Abstract
Potential of root system of plants from wide range of families to effectively reduce membrane impermeable ferricyanide to ferrocyanide and blue coloured 2,6-dichlorophenol indophenol (DCPIP) to colourless DCPIPH2 both under non-sterile and sterile conditions, revealed prevalence of immense reducing strength at root surface. As generation of silver nanoparticles (NPs) from Ag+ involves reduction, present investigations were carried to evaluate if reducing strength prevailing at surface of root system can be exploited for reduction of Ag+ and exogenous generation of silver-NPs. Root system of intact plants of 16 species from 11 diverse families of angiosperms turned clear colorless AgNO3 solutions, turbid brown. Absorption spectra of these turbid brown solutions showed silver-NPs specific surface plasmon resonance peak. Transmission electron microscope coupled with energy dispersive X-ray confirmed the presence of distinct NPs in the range of 5–50 nm containing Ag. Selected area electron diffraction and powder X-ray diffraction patterns of the silver NPs showed Bragg reflections, characteristic of crystalline face-centered cubic structure of Ag0 and cubic structure of Ag2O. Root system of intact plants raised under sterile conditions also generated Ag0/Ag2O-NPs under strict sterile conditions in a manner similar to that recorded under non-sterile conditions. This revealed the inbuilt potential of root system to generate Ag0/Ag2O-NPs independent of any microorganism. Roots of intact plants reduced triphenyltetrazolium to triphenylformazon and impermeable ferricyanide to ferrocyanide, suggesting involvement of plasma membrane bound dehydrogenases in reduction of Ag+ and formation of Ag0/Ag2O-NPs. Root enzyme extract reduced triphenyltetrazolium to triphenylformazon and Ag+ to Ag0 in presence of NADH, clearly establishing potential of dehydrogenases to reduce Ag+ to Ag0, which generate Ag0/Ag2O-NPs. Findings presented in this manuscript put forth a novel, simple, economically viable and green protocol for synthesis of silver-NPs under ambient conditions in aqueous phase, using root system of intact plants.
Highlights
Nanotechnology has witnessed spectacular advancement in fabrication and utilization of nanomaterials
For present investigations 20 day old plants of L. esculentum, 9–10 day old plants of B. juncea, C. arietinum, and 4–5 day old plants of T. aestivum and V. mungo were carefully removed from glass beads with least damage to the root system, and incubated for 6– 12 h in AgNO3 solution
It is well established that generation of silver nanoparticles similar to other metal nanoparticles primarily involves reduction of their ions [10,11]
Summary
Nanotechnology has witnessed spectacular advancement in fabrication and utilization of nanomaterials. Owing to small size and large surface to volume ratio, nanoparticles possess unique physicochemical and biological properties which differ entirely from the bulk material. Due to immense antimicrobial properties, silver NPs find wide application in medicine especially artificial teeth, bone coating, medical catheters, wound dressings besides surgical instruments. Electronic application of silver nanoparticles includes its usage for the preparation of optical devices, inks for circuit boards, high density recording devices, battery-based intercalation materials [6,7,8,9]. Silver NPs of different sizes and shapes are routinely synthesized by various chemical and physical methods [11,12,13]. The Lee-Meisel method using sodium citrate along with heating for 1 h for generation of silver nanoparticles continues to be the standard by which other
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