On your wavelength

Behind the paper: A bioengineering mission that led to a rendezvous with Anderson localization

Posted on behalf of Seung Ho Choi, Michelle Visbal and Young Kim, commissioned by Lina Persechini.
The paper in Nature Communications is here.

Capture

The field of biomedical optics and biophotonics has changed.  We felt it in the community.  “Much that once was is lost”.  This change might have originated from the perception that light in biological media is simply diffusing.  Such long-standing perception made everything seem trivial, which caused scientists and engineers to progressively lose interest in light transport in biological materials and structures.  In this story, we will tell you about the journey that led us to the observation of a totally unexpected linear optical phenomenon in biological systems:  Anderson localization of light (a phenomenon named after Nobel laureate Philip Anderson).

Initially, our research group was busy with realizing naturally occurring lasers (also known as random lasers) from biological and natural materials (such as bone and nacre of seashells).  In 2014, we happened to watch a Korean television news channel that made us come across a fluorescent silkworm.  This fluorescent silkworm opened an exciting prospect for investigating random lasing from a recombinant fluorescent organism.  We decided to fly to South Korea.  After presenting our ambitious proposal for high-tech biogenic lasers to the rural farmers there, we were able to receive the magical recombinant substances.  Using them, we obtained laser-like spectral lines, but was it really a lasing signal?  To address this question, we had to demonstrate additional lasers using different samples (later we realized that our first observation was not lasing).

However, we overlooked the fact that silkworms grow slowly eating mulberry leaves, and that these leaves can be harvested only once a year, in summer. For researchers with tight funding, an even more important issue than the topic of research can be the funding cycle; “To be, or not to be: that is the question”.  At that moment, we had to make a big decision.  We could not wait for the silkworms’ next life cycle to let them spin another batch of fluorescent silk.  Since we were not certain as to whether the silk had the capability to confine light, we decided to study a more fundamental optical phenomenon: Anderson localization of light.  During our random lasing study, we were able to observe a glimpse of extremely strong light–matter interactions from the lustrous reflection of native silk.  To investigate Anderson light localization with a minimal budget, we built our own transmission matrix measurement setup using components that were already comprised in other instruments. We had to combine three academic disciplines:  biomedical engineering, mesoscopic physics and structural biology.

Through our interdisciplinary approach, we held in-depth discussions, in particular with scientists in the field of mesoscopic physics.  When we were addressing peer-reviewers’ comments from hardcore physicists, one of our collaborators said “your work will be published, once your language is understandable to physicists”.  At the submission stage, we didn’t know what this really meant, but after multiple rounds of review, we completely understood it.  From a personal perspective, when combining several academic disciplines, different perceptions coming from different academic disciplines often appear to be conflicting.  Only once they completely understand each other, one discipline can realize the true meaning of the other.  At last, the reviewers in the field of mesoscopic physics were convinced of the experiment, analysis, theory and conclusion in our study.  Following this experience, we dream of a future where everyone realizes the beauty of others by overcoming differences between academic disciplines, religions, national origins, races, sexes and even species (humans and silkworms).

Seung Ho Choi, Michelle Visbal and Young Kim

Reference: Nature Commun. 9452 (2018doi:10.1038/s41467-017-02500-5

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