The researcher and his group in Purdue’s Natural and Biological Photonics Laboratory focus on wearable, scalable, and thermal materials using natural protein fibers. They are studying disordered photonics with the goal of overcoming the obstacle of variations and imperfections during nanofabrication. Recent experiments have revealed unexpectedly strong light scattering, resulting from the interactions of light with disordered nanostructures found in nature.

Kim is especially interested in better understanding the possible origins of vibrant, sparkling, and bright qualities of natural materials and biological media. Objects found in nature -- pearls, silk, fish, insects, plants, and even human bone -- often have lustrous or silvery colors. Using nature as a laboratory, Kim is applying the concept of “mesoscopic” light-matter interactions, in which coherent light effects are preserved due to strong light scattering. His work in photonics has many applications: lasers, optics, fiber optics, thermal photonic devices, and even quantum information processing.

Kim will use the grant to study the light scattering properties of native silk.

Like the thousands of layers that make up a pearl and create a unique luminescence, each silk fiber is composed of a large number of nanofibrils that both scatter light and can trap it inside the silk fiber. This nanoarchitecture allows for uniquely strong light-matter interaction and efficient nanomaterial hybridization.

“Our results will provide the groundwork for exploiting natural silk as a photonic nanomaterial hybridization platform to implement embedded functionalities in a fiber geometry, which can be constructed into large-area and continuous fabrics,” Kim says.

At the heart of the research is a desire to create affordable, flexible, synthetic nanomaterials that can be manufactured in large quantities. Kim is exploring the unique combination of transgenic silk, produced by genetically engineered silkworms in collaboration with a Korean team, and facile metal nanoparticle hybridization, which offers not only nontoxic fluorescent media, but also utilizes plasmonics for enhanced photoluminescence. This particular hybridization is inspired by a common method in the 19th century of adding metal to the thread to increase the weight of silk fabrics and raise the sale price. 

The unprecedentedly strong affinity of silk to metal ions, enhanced with plant-derived polyphenolic chemistry, forms nanoparticulated metal with finite sizes inside the interfibrillar nanostructures of silk. These wholly integrated plasmonic native fibers are distinct from other nanomaterial hybridizations that are focused on attaching metal nanoparticles on the fiber surface.   This research has recently been published in Materials Horizons, which is a new premier journal of Royal Society of Chemistry, at http://pubs.rsc.org/en/content/articlelanding/2017/mh/c6mh00423g#!divAbstract

One of the immediate applications of the silk research is a photoinducible, genetically encoded approach for killing harmful pathogens. For example, fluorescent silk (produced by silkworm transgenesis of fluorescent proteins) can be used as wearable garments, such as masks and gloves, to potentially inactivate harmful viruses and bacteria. Fluorescent proteins may serve as photoinducible, genetically encoded proteins to generate phototoxic radicals. The unique physical properties of silk serve as a fundamental mechanism of enhanced light-protein interactions. Other applications include battlefield environment sensing: soldier health monitoring, soldier therapeutics, and combat casualty care. 

Researchers in nanomaterials have been focused for many years on synthetic ways to create materials, Kim says, but silk may offer a natural and sustainable alternative. The use of silk fiber and silk materials has immediate advantages, in that existing textile technologies and infrastructures are already in place. “This insect factory could also open an alternative nanomanufacturing strategy in an eco-friendly, scalable, and sustainable manner,” he says.

The research is also funded by the Cooperative Research Program for Agriculture Science & Technology Development of the Rural Development Administration, South Korea.