A biogenic extracellular synthesis of Ag nanoparticles using live Chaetoceros sp. diatom and application as optical ammonia sensor in solution

In the present work, the biosynthesis of AgNPs using live normal cells of Chaetoceros sp. diatom was studied by two routes applying the fresh harvested diatom biomass (DB route) and culture medium (DC route) as the diatom source in the reaction medium, and the results revealed that the DB route is more efficient in this biosynthesis. Here, the living diatom as green part plays a dual role as both an effective reducing agent and an excellent support to synthesize and stabilize Ag nanoparticles. The effect of physical controlling factors such as pH, AgNO 3 concentration, diatom content, and reaction time was investigated and the optimal values were observed in pH=7–7.5 with concentrations 20 and 50 μM of AgNO 3 and reaction time 18 h. The as-prepared AgNP/diatom biocomposite was characterized by UV-visible spectroscopy, FE-SEM, EDX, XRD, TEM, FTIR, BET, and ICP analysis, and the results confirmed the formation of spherical Ag nanoparticles with average size 5–8 nm incorporated in the diatom cells. Based on FTIR analysis, amide groups present in diatom cells were assumed to be responsible for the bioreduction process. The BET analysis showed a significant decrease in the specific surface area of the diatom after the AgNP formation and the ICP-MS analysis confirmed the presence of 960 ppm of the total silver concentration in the sample DB(50 ml)/20 μM. This biocomposite successfully evaluated as an optical ammonia sensor and indicated a great potential for detection of ammonia concentration in aqueous solutions based on the change in surface plasmon resonance. Graphical Abstract