Abstract

Recent developments in a microbial fuel cell (MFC) research have demonstrated that this electrochemical technique is an effective method of producing electrical power from organic compounds through microbial activities during the respiration process. This led to the development of micro-photosynthetic power cell (µPSC) that generates electrical power by harnessing solar energy through photosynthesis and the respiration process of photosynthetic organisms. Micro-photosynthetic power cells convert light energy to electricity using photosynthetic microorganisms such as microalgae and cyanobacteria. Herein we describe the readily producible inexpensive, and economically feasible novel fabrication of µPSC through a thin arrayed metal grid. Several key factors limiting the performance efficiency, including the optimal photosynthetic cell culture, light intensity, performance of the µPSC in the dark condition, are investigated in detail. These experiments suggested that high illumination may damage the photosynthetic pigments of photosynthetic organisms and lead to reduced performance. An illumination intensity of 2-5 µEm-2s-1 was found to be the optimal illumination necessary for the enhanced performance.
Nano-bio interactions enhanced the current limitation of the low power density of the µPSC through the incorporation of inorganic efficient light absorbers in the form of gold nanoparticles into photosynthetic cells. The photosynthetic parameters such as maximum quantum yield, operational quantum yield, photochemical quenching, excitation pressure were studied through a pulse width modulated fluorometry. The experimental results demonstrated that by incorporating gold nanoparticles of size 24 ± 2 nm of 50 µg/ml into 1 ml of algal cells, photosynthetic efficiency was improved by 30.2 %. The spectral characteristics with gold nanoparticle internalized algal cells studied through dark-field hyperspectral microscopy demonstrated a redshift of 120 – 130 nm depending upon size and aggregations compared to control algal cells. Indicating the biocompatible light-absorbing inorganic particles internalized into photosynthetic cells could improve the light absorption in the whole visible wavelength range. Results showed that the synergy between nanotechnology and living photosynthetic cells could increase natural photosynthesis functionality. Through the amalgamation of gold nanoparticle concentration of 50 µg/ml into 1 ml of photosynthetic cells, the power density of the µPSC was increased by 46%. The study provides an understanding of the interaction of inorganic nanoparticles and living cells, which will improve the performance of nano-bio hybrid photosynthetic systems for energy applications.
A novel method for diagnosing intracellular conditions and organelles of cells with Localized Surface Plasmonic Resonance (LSPR) by directly internalizing the gold nanoparticles into the cells and measuring their plasmonic properties through hyperspectral imaging is studied. For the proof of the concept, a well-established cell line, the HeLa cancer cell line, was utilized. This technique will be useful for the direct diagnosis of cellular organelles, which have the potential for cellular biology, proteomics, pharmaceuticals, and drug discovery.
In order to overcome the thermodynamic limits of performance of single µPSC, arrayed configurations such as series, parallel, and combinations of series and parallel configurations were studied in detail. Experimental results suggested that combinations of series and parallel configurations are ideal for real-time electrical loading conditions. In order to demonstrate the capability of the arrayed µPSC for low power application, the light-emitting diode of rating 2 V, 2 mA, and 1.7 V, 2 mA was powered both in light and dark conditions. The electrical equivalent model of arrayed µPSCs has been developed and validated with the experimental results. The model has successfully predicted the electrical loading conditions, polarization characteristics, and power- current characteristics for all the array configurations. The results indicated that the model could be utilized to predict the performance of all kinds of array configurations. Further, the economics of the µPSCs has been studied and compared with the well-established photovoltaic cell technology. The cost comparison of both technologies has been carried out for low (mobile battery) and ultra-low power (humidity sensors) applications. Currently, the photovoltaic technology outperforms the µPSC. Nevertheless, opportunities for improving the µPSC’s performance and niche applications have also been reported.
With this thesis, it has been demonstrated that the potential of harnessing energy from photosynthesis is enormous. In this thesis, simple novel fabrication of µPSCs, optimal operating parameter testing, the necessity of array configurations, and enhancement of power output by nano-bio interactions using gold nanoparticles, the feasibility of the µPSC in comparison with photovoltaic technology, arrayed electrical equivalent model has been demonstrated. With this approach, we envision the µPSC to power low power applications such as mobile phones, e-readers, headphones, earphones, and ultra-low power applications such as humidity, temperature, and IoT sensors, in the future. One such prospective application to the automotive sector has also been provided. As the µPSCs could be installed indoors or outdoors and in any manner like vertical or horizontal, this could open a new avenue for low and ultra-low power applications.