(25e) Kinetics, Yield and Rate Limiting Processes in the Biosynthesis of Colloidal Silver Nanoparticles By a Fresh Water Microalga

In the current study, a fresh water microalga, Chlamydomonas reinhardtii has been used to synthesize colloidal AgNPs through bio-reduction, and a mathematical model is developed to study the reaction kinetics and yield. The properties of silver nanoparticles (AgNPs) make them excellent candidates for fabricating biosensors, therapy and diagnostic tools, medical imaging agents and biomaterials. The prevailing synthesis methodologies consume imprudent amounts of energy and use harmful chemicals such as sodium borohydride hence creating a need to look for sustainable technologies. The present set up uses live culture of C. reinhardtii therefore reducing the energy, cost and doing away with toxic chemicals. The biosynthesis takes place inside the thylakoids that have abundance of reducing equivalents, and through reduction catalyzed by the cell’s exopolymeric substances (EPS). The production of AgNPs was confirmed by the characteristic SPR band in the range of 415- 430 nm using UV-vis spectrophotometry. Crystallinity of nanoparticles was determined using X-ray diffraction (XRD) and the mean particle size was calculated from Scherrer equation. Micrographs from scanning and transmission electron microscopy (SEM and TEM) were analyzed to study the shape and the size of AgNPs. Ag⁺ to AgNP conversion kinetics and yields were determined by measuring the composition of the solid and liquid phases by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The AgNPs were stable over time as determined through negligible change in the intensity of the SPR band. The results of this study will be used evaluate the prospects of a scalable, fully automated, and permanent photobioreactor for the continuous production of different biogenic inorganic nanoparticles.