A Living Photosynthetic Microcavity

Living microalgae – sandwiched between two optical mirrors – are forming a living photosynthetic optical microresonator. Enhanced bioelectricity was generated with the effect of strong energy coupling. (Source: Y.-C. Chen et al., NTU)

An international research team at the Nanyang Techno­logical University, Singapore, has developed a novel approach to boost the tiny nano-energy and nano-elec­tricity generated by living micro­algaes commonly found in the pounds through the encapsulation into a living optical microresonator. The notable single-celled freshwater algae Chlorella has known for its promising potential as bioenergy resources. Photo­synthetic reactions were signi­ficantly enhanced by embedding the bio-photo­electro­chemical cell in the micro­cavity, in which the Fabry-Perot cavity is formed by two highly reflec­tive mirrors corresponding to photo­systems.

Without the need of a bulky system, the design aims to boost the photo­synthetic bioenergy effi­ciency in tiny microalgae by employing strong energy coupling in a micro-cavity. The team also demonstrated a signi­ficant enhance­ment in a biomimetic nanosystem using the same approach via nanocavity enhancement. The team believes that this new concept will open new possi­bilities for future energy device appli­cations and sustainable bio­photonics.

As the world seeks to devise techno­logical solutions for sus­tainable energy production and to the threat of climate change, an important topic emerging within this is bioenergy. Bioenergy is renewable energy produced by living organisms, and the photo­systems found in plants, cyanobacteria, algae, and other living organisms are promising sources for bioenergy harvesting and bio-electricity generation. With the enormous interest in this area, extracting bioelec­tricity from living photo­synthetic organisms has always been a challenging task, particu­larly at a whole-cell level like micro­algae. The greatest challenge originated from the extremely low tran­sition rate from light to elec­tricity, presumably due to the shielding of complex membrane systems and the barrier between intra­cellular chloroplast to an electrode.

The team’s novel photonic techno­logy-enabled approach uses optical resonator to enhance the photo­synthetic reactions in electro­chemical cells. Instead of enhancing the light-conversion effi­ciency, in the present work, they explored the possibility of improving the energy-transfer effi­ciency in photosystems through the encapsu­lation of a living photo­synthetic center in an optical micro­cavity. Whereas micro­cavities have been utilized to amplify bio-optical signals in many ways, they have never been employed to amplify bioelec­trical signals.

Here the optical cavity, which is formed by two mirrors, was specifically designed to only reflect red emission wave­length to match with the fluores­cence emission by generated by chloro­phylls in microalgae. When light is excited, the fluores­cence emission from algae will form a strong coupling resonance within the mirrors, therefore it could amplify the bio-photo­current. Systematic studies on the photo­system fluorescence and photo­current suggested the possible amplifi­cation of intra­cellular energy-transfer effi­ciency.

This work demons­trated the huge potential of using an optical cavity to enhance bioelec­tricity generation and bioenergy-harvesting for the first time. Both artificial and living photo­synthesis in living algae were explored, where the power was markedly increased more than 600% and 200%, respectively. Finally, we developed an optofluidic device to illus­trate the potential imple­mentation of such living photo­synthetic optical resonators.

Yu-Cheng Chen at Nanyang Techno­logical Univer­sity mentioned that the developed photo­synthetic microcavity not only can be applied to the species used in this work, but can be widely applied to a broad range of living photo­synthetic species from the molecular to the micro­organism level, such as cyano­bacteria, photo­synthetic proteins, and biofilms. We envisage that the key inno­vations found in this study offer new possi­bilities for appli­cations in bioenergy generation, biofuel-powered devices, and sustainable bio­photonics. (Source: NTU)

Reference: D. N. Roxby et al.: Enhanced Biophotocurrent Generation in Living Photosynthetic Optical Resonator, Adv. Sci. 1903707 (2020); DOI: 10.1002/advs.201903707

Link: Bio+Intelligent Photonics Laboratory, Nanyang Technological University, Singapore, Singapore

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