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Title: Microfluidics-based artificial photosynthesis for coenzyme regeneration
Authors: Huang, Xiaowen
Degree: Ph.D.
Issue Date: 2017
Abstract: Artificial photosynthesis (APS) is a process that mimics the natural photosynthesis (NPS) to produce energy-rich fuel or carbohydrates with the usage of solar energy. Green crops rely on NPS to capture sunlight and CO₂ to produce carbohydrates, but the energy efficiency of NPS is very low (typically <1%), far from its theoretical limit 30%. This makes a big room to develop a scientific solution to produce basic food materials with high energy efficiency while circumventing all the existing problems. In plants, carbohydrate production relies on Calvin cycle, among which the coenzyme regeneration is the key step. It is the aim of this research to take advantages of microfluidic structure to regenerate the coenzymes with high efficiency. For this purpose, this study covers three parts for the microfluidics-based APS coenzyme regeneration: (1) to simplify the traditional coenzyme regeneration chain, (2) to improve the photocatalysts immobilization, (3) to enable quick detection of the photocatalysts efficiency. Firstly, we proposed a one-step method to assemble the immobilized artificial Photosystem I (IAPSI) in the microfluidic chip, which integrated the preformed graphitic carbon nitride photocatalyst (g-C₃N₄) and electron mediator (M) in one chip and mimicked the wisdom of photosystem I. The simultaneous assembly of g-C₃N₄ and M could efficiently regenerate NADH from NAD⁺ under visible light irradiation. The in-situ assembly method was thought to outperform traditional methods in two aspects in terms of facile synthesis, (1) promotion of the combination of g-C₃N₄ and M through π-π stacking, (2) enhanced coenzyme regeneration rate. For comparison, we used the bulk g-C3N4-slurry and the few-layer g-C₃N₄-slurry system as the control to regenerate the photocatalytic cofactor/coenzyme NADH. Specifically, our IAPSI microreactor is faster than the other two by the factors of 23 times and 2.3 times. After this experiment, we notice the importance of the immobilization of the photocatalysts on the substrate and proceed to the following work.
In the second, we proposed a novel biomimetic method to immobilize nanoparticles by using a common adhesive tape as the substrate of microfluidic chip, which mimics the clams' feeding system that utilizes the mucus (i.e., sticky fluid) to capture small phytoplankton particles in water. This work proves experimentally that this method has a better immobilization effect and a stronger shear stress resistance than the traditional methods using hard glass substrates. Moreover, this method is applied to immobilize Au nanorods for the detection of R6G of various concentrations using the surface-enhanced Raman scattering (SERS) effect. This method enjoys several major merits such as simple bonding, no need for expensive reagents, flexible substrate, ease for off-chip detection and being reusable. With these, the biomimetic method will be useful in immobilizing the photocatalysts of artificial photosynthesis for coenzyme regeneration. Then we realize the importance of the photocatalysts. Methods to quickly detect the efficiency of them is crucial to the artificial photosynthesis field. Thus, in the third work, we developed a quick verification method to process rapid coenzyme regeneration based on a one-step artificial photosystem I method. These tests were processed in a very simple PDMS well with two kinds of g-C3N4, the few layer g-C₃N₄ and mesoporous carbon nitride (mpg-C₃N₄). This method is advantageous over the traditional slurry method that has numerous of steps, consumes volumes of reagents and requires long experimental time. The regeneration rate of mpg-C₃N₄-in a drop system is 4.3 times and 7.16 times of the few layer g-C₃N₄-slurry system and mpg-C₃N₄-slurry system, respectively. Moreover, this one-drop method reduces the typical verification time from 90 min to 5 minutes and lowering the liquid volume from 20 mL to 20 μL, which is one-thousandth times of the traditional slurry one. Based on these advantages, we propose that the simple, yet highly efficient method offers a convenient tool for the artificial photosynthesis especially in terms of photocatalyst screening. The three parts of this research have well demonstrated the benefits of microfluidics for the APS coenzyme regeneration in the aspects such as highly efficient conversion, easy immobilization and quick detection. In the future, we will combine these photo-regeneration parts with the Calvin Cycle enzymes for the function carbohydrates production. These techniques may find useful applications in organic production, rapid screening and standardized tests of photocatalysts and may also be the platform in researching the mechanism of coenzyme regeneration.
Subjects: Hong Kong Polytechnic University -- Dissertations
Pages: xxiii, 120 pages : color illustrations
Appears in Collections:Thesis

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