Charge transfer at abiotic-biotic interface for photosynthetic biohybrids

This award is Co-Funded with ENG/CBET Electrochemical Systems program Charge transfer at the abiotic-biotic interface for photosynthetic biohybrids NON-TECHNICAL SUMMARY

A rapidly developing industrial world requires creative and sustainable strategies for dealing with the unidirectional carbon cycle. The conversion of CO2 to value-added products powered with solar energy is an ideal solution. Combining single-cell microorganisms with light-harvesting nanomaterials into photosynthetic biohybrid systems (PBS) represents a promising approach.

Biological microorganisms engage a collection of enzymes and reductive pathways to produce long-chain hydrocarbons from simple building blocks, including CO2, N2, and H2O. Semiconducting nanomaterials are highly configurable with tunable broadband light absorption and surface charge, pair well with microorganisms and enable significant sunlight capture, hence solar-to-chemical conversion.

These photosynthetic biohybrids boost the best functions of biological whole-cell catalysts and semiconducting nanomaterials. However, the fundamental electron transfer and energy transduction pathway in these emerging photosynthetic biohybrids remains largely unexplored due to the complex nature of the biotic/abiotic semiconductor/bacteria interfaces.

The purpose of this project is to examine this energy transduction pathway, starting from solar light absorption by the semiconductor nanostructures, electron generation and transfer from the semiconductor to microorganism, and then CO2 reduction by the microorganism using transferred electron. By reducing CO2, the major byproduct of fossil fuel combustion, into value-added fuels using renewable energy sources (i.e., solar energy and artificial photosynthesis), one can help close the carbon emission loop, mitigate CO2 emissions, and make our society more sustainable.

Starting from the simple molecules produced by photosynthetic biohybrid systems, more complex substances, like fertilizers, industrial and commodity chemicals, polymers, and pharmaceuticals, among others, can be constructed, all originating from capturing atmospheric CO2. Integrated with the research effort, the PI also proposes an educational project that stimulates and prepares pre-college students for careers in materials science and energy research, including outreach efforts at local middle-high schools (Bay Area Scientists in Schools, and summer STEM internship).

TECHNICAL SUMMARY

Liquid sunlight represents a new form of chemical energy converted and stored in chemical bonds from solar energy. Photosynthetic biohybrids produce liquid sunlight through a “photon-in, chemical bond-out” materials/biology interface that can be probed through spatiotemporal imaging, and spectroscopic analyses. Photosynthetic biohybrid systems (PBS) combine the best attributes of biological whole-cell catalysts and semiconducting nanomaterials.

Enzymatic machinery enveloped in its native cellular environment offers exquisite product selectivity and low substrate activation barriers while semiconducting nanomaterials harvest light energy stably and more efficiently than biomolecules. Recently, it has been demonstrated that a collection of value-added chemicals, such as liquid fuels, biodegradable polymers, and other complex natural products can be directly produced from CO2 using these photosynthetic biohybrids.

However, the fundamental electron transfer and energy transduction pathway in these emerging photosynthetic biohybrid systems remains unexplored due to the complex nature of the biotic/abiotic semiconductor/bacteria interfaces. Fundamentally, the photosynthetic function of these PBSs originates from a “photon-in, chemical bond-out” materials/biology interface that spans multiple orders of magnitude both in the length and time scale.

The objective of this research is to design and explore the fundamental abiotic-biotic interfaces of a model system for inorganic-biological artificial photosynthesis through studies on interfacial charge transfer and biogenic mineralization of inorganic photosensitizers. This model system study will require three phases: 1) elucidation of charge transfer between photosensitizers and biological participants in the Wood-Ljungdahl Pathway; 2) a detailed study of photosensitizer biomineralization and photosensitizer-whole cell charge transfer; and 3) development of a functional whole-cell photosensitized system and screening the effects of mineral precursor and hole scavenger on system productivity.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.