Citrate Silver Nanoparticles Research Articles

Citrate-silver nanoparticles and their impact on some environmental beneficial fungi.

Colloidal suspensions of silver nanoparticles (AgNPs) with surface modified by capping with citrate ions were synthesized by chemical reduction method. Transmission and Scanning Electron Microscopy as well as darkfield Optical Microscopy provided information on the nanoparticle morphology, with fine symmetrical grains and log-normal fitted size distribution. Small Angle X-ray Scattering method allowed theoretical confirmation of colloidal silver nanoparticle fine granularity, based on measurements in the native fluid sample. UV–Vis spectrophotometry allowed studying the Localized Surface Plasmon Resonance band versus the stability of the citrate-AgNP sample after storage and after UV-C exposure. The colloidal AgNP impact on Phanerochaete chrysosporium environmental microorganisms was studied by specific biochemical investigations. Silver released from the colloidal suspension of AgNPs was supposed to induce changes in some antioxidant enzymes and in some enzymes of Krebs’ cycle. Catalase activity was moderately changed (an increase with over 50%) as well as superoxide dismutase activity, while the diminution of the activities of four dehydrogenases synthesized in the fungus mycelium was emphasized also: a decrease with about 60% for malate dehydrogenase, with over 50% for isocitrate dehydrogenase and succinate dehydrogenase and with about 40% for alpha-ketoglutarate dehydrogenase. These findings suggested the nano-toxicological issues of citrate-AgNPs impact on the environmental beneficial microorganisms.

Two phase photochemical synthesis of silver nanoparticles and their impact on the chlorophylls

We have designed an experimental study dedicated to silver nanotoxicity using a suspension of citrate-silver nanoparticles, obtained by photochemical reduction. Fine granularity of generally symmetrical shape nanoparticles were evidenced by tansmission electron microscopy. The localized surface plasmon resonance spectral band revealed the intensification of silver nanoparticle formation under UV exposure. The nanotoxicity of silver nanoparticles was tested on cereal sprouts by measuring the concentrations of chlorophylls and carotenes in the green tissue. The differences between control samples, supplied with distilled water and test samples, loaded with different volumes of silver nanoparticles suspension were analyzed statistically, and compared with literature reports.

Gill Histopathologies Following Exposure to Nanosilver or Silver Nitrate

Fish gill is the site for many crucial physiological functions. It is among the first sites of xenobiotic exposure, and gill histopathological alterations may be detected soon after toxicant exposure. Silver (Ag) is one of the most toxic metals to aquatic organisms mainly due to its ability to disrupt ionic regulation. The goal of this study was to determine the effect of ionic and nanoscale Ag on fathead minnow gills by examining gill histology and Na+/K+-ATPase immunoreactivity. Fathead minnows were exposed to two measured concentrations of silver nitrate (AgNO3: 1.3 or 3.7 μg/L as Ag+), citrate silver nanoparticles (citrate-AgNP: 15 or 39 μg/L), and polyvinylpyrrolidone-AgNP (PVP-AgNP) (AgNP: 11 or 50 μg/L). Circulatory disturbances were the most prevalent gill alterations detected and were significantly increased in all Ag treatment groups compared to control. AgNO3 (1.3 μg/L) was the only treatment that significantly elevated the number of total mucous goblet cells present. In all other Ag treatments, the percent of degenerated goblet cells was significantly increased compared to control. When the sum of all histopathological abnormalities (weighted index) was calculated, all Ag groups displayed a significantly higher index, with citrate-AgNP having the highest toxicity (index of 10 ± 0.32 versus 2.4 ± 0.6 in controls). Gill Na+/K+-ATPase immunoreactivity was decreased by Ag. These results indicated that both AgNO3 and AgNP created similar disruptions in gill structure and ionic regulation, possibly due to the ionic Ag portion of each treatment.

Influence of Water Hardness on Silver Ion and Silver Nanoparticle Fate and Toxicity Toward Nitrosomonas europaea.

This study investigated the influence of water hardness (Mg2+ and Ca2+) on the fate and toxicity of 20 nm citrate silver nanoparticles (AgNPs) and Ag+ toward Nitrosomonas europaea, a model ammonia-oxidizing bacterium. Nitrification inhibition of N. europaea by 1 ppm AgNPs and 0.5 ppm Ag+ was reduced from 80% and 83%, respectively, in the absence of Mg2+ to 2% and 33%, respectively, in the presence of 730 μM Mg2+. Introduction of Mg2+ resulted in the rapid aggregation of the AgNP suspensions and reduced the 3 h Ag+ dissolution rates from 30%, in the absence of Mg2+, to 9%, in the presence of 730 μM Mg2+. Reduced AgNP dissolution rates resulted in decreased concentrations of silver that were found adsorbed to N. europaea cells. Increasing AgNP concentrations in the presence of Mg2+ increased the observed inhibition of nitrification, but was always less than what was observed in the absence of Mg2+. The presence of Mg2+ also reduced the adsorption of Ag+ to cells, possibly due to multiple mechanisms, including a reduction in the negative surface charge of the N. europaea membrane and a competition between Mg2+ and Ag+ for membrane binding sites and transport into the cells. Ca2+ demonstrated similar protection mechanisms, as Ag+ toxicity was reduced and AgNP suspensions aggregated and decreased their dissolution rates. These results indicate that the toxicity of Ag+ and AgNPs to nitrifying bacteria in wastewater treatment would be less pronounced in systems with hard water.

Influence of Bovine Serum Albumin and Alginate on Silver Nanoparticle Dissolution and Toxicity to Nitrosomonas europaea

Bovine serum albumin (BSA), a model protein, reduced the toxicity of 20 nm citrate silver nanoparticles (AgNP) toward Nitrosomonas europaea, a model ammonia oxidizing bacteria, through a dual-mode protection mechanism. BSA reduced AgNP toxicity by chelating the silver ions (Ag(+)) released from the AgNPs. BSA further reduced AgNP toxicity by binding to the AgNP surface thus preventing NH3-dependent dissolution from occurring. Due to BSA's affinity toward Ag(+) chemisorbed on the AgNP surface, increased concentrations of BSA lead to increased AgNP dissolution rates. This, however, did not increase AgNP toxicity as the dissolved Ag(+) were adsorbed onto the BSA molecules. Alginate, a model extracellular polysaccharide (EPS), lacks strong Ag(+) ligands and was unable to protect N. europaea from Ag(+) toxicity. However, at high concentrations, alginate reduced AgNP toxicity by binding to the AgNP surface and reducing AgNP dissolution rates. Unlike BSA, alginate only weakly interacted with the AgNP surface and was unable to completely prevent NH3-dependent AgNP dissolution from occurring. Based on these results, AgNP toxicity in high protein environments (e.g., wastewater) is expected to be muted while the EPS layers of wastewater biofilms may provide additional protection from AgNPs, but not from Ag(+) that have already been released.