Ag/TiO2/bentonite nanocomposite for biological applications: Synthesis,characterization, antibacterial and cytotoxic investigations

Bentonite (bent) clay supported silver (Ag)/titanium dioxide (TiO₂) nanocomposite material was green synthesized by facile thermal decomposition method in the absence of reducing and precipitating agents. The samples were characterized by XRD, BET, HR-SEM with EDX mapping, TEM with SAED patterns, XPS, PSA, FT-IR, and UV–Vis DRS. XRD and EDX spectra showed peaks of Ag and TiO₂, confirming the formation of the Ag/TiO₂ nanoparticles in the composite. TEM revealed the uniform distribution of Ag/TiO₂ nanoparticles cluster on the surface of the bent with an average size of ～5 to 50 nm. The antibacterial activities of Na-bent, Ag, TiO₂, and Ag/TiO₂/bent nanocomposite samples were tested against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) bacteria by the well diffusion method. Furthermore, the cytotoxicity of Ag/TiO₂/bent nanocomposite material was determined by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. Also, the succinate-dehydrogenase release showed the nontoxic nature of the nanocomposite at low concentrations. The cytotoxicity results of samples were evaluated using human embryonic kidney cell line (HEK 293) and have given excellent biocompatibility and cell proliferation in the in vitro studies.     

Preparation and properties of antibacterial TiO2@C/Ag core–shell composite

Abstract

An environment-friendly hydrothermal method was used to prepare TiO₂@C core–shell composite using TiO₂ as core and sucrose as carbon source. TiO₂@C served as a support for the immobilization of Ag by impregnation in silver nitrate aqueous solution. The chemical structures and morphologies of TiO₂@C and TiO₂@C/Ag composite were characterized by x-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, energy dispersive x-ray spectroscopy and Brunauer–Emmett–Teller (BET) analysis. The antibacterial properties of the TiO₂@C/Ag core–shell composite against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were examined by the viable cell counting method. The results indicate that silver supported on the surface of TiO₂@C shows excellent antibacterial activity.     

Quantification of silver ion release,in vitro cytotoxicity and antibacterial properties of nanostuctured Ag doped TiO2 coatings on stainless steel deposited by RF magnetron sputtering

Surface treatments on biomaterials using several methods have greatly reduced the in vivo bacterial attachment, surface colonization and formation of biofilm. In this study, the effect of silver (Ag) ion release against in vitro antibacterial activity and cytotoxicity of 1–4wt% Ag doped titania (TiO₂) thin film coatings were evaluated. These coatings were deposited for 1–6 h onto stainless steel substrate (SS) using (radio frequency) RF magnetron sputtering technique. The coatings predominantly in the crystalline anatase phase were configured using X-ray Diffraction (XRD). Scanning electron microscopy (SEM) observation showed the presence of Ag–TiO₂ nanoparticles of less than 100 nm in all the coated surfaces confirming the formation of nanostructured coatings. An initial rapid release, followed by a sustained lower release of Ag ion concentration was measured between 0.45 and 122 ppb when all the coated substrates immersed in Phosphate Buffered Saline (PBS) for 1–10 days. The obtained concentration was less than the maximum toxic concentration for human cells; yet achieved antibacterial concentration, sufficient to kill or inhibit the growth of bacteria. In vitro cytotoxicity results have indicated that 1–4 wt% of Ag doped TiO₂ coatings had no adverse effect on mouse fibroblast proliferation, confirming its cytocompatibility. The antibacterial assessment was performed on 1 and 2 wt% Ag–TiO₂ coatings using Staphylococcus aureus (S. aureus) whereby significant antibacterial activity was observed in 2 wt% Ag–TiO₂ coatings.     

Quantification of silver ion release, in vitro cytotoxicity and antibacterial properties of nanostuctured Ag doped TiO2 coatings on stainless steel deposited by RF magnetron sputtering

Surface treatments on biomaterials using several methods have greatly reduced the in vivo bacterial attachment, surface colonization and formation of biofilm. In this study, the effect of silver (Ag) ion release against in vitro antibacterial activity and cytotoxicity of 1-4wt% Ag doped titania (TiO₂) thin film coatings were evaluated. These coatings were deposited for 1-6 h onto stainless steel substrate (SS) using (radio frequency) RF magnetron sputtering technique. The coatings predominantly in the crystalline anatase phase were configured using X-ray Diffraction (XRD). Scanning electron microscopy (SEM) observation showed the presence of Ag-TiO₂ nanoparticles of less than 100 nm in all the coated surfaces confirming the formation of nanostructured coatings. An initial rapid release, followed by a sustained lower release of Ag ion concentration was measured between 0.45 and 122 ppb when all the coated substrates immersed in Phosphate Buffered Saline (PBS) for 1-10 days. The obtained concentration was less than the maximum toxic concentration for human cells; yet achieved antibacterial concentration, sufficient to kill or inhibit the growth of bacteria. In vitro cytotoxicity results have indicated that 1-4 wt% of Ag doped TiO₂ coatings had no adverse effect on mouse fibroblast proliferation, confirming its cytocompatibility. The antibacterial assessment was performed on 1 and 2 wt% Ag-TiO₂ coatings using Staphylococcus aureus (S. aureus) whereby significant antibacterial activity was observed in 2 wt% Ag-TiO₂ coatings.     

Evaluation of the physical and antimicrobial properties of silver doped hydroxyapatite depending on the preparation method

In the present study, the effect of the preparation method on the physical and antibacterial properties of silver doped hydroxyapatite (HAp/Ag) samples was investigated. HAp/Ag with 0.1–5 % of silver was prepared using two different modified wet chemical precipitation methods. A comparison of thermal stability and thermodynamical properties indicated that the thermal stability and sintering temperature of HAp/Ag were higher than those of pure hydroxyapatite if Ca(NO₃)₂·4H₂O, AgNO₃, NH₄OH and (NH₄)₂HPO₄ were used as raw materials. Phase composition and silver release were determined by XRD and ICP-MS. The study showed that, after 50 h in simulated body fluid 0.8–1.8 % of silver of the total silver amount was released from compact HAp/Ag scaffolds, and release kinetics strongly depended on the HAp/Ag preparation method. In vitro antibacterial activity of samples from each method against the bacterial strains Staphylococcus epidermidis and Pseudomonas aeruginosa was approved. Results showed that, in the case of using Ca(OH)₂, H₃PO₄ and AgNO₃ as raw materials for HAp/Ag synthesis, higher antibacterial activity towards both bacterial strains could be obtained.     

Evaluation of the toxicities of silver and silver sulfide nanoparticles against Gram‐positive and Gram‐negative bacteria

In this study, the endogenous lipid signalling molecules, N ‐myristoylethanolamine, were explored as a capping agent to synthesise stable silver nanoparticles (AgNPs) and Ag sulphide NPs (Ag₂ S NPs). Sulphidation of the AgNPs abolishes the surface plasmon resonance (SPR) maximum of AgNPs at 415 nm with concomitant changes in the SPR, indicating the formation of Ag₂ S NPs. Transmission electron microscopy revealed that the AgNPs and Ag₂ S NPs are spherical in shape with a size of 5–30 and 8–30 nm, respectively. AgNPs and Ag₂ S NPs exhibit antimicrobial activity against Gram‐positive and Gram‐negative bacteria. The minimum inhibitory concentrations (MIC) of 25 and 50 μM for AgNPs and Ag₂ S NPs, respectively, were determined from resazurin microtitre plate assay. At or above MIC, both AgNPs and Ag₂ S NPs decrease the cell viability through the mechanism of membrane damage and generation of excess reactive oxygen species.Inspec keywords: cellular biophysics, biomembranes, transmission electron microscopy, nanomedicine, microorganisms, molecular biophysics, antibacterial activity, nanofabrication, silver, biomedical materials, surface plasmon resonance, nanoparticles, materials preparation, silver compounds, lipid bilayersOther keywords: Gram‐negative bacteria, Gram‐positive bacteria, endogenous lipid signalling molecules, N‐myristoylethanolamine, capping agent, silver nanoparticles, Ag sulphide NPs, sulphidation, surface plasmon resonance, concomitant changes, transmission electron microscopy, minimum inhibitory concentrations, resazurin microtitre plate assay, cell viability, membrane damage, reactive oxygen species, Ag toxicities, Ag, Ag₂ S     

In situ generation of Ag nanoparticles on polyester fabrics by photoreduction using TiO2 nanoparticles

This study discusses the possibility of in situ generation of Ag nanoparticles on polyester fabric by photoreduction of Ag⁺ ions with deposited TiO₂ nanoparticles in the presence of amino acid alanine and methyl alcohol. The presence of TiO₂/Ag nanoparticles on the polyester fiber surface was confirmed by XRD, XPS, and SEM analyses. Such nanocomposite textile material provides excellent antimicrobial activity against Gram-negative bacterium E. coli, Gram-positive bacterium S. aureus, and fungus C. albicans. Maximum microbial reduction was preserved even after ten washing cycles. In spite of satisfactory laundering durability, the release of silver occurred during washing. The leaching of silver was also present when the fabrics were exposed to artificial sweat at pH 5.5 and pH 8.0 for 24 h. In addition to excellent antimicrobial properties, TiO₂/Ag nanoparticles imparted maximum UV protection to polyester fabrics.     

Sol-gel synthesis of silver/titanium dioxide (Ag/TiO2) core-shell nanowires for photocatalytic applications

Silver/titanium dioxide (Ag/TiO₂) core-shell nanowires were synthesized by direct coating of TiO₂ shells on the surface of silver nanowires (AgNWs) through a simple sol-gel process. TEM image and EDX elemental analysis had confirmed the presence of TiO₂ coating on the surface of AgNWs. The thickness of titanium dioxide coating was about 10 nm. These Ag/TiO₂ core-shell nanowires showed good photocatalytic activities in the decomposition of methylene blue as a model organic dye in aqueous solution under UV light irradiation. Ag/TiO₂ core-shell nanowires are potentially useful in photocatalytic applications.     

Influence of silver doping on the phase transformation and crystallite growth of electrospun TiO2 nanofibers

Ag doped TiO₂ nanofibers were fabricated by electrospinning technique using polyvinyl pyrrolidone (PVP) and titanium isopropoxide (TiP) as precursor. The effects of silver and calcination temperature on the preparation of electrospun TiO₂ nanofibers were investigated. The calcination temperature determines the TiO₂ phases as ether anatase or rutile. When the calcination temperature increased, crystallite size of TiO₂ nanofiber increased. The crystallite size of Ag doped TiO₂ nanofiber is smaller than that of the pure TiO₂ nanofiber because silver is retrained in this phase transformation. Silver controlled the phase transformation as well as had an inhibition effect on the growth of anatase crystallite.     

Photoelectrocatalytic properties and bactericidal activities of silver-treated carbon nanotube/titania composites

Two types of carbon nanotube/TiO₂ and silver-treated carbon nanotube/TiO₂ electrodes were prepared and characterized by X-ray diffraction, transmission and scanning electron microscopy, energy dispersive X-ray analysis, photoelectrocatalytic activity and antibacterial activity. The photoelectrocatalytic degradation of a methylene blue solution was attributed to the combined effects of the photo-degradation of TiO₂, the electron assistance of carbon nanotube network and the enhancement of silver and was a function of the applied potential. The composites treated with silver showed enhanced photo-degradation of methylene blue, and the photoelectrocatalytic activity increased with increasing amount of silver. The silver-treated carbon nanotube/TiO₂ prepared as bactericides have stronger antibacterial activity against Escherichia coli K-12 than standard ampicillin, tetracycline and carbon nanotube/TiO₂ under sunlight or dark conditions. The presence of silver in the silver-treated carbon nanotube/TiO₂ composites enhanced the inactivation of the E. coli K-12.     

Effects of silver concentrations on microstructure and properties of nanostructured titania films

To prevent bacterial proliferation on biomedical titanium implants, significant efforts have been focused on modifying its surface composition and structure. In this study, nanostructured titania (TiO₂) films with different concentrations of silver were prepared by magnetron sputtering and subsequently annealed at 600 °C in air. The effects of silver concentrations on microstructure, antibacterial property, corrosion resistance and hardness were studied. The results indicate that silver contribute to the growth of the TiO₂ grains and is uniformly dispersed on the surface of annealed samples. The annealed films with a thickness of about 2.5 μm are uniform and mainly composed of rutile phase and pure titanium. Silver mainly exists in the metallic state in the TiO₂ films. The Ag-doped TiO₂ films can effectively kill Staphylococcus aureus within 24 h and the antibacterial ability increases with the silver content. The dynamic potential polarization results show that silver incorporation into TiO₂ films slightly lower the corrosion potential, but significantly decrease the current density, and the current density decreases as the silver addition increases. Moreover, the hardness of the Ag-doped TiO₂ films is also greatly improved.     

Synthesis and enhanced light absorption of alumina matrix nanocomposites containing multilayer oxide nanorods and silver nanoparticles

In this paper, multilayer oxide nanorods were deposited in the nanopores of anodic aluminum oxide (AAO) via solution infiltration followed by heat treatment. The nanorods have a core–shell structure. First, the shell (nanotube) with the thickness of about 40 nm was made of TiO₂ through the hydrolysis of (NH₄)₂TiF₆. Second, silver nanoparticles with the diameter of about 3 nm were added into the TiO₂ layer through thermal decomposition of AgNO₃ at elevated temperatures. Then, cylindrical cores (nanorods) of CoO and ZnO with 200 nm diameter were prepared, respectively. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the structure and composition of the nanorods. UV–vis light absorption measurements in the wavelength range from 350 to 1000 nm were performed to study the effect of nanorod and nanoparticle addition on the light absorption property of the alumina nanocomposites. It is found that CoO nanorods increase the light absorption of the alumina matrix composite in the wavelength range from 500 nm to 800 nm, but the TiO₂ shell does not increase the light absorption much. The ZnO nanorods do not change the light absorption either. However, the addition of silver nanoparticles significantly enhances light absorption of both AAO/TiO₂/Ag/CoO and AAO/TiO₂/Ag/ZnO nanocomposites. This increase in the visible light absorption reveals that there exists surface plasmon around the fine silver nanoparticles in the nanorods.     

Mechanisms of antibacterial activity and stability of silver nanoparticles grown on magnetron sputtered TiO<Subscript>2</Subscript> coatings

Nanomaterials with high stability and efficient antibacterial activity are of considerable interest. The preparation of silver nanoparticles (AgNPs) on titania coatings and their effective antibacterial activity against Staphylococcus aureus ATCC 6538 were reported. Titanium dioxide (TiO₂) coatings with AgNPs were prepared on Si wafers using the reactive magnetron sputtering method. The surface topography of AgNPs/TiO₂ coatings imaged using scanning electron microscopy revealed that the size and surface density of AgNPs grown by the photoreduction of silver ions were dependent on the concentration of AgNO₃ in the primary solution and the time of TiO₂ exposure to UV illumination. Evaluation of the antimicrobial properties and surface analysis before and after the biological test of AgNPs/TiO₂ coatings indicates their high antimicrobial stability and durability. Furthermore, the interdependence between the concentration of released silver and bacterial growth inhibition was demonstrated. In addition, direct contact killing and released silver-mediated killing have been proposed as a bactericidal mechanism of action of tested coatings with AgNPs.     

Antibacterial effect of silver nanoparticles against Streptococcus mutans

Dental caries is a very infectious disease; in humans, 95% of the worldwide population is affected. The microorganism associated with dental caries is Streptococcus mutans (S. mutans). Although several mechanisms for its control have been used, its prevalence and incidence are still high. New alternatives are silver nanoparticles due to their antibacterial effect. In this work, we determined the antibacterial effect of silver nanoparticles on S. mutans. Three sizes of silver nanoparticles were used to find minimum inhibitory concentrations (MIC) in S. mutans using reference and clinical stocks. Kruskal-Wallis and U of Mann-Whitney statistical tests were applied. We found bactericidal effect for the three groups, with significant statistical differences between them. Our results agree with those already reported by several authors. This study concludes that silver nanoparticles present antibacterial activity on S. mutans and this property is better when the particle size is diminished.     

Preparation and antibacterial activities of Ag-doped SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript> composite films by liquid phase deposition (LPD) method

In the present study, Ag/SiO₂–TiO₂ thin films on ceramic tiles with glazed surface were successfully prepared by a liquid phase deposition method (LPD) at a low temperature. The Ag/SiO₂–TiO₂ thin films obtained were homogenous, well adhered and colored by interference of reflected light. The films were characterized by scanning electron microscopy and X-ray diffraction. From these analysis data, it was found that silver (Ag) nanoparticles were trapped in SiO₂–TiO₂ matrix. The antibacterial effects of Ag/SiO₂–TiO₂ thin films against S. aureus and E. coli were examined by the so-called antibacterial-drop test. The bactericidal activity for the above bacteria cells was estimated by relative number of bacteria survived calculated from the number of viable cells which form colonies on the nutrient agar plates. The Ag/SiO₂–TiO₂ thin films had an excellent antibacterial performance. Atomic absorption spectroscopy (AAS) was used for the quantitative determination of the Ag ion concentration releasing from the Ag/SiO₂–TiO₂ thin film. The releasing rate of Ag ions from the Ag/SiO₂–TiO₂ film is 0.123 μg/mL during 192 h. The antibacterial effect of Ag/SiO₂–TiO₂ thin film before and after aging in a weathering chamber for 48 h was compared and the results show that the antibacterial activity is not compromised after weathering.     

Antibacterial activity of Cu2O and Ag co-modified rice grains-like ZnO nanocomposites

In this work, a series of Cu₂O-Ag/ZnO, Cu₂O/ZnO and Ag/ZnO nanocomposites with various compositions were prepared via a hydrothermal method followed by chemical modification, and their antibacterial performance was investigated in detail. X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy results confirmed that 31?nm Cu₂O and 30?nm Ag nanoparticles are well-dispersed on 202?nm ZnO grains to form a Cu₂O/ZnO and Ag/ZnO heterojunction, respectively. The bi-heterojuction structure in the Cu₂O-Ag/ZnO provided a synergistic effect on antibacterial activity, and the (Cu₂O)_0.04Ag_0.06ZnO_0.9 nanocomposites showed the highest antimicrobial activity of all samples with minimum inhibitory concentration and minimum bactericidal concentration against Escherichia coli and Staphylococcus aureus as low to 31.25?μg/mL, 250?μg/mL, 125?μg/mL and 500?μg/mL, respectively. This is the first report of the antibacterial activities of Cu₂O and Ag co-modified ZnO nanocomposites.     

Antibacterial activity of SiO2/hydroxypropyl cellulose hybrid materials containing silver nanoparticles

Silica hybrid materials containing tetraethyl orthosilicate (TEOS) as SiO₂ precursor, hydroxypropyl cellulose (HPC) as an organic compound with incorporation of silver were prepared, and their structure and surface morphology were examined by FTIR measurements and SEM. The quantity of organic substance was 5 wt.% and the silver concentration varied from 0.5 to 2.5 wt.%. It is suggested that the main structural units build an amorphous network of synthesized hybrids from depolymerized [SiO₄] tetrahedra giving strong bands at 1050 and 790 cm^? 1. The surface morphology changed from smooth to rough with the increasing amount of silver. The possible antibacterial behavior of the hybrid materials was also studied. The results indicate pronounced antibacterial performance against Escherichia coli and Bacillus subtilis. Highest antibacterial activity was detected against B. subtilis. The increase of silver concentration up to 2.5 wt.% Ag leads to stronger antibacterial effects with both strains.     

Synthesis and characterization of silver nanoparticles impregnated into bacterial cellulose

This article presents a study about the synthesis of colloidal silver (Ag)/biopolymer where Ag submicron particles were prepared in situ on bacterial cellulose (BC) produced by Gluconacetobacter xylinus. Different reducing agents were compared (hydrazine, hydroxylamine or ascorbic acid) together with the influence of gelatin or polyvinylpyrrolidone (PVP) employed as colloid protectors. Particle size distribution and morphology were investigated by scanning electron microscope (SEM). SEM images show silver nanoparticles (40–100 nm) size range attached on (BC) microfibrils. XRD analyses confirmed the Ag cubic phase deposited on to BC fibrils. The ash contents determined by thermogravimetric analyses have indicated high level of silver loading on the obtained composites.     

Enhanced antibacterial effect of azlocillin in conjugation with silver nanoparticles against Pseudomonas aeruginosa

In recent years, the problems associated with bacterial resistance to antibiotics caused nanodrugs to be considered as a new way for infectious diseases treatment. The main purpose of this study was to develop a new agent against Pseudomonas aeruginosa, a very difficult bacterium to treat, based on azlocillin antibiotic and silver nanoparticles (AgNPs). Azlocillin was conjugated with AgNPs by chemical methods and its antimicrobial activity was studied against P. aeruginosa using well diffusion agar method. Then, minimum inhibitory concentration and minimum bactericidal concentration of the new conjugate was specified with macro‐dilution method. The animal study showed the considerable enhanced antibacterial effect of azlocillin in conjugation with AgNPs against P. aeruginosa in comparison with azlocillin alone, AgNPs alone and azlocillin in combination with AgNPs.Inspec keywords: antibacterial activity, silver, nanoparticles, organic compounds, microorganisms, drugs, nanomedicine, biomedical materials, diseases, diffusion, nanofabricationOther keywords: Ag, macrodilution method, minimum bactericidal concentration, minimum inhibitory concentration, well diffusion agar method, P. aeruginosa, antimicrobial activity, chemical methods, azlocillin antibiotic nanoparticles, infectious diseases treatment, nanodrugs, bacterial resistance, Pseudomonas aeruginosa, silver nanoparticles, antibacterial effect     

Synthesis of polypyrrole nanocomposites decorated with silver nanoparticles with electrocatalysis and antibacterial property

Polypyrrole nanowire/silver nanoparticle composites (PPy/Ag) are obtained in aqueous media through a one-pot method without any external stimulus. PPy nanowires were assembled on the reactive self-degraded template of the complex of AgNO₃ and methyl orange (MO). During the synthesis process in the dark surrounding, Ag nanoparticles could be uniformly decorated onto the surface of PPy nanowires in situ by the redox reaction of pyrrole and AgNO₃. Neither additional reducing agents for the growth of silver nanoparticles nor oxidizing agents for the polymerization of pyrrole are utilized. The formation mechanism, morphologies, structural characteristics, and conductivity of the obtained PPy/Ag nanocomposites are reported. The as-prepared PPy/Ag nanocomposites exhibit well-defined response to the electrochemical reduction of hydrogen peroxide. Moreover, the preliminary antibacterial assays indicate that the PPy/Ag nanocomposites also possess antibacterial abilities against Escherichia coli.