A comparative study of morphology, reactivity and stability of synthesized silver nanoparticles using Bacillus subtilis and Catharanthus roseus (L.) G. Don.

Large number of papers has been published recently on the eleventh group metallic elements such as Ag, Au and Cu. Our study was focused on biosynthesis of silver nanoparticles, their morphology, reactivity and stability. We were interested to check these properties in two different samples, S1 and S2, respectively. The biosynthesis of silver nanoparticles was achieved by reacting the samples with 1 mM concentration of silver nitrate, one involves bacteria (S1) and the other involves the plant extract (S2). Spectrophotometric analysis revealed that the particles exhibited two peaks, one at 440 nm (for S1) and the other at 390 nm (for S2). It is well known that longer wavelength corresponds to increase in particle size. Since, S1 has got a longer wavelength; it is not known, whether it forms isolated particles or agglomerates? Morphological characterization has been done by adopting the procedures of Negative staining and Wedge smear preparation methods. This hybrid method may be of interest to study agglomerated particles. Microscopic examination of the smear S1 shows predominantly triangular or hexagonal shaped agglomerated particles which were not observed in S2. Hence further characterization was done using SEM, EDAX and XRD. The S2 particles were in the range of 45-70 nm and were stable for even four months. This study indicated that particle size can be controlled from micrometer to nanometer size by varying biological reductants.