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Solar radiation led into the planet earth by photosynthesis is the main energy basis for survival. Photosynthesis is a physico-chemical process where photosynthetic organism transform solar energy into chemical energy with simultaneous use of bioenergetic processes (Georgianna and Mayfield 2012; Strik et al. 2011). Photosynthetic microbial fuel cells (PhFCs) are newly established tools that harvest sun energy to yield electricity and has gained major attentiveness in applied and academic research due to its sustainable and renewable nature (Chandra et al. 2012; Venkata Mohan et al. 2014). PhFCs use plants or phototrophic microorganisms to trap sun light and use photo-bioelectrochemical system to produce bioelectricity (El Mekawy et al. 2014). This technology symbolizes a multi-disciplinary method to search for renewable energy. It represents the convergence for the life-sciences, chemical and physical science (McCormick et al. 2015; Xiao and He 2014). Microbial fuel cells (MFCs) are mainly focused towards anodic reaction with dark fermentation as microbial metabolic function. Analogous to dark fermentation, photosynthetic fuel cells (PhFC) or biophotovoltaic system (BPV) will also be functioned using photo synthetic bacteria (PSB) or algae/cyanobacteria based on their photosynthetic mechanism (oxygenic or anoxygenic) (Chandra et al. 2012; Rosenbaum et al. 2010a). Oxygenic photosynthesis based autotrophic PhFCs include diverse categories of MFC containing both heterotrophs and autotrophs (Venkata Mohan et al. 2010a, b, 2011) (Fig. 19.1). The current chapter has made an attempt to convey the present photosynthetic mechanism for PhFC application in understanding on the innate potential of photosynthetic mechanism.

The use of Nile Red for rapid monitoring of the neutral lipid content in microalgae has gained interest over the last decade, since neutral lipids are feedstock for renewable transportation fuel. In this review, we discuss the main considerations needed to make an NR protocol reliable for staining neutral lipids in microalgae. Cell wall permeability must be enhanced by using stain carriers: DMSO (5% v/v to 25% v/v), glycerol (0.1 to 0.125 mg/mL), or EDTA (3.0 to 3.8 mg/mL). Temperatures between 30 and 40 °C facilitate the diffusion of NR through the cell wall without incurring excess quenching. Good NR-lipid interaction requires using a low NR/cell ratio; the NR concentration must be between 0.25 μg/mL and 2.0 μg/mL, and the cell concentration > 5 × 104 cells/mL. In order to have the maximum and stable NR fluorescence, it is necessary to scan the excitation/emission wavelengths for up to a 40-min of incubation time. We outline a five-step method to customize the Nile Red protocol to a specific strain: 1) Evaluate the strain's suitability by checking for the presence of neutral lipid, 2) Select of the best excitation/emission wavelength, 3) Optimization of incubation time, stain carrier, dye concentration, and temperature, 4) Prepare single-strain algal cultures with different lipid contents to calibrate NR fluorescence with neutral-lipid content, and 5) Correlate NR fluorescence intensity to neutral lipid content for the same strain. Once the protocol is customized, the NR method allows for rapid and reliable monitoring of neutral lipid content of a microalgae strain.