Enhanced bactericidal efficacy of polymer stabilized silver nanoparticles in conjugation with different classes of antibiotics

The paper presents the interaction mechanism of silver nanoparticles (AgNPs) with different antibiotics and the antibacterial efficacy of the formed conjugates. The AgNPs used in this study were synthesized from silver nitrate using sodium borohydride as a reducing agent, in the presence of PVP as a protecting agent. Two antibiotics, amikacin and vancomycin with different modes of action, were used to functionalize the synthesized PVP-capped AgNPs. The formation of antibiotic-AgNPs conjugate was confirmed by UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS) and X-ray diffraction (XRD) and the results suggest the conjugation of both drugs to silver nanoparticle surfaces. FTIR results indicate that intermolecular hydrogen bonding exists between PVP-coated AgNPs and antibiotics. The oxygen atom coordinated with PVP was available for interaction with either amine or amide groups of drugs. Further, the antibacterial efficacy of these PVP-capped AgNPs with selected antibiotics was evaluated against Escherichia coli and Staphylococcus aureus by agar well diffusion test. Synergetic bactericidal activity for antibiotic-AgNPs conjugate was observed against both microbes.

The paper presents the interaction mechanism of silver nanoparticles (AgNPs) with different antibiotics and the antibacterial efficacy of the formed conjugates.     

Flavonoid-derived anisotropic silver nanoparticles inhibit growth and change the expression of virulence genes in Escherichia coli SM10

We hereby present a novel greener and ecofriendly synthesis of anisotropic silver nanoparticles (AgNPs) using water soluble quercetin diphosphate (QDP). QDP was employed as a reducing, capping and stabilizing agent at room temperature without any extraneous reagents. The purpose of this study was to determine the effects of modified quercetin pentaphosphate silver nanoparticles (QPP-AgNPs) and quercetin diphosphate derived silver nanoparticles (QDP-AgNPs) on microbial growth and expressions of virulence-related genes in Escherichia coli SM10. The gene expression analysis was carried out for 12 genes which are related to virulence and stress in E. coli SM10, namely: RpoD, RpoS, ibpB, clpB, uspA, fliC, fimH, fimF, kdpE, artJ, hyaA, and gyrA. Results showed that QDP-AgNPs reduced the swarming motility by 98% which correlated with the reduction in the expression of FliC flagellar gene. A simultaneous increase in the expression of the fimbrial genes FimH and FimF that are related to motility was recorded. In contrast, treatment of the microbes with QPP-AgNPs resulted in 90% of the swarming motility at different patterns compared to QDP-AgNPs treatment for the gene expressions of motility elements. The study revealed that QDP-AgNPs up-regulated the stress related RpoD and ibpB expressions, while QPP-AgNPs up-regulated the stress related RpoS and uspA gene expressions. However, both QDP-AgNPs and QPP-AgNPs up-regulated kpdE, artJ and gry at different levels. QDP-AgNPs were also tested for their antibacterial and antifungal activities, which showed μmolar cidal activity. The growth kinetics of both Gram (−) and Gram (+) bacteria were strongly altered by QDP-AgNPs activity. Energy dispersive absorption spectroscopy (EDS) studies revealed that silver ions and/or the nanoparticles themselves transferred into bacterial cells. To the best of our knowledge, this is the first report of studying the genetic and kinetic response of bacteria to modified quercetin phosphate mediated silver nanoparticles and we hereby report that the molecules used to synthesize AgNPs bring about a strong effect on AgNPs manipulatory activity on the tested 12-genes.

We hereby present a novel greener and ecofriendly synthesis of anisotropic silver nanoparticles (AgNPs) using water soluble quercetin diphosphate (QDP). QDP was employed as a reducing, capping and stabilizing agent at room temperature without any extraneous reagents.     

Facile one-pot synthesis of silver nanoparticles encapsulated in natural polymeric urushiol for marine antifouling

Silver nanoparticle-based coatings have been regarded as promising candidates for marine antifouling. However, current toxic fabrication methods also lead to environment risks. Nanoparticle agglomeration, poor compatibility with polymer, and rapid release of Ag⁺ result in short-term efficacy. In this study, a facile one-pot synthesis method of silver nanoparticles (AgNPs) encapsulated in polymeric urushiol (PUL) was developed. AgNPs were synthesized in situ by natural urushiol, serving as a reductant, dispersant and surfactant. Simultaneously, silver nitrate catalyzed the polymerization of urushiol into PUL. This in situ reduction method made AgNPs uniformly distributed in the polymer matrix. The binding between the AgNPs and the PUL resulted in the stable release of Ag⁺. Results showed the antibacterial rate of a 0.1% AgNPs coating is 100% in laboratory experiments. This environment-friendly coating showed good microbial inhibition performance with long-term (120 days) marine antifouling efficacy. This study shows the potential of preparing an eco-friendly coating with long-term marine antifouling ability.

PUL/AgNPs was developed by a one-step reaction, PUL/AgNPs coatings showed excellent antifouling performance in antimicrobial experiments and marine field tests.     

Antifouling and antimicrobial polyethersulfone/hyperbranched polyester-amide/Ag composite

This study provided a facile approach for the development of antifouling and antibacterial polyethersulfone (PES) composite film. Mainly, hyperbranched polyester-amide (PESAM) was used as both the reducing and capping agent for the in situ formation of AgNPs. The nanoparticles were intensively investigated using Fourier transform infrared spectroscopy (FTIR), ultra-violet spectroscopy (UV-vis), scanning and transmission electron microscopy (SEM & TEM) and X-ray diffraction (XRD). AgNPs were narrowly distributed with an average particle size of about 6 nm. PESAM was mixed with PES to realize free-standing film using the phase inversion method. The inclusion of PESAM in the composite film significantly improved hydrophilicity as confirmed by the contact angle measurements. Furthermore, SEM and EDX investigations confirmed that PESAM induced the in situ formation of AgNPs not only on the film surface but also inside its macro-voids. The composite film (PES/PESAM/Ag) displayed significant antibacterial potential against Gram positive and Gram negative bacteria. Overall, the described method paves the way towards development of advanced PES composite films with antimicrobial properties for broad application areas that include desalination membranes or active packaging materials.

This study provided a facile approach for the development of antifouling and antibacterial polyethersulfone (PES) composite film.     

Antibacterial activity of AgNPs–TiO2 nanotubes: influence of different nanoparticle stabilizers

Enhanced antibacterial properties of nanomaterials such as TiO₂ nanotubes (TNTs) and silver nanoparticles (AgNPs) have attracted much attention in biomedicine and industry. The antibacterial properties of nanoparticles depend, among others, on the functionalization layer of the nanoparticles. However, the more complex information about the influence of different functionalization layers on antibacterial properties of nanoparticle decorated surfaces is still missing. Here we show the array of ∼50 nm diameter TNTs decorated with ∼50 nm AgNPs having different functionalization layers such as polyvinylpyrrolidone, branched polyethyleneimine, citrate, lipoic acid, and polyethylene glycol. To assess the antibacterial properties, the viability of Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) has been assessed. Our results showed that the functional layer of nanoparticles plays an important role in antibacterial properties and the synergistic effect such nanoparticles and TiO₂ nanotubes have had different effects on adhesion and viability of G⁻ and G⁺ bacteria. These findings could help researchers to optimally design any surfaces to be used as an antibacterial including the implantable titanium biomaterials.

Synergictic antibacterial effect of AgNPs–TiO₂ nanotubes is influenced by different nanoparticle stabilizers.     

Variation in surface properties,metabolic capping,and antibacterial activity of biosynthesized silver nanoparticles: comparison of bio-fabrication potential in phytohormone-regulated cell cultures and naturally grown plants

We compared surface properties, metabolic capping and antibacterial activity of silver nanoparticles, synthesized through extracts of cell cultures of Fagonia indica and its naturally grown form. Extracts from cell cultures (produced with thidiazuron (TDZ) or melatonin (MLN)) were compared to the naturally grown whole plant extracts (WPEs) for their reducing potential, and their effects on physical and biochemical properties of the biosynthesized silver nanoparticles. UV-Vis spectroscopy revealed that the surface plasmon resonance peaked at λ = 415 nm for MLN-AgNPs, λ = 430 nm for TDZ-AgNPs and λ = 460–465 nm for WPE-AgNPs. Transmission electron microscopy and energy dispersive X-rays of AgNPs showed that compared to WPE-AgNPs (mean diameter = 22 nm), extracts from MLN- and TDZ-induced cell cultures produced particles with spherical shapes and smaller diameters (i.e. mean diameter = 15 nm and 19 nm, respectively). Size distribution analysis also showed that TDZ-AgNPs were nearer to a symmetric distribution in terms of diameter (skewness = 0.80) as compared to WPE-AgNPs (skewness = 0.9) and MLN-AgNPs (skewness = 1.4). Furthermore, MLN-induced cell culture extracts produced AgNPs in higher concentration (210 μg mL⁻¹) compared to AgNPs from TDZ-induced cell culture extracts (160 μg mL⁻¹) and WPE (138 μg mL⁻¹). Two-way comparisons of LC-MS/MS profiles of TDZ-AgNPs, MLN-AgNPs, and WPE-AgNPs revealed differences in their secondary metabolite profiles, which might account for differences in their differential response in bio-fabrication, and size distribution. Activity against different pathogenic bacterial strains, Escherichia coli, Bacillus cereus, Xanthomonas citri, Agrobacterium tumefaciens, Streptomyces griseus, and Erwinia carotovora suggested that MLN-AgNPs were more effective compared to TDZ- and WPE-AgNPs. These results indicated that phytohormones induced cell cultures can enhance the production, physical and biochemical properties of AgNPs.

We compared surface properties, metabolic capping and antibacterial activity of biosynthesized silver nanoparticles, synthesized through extracts of cell cultures of Fagonia indica and its naturally grown form.     

Magnetic polymer bowl for enhanced catalytic activity and recyclability

This work introduces the fabrication of a magnetic polymer bowl for enhanced catalytic activity and recyclability, which involves the synthesis of silica-coated Fe₃O₄ magnetic clusters, seeded dispersion polymerization using the magnetic clusters, and transformation into a bowl-like structure via a phase separation route. The additional treatment with tannic acid (TA) on the bowls allows the in situ formation of silver nanoparticles (AgNPs) on their surfaces. The openness and larger surface area of the bowls, as compared with those of other structured particles, such as spheres and flowers, enable a considerably higher immobilization of AgNPs, thus leading to an excellent catalytic reduction for 4-nitrophenol (4-NP), methylene blue (MB), and rhodamine B. Furthermore, the strong magnetic response originating from the magnetic clusters inside the bowls endows a good magnetic recovery and an excellent reusability for the repeated reduction of the organic dyes without loss of catalytic activity.

The fabrication of a magnetic polymer bowl with a considerably higher immobilization of AgNPs was demonstrated for enhanced catalytic activity and recyclability.     

Biosynthesis of silver nanoparticles using endophytic bacteria and their role in inhibition of rice pathogenic bacteria and plant growth promotion

The biosynthesis of silver nanoparticles (AgNPs) through the use of endophytic bacteria is a safe replacement for the chemical method. The study aimed to synthesize AgNPs using endophytic bacterium Bacillus siamensis strain C1, which was isolated from the medicinal plant Coriandrum sativum. The synthesized AgNPs with the size of 25 to 50 nm were further confirmed and characterized by UV-visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy and scanning electron microscopy with EDS profile. The synthesized AgNPs at 20 μg mL⁻¹ showed a strong antibacterial effect against the pathogen of rice bacterial leaf blight and bacterial brown stripe, while an inhibition zone of 17.3 and 16.0 mm was observed for Xanthomonas oryzae pv. oryzae (Xoo) strain LND0005 and Acidovorax oryzae (Ao) strain RS-1, respectively. Furthermore, the synthesized AgNPs significantly inhibited bacterial growth, biofilm formation and swimming motility of Xoo strain LND0005 and Ao strain RS-1. In addition, the synthesized AgNPs significantly increased root length, shoot length, fresh weight and dry weight of rice seedlings compared to the control. Overall, this study suggests that AgNPs have the potential to protect rice plants from bacterial infection and plant growth promotion.

The mechanism of silver nanoparticles (AgNPs) to inhibit rice pathogenic bacteria.     

Antibacterial performance of polymer quaternary ammonium salt–capped silver nanoparticles on Bacillus subtilis in water

In this study, we prepared polymer quaternary ammonium salt–capped silver nanoparticles (PQAS–AgNPs) and investigated their antimicrobial activities. The antimicrobial effectiveness of PQAS–AgNPs on Bacillus subtilis (B. subtilis), and the effect of dose, pH, chloride ion and humic acid (HA) were studied. It was found that PQAS–AgNPs revealed excellent antimicrobial activity to B. subtilis, compared with polyvinylpyrrolidone-capped silver nanoparticles (PVP-AgNPs), which was the reference antimicrobial material. The positive surface, the antimicrobial activity of PQAS, and the synergistic antibacterial effect between PQAS and AgNPs contributed to the significant antibacterial superiority of PQAS–AgNPs. This study demonstrated that the impact of the dose of the material was positive and the microbiocidal efficacy of PQAS–AgNPs was stronger at lower pH. In addition, the antibacterial performance of PQAS–AgNPs decreased in the presence of Cl⁻ and HA. Finally, in combination with the results of FCM and adenosine triphosphate (ATP) content, it was found that PQAS–AgNPs destroyed the respiratory chain of bacterial cells, reduced the synthesis of ATP, and destroyed the cell wall and cell membrane function.

Polymer quaternary ammonium salt–capped silver nanoparticles (PQAS–AgNPs) were synthesized, and they exhibited significant antibacterial capacity against Bacillus subtilis.     

Enhanced photocatalytic and antibacterial activity of plasma-reduced silver nanoparticles

A non-thermal atmospheric pressure plasma jet has been used for the green synthesis of highly dispersed colloidal silver nanoparticles. The reducing species such as hydrogen radicals and hydrated electrons are identified, and the change in the solution pH is studied during AgNP formation. The structural properties and size of the plasma-reduced silver nanoparticles are characterized via X-ray diffraction, ultraviolet-visible spectroscopy, fluorescence spectroscopy and transmission electron microscopy. The size of the colloidal AgNPs is tuned by adjusting the initial concentration of AgNO₃. The effect of terephthalic acid, a hydroxyl radical scavenger, on the reduction of Ag⁺ ion is studied. The typical catalytic activity data indicate the better performance of the plasma-reduced colloidal Ag nanoparticles than that obtained from the chemical reduction method. The antibacterial activity of the plasma-reduced Ag nanoparticles also shows a better performance than that of the chemically reduced AgNPs, highlighting the potential of the plasma reduction approach for the synthesis of metal nanoparticles, which are stable even after 30 days without a stabilizing agent. Additionally, the effects of hydroxyl scavengers (isopropyl alcohol) and Fenton''s reagent (Fe²⁺ salt) on CV degradation are studied.

A non-thermal atmospheric pressure plasma jet has been used for the green synthesis of highly dispersed colloidal silver nanoparticles.     

Novel morphologies of poly(allyamine hydrochloride)–methotrexate nanoassemblies for methotrexate delivery

Poly(allylamine hydrochloride)–methotrexate (PAH–MTX) nanoassemblies with novel morphologies (i.e. nanostrips, nanorolls, nanosheets, and nanospheres) were achieved for the first time via supramolecular self-assembly directed by the synergistic action of various non-covalent interactions between PAH and MTX molecules in aqueous solution. Herein, MTX acted in a versatile manner as both a morphology-regulating agent and a small molecular hydrophobic anticancer drug. Moreover, different morphologies presented diverse drug release profiles, which may be caused by the distinctive interactions between PAH and MTX molecules. Synergistically non-covalent interactions, including electrostatic interactions, van der Waals forces, and hydrogen bonding, favored easier matrix corrosion and more rapid drug release of non-spherical structures (i.e. nanostrips, nanorolls, and nanosheets) through the ligand exchange process. On the other hand, the highly sealed encapsulation mode for hydrophobic MTX molecules made the nanospheres exhibit slower and better controlled release. In addition, in vitro bioassay tests showed that nanostrips displayed the most obvious suppression on the viability of cancer cells among other morphologies, especially after a longer duration. The strategy of using small molecular anticancer drugs not as passively delivered cargoes but as effective molecular building blocks, opens up a new way to develop self-delivering drugs for anticancer therapy.

Nanospheres exhibited the best controlled drug release and nanostrips displayed the most obvious suppression of A549 cells.     

Interaction of Silver Nanoparticles with Serum Proteins Affects Their Antimicrobial Activity In Vivo

The emergence of multidrug-resistant bacteria is a global threat for human society. There exist recorded data that silver was used as an antimicrobial agent by the ancient Greeks and Romans during the 8th century. Silver nanoparticles (AgNPs) are of potential interest because of their effective antibacterial and antiviral activities, with minimal cytotoxic effects on the cells. However, very few reports have shown the usage of AgNPs for antibacterial therapy in vivo. In this study, we deciphered the importance of the chosen methods for synthesis and capping of AgNPs for their improved activity in vivo. The interaction of AgNPs with serum albumin has a significant effect on their antibacterial activity. It was observed that uncapped AgNPs exhibited no antibacterial activity in the presence of serum proteins, due to the interaction with bovine serum albumin (BSA), which was confirmed by UV-Vis spectroscopy. However, capped AgNPs [with citrate or poly(vinylpyrrolidone)] exhibited antibacterial properties due to minimized interactions with serum proteins. The damage in the bacterial membrane was assessed by flow cytometry, which also showed that only capped AgNPs exhibited antibacterial properties, even in the presence of BSA. In order to understand the in vivo relevance of the antibacterial activities of different AgNPs, a murine salmonellosis model was used. It was conclusively proved that AgNPs capped with citrate or PVP exhibited significant antibacterial activities in vivo against Salmonella infection compared to uncapped AgNPs. These results clearly demonstrate the importance of capping agents and the synthesis method for AgNPs in their use as antimicrobial agents for therapeutic purposes.     

A colorimetric nanoprobe based on enzyme-immobilized silver nanoparticles for the efficient detection of cholesterol

A large number of cardiovascular diseases have recently become of serious concern throughout the world. Herein, we developed a colorimetric probe based on functionalized silver nanoparticles (AgNPs) for the efficient sensing of cholesterol, an important cardiovascular risk marker. A simple sodium borohydride reduction method was employed to synthesize the AgNPs. The cholesterol oxidase (ChOx)-immobilized AgNPs interact with free cholesterol to produce H₂O₂ in proportion to the concentration of cholesterol, resulting in decreased AgNP absorbance (turn-off) at 400 nm due to electron transfer between the AgNPs and H₂O₂. The response of the sensor can also be observed visually. The absorption intensity of the AgNPs is recovered (turn-on) upon the addition of sodium dodecyl sulfate due to the inhibition of ChOx. This on–off mechanism was effectively applied to detect cholesterol within the concentration range 10–250 nM with a low detection limit of approximately 0.014 nM. Moreover, the selectivity of the sensor toward cholesterol was analyzed in the presence of a range of interfering organic substances such as glucose, urea, and sucrose. Finally, the potential of the proposed sensor was evaluated using real samples.

A functionalized silver nanoparticle (AgNP) based colorimetric probe have been developed for efficient sensing of cholesterol, most important cardio-risk-marker.     

Facile synthesis of a carbon dots and silver nanoparticles (CDs/AgNPs) composite for antibacterial application

Bacterial infections can seriously harm human health, and the overuse of traditional antibiotics and antibacterial agents will increase the resistance of bacteria. Therefore, it is necessary to prepare a new kind of antibacterial material. In this work, a carbon dots and silver nanoparticles (CDs/AgNPs) composite has been synthesized in a one-step facile method without the introduction of toxic chemicals, wherein CDs could serve as a reducing and stabilizing agent. The CDs/AgNPs composite was characterized by UV-vis spectrophotometry, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM), which demonstrate that the silver nanoparticles were successfully synthesized in the composite. The zeta potential of the CDs/AgNPs composite was −15.3 mV, indicating that the composite possesses high stability. Furthermore, the composite also exhibited biocidal effects for both Gram-negative E. coli bacteria and Gram-positive S. aureus bacteria. Thus, the composite is considered to be of great potential in bactericidal and biomedical applications.

One-step facile synthesis of a carbon dots and silver nanoparticles (CDs/AgNPs) composite without the introduction of toxic chemicals.     

Synthesis,characterization and antifungal activities of eco-friendly palladium nanoparticles

Palladium is a versatile catalyst, but the synthesis of palladium nanoparticles (PdNPs) is usually attained at a high temperature in the range of 160 °C to 200 °C using toxic reducing agents such as sodium borohydride. We report the synthesis of PdNPs using a low-cost and environmentally-friendly route at ambient temperatures. Quercetin diphosphate (QDP), a naturally-derived flavonoid, was employed as a reducing, capping, and stabilizing agent. The effect of temperature was optimized to produce perfectly spherical PdNP nanoparticles with sizes ranging from 0.1 to 0.3 microns in diameter. At relatively higher concentration of QDP, significantly smaller particles were produced with a size distribution of 1–7 nm. Perfectly spherical PdNP nanoparticles are a rare occurrence, especially under ambient room temperature conditions with fast reaction time. The formation of the nanoparticles was confirmed using UV-vis, TEM, EDS, and XRD. HRTEM demonstrated the lattice structure of the PdNPs. The synthesized PdNPs were also tested for their antifungal properties against Colletotrichum gloeosporioides and Fusarium oxysporum. Results showed that the size of the PdNPs played a critical role in their antifungal activity. However, for F. oxysporum, other factors beyond size could affect the antifungal activity including fine-scale, nutrient composition, and target organisms.

Palladium is a versatile catalyst, but the synthesis of palladium nanoparticles (PdNPs) is usually attained at a high temperature in the range of 160 °C to 200 °C using toxic reducing agents such as sodium borohydride.     

Folate receptor-targeting mesoporous silica-coated gold nanorod nanoparticles for the synergistic photothermal therapy and chemotherapy of rheumatoid arthritis

The synergy of photothermal therapy (PTT) and chemotherapy is widely regarded as an effective treatment for complex diseases, such as cancer and inflammation. In this paper, we report the synthesis of a nanoscaled drug delivery system, which was composed of a gold nanorod (GNR) as the photothermal agent and a mesoporous silica shell as the methotrexate (MTX) reservoir, named FAGMs. Due to folate modification on the surface, FAGMs targeted specifically activated macrophages in rheumatoid arthritis (RA). Under 808 nm laser irradiation, FAGMs could kill macrophages by reaching sufficient local hyperthermia with excellent efficiency in the photothermal conversion of GNRs. Meanwhile, internal heating caused hydrogen bond fracture; thus, MTX released rapidly from FAGMs for localized synergistic PTT and chemotherapy. The FAGMs had a mean particle size of about 180 nm and a zeta potential of 14.36 mV. The release rate of MTX from FAGMs in vitro increased markedly under 808 nm laser irradiation. In a cellular uptake study, stronger fluorescence signals were observed in activated macrophages when treated with FAGMs, suggesting that folic acid molecules enabled the enhancement of endocytosis into activated macrophages. In rats with adjuvant-induced arthritis, synergistic treatment excellently inhibited the progression of RA. These results demonstrated that FAGMs could be promising for the treatment of RA.

The use of targeted nanoparticles MTX-FAGMs in combined NIR-induced PTT and traditional chemotherapy has potential as a desirable nanopharmaceuticals platform for the treatment of RA.     

Application of Enteromorpha polysaccharides as a new coagulant aid to remove silver nanoparticles: role of dosage sequence and solution pH

Silver nanoparticles (AgNPs) in surface water cause a serious threat to the health of humans and aquatic organisms. However, it is difficult to remove AgNPs completely since they could adsorb onto the surface of humic acid (HA) and meanwhile release Ag⁺ into water. In this paper, Enteromorpha polysaccharides (Ep) were applied as a coagulant aid with polyaluminum chloride (PAC) to solve this problem. The influences of Ep dosage, dosing sequence and solution pH on the coagulation efficiency, kinetics and removal mechanism of AgNPs were discussed systematically. Results showed that when Ep was applied, AgNPs could be removed effectively due to charge neutralization of PAC hydrolysate and the bridging-sweeping role of Ep gel network. When Ep was added 30 s after PAC dosing, the coagulation efficiency was about 10–20% higher than that of the reverse order. Under this condition, flocs sizes achieved 450 μm when the solution pH was 6.0, which is much larger than that using Ep–PAC. Additionally, Ep showed an ability to promote the re-aggregation of broken flocs, and AgNP–HA flocs exhibited larger sizes, better shear resistance, higher recovery ability and denser structure at pH 6.0. Factorial analysis results indicated that PAC dosage had the greatest impact on HA and AgNP removal, while Ag⁺ removal is more sensitive to Ep dosage.

Silver nanoparticles (AgNPs) could be removed effectively due to bridging-sweep role of Enteromorpha polysaccharides (Ep), and flocs exhibited larger sizes, better shear resistance, higher recovery ability and denser structure when Ep was added.     

Microwave-assisted preparation of a silver nanoparticles/N-doped carbon dots nanocomposite and its application for catalytic reduction of rhodamine B,methyl red and 4-nitrophenol dyes

In the current work, a silver nanoparticles/nitrogen-doped carbon dots (AgNPs/NCDs) nanocomposite was prepared by a microwave-assisted method that does not require additional reducing or stabilizing agents. Multiple analytical techniques were used to characterize the prepared nanocomposite. The nanocomposite exhibited a surface plasmon resonance (SPR) absorption peak at 420 nm, indicating the development of AgNPs with NCDs. Further, HRTEM results confirmed the formation of the nanocomposite with the appearance of lattice fringes of both materials. Additionally, the nanocomposite did not show any precipitation even after two months of storage. The nanocomposite exhibited high catalytic activity towards the reduction of rhodamine B (RhB, 98.83%), methyl red (MR, 97.14%) and 4-nitrophenol (4-NP, 99.95%) at ambient temperature. Besides, the kinetic analysis revealed that the reduction reaction followed pseudo-first-order kinetics and the calculated rate constants (k) for rhodamine B (RhB), methyl red (MR) and 4-nitrophenol (4-NP) were found to be 0.0296 s⁻¹, 0.0233 s⁻¹ and 0.029 s⁻¹, respectively. Moreover, it is a reusable and stable catalyst for reduction reactions up to five cycles without significant loss in catalytic activity. Finally, a plausible mechanism for the reduction of pollutants is also discussed in detail. As a whole, the prepared nanocomposite might display stunning behaviour for wastewater treatment applications.

A silver nanoparticles/nitrogen-doped carbon dots (AgNPs/NCDs) nanocomposite was prepared by a microwave-assisted method, and exhibited high catalytic activity towards the reduction of rhodamine B, methyl red and 4-nitrophenol at ambient temperature.     

Synthesis of silver nanoparticles via traditional Chinese medicine and evaluation of their antibacterial activities

Silver nanoparticles (AgNPs) are widely used in antibacterial research, but diverse methods for the green synthesis of AgNPs are still underexplored. Phenols, the major components in traditional Chinese medicines (TCMs), can reduce silver ions (Ag⁺) to prepare AgNPs. The representative phenolic compounds are flavonoids and chlorogenic acid (CA) in TCMs. Herein, we report a new strategy to prepare AgNPs via decoctions and dregs of TCMs as reductants and dispersants. Lonicera japonica flos (LJ), Astragalus membranaceus (AM), and Eucommia ulmoides bark (EU) were chosen due to their high contents of phenols. ¹H-NMR and HPLC were run to monitor the reaction for AgNP synthesis in decoctions, and XRD and TEM analyses were performed to characterize the synthesized TCMs-AgNPs. In addition, AgNPs prepared by spent Chinese medicinal grounds (SCMGs) were characterized by IR and XRD. The antibacterial assessment demonstrated that these TCMs-AgNPs significantly inhibited the growth of S. aureus and P. aeruginosa and effectively protected lettuce leaves against P. aeruginosa infection. Taken together, this study developed a new synthetic strategy that used decoctions and dregs of TCMs to obtain AgNPs with excellent antibacterial activity, which indicated the potential antibacterial application of these new TCM-based AgNP materials.

Two types of silver nanoparticles were synthesized via traditional Chinese medicine. Both of them exhibited excellent antibacterial activities, which could be promising in the development of new antibacterial agents and materials.     

Efficacy and safety of alpha lipoic acid-capped silver nanoparticles for oral applications

Silver nanoparticles (AgNPs) are widely studied for their broad-spectrum antimicrobial effects, and can be utilised readily in biomaterials, however the cellular safety of specific AgNP formulations should be profiled prior to clinical usage. This study determined the cytotoxic effect of small sized (6 nm) alpha lipoic acid capped-AgNPs on human gingival fibroblasts (HGF), as compared to ionic silver and clinical antiseptics. The metabolic pathway was investigated to determine the cellular effects on HGF cells. The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) was established for a range of oral related bacteria. Results showed that cell viability decreased with increasing AgNP concentration, whereas lower concentrations of AgNPs, (≤5 μg ml⁻¹) caused a significant increase in cell proliferation at 24 and 72 hour time points. The cytotoxicity profile of AgNPs exhibited significantly lower concentrations, relative to the dose of clinical efficacy, when compared to clinical antiseptics. Caspase 3/7 was not significantly altered when HGF cells were treated with 0.225 μg ml⁻¹ AgNPs, indicating cell necrosis rather than apoptosis. Quantitative RT²-PCR detected an upregulation of genes associated with oxidative stress and the G2M cell cycle checkpoint at ≤4 hours, but expression levels returned to levels consistent with control cells at 24–96 hours. An MIC range of 2.5–12.5 μg ml⁻¹ (min. Escherichia coli, Streptococcus mutans, S. mitis; max. Staphylococcus aureus) was determined across the bacterial species tested and an MBC range of 5–100 μg ml⁻¹ (min. E. coli, max. S. mutans). The antimicrobial profile was similar to that of AgNO₃ which suggested that the antimicrobial effect may be influenced by free Ag⁺ release. It was concluded that alpha lipoic acid capped AgNPs possess limited cytotoxic activity to HGF cells when compared to clinically utilised oral antiseptics, observed via the cellular recovery after initial AgNP treatment and a lack of cumulative cytotoxic effect, whilst maintaining a broad range antimicrobial effect of the AgNPs.

Presentation of the limited cumulative cytotoxic effects of an alpha lipoic-acid capped silver nanoparticle on human gingival fibroblasts, with broad range antimicrobial activity, for potential use in biomaterials.