Limonia acidissima L. leaf mediated synthesis of silver and zinc oxide nanoparticles and their antibacterial activities.

Green chemistry is a novel method for the synthesis of silver and zinc oxide nanoparticles. The present investigation focused on synthesis of biogenic silver and zinc oxide nanoparticles. They were assayed for their antibacterial activities against test bacterial species. The results revealed that the silver nanoparticles showed the maximum zone of inhibition 15.16, 15.5 and 13.33 mm at 400 µg/mL to S. aureus, S. typhi and P. aeruginosa respectively, when compared to the Erythromycin. While zinc oxide nanoparticles showed less activity in comparison to silver nanoparticles owing to the agglomeration of nanoparticles. It is evident from our investigation that silver nanoparticles could be used as an antimicrobial due to their intrinsic properties in biomedical application and food packing industries.

Biochemical responses and accumulation of cadmium in Spirodela polyrhiza.

The present study focused on biochemical responses of Spirodela polyrhiza to cadmium stresses and its accumulation. The laboratory experiments were conducted for the assessment of biochemical responses and accumulation of cadmium in plants at its various concentrations (0.1, 0.5, 1.5 and 2.0 ppm) at the regular interval for twelve days exposure. Spirodela showed visible symptoms like withering of roots and chlorosis at higher concentration (2.0 ppm), however the plant showed normal growth at lower concentration (0.1 ppm). The estimation of biochemical parameters (total chlorophyll, protein and carbohydrate) of test plants showed a significant increase at lower concentration (0.1 ppm) of cadmium. The biochemical changes decrease with increase in exposure concentration and duration. The toxic effect of cadmium is directly proportional to its concentration and duration. The accumulation of cadmium by Spirodela polyrhiza was maximum at four days exposure duration and gradually decreases.

Cytotoxicity of zinc nanoparticles fabricated by Justicia adhatoda L. on root tips of Allium cepa L.--a model approach.

Zinc nanoparticles were synthesized using aqueous leaf extract of Justicia adhatoda L. The characterization of nanoparticles was done by ultraviolet-visible (UV-vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), and high-resolution transmission electron microscopy (HR-TEM). The characteristic absorption peak of the UV spectrum was recorded at 379 nm. The FTIR data revealed the possible biomolecules involved in bioreduction and capping of zinc nanoparticles for efficient stabilization. AFM and HR-TEM images have shown that the size of zinc nanoparticles ranges from 55 to 83 nm and they are spherical in shape. The biogenic zinc nanoparticles were evaluated for their toxic effect on mitotic chromosomes of Allium cepa as a model system. Experiments were conducted in triplicate to assay the effect of 25, 50, 75, and 100 % of zinc nanoparticles on mitotic chromosomes at an interval of 6 h duration for 24 h. The investigation revealed that the mitotic index (MI) was decreased with increased concentration of zinc nanoparticles and exposure duration. The results revealed that zinc nanoparticles have induced abnormalities like anaphase bridge formation, diagonal anaphase, C-metaphase, sticky metaphase, laggards, and sticky anaphase at different percentages and times of exposure. It is evident from the observation that mitotic cell division becomes abortive at 100 % treatment of zinc nanoparticles.

Biosynthesis of nanoparticles using microbes- a review.

The biosynthesis of nanoparticles by microorganism is a green and eco-friendly technology. This review focuses on the use of consortium of diverse microorganisms belonging to both prokaryotes and eukaryotes for the synthesis of metallic nanoparticles viz. silver, gold, platinum, zirconium, palladium, iron, cadmium and metal oxides such as titanium oxide, zinc oxide, etc. These microorganisms include bacteria, actinomycetes, fungi and algae. The synthesis of nanoparticles may be intracellular or extracellular. The several workers have reported that NADH dependent nitrate reductase enzyme plays a vital role in the conversion of metallic ions to nanoparticles. The FTIR study reveals that diverse biomolecules viz. carboxyl group, primary and secondary amines, amide I, II, and III bands etc serve as a tool for bioreduction and capping agents there by offering stability to particles by preventing agglomeration and growth. The size and shape of the nanoparticles vary with the organism employed and conditions employed during the synthesis which included pH, temperature and substrate concentration. The microorganisms provide diverse environment for biosynthesis of nanoparticles. These particles are safe and eco-friendly with a lot of applications in medicine, agriculture, cosmetic industry, drug delivery and biochemical sensors. The challenges for redressal include optimal production and minimal time to obtain desired size and shape, to enhance the stability of nanoparticles and optimization of specific microorganisms for specific application.