts of antimicrobials), based only on motion.
"In fact, the nanomotion detector exploits the fundamental correlation between life and movement," co-author Giovanni Longo said in an email. "Even apparently non-motile systems have a metabolic activity and exhibit small vibrations and fluctuations that can be measured by the nanomotion detector."
"This means that we can study any kind of moving system [...] even without knowing what we are looking at," he added. He gave the example of detecting conformational changes in proteins, which emphasizes how sensitive the nanomotion detector is to incredibly subtle movements.
In the new report, they extend the technique to a wide variety of tiny lifeforms, from prokaryotic to eukaryotic organisms. These systems were artificially activated and repressed using chemical triggers while being monitored via nanosensor, which recorded the creatures' fluctuations over time.
"In all cases, the presence of the living systems on the cantilever surface produced an increase in the amplitude of the measured fluctuations," Kasas and his team write. "The evidence suggests that these fluctuations reflected the metabolic state of the microbes or of the cells. Upon the injection of nutrients into the analysis chamber, the amplitude of the oscillations increased whereas the exposure to inhibiting agents stopped the movements of the cantilever, indicating that the chemical affected the specimens
The detection system is based on an existing scheme called atomic force microscopy (AFM). The basic idea is that some very, very, very tiny probe, on the scale of nanometers, is put near some sample surface, where it's deflected in different ways specific to the composition of the sample surface.
The technique can take many different forms, depending on the forces being probed (electrostatic, chemical bonding, Casimir forces), but concept remains more or less the same. Using AFM it's possible to get a resolution up to 1,000 times better than the fundamental limit of optics.
As Kasas explains, the technique can be used in parallel, where many AFM probes are brought together, forming a lab-on-a-chip that's capable of detecting and characterizing unknown organisms. The result is nothing less than a "life detector."
The nanosensor technique is more than a backup or failsafe for current chemical detection methods, according to the researchers. Mechanical nanosensing might find life ignored by chemical methods. "For instance, it could allow the detection of systems with novel and unexpected metabolic pathways," Kasas writes. "By combining chemical and dynamical measurements, we could achieve an unprecedented depth in the characterization of life in extreme and extraterrestrial environments."
Becky Ferreira contributed additional reporting.