Researchers propose light test to detect hypothetical mirror life

Two molecules can contain exactly the same atoms, in the same order, and still behave differently in a living body. One version of a medicine may cure an illness, while its mirror image may do nothing, or cause harm. Researchers at the University of Strathclyde and Durham University have now sketched a way to check whether a biological sample is built the conventional way or with the mirror-image molecules of a hypothetical form of life called 'mirror life'. That form does not exist today.

The concern is a biosecurity one. Mirror life is considered a low-likelihood but potentially high-severity threat, because artificially created mirror organisms could interact with the natural world in unpredictable ways and potentially evade some of the biological defenses that protect humans, animals and plants. Scientists have called for restrictions on research aimed at creating self-replicating mirror organisms, and governments and international organizations have considered the risks.

The proposed method rests on circularly polarized luminescence, or CPL: light emitted by molecules in a rotating, twisted pattern, which reveals the handedness, or chirality, of the molecules that emit it. The same property of light is already used in everyday objects, such as the stereoscopic effect of 3D movie glasses. The researchers propose fluorescent probes that bind to structures inside cells and produce distinctive CPL signals. Together these signals form a molecular fingerprint indicating whether a sample has the conventional chirality of terrestrial life or its mirror image. To reduce the risk of false results, the paper proposes a panel of probes targeting several biological structures instead of a single measurement.

The technique is not yet a finished test. The team notes that existing CPL instruments, including microscopes, cameras and biological cell plate readers, have already been demonstrated at laboratory scale, in work led at Durham by Professor Robert Pal. A complete mirror-life detection assay, however, has not yet been demonstrated experimentally. The authors present the method as a contingency measure, and stress that it can be developed on conventional biological samples, without making any mirror organism.

For laboratories and authorities charged with monitoring biological risks, the benefit would be a surveillance tool ready before any such organism appears, rather than after. Neither the paper nor its authors give a date for when the approach could be used outside the laboratory, and the next step they describe is validation with conventional samples.