Cell-free artificial photosynthesis system

Xiang Ren

doi:10.17918/etd-6673

The objective of this research is to create a cell-free artificial platform for harvesting light energy and transforming the energy to organic compounds. In order to achieve this objective, we took the approach of mimicking the photosynthetic processes of a plant leaf and integrating them into a compact system using microfabrication technology. Photosynthesis consists of two parts: light reaction and dark reaction. During the light reaction, light energy is transformed to chemical energy in ATP that is a biological energy source, while during the dark reaction. Carbon dioxide is absorbed and used to synthesize organic compounds such as glucose and fructose. Many scientists had tried to realize artificial photosynthesis for energy harvesting for decades. However, most of the previous systems were simply based on light reaction and produced less desirable energy sources, such as explosive hydrogen gas and unstable electricity. Other works had been reported that combined both light and dark reactions to produce useful organic compounds, but they were all based on utilizing living cells that were difficult to maintain and were not reusable. We developed a cell-free artificial platform conducting both light and dark reactions. To the best of our knowledge, such a device had not been reported so far. This device was able to harvest light energy and transform the energy to organic compounds, mimicking a plant leaf. We envision integrating the "artificial leaves" to create a compact energy harvesting system with a promising efficiency. In order to create an artificial photosynthesis device, we had come up with four specific parts as follows. Part 1: Light reaction was realized in a microfluidic platform that consists of two fluid chambers separated by a planar membrane with embedded proteins that convert light energy into ATP. Four different materials were investigated as potential membrane materials and the optimal (most stable) material was identified through impedance spectroscopy. Since these membrane materials were very soft, it was challenging to integrate them in a microfluidic platform. Diverse support materials and fabrication techniques were investigated to identify the optimal fabrication process. Once the best membrane material was identified and a microfluidic platform was constructed, we would have light-converting proteins embedded in the membrane followed by the evaluation its light reaction performance. Part 2: Dark reaction was realized in another microfluidic platform porous PDMS cubes as gas-liquid interface media. We used porous PDMS as a gas-liquid interface between microfluidic channels to create a "one-way" diffusion path for carbon dioxide. The CO₂ transport was evaluated based on pH change and successful CO₂ transport would produce precursors (C3 compounds) for glucose production. Part 3: Glucose synthesis and storage unit was developed by mimicking sponge mesophyll found in a leaf (dicotyledons leaf). Chitosan porous structures with interconnected pores were used for this purpose and they were fabricated by lyophilization after casting or 3D printing. Part 4: The circuits for an integrated light reaction platform was designed and simulated. The digital encode/decode of microchip array was simulated. A high-resolution, low-speed analog-to-digital converter was also designed and simulated for ion channel monitoring purpose. While carrying out this research, the following scientific contributions were also made. First, electrochemical property database of planar membranes made of different biomaterials were established. Second, a novel gas-liquid interface was developed for microfluidic platforms using porous PDMS and its performance was thoroughly investigated by on-chip pH measurement. Third, during the study on 3D printing of chitosan porous structure, a mathematical model was established for identifying optimal operational parameters for printing non-Newtonian fluids with a pneumatic printer. This research brought together expertise in advanced manufacturing (MEMS and additive manufacturing), biochemistry and biomaterials, and system control and integration. We envisioned integrating the "artificial leaves" to create a compact energy harvesting system with high efficiency.

Cell-free artificial photosynthesis system

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Cell-free artificial photosynthesis system

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