AgNPs In Water Research Articles

Inter-transformation between silver nanoparticles and Ag+ induced by humic acid under light or dark conditions.

The fate and toxicity of silver nanoparticles (AgNPs) and ions in water bodies is largely determined by the natural organic matter (NOM)-mediated redox cycling. However, the process of NOM-mediated redox cycling in the day/night cycles remains elusive. In this study, the inter-transformation between AgNPs and Ag+ ion caused by humic acid (HA) was investigated under controlled light and dark conditions. It was shown that HA induced the reduction of Ag+ into AgNPs in simulated sunlight, and also oxidize AgNPs to release Ag+ in darkness. Kinetics data demonstrated that the rates of AgNPs formation and dissolution increased along with the increment of HA concentrations. Along with the pH increase, the reduction of Ag+ accelerated, but the oxidative dissolution of AgNPs was inhibited. In day-night cycles, the AgNPs and Ag+ concentrations exhibited similar wave-shaped change curves. The peaks of AgNPs and Ag+ ion appeared at 7 p.m. and 7 a.m., respectively. The toxicity of AgNPs/Ag+ to Escherichia coli was determined primarily by the concentration of dissolved Ag+, but also affected by the particle-specific toxicity. The dual role of HA implied that previous reports about the photo-reduction of Ag+ to AgNPs by NOM should be reconsidered, and the oxidizability of HA in darkness strongly affect the transformation and toxicity of AgNPs in water.

Effects of silver nanoparticles on coupled nitrification–denitrification in suspended sediments

The effects of varying concentrations of Ag NPs on coupled nitrification and denitrification (CND) in two suspended sediments (SPSs) sizes were investigated using isotopic tracer method. In general, 0.5 and 5 mg/L Ag NPs had less effect on CND, while 2 and 10 mg/L Ag NPs exhibited the improvement and inhibition effect, respectively. The CND improvement by 2 mg/L NPs was mainly due to the enhanced nitrifying and denitrifying enzyme activity. However, 10 mg/L Ag NPs inhibited NH4+ oxidation by directly reducing the AMO activity and AOB abundance. The inhibition on NAR and NIR activity and their encoding narG and nirK gene abundance further inhibited NO3− and NO2− reduction, leading to a dramatic decrease in the 15N–N2 production. The above inhibition effects were attributed to the nano-effects of Ag NPs, which led to the excessive ROS amount and the decreased T-AOC level in microbial systems. But the connection between nitrification and denitrification was not broken after Ag NPs exposure. Moreover, the results indicated that N-cycling in clay and silt-type SPS systems could be more sensitive than sand-type SPS systems to NP exposure. The findings provide a basis for evaluating the environmental risks of Ag NPs in water–sediment systems.

Callus Extract Mediated Green Synthesis of Silver Nanoparticles, Their Characterization and Cytotoxicity Evaluation Against MDA-MB-231 and PC-3 Cells

The green synthesis of nanoparticles using callus extract as reducing agent is an eco-friendly, cost-effective approach. In the present study, silver nanoparticles (AgNPs) were prepared using aqueous callus extract of Hyptis suaveolens and their cytotoxic efficacy against cancer cells namely MDA-MB-231 and PC-3 was reported. Callus growth was observed on Murashige and Skoog (MS) medium supplemented with (BAP) benzylaminopurine (0.5 mg/L) + naphthalene acetic acid (NAA) (2 mg/L), and 45-day-old callus was used as a source for synthesis of AgNPs. The synthesis of AgNPs was identified initially by color change (yellow to brown) of the reaction mixture and was further confirmed by characteristic UV–visible surface plasmon resonance peak at 447 nm. The presence of elemental silver in synthesized AgNPs was confirmed through Energy dispersive X-ray spectroscopy (EDS). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis revealed randomly dispersed, spherical shaped AgNPs, with size ranging from 12 to 25 nm, and the mean particle diameter is 18 ± 4 nm. Crystalline and monophasic nature of AgNPs was identified using XRD studies and distinct Bragg diffraction peaks corresponding to the planes of face-centered cubic lattice. The hydrodynamic diameter measured by dynamic light scattering was 207 nm, and it is higher than TEM and XRD analyses. The zeta potential of AgNPs in water was found to be − 24.5 mV, reflecting their higher stability, and FTIR revealed the presence of phenolic compounds and proteins. The cytotoxic effects of AgNPs against MDA-MB-231 and PC-3 cells were evaluated and their IC50 values were found to be 74.66 and 173.21 μg/mL, respectively. The results of the present study clearly demonstrate that the AgNPs prepared from Hyptis suaveolens have the potential to exert cytotoxic effect on cancer cell lines.

Time temperature indicators (TTIs) based on silver nanoparticles for monitoring of perishables products

This work presents the results of the production and characterization of silver nanoparticles (AgNPs) to applications in Time Temperature Indicators (TTIs). AgNPs were synthetized by chemical processes. The suspensions (AgNPs in water) were characterized for different temperatures (4°C and 22°C) and time (0 to 5h). The AgNPs were characterized by energy dispersive X-ray spectrometry (EDS), UV–vis spectrophotometry and dynamic light scattering (DLS). AgNPs with diameters between 40 to 160nm were produced. The UV-Vis spectra reveal a characteristic absorption peak of the Ag in 420nm. This suspension shows shifts in the emission wavelength when exposed to room temperature compared to when exposed to a temperature of 4°C for different periods of time. Δλ = 20nm in the absorption spectra were found. Size distribution showed that the nanoparticles size decreases from 164 ±8 nm to 44±3 nm in the period of time studied. Suspension with nanoparticles concentration of 1,26· 10-10 M were obtained. TTIs manufactured with nanomaterials base its operation on the variations of the characteristics of nanoparticles suspended due to absorbing heat.

Route of exposure has a major impact on uptake of silver nanoparticles in Atlantic salmon (Salmo salar).

The potential impact of silver nanoparticles (Ag NPs) on aquatic organisms is to a large extent determined by their bioavailability through different routes of exposure. In the present study juvenile Atlantic salmon (Salmo salar) were exposed to different sources of radiolabeled Ag (radiolabeled 110m Ag NPs and 110m AgNO3 ). After 48 h of waterborne exposure to 3 μg/L citrate stabilized 110m Ag NPs or 110m AgNO3 , or a dietary exposure to 0.6 mg Ag/kg fish (given as citrate stabilized or uncoated 110m Ag NPs, or 110m AgNO3 ), Ag had been taken up in fish regardless of route of exposure or source of Ag (Ag NPs or AgNO3 ). Waterborne exposure led to high Ag concentrations on the gills, and dietary exposure led to high concentrations in the gastrointestinal tract. Silver distribution to the target organs was similar for both dietary and waterborne exposure, with the liver as the main target organ. The accumulation level of Ag was 2 to 3 times higher for AgNO3 than for Ag NPs when exposure was through water, whereas no significant differences were seen after dietary exposure. The transfer (Bq/g liver/g food or water) from exposure through water was 4 orders of magnitude higher than from feed using the smallest, citrate-stabilized Ag NPs (4 nm). The smallest NPs had a 5 times higher bioavailability in food compared with the larger and uncoated Ag NPs (20 nm). Despite the relatively low transfer of Ag from diet to fish, the short lifetime of Ag NPs in water and their transfer to sediment, feed, or sediment-dwelling food sources such as larvae and worms could make diet a significant long-term exposure route. Environ Toxicol Chem 2018;37:2895-2903. © 2018 SETAC.

Correction: The Molecular Mechanisms of the Antibacterial Effect of Picosecond Laser Generated Silver Nanoparticles and Their Toxicity to Human Cells.

[This corrects the article DOI: 10.1371/journal.pone.0160078.].

Biogenic silver nanoparticles from Trachyspermum ammi (Ajwain) seeds extract for catalytic reduction of p-nitrophenol to p-aminophenol in excess of NaBH4

Plasmonic silver nanoparticles (AgNPs, size = 3–50 nm) were synthesized by biogenic reduction of aqueous AgNO3 using Trachyspermum ammi (TA, Ajwain) seeds extract. Increase in concentration of TA, accelerated the reduction rate of Ag+ and affected the AgNPs particle size. Pronounce effect of the AgNP's aging (24, 48 and 72 h) on particle concentration/size and their corresponding catalytic activity, was exhibited by the systems. Surface plasmonic resonance band centered between 420 and 430 nm wavelength, recognized as first exitonic peak of UV–vis absorption spectra of Ag NPs, was used to estimate the particle size (10–30 nm) of Ag NPs, which was consistent with the particle size observed with the FESEM (5–20 nm) and XRD observations (12.74 nm). XRD analysis also indicated that the silver nanoparticles were crystallized in the cubic crystal pattern. However, some cubic/rod like patterns grown along the 111 plane, was also observed by FESEM and HRTEM. ATR (Attenuated total reflectance) profile of aging of TA supported Ag NPs, exhibited the decrease in intensity of 3394, 1716 and 1618 cm− 1 peaks with respect to the pristine TA extract sample. That reflects the increase in particle concentration with time (24–48 h). These peaks correspond to the OH group, carbonyl group and C C stretching along with COC and CN stretching in TA-AgNPs aggregates. ATR and IR results suggested the presence of the reducing agent/phytochemicals (nicotinic acid, thymol, sugars, proteins, saponin, etc) incorporated NPs. Impedance study revealed that the rate of charge transfer in TA-Ag NPs aggregates is inversely proportional to the concentration of TA that confirms the stability of the Ag NPs in water. These biogenic Ag NPs are also characterized using transmission electron microscopy (TEM) and their corresponding energy dispersive X-ray analysis (EDX), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) studies, etc. On the basis of the above observations and optoelectronic characteristics, the most probable mechanism of biogenesis of the stable Ag NPs, is suggested. As-synthesized 24, 48 and 72 h aged Ag NPs, were tested for their catalytic reduction activity towards the conversion of p-nitro phenol to p-aminophenol in excess of NaBH4. 48 h-aged Ag NPs show highest catalytic activity for conversion of p-nitrophenol to p-aminophenol in excess of NaBH4 in terms of rate (r = 0.34539 min− 1) with complete reduction time 12 min.

Formation and Physiochemical Properties of Silver Nanoparticles with Various Exopolysaccharides of a Medicinal Fungus in Aqueous Solution.

Natural polysaccharides are the most widely used biopolymers for green synthesis of eco-friendly silver nanoparticles (AgNPs). In a previous study, a high molecular weight (MW) fraction of exopolysaccharides (EPS) produced by a medicinal fungus Cs-HK1 has been shown useful for green and facile synthesis of AgNPs in water. This study was to further evaluate the effects of molecular properties of EPS on the formation, stability and properties of AgNPs with different EPS fractions at various pH conditions. Three EPS fractions (P0.5, P2.0 and P5.0: MW high to low and protein content low to high) were reacted with silver nitrate at various pH 3.0–8.0 in water. The most favorable pH range was 5.5–8.0 for the formation and stable dispersion of AgNPs. At a given pH, the maximum amount of AgNPs was produced with P5.0, and the minimum with P0.5. The shape, size and physiochemical properties of AgNPs were strongly affected by the molecular characteristics of EPS (MW and conformation). The results may be helpful for understanding the factors and mechanisms for formation of stable AgNPs with natural polysaccharides and the interactions between AgNPs and the polysaccharide hydrocolloids in water.

Chiroptically Active Plasmonic Nanoparticles Having Hidden Helicity and Reversible Aqueous Solvent Effect on Chiroptical Activity.

The geometrical prerequisite for forming a helix is P (helical pitch) > d (wire diameter). Limited by the current development of nanofabrication techniques, it is difficult to minimize d and consequently P to the sub-10 nm molecule-comparable scale, preventing the study of chiral plasmonics at dimensions approaching the physical limit. Herein, glancing angle deposition is operated at substrate temperature of 0 °C and high speed of substrate rotation to generate silver nanoparticles (AgNPs) with nominal P < d. The AgNPs have intrinsic chiroptical activity characterized by circular dichroism (CD), originating from the hidden helicity. With increasing P from 3 to 66 nm, the plasmonic mode barely shifts but shows a logarithmic increase in CD amplitude. Immersing AgNPs in water causes the plasmonic mode to redshift and rise in CD amplitude, i.e., a water effect on chiroptical activity. Hydrophilic AgNP arrays with low array porosity show a reversible water effect, but hydrophobic Ag nanospiral arrays with P > d and high array porosity have an irreversible water effect. This work introduces a cost-effective, facile approach to minimize P to sub-10 nm at a regular substrate temperature, paving the way to study chiral plasmonics approaching the physical limit and exploit chirality-related bioapplications typically operated in aqueous solutions to tackle significant health and environmental problems.

The Molecular Mechanisms of the Antibacterial Effect of Picosecond Laser Generated Silver Nanoparticles and Their Toxicity to Human Cells.

Silver nanoparticles (Ag NPs) are known to have antibacterial properties. They are commonly produced by chemical synthesis which involves the use of harmful reducing agents. Contras, the laser technique is able to generate high-purity Ag NPs in water with specified surface charge characteristics. In the past, the molecular mechanisms contributing to the bactericidal effects of Ag NPs have been investigated extensively, but little is known of the antibacterial and toxic effects and mechanisms involved in laser-generated Ag NPs. In the current study Ag NPs were generated by picosecond laser ablation. Their antibacterial activity was determined on the gram-negative bacteria E. coli and Pseudomonas aeruginosa, and the gram positive bacteria Staphylococcus aureus including the methicillin resistant strain MRSA. Results showed that the laser generated Ag NPs exhibited strong dose-dependent antibacterial activity against all the three bacterial strains tested. Using E.coli as a model system, the laser Ag NPs treatment induced significantly high levels of reactive oxygen species (ROS). These ROS did not include detectable hydroxyl radicals, suggesting for the first time the selective ROS induction in bacterial cells by laser generated Ag NPs. The increased ROS was accompanied by significantly reduced cellular glutathione, and increased lipid peroxidation and permeability, suggesting ROS related bacterial cell damage. The laser generated Ag NPs exhibited low toxicity (within 72 hours) to five types of human cells although a weak significant decrease in cell survival was observed for endothelial cells and the lung cells. We conclude that picosecond laser generated Ag NPs have a broad spectrum of antibacterial effects against microbes including MRSA with minimal human cell toxicity. The oxidative stress is likely the key mechanism underlying the bactericidal effect, which leads to lipid peroxidation, depletion of glutathione, DNA damages and eventual disintegration of the cell membrane.

Separation and determination of silver nanoparticle in environmental water and the UV-induced photochemical transformations study of AgNPs by cloud point extraction combined ICP-MS

In this study, cloud point extraction (CPE) combined inductively coupled plasma mass spectrometry (ICP-MS) was used to determinate silver nanoparticles (AgNPs) in environmental water. AgNPs dispersed in water could be extracted into surfactant phase based on optimized CPE parameters which including pH, incubation temperature and equilibration time, the content of nonionic surfactants (Triton X-114, TX-114) and Na2S3O3. Good separation results of AgNPs and ionic silver Ag(I) in aqueous environment was obtained with the addition of Na2S3O3 when the concentration of Ag(I) was lower than ten times of AgNPs. High recoveries of different diameter AgNPs spiked into ultrapure water were obtained. The influence of environmentally relevant matrix on CPE of AgNPs was studied in detail. Our results showed that there were little interference of environmentally relevant ions and five representative engineering nanomaterials (ENMs) on CPE of AgNPs. Moreover high recoveries and good separation were obtained when natural organic matter (NOM) up to 30mg/L mixed with AgNPs in ultrapure water. The detection limit of AgNPs in water using CPE combined ICPMS was 5ng/L. The recoveries of the AgNPs spiked into natural and effluents water with this method were in the range of 79±1–123±13%. Furthermore CPE-ICPMS and Single particle-ICPMS were used to study the UV induced photochemical transformations of AgNPs suspension at environmental relevant concentrations.

High Resolution STEM-EELS Study of Silver Nanoparticles Exposed to Light and Humic Substances.

Nanoparticles (NPs) are defined as particles with at least one dimension between 1 and 100 nm or with properties that differ from their bulk material, which possess unique properties. The extensive use of NPs means that discharge to the environment is likely increasing, but fate, behavior, and effects under environmentally relevant conditions are insufficiently studied. This paper focuses on the transformations of silver nanoparticles (AgNPs) under simulated but realistic environmental conditions. High resolution aberration-corrected scanning transmission electron microscopy (HAADF STEM) coupled with electron energy loss spectroscopy (EELS) and UV-vis were used within a multimethod approach to study morphology, surface chemistry transformations, and corona formation. Although loss, most likely by dissolution, was observed, there was no direct evidence of oxidation from the STEM-EELS. However, in the presence of fulvic acid (FA), a 1.3 nm oxygen-containing corona was observed around the AgNPs in water; modeled data based on the HAADF signal at near atomic resolution suggest this was an FA corona was formed and was not silver oxide, which was coherent (i.e., fully coated in FA), where observed. The corona further colloidally stabilized the NPs for periods of weeks to months, dependent on the solution conditions.

Ecotoxicity of bare and coated silver nanoparticles in the aquatic midge, Chironomus riparius.

Although sediment is generally considered to be the major sink for nanomaterials in aquatic environments, few studies have addressed the ecotoxicity of nanomaterials in the presence of sediment. In the present study, the ecotoxicity of silver nanoparticles (AgNPs) with a range of organic coatings was examined in a freshwater sediment-dwelling organism, Chironomus riparius, using acute and chronic ecotoxicity endpoints, including molecular indicators. The toxicity of AgNPs coated with different organic materials, such as polyvinylpyrrolidone, gum arabic, and citrate, to C. riparius was compared with that of bare-AgNPs and AgNO3 (ionic silver). Total silver concentration was also measured to monitor the behavior of the AgNPs in water and sediment and to determine how ion dissolution affects the toxicity of all AgNPs. The coated- and bare-AgNPs caused DNA damage and oxidative stress-related gene expression. In addition, the bare-AgNPs and AgNO3 had a significant effect on development and reproduction. The surface coatings generally mitigated the toxicity of AgNPs to C. riparius, which can be explained by the reduced number of ions released from coated-AgNPs. Citrate-AgNPs caused the most significant alteration at the molecular level, but this did not translate to higher-level effects. Finally, comparing previously conducted studies on AgNP-induced gene expression without sediments, the authors show that the presence of sediment appears to mitigate the toxicity of AgNPs.

Structures and Conformations of Alkanedithiols on Gold and Silver Nanoparticles in Water

Organodithiols with two distal thiols have been used extensively in gold and silver nanoparticle (AuNP and AgNP) applications. However, understanding the structures and conformations of organodithiols on these nanoparticles is challenging. Reported in this work is a combined surface enhanced Raman spectroscopy (SERS), transmission electron microscope (TEM), inductively coupled plasma mass-spectrometry (ICP-MS), and localized surface plasmonic resonance (LSPR) study of alkyldithiol (ADT, (HS-(CH2)n-SH, n = 2, 4, and 6) interactions with AuNPs and AgNPs in water. These complementary techniques revealed a series of new insights that would not be possible using individual methods. A large-fraction of ADTs lies flat on AuNP surfaces. The upright ADTs are dimerized horizontally through disulfide-bond, or remain as monothiolates on the AuNP surfaces. The possibility of a significant amount of vertically disulfide-linked organodithiol on the surface is excluded on the basis of ICP-MS and AuNP LSPR experiments. AD...

In vitro toxicity study of plant latex capped silver nanoparticles in human lung carcinoma cells

Organically modified silver nanoparticles were prepared by biosynthetic route induced by stem latex of a medicinally important plant, Euphorbia nivulia. The reduction and stabilization is assisted by certain peptides and terpenoids present within the latex. The aqueous formulation of latex capped silver nanoparticles (LAgNPs) being completely free of toxic chemicals can be directly used for administration/ in vivo delivery of nanoparticles. The in vitro cytotoxicity evaluation of the latex capped nanoparticles was carried out using human lung carcinoma cells (A549) by MTT cell viability assay. Further, possible cytotoxic mechanisms were evaluated using various biomarkers for cytotoxicity and oxidative stress viz. extracellular lactate dehydrogenase (LDH) release, reactive oxygen species (ROS) generation, intracellular reduced glutathione (GSH), malondialdehyde (MDA), superoxide generation and acridine orange/ethedium bromide staining. It can be concluded from the present study that LAgNP formulation is toxic to A549 cells in a dose dependent manner. Thus plant latex solubilizes the AgNPs in water and acts as a biocompatible vehicle for transport of AgNPs to tumor/cancer cells.