Biogenic production of gold, silver and some other metal nanoparticles have been extensively explored using algae and cyanobacteria. However, these photosynthetic organisms have been less investigated for their nano iron biofabricating potency. Selected strains Leptolyngbya valderiana and Lyngbya sordida were screened for their nano-iron synthesizing capacity by exposing them to 0.01M FeCl3 solution for four days. The biomass, as well as the cell-free suspensions, has shown a significant change of color from yellowish to brownish as a result of the transformation to nano form both in the intracellular and extracellular regimes. The particles were initially characterized using UV-vis spectroscopy, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Energy Dispersive X-Ray Analysis (EDX) study. In the case of L. sordida and L.valderiana intracellular particle dimensions were 22.92×19.12nm and 47.42×7.7nm, whereas extracellular particle dimensions were 49×10.36nm and 66.37×12.49nm respectively with a spindle-shaped morphology. The particles were zerovalent (Fe0) as found from EDX study. Cellular sections under TEM revealed the exact location of the particles in the cells. The extracellularly synthesized particles have shown a relatively larger dry size as inferred from their TEM analyses. The size discrimination between the two species and their intracellular and extracellular compartment was also reflected in hydrodynamic size analysis using Dynamic Light Scattering. The particles were monodisperse having polydispersity index (PDI) values within 0.2-0.4. The dry sizes, as well as hydrodynamic sizes, showed a species-specific as well as a compartment-specific size distribution pattern. Electron microscopic characterizations have revealed magnetic force of interaction between the particles depicted from their arrangement like typical magnetic dipoles. The property was confirmed when the particles were exposed to a static magnetic field (SMF) exposure. For intracellular particles, 1-2 fold and extracellular particles 4-5 fold increase in hydrodynamic size was observed with also increase in PDI values to 0.4-0.5. The nano-irons were found to be fluorescent as inferred from the fluorimetric analyses. Interestingly a rise in fluorescence was seen after SMF exposure for 10 mins which may be due to a magnetic field induced clustering effect. SQUID-VSM analyses of intracellular nano irons of L. valderiana were carried out for magnetic characterization.
Such a compartment-specific magnetic and fluorescent nanoparticle synthesis is an interesting approach where the microbial biomass is producing 40-50mg particles/g tissue. Another major focus is the scaling up of the process to increase the production of nanoparticles with high medicinal value.
Take Away Notes:
• Cyanobacteria mediated green nanotechnology will be discussed in detail and anyone who will be interested in this work can go ahead with other algae mediated nanoiron synthesis.
• The iron nanoparticles can be investigated further in detail, the uptaking and nucleation of nanoiron can be studied.
• This can be taken as an alternative approach of chemical synthesis of nanoiron. It will pave a new way towards environmentally benign nanoiron production.
• Considering the fluoromagnetic nature of the particles, it can be used to design MRI contrast agent.