Laser-egg interaction shows potential for embryonic spectroscopy

A research collaboration in The Netherlands and Italy has discovered that laser photons have a surprisingly long time of flight within chicken eggs - suggesting that spectroscopy could one day be used to sex bird embryos before they hatch.

Working with the Veenendaal-headquartered company HatchTech, which specializes in egg incubators used by the poultry industry, Vamshi Damagatla from Politecnico di Milano and colleagues have just published a paper in the journal Newton outlining how eggshells behave like integration spheres, bouncing photons around for several nanoseconds.

While that doesn’t sound like a long time, it is enough to produce an optical path length of a couple of meters, meaning that a spectroscopic technique could interrogate the inside of the egg non-destructively.

Ethical dilemma

“After eight days of incubation, both the absorption and scattering properties showed the expected increase due to embryonic vascularization and tissue formation, demonstrating that time-domain diffuse optical spectroscopy can non-invasively detect developmental changes of the embryo,” reported the team.

“Phantom experiments demonstrate that other relevant spectroscopic techniques, such as time-resolved fluorescence and Raman spectroscopy, are subject to the same photon-trapping behavior.”

One potential outcome of that new understanding would be to use an optical technique to “sex” the developing chick inside an egg before it hatches.

Lennard van den Tweel, a researcher at HatchTech who co-authored the study funded via the Horizon 2020 LASERLAB-EUROPE scheme, commented:  

“This previously unobserved phenomenon might help to investigate the content of the egg non-invasively even during the embryo development in fertilized and incubated eggs, addressing the ethical dilemma of culling male chicks.”

Since male chicks cannot lay eggs and don’t grow fast enough to be profitable, more than 300 million of them are slaughtered shortly after birth each year in European hatcheries alone - something widely opposed by animal rights advocates.

Eggshell trap

The key finding outlined in the paper is that the longer-than-expected time of flight is not due to fluorescence, as had been previously suspected, but the result of multiple reflections at the internal eggshell surfaces.

“We were impressed by how efficiently the eggshell traps photons,” said Damagatla. “Two meters is a very long path length, not easily matched by other natural materials.”

The researcher added that discovering the integrating sphere effect helped the team make sense of several earlier studies showing emission characteristics that were initially attributed to fluorescence.

However, before any chicks can be saved further research will be needed to get a better understanding of how light interacts with the molecules found inside eggs.

The researchers now plan to study how the photon effects they observed change throughout a chicken embryo’s developmental process, and the optical properties of each individual component of the egg.  

“The highly scattering nature of the avian eggshell might have evolved to protect the embryo from ultraviolet light or reduce heat dissipation when parents are out foraging,” speculates Damagatla.