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Postdoctoral Research Associate, Washington University in St. Louis

PINBOARD SUMMARY

An optical study of nature's finely tuned, diverse and efficient design using structural proteins.

Nature provides a set of solutions for photonic structures that are finely tuned, organically diverse and optically efficient. Exquisite knowledge of structure-property relationships in proteins aids in the design of materials with desired properties for building devices with novel functionalities, which are difficult to achieve or previously unattainable. On the other hand, whispering-gallery-mode (WGM) microresonators provide ultrahigh light-matter interactions. WGM resonators fabricated entirely from semi-crystalline structural proteins (i.e., squid ring teeth, SRT, from Loligo vulgaris and its recombinant) allows demonstration of versatility of protein-based devices by facile doping, engaging secondary structures and investigation of their thermal and optical properties. As an example, an all-protein optical switch is proven to be ten times more energy efficient than a conventional material (silica) based one. SRT protein based WGM resonators also provide a set of photonic devices such as add-drop filters and fibers which are highly flexible and robust where optical quality and performance are unaffected from mechanical strains. Expression of squid DNA allows for efficient generation of recombinant SRT proteins which can be utilized as materials that address specific needs in science and engineering applications. As an optical material, study of SRT proteins and their recombinants have the potential to create a paradigm shift in materials design by following nature's footsteps and this work takes a first step towards this design method.

5 ITEMS PINNED

Highly sensitive detection of nanoparticles with a self-referenced and self-heterodyned whispering-gallery Raman microlaser.

Abstract: Optical whispering-gallery-mode resonators (WGMRs) have emerged as promising platforms for label-free detection of nano-objects. The ultimate sensitivity of WGMRs is determined by the strength of the light-matter interaction quantified by quality factor/mode volume, Q/V, and the resolution is determined by Q. To date, to improve sensitivity and precision of detection either WGMRs have been doped with rare-earth ions to compensate losses and increase Q or plasmonic resonances have been exploited for their superior field confinement and lower V. Here, we demonstrate, for the first time to our knowledge, enhanced detection of single-nanoparticle-induced mode splitting in a silica WGMR via Raman gain-assisted loss compensation and WGM Raman microlaser. In particular, the use of the Raman microlaser provides a dopant-free, self-referenced, and self-heterodyned scheme with a detection limit ultimately determined by the thermorefractive noise. Notably, we detected and counted individual nanoparticles with polarizabilities down to 3.82 × 10(-6) μm(3) by monitoring a heterodyne beatnote signal. This level of sensitivity is achieved without exploiting plasmonic effects, external references, or active stabilization and frequency locking. Single nanoparticles are detected one at a time; however, their characterization by size or polarizability requires ensemble measurements and statistical averaging. This dopant-free scheme retains the inherited biocompatibility of silica and could find widespread use for sensing in biological media. The Raman laser and operation band of the sensor can be tailored for the specific sensing environment and the properties of the targeted materials by changing the pump laser wavelength. This scheme also opens the possibility of using intrinsic Raman or parametric gain for loss compensation in other systems where dissipation hinders progress and limits applications.

Pub.: 10 Sep '14, Pinned: 28 Jun '17

Structural Protein-based Flexible Whispering Gallery Mode Resonators

Abstract: Nature provides a set of solutions for photonic structures that are finely tuned, organically diverse and optically efficient. Exquisite knowledge of structure-property relationships in proteins aids in the design of materials with desired properties for building devices with novel functionalities, which are difficult to achieve or previously unattainable. Recent bio-inspired photonic platforms made from proteinaceous materials lay the groundwork for many functional device applications, such as electroluminescence in peptide nucleic acids1, multiphoton absorption in amyloid fibers2 and silk waveguides and inverse opals3-5. Here we report whispering-gallery-mode (WGM) microresonators fabricated entirely from semi-crystalline structural proteins (i.e., squid ring teeth, SRT, from Loligo vulgaris and its recombinant, and silk from Bombyx mori) with unconventional thermo-optic response. We present a striking example of how small modifications at the molecular level lead to structural changes and alter macroscopic properties of proteins by demonstrating the variation in thermo-optic response as a function of crystallinity. We demonstrated waveguides, add-drop filters and flexible resonators as first examples of energy-efficient, highly flexible, biocompatible and biodegradable protein- based photonic devices. Optical switching efficiency in these devices is over thousand times greater than the values reported for Silica WGM resonators. This work opens the way for designing energy efficient functional photonic devices using structure-property relationships of proteins.

Pub.: 27 Jun '16, Pinned: 28 Jun '17