The things one can do with light - and messages in the dark



One day in the future, we may be treating our ailments with microbiotic combinations designed specifically to correct imbalances in our personal microbiomes. We’ll bring our prescriptions on rewritable paper and pay using shimmery optical chips embedded in our cell phone cases or maybe our jewelry. Or we’ll be waiting in our doctor’s office for a simple test of our microbiogenome to see if a light-based nanoparticle delivery treatment is working, while watching iridescent optical displays that change as we move...

These future scenarios (and many more) are all imaginary, but they are imminently feasible, given today’s new stories on basic research at the Weizmann Institute. These are about several things one can do with light, including a disappearing trick or two, and messages hidden in deep, dark places.

Dr. Rafal Klajn’s messages are written with light. Printed images on a unique surface disappear within a few minutes. This system, made of nanoparticles in a gel-like medium, can be rewritten over and over again, so it could, one day, be the basis of rewritable paper. Klajn’s innovation is to put light-sensitive molecules into the medium (rather than engineering the nanoparticles); light exposure turns the gel acidic and leads to a fairly simple chemical reaction with the nanoparticles that causes them to disperse. The molecules Klajn uses, by the way, were developed back in the day (1950s) at the Weizmann Institute, and they have been used, among other things for photosensitive coatings on glasses.

Lighting the medium causes nanoparticles to disperse. Image: lab of Dr. Rafal Klajn Lighting the medium causes nanoparticles to disperse. Image: lab of Dr. Rafal Klajn

A different trick of the light is that of a tiny marine creature commonly known as a sea sapphire. Only a millimeter or so in length, the males of several species flash in brilliant colors ranging from purple to green for a second or so, and in the next they appear to completely vanish from sight. Though we still don’t know if the colors are meant to attract females or warn other males, thanks to Profs. Lia Addadi, Steve Weiner and Dan Oron, and their students Dvir Gur and Ben Leshem, we now know exactly how they perform the trick. Thin, clear crystals on the sea sapphires’ backs are stacked in precise arrays with “spacers” of cellular material holding them in place. It is the tuning of the spaces between the crystals that cause light to be directed in very specific wavelengths. In some species, this creates a glitzy blue iridescence when the light hits them full-on, from above. But when the sea sapphire performs an evasive corkscrew maneuver in the water, the angles are foreshortened as it turns sideways and the reflected light is shifted into the ultraviolet – effectively creating a sort of temporary invisibility cloak.

The precise stacking of the crystals, say the researchers, could lead to the design of artificial nanophotonic structures that would have numerous applications.


Finally, a study that brings to light a signal hidden in a place that daylight never reaches – deep inside our intestinal tracts. We know by now that the thousands of different types of bacteria living there are writing their own messages, which our immune systems interpret to our benefit or detriment. Type 2 diabetes, for example, and inflammatory bowel disease are mediated by the mix of microorganisms in our guts. Today we can work out the makeup of a person’s gut microbiome, but its message is mostly still too faint to read.

Computer scientist Prof. Eran Segal and his research students, working together with the group of Dr. Eran Elinav, an immunologist, have come up with a way of identifying a sort of communiqué within the broad picture. The idea is to sequence all of the DNA in a single sample, a task that is already available today with advanced sequencing techniques. Such techniques break the DNA into pieces and then reassemble the short sequences into long ones. But the group showed that this information can tell you not just quantities each kind of bacterium, but how fast each is reproducing. That’s because many of them are in the process of copying out their genomes in preparation for splitting into daughter cells; thus an overall sequencing will turn up lots of partial genomes. Since each kind of bacterium conveniently starts copying at the same point in its circular genome, one can figure out the first and last sequences to be copied and compute the ratio between the two. That will tell you, from a single sample, how fast each is replicating.

And changes in growth rates, according to the team’s further analysis, is a better indicator of the above-mentioned disorders than any other attempt to read our microbiomic messages, so far.

Three different studies – all basic research – in departments ranging from physics to computer science to chemistry and biology. The future possibilities are endless.














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