Phytotoxicity of silver nanoparticles on Vicia faba: evaluation of particle size effects on photosynthetic performance and leaf gas exchange

Nanotechnology is an emerging field in science and engineering, which presents significant impacts on the economy, society and the environment. The nanomaterials’ (NMs) production, use, and disposal is inevitably leading to their release into the environment where there are uncertainties about its fate, behaviour, and toxicity. Recent works have demonstrated that NMs can penetrate, translocate, and accumulate in plants. However, studies about the effects of the NMs on plants are still limited because most investigations are carried out in the initial stage of plant development. The present study aimed to evaluate and characterize the photochemical efficiency of photosystem II (PSII) of broad bean (Vicia faba) leaves when subjected to silver nanoparticles (AgNPs) with diameters of 20, 51, and 73 nm as well as to micrometer-size Ag particles (AgBulk). The AgNPs were characterized by transmission electron microscopy and dynamic light scattering. The analyses were performed by injecting the leaves with 100 mg L-1 aqueous solution of Ag and measuring the chlorophyll fluorescence imaging, gas exchange, thermal imaging, and reactive oxygen species (ROS) production. In addition, silver ion (Ag+) release from Ag particles was determined by dialysis. The results revealed that AgNPs induce a decrease in the photochemical efficiency of photosystem II (PSII) and an increase in the non-photochemical quenching. The data also revealed that AgNPs affected the stomatal conductance (gs) and CO2 assimilation. Further, AgNPs induced an overproduction of ROS in Vicia faba leaves. Finally, all observed effects were particle diameter-dependent, increasing with the reduction of AgNPs diameter and revealing that AgBulk caused only a small or no changes on plants. In summary, the results point out that AgNPs may negatively affect the photosynthesis process when accumulated in the leaves, and that the NPs themselves were mainly responsible since negligible Ag+ release was detected

Experimental study of the electrical properties of copper nitride thin films prepared by dc magnetron sputtering

In this work the main effective parameters on the electrical resistivity of copper nitride thin films are investigated. Copper nitride thin films were successfully deposited on glass substrates by reactive dc magnetron sputtering at room temperature but different sputtering time. Working gas was a mixture of argon and nitrogen with equal amounts. The effect of deposition time on the structural, optical and electrical properties of deposited films was investigated. X-ray diffraction measurements show different lattice orientation in the structure of deposited films. By increasing the time of sputtering an orientation change from (100) to (111) can be observed in the films. Film morphology of samples is not changed with the sputtering time. The optical transmittance of deposited films decreases with increasing the deposition time. Results confirm that when the amount of nitrogen in working gas is 50%, we have more (100) planes in the structure of the deposited films, leads to higher resistivity of the films