Micro-sized Silver Particles Research Articles

Synthesis of Functional Silver Nanoparticles and Microparticles with Modifiers and Evaluation of Their Antimicrobial, Anticancer, and Antioxidant Activity.

An accumulating body of evidence reports the synthesis and biomedical applications of silver nanoparticles. However, the studies regarding the use of maleic acid and citric acid in the synthesis of nano-sized silver particles (AgNPs) and micro-sized silver particles (AgMPs) as well as their antibacterial, antifungal, and anticancer activities have not been reported. In the current study, we synthesized AgNPs and AgMPs using maleic acid and citric acid as capping agents and have characterized them by UV-Vis, energy-dispersive X-Ray spectroscopy (EDS), X-Ray diffraction (XRD), and scanning electron microscope (SEM) analysis. The capped silver particles were examined for their antimicrobial activity and cytotoxicity against bacteria, fungi, and brine shrimp. Additionally, the anticancer activity of these particles was tested against human breast and liver cancer cell lines. The free radical scavenging activity of capped silver particles was evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. SEM analysis revealed a round plate-like morphology of maleic acid capped particles with an average size of 39 ± 4 nm, whereas citric acid capped particles display flower-shaped morphology with rough surfaces and an average size of 250 ± 5 nm. The uncapped AgMPs were hexagonal with 500 ± 4 nm size. EDS and XRD analysis confirmed the presence of Ag and face-centered cubic crystalline nature, respectively. Functionally, capped silver particles exhibited antibacterial activity against Gram-positive (Staphylococcus aureus, Bacillus subtilis, and Micrococcus luteus) and Gram-negative bacteria (Salmonella setubal, Enterobacter aerogenes, and Agrobacterium tumefaciens). The bactericidal activity was more active against Gram-negative bacteria with minimum inhibitory concentration (MIC) as low as 5 ppm as compared to 25 ppm for Gram-positive. Similarly, the silver particles demonstrated antifungal activity by inhibiting the growth of five fungal strains (Mucor species, Aspergillus niger, Aspergillus flavus, Aspergillus fumigatus, and Fusarium solani) up to 50% at the concentration of 500 ppm. Additionally, these particles showed substantial toxicity against brine shrimp and also significantly inhibited the proliferation of breast cancer (MCF7) and liver cancer (HePG2) cell lines (IC50 8.9–18.56 µM). Uncapped AgMPs were less effective, inhibiting only the proliferation of MCF7 cells with IC50 46.54 µM. Besides cytotoxicity, these particles acted as potential antioxidants, showing free radical scavenging up to 74.4% in a concentration-dependent manner. Taken together, our results showed that the modifiers affect the shape and size of silver particles and may, in part, contribute to the antimicrobial and antioxidant activity of silver particles. However, the contribution of maleic acid and citric acid in enhancing the antimicrobial, anticancer, and antioxidant potential independent of silver nano and microparticles needs to be studied further. In vivo experiments may determine the therapeutic effectiveness of silver particles capped with these modifiers.

Effect of I/Ag molar ratio on silver thick films below 550 °C

The effect of low I/Ag ratios on the performance of silver thick films containing micro-sized silver particles treated with surface iodination has been investigated. The film with I/Ag ratio of 1:100 exhibited high electrical conductivity and densification, while that of 2:100 presented better adhesion. The conductivity and densification of the film reached the highest at 550 °C. Optimal conductivity of the film with I/Ag ratio of 1:100 and 2:100 was 11.45 and 15.85 mΩ/sq., respectively. In addition, the film adhesion was enhanced by heating. Different trends observed in electrical conductivity and adhesion as functions of temperature is primarily attributed to shrinkage of modified particles. This work suggested that the I/Ag ratio plays a vital effect on the performance of the silver thick film.

Low-Temperature Sintering Behavior (≤ 400°C) of Micro-sized Silver Particles Decorated by Silver Nanoparticles Through Surface Iodination

This paper introduces a facile and effective route to decorate micro-sized silver particle surfaces with Ag/AgI nanoclusters through a wet chemical reaction at room temperature using iodine and ethanol as reactant and solvent, respectively. Photosensitivity of AgI is utilized in the route, and AgI decomposes into Ag upon contact with sunshine, forming Ag/AgI nanoclusters. The modified micro-sized Ag particles showed sinterability even at 200°C and formed rigid electrical conductive networks at 350°C. Moreover, sintered film containing the modified Ag particles reached the best conductivity, 9.35 mΩ/sq, after sintering at 350°C for 20 min, while the film with untreated control Ag particles obtained its best conductivity at 400°C. The excellent sinterability should be attributed to the nanoclusters which served as a sintering aid during the heating process. However, increase of sintering temperature and time destroyed densification and conductivity of the sintered film containing the modified particles.

The preparation of oleylamine modified micro-size sphere silver particles and its application in crystalline silicon solar cells.

In this paper, micro-sized silver particles were prepared using a simple chemical approach without adjusting the pH of the solution, and oleylamine as a capping agent was described to promote the dispersion of the silver particles. The effects of temperature, feeding time and stirring speed on the morphology and size distribution of silver particles were discussed. The optimal reaction parameters (35 °C, 45 min, 300 rpm) for large scale industrial production were selected to obtained optimal silver particles for preparation of the silver paste for poly-crystalline silicon solar cells. The photoelectric conversion efficiency of the solar cells made with silver paste by using the silver particles can reach 18.623%, which is similar to the industrial production of solar cell made with commercial silver paste. This work contributes to the development of the synthesis of highly disperse silver particles used in solar cells in large scale industrial productions.

Disinfection and removal performance for Escherichia coli and heavy metals by silver-modified zeolite in a fixed bed column

This study investigates the simultaneous removal of Escherichia coli and metals (Pb, Cd and Zn) in a continuous flow system and provides an insight into the mechanisms involved during bacterial cells kill when in contact with silver-modified zeolite. Results showed complete disinfection and metal removal at 570min contact time, thereafter E. coli breakthrough followed by Cd and Zn at 1080min. Due to the zeolite’s high selectivity for Pb removal, no breakthrough was observed up to 7920min run time. Column performance was influenced by changes in flow rate and bed height, as breakthrough occurred at 240min when the flow rate was increased from 2 to 5mL/min and the bed height decreased from 1 to 0.5cm. Morphological characterisation of treated cells revealed extensive damage and synthesis of nano- and micro-sized silver particles as a part of their defence mechanism. The treated effluent was passed through a non-modified zeolite column with 98% silver recovery achieved. This study showed the capability of this system to simultaneously handle bacterial and heavy metals contamination while providing an insight into the mechanism of disinfection via complex E. coli–silver ion interactions that occur during treatment and demonstrating the potential of silver recovery for reuse.

Toxicity of nano- and micro-sized silver particles in human hepatocyte cell line L02

Silver nanoparticles (Ag NPs) previously classified as antimicrobial agents have been widely used in consumers and industrial products, especially food storage material. Ag NPs used as antimicrobial agents may be found in liver. Thus, examination of the ability of Ag NPs to penetrate the liver is warranted. The aim of the study was to determine the optimal viability assay for using with Ag NPs in order to assess their toxicity to liver cells. For toxicity evaluations, cellular morphology, mitochondrial function (3-(4, 5-dimethylazol-2-yl)-2, 5-diphenyl-tetrazolium bromide, MTT assay), membrane leakage of lactate dehydrogenase (lactate dehydrogenase, LDH release assay), Oxidative stress markers (malonaldehyde (MDA), glutathione (GSH) and superoxide dismutase (SOD)), DNA damage (single cell gel eletrophoresis, SCGE assay), and protein damage were assessed under control and exposed conditions (24 h of exposure). The results showed that mitochondrial function decreased significantly in cells exposed to Ag NPs at 25 μg·mL−1. LDH leakage significantly increased in cells exposed to Ag NPs (≥ 25 μg mL−1) while micro-sized silver particles tested displayed LDH leakage only at higher doses (100 μg·mL−1). The microscopic studies demonstrated that nanoparticle-exposed cells at higher doses became abnormal in size, displaying cellular shrinkage, and an acquisition of an irregular shape. Due to toxicity of silver, further study conducted with reference to its oxidative stress. The results exhibited significant depletion of GSH level, increase in SOD levels and lead to lipid peroxidation, which suggested that cytotoxicity of Ag NPs in liver cells might be mediated through oxidative stress.The results demonstrates that Ag NPs lead to cellular morphological modifications, LDH leakage, mitochondrial dysfunction, and cause increased generation of ROS, depletion of GSH, lipid peroxidation, oxidative DNA damage and protein damage. Though the exact mechanism behind Ag NPs toxicity is suggested oxidative stress and lipid peroxidation playing an important role in Ag NPs elicited cell membrane disruption, DNA damage, protein damage and subsequent cell death. Our preliminary data suggest that oxidative stress might contribute to Ag NPs cytotoxicity. To reveal whether apoptosis involved in Ag NPs toxicity, further studies are underway.

Printed UHF RFID Antennas with High Efficiencies Using Nano-Particle Silver Ink

One of the most popular targets of conductive ink technology is to print RFID tag antennas. However, the printed RFID antennas, manufactured by conductive silver ink which is generally based on microsized silver particles, have lower conductivity and consequently lower radiation efficiency than those by conventional copper etching method. This work demonstrates nano-particle conductive silver ink that is capable of printing UHF RFID antennas with improved radiation efficiency. Compared with commercial micro-particle silver ink, the solid content of metal is much higher in the proposed nanoparticle silver ink, leading to better electrical properties. Two types of dipole antennas are printed with the proposed nano-particle as well as with commercial micro-particle inks. Also, the same antennas are fabricated by copper etching. With these conductive inks, a straight and a meandered dipole antennas are fabricated and their radiation efficiencies are measured with the Wheeler cap method. Experimental results show that the radiation efficiencies of the antennas based on nanoparticle silver ink are superior to those printed with the micro-particle silver ink, and are comparable to those of popular copper antennas.

Comparison of acute responses of mice livers to short-term exposure to nano-sized or micro-sized silver particles

Mice were fed either 13 nm silver nanoparticles or 2-3.5 mum silver microparticles. The livers were then obtained after 3 days and subjected to a histopathological analysis. The nanoparticle-fed and microparticle-fed livers both exhibited lymphocyte infiltration in the histopathological analysis, suggesting the induction of inflammation. In vitro, a human hepatoma cell line (Huh-7) was treated with the same silver nanoparticles and microparticles. The mitochondrial activity and glutathione production were hardly affected. However, the DNA contents decreased 15% in the nanoparticle-treated cells and 10% in the microparticle-treated cell, suggesting a more potent induction of apoptosis by the nanoparticles. From a microarray analysis of the RNA from the livers of the nano- and micro-particle-fed mice, the expression of genes related to apoptosis and inflammation was found to be altered. These gene expression changes in the nanoparticle-treated livers lead to phenotypical changes, reflecting increased apoptosis and inflammation. The changes in the gene expression were confirmed by using a semi-quantitative RT-PCR.

Study on LCD Micro Stereolithography using Silver Particles Photosensitive Resin

In order to apply the LCD micro stereolithography to the fabrication of electric devices, we developed silver particles photosensitive resins, which were made by mixing micro-sized silver particles into an acrylic photosensitive resin. In this report, 3D microelectrode with high electrical conductivity was typically fabricated as a test piece. Electrical conductivity was then examined as a function of silver mixing rates by the use of four-terminal micro resistance patterns before and after heat treatment under the condition of 200±10°C for 1hour. After the heat treatment, micro resistance patterns with silver mixing rates of 50wt% showed a low electrical resistance less than 3×10-5Ω·cm. Our results indicated that the electrical conductivity was improved with an increase of conductive path equivalent to the mixing rate of silver particles. Consequently, 100 numbers of microelectrodes with the high electrical conductivity were able to fabricate in the high speed of 1.3second by using the LCD mask designed with four grayscale levels of 255, 170, 130 and 80. Also, the good fabrication accuracy could be accomplished within the error rate of 2.8% or 1.4% in height or width after the heat treatment.