Effect of gemini surfactant (16-6-16) on the synthesis of silver nanoparticles: A facile approach for antibacterial application

The Substantial Role of Cell and Nanoparticle Surface Properties in the Antibacterial Potential of Spherical Silver Nanoparticles

Purpose

Although it is well known that the size, shape, and surface chemistry affect the biological potential of silver nanoparticles (AgNPs), the published studies that have considered the influence of AgNP surface on antibacterial activity have not provided conclusive results. This is the first study whose objective was to determine the significance of the surface net charge of AgNPs on their antibacterial potential, attraction to bacterial cells, and cell envelope disruption, considering differences in bacterial surface properties.

Methods

We evaluated five commercial AgNP colloids with identical size and shape but different surface ligands. We thoroughly characterized their physicochemical properties, including the zeta potential, hydrodynamic diameter, and polydispersity index, and determined the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC), along with silver absorption into bacterial cells. Moreover, we investigated structural changes in bacteria treated with AgNPs by using a crystal violet assay and electron microscopy.

Results

The zeta potential of AgNPs ranged from -47.6 to +68.5 mV, with a hydrodynamic diameter of 29-87 nm and a polydispersity index of 0.349-0.863. Bacterial susceptibility varied significantly (0.5 ≤ MIC ≤ 256 µg Ag/mL; 1 ≤ MBC ≤ 256 µg Ag/mL); we found the lowest susceptibility in bacteria with a cell wall or a polysaccharide capsule. The most active AgNPs (0.5 ≤ MIC ≤ 32 µg Ag/mL; 2 ≤ MBC ≤ 64 µg Ag/mL) had a moderate surface charge (-21.5 and +14.9 mV). The antibacterial potential was unrelated to ion dissolution or cell envelope disruption, and bacterial cells absorbed less of the most active AgNPs (1.75-7.65%).

Conclusion

Contrary to previous reports, we found that a moderate surface charge is crucial for the antibacterial activity of AgNPs, and that a significant attraction of the nanoparticle to the cell surface reduces the antibacterial potential of AgNPs. These findings challenge the existing views on AgNP antibacterial mechanisms and interactions with bacterial cells.

Pharmacological Activity of Garcinia indica (Kokum): An Updated Review

Garcinia indica (commonly known as kokum), belonging to the Clusiaceae family (mangosteen family), is a tropical evergreen tree distributed in certain regions of India. It has been used in culinary and industrial applications for a variety of purposes, including acidulant in curries, pickles, health drinks, wine, and butter. In particular, G. indica has been used in traditional medicine to treat inflammation, dermatitis, and diarrhea, and to promote digestion. According to several studies, various phytochemicals such as garcinol, hydroxycitric acid (HCA), cyanidin-3-sambubioside, and cyanidin-3-glucoside were isolated from G. indica, and their pharmacological activities were published. This review highlights recent updates on the various pharmacological activities of G. indica. These studies reported that G. indica has antioxidant, anti-obesity, anti-arthritic, anti-inflammatory, antibacterial, hepatoprotective, cardioprotective, antidepressant and anxiolytic effects both in vitro and in vivo. These findings, together with previously published reports of pharmacological activity of various components isolated from G. indica, suggest its potential as a promising therapeutic agent to prevent various diseases.

Synthesis of Silver Nanoparticles with Gemini Surfactants as Efficient Capping and Stabilizing Agents

The scientific community has paid special attention to silver nanoparticles (AgNPs) in recent years due to their huge technological capacities, particularly in biomedical applications, such as antimicrobials, drug-delivery carriers, device coatings, imaging probes, diagnostic, and optoelectronic platforms. The most popular method of obtaining silver nanoparticles as a colloidal dispersion in aqueous solution is chemical reduction. The choice of the capping agent is particularly important in order to obtain the desired size distribution, shape, and dispersion rate of AgNPs. Gemini alkylammonium salts are named as multifunctional surfactants, and possess a wide variety of applications, which include their use as capping agents for metal nanoparticles synthesis. Because of the high antimicrobial activity of gemini surfactants, AgNPs stabilized by this kind of surfactant may possess unique and strengthened biocidal properties. The present paper presents the synthesis of AgNPs stabilized by gemini surfactants with hexadecyl substituent and variable structure of spacer, obtained via ecofriendly synthesis. UV-Vis spectroscopy and dynamic light scattering were used as analyzing tools in order to confirm physicochemical characterization of the AgNPs (characteristic UV-Vis bands, hydrodynamic diameter of NPs, polydispersity index (PDI)).

Synthesis of biosurfactant stabilized silver nanoparticles, characterization and their potential application for bactericidal purposes

Uniformly dispersed silver nanoparticles (AgNPs) with remarkable colloidal stability were synthesised using chemical reduction method in lipopeptide biosurfactant reverse micelles. Transmission Electron microscopy (TEM), Scanning electron microscopy (SEM) and UV-vis spectroscopy analysis exhibited monodisperse nanoparticles with spherical morphology of diameter of 21 ± 2. The lipopeptide stabilized AgNPs displayed remarkable antibacterial activity with minimum inhibitory concentration (MIC) value of 15.625 μg/mL against Gram-negative Pseudomonas aeruginosa CB1 and Gram-positive Bacillus subtilis CN2 strains with a significant dose-dependent reduction of cell viability and loss of membrane integrity. Investigation of AgNPs internalization and dissolution assays demonstrated 42-fold higher leaching of the lipopeptide-stabilized AgNPs compared to the bare AgNPs, and concentration dependent increase in cellular uptake with subsequent damage to intracellular organelles. Further ultrastructural observation using TEM revealed internalization and strong binding of considerable amount of AgNPs on the lipopolysaccharide layer of the Gram-negative and peptidoglycans layer of Gram-positive bacteria indiscriminately, demonstrating robust antibacterial activity and potential application to treat multidrug resistant bacteria.

Counterion coupled (COCO) gemini surfactant capped Ag/Au alloy and core–shell nanoparticles for cancer therapy

In this work hybrid silver (Ag)–gold (Au) nanoparticles (NPs) with different sizes and compositions were synthesized and applied for anticancer evaluations and which is effectively involved in cancer cell apoptosis through DNA damage.

Engineered nanomaterials growth control by monomers and micelles: From surfactants to surface active polymers

In pseudo-micellar phase, the crystal growth is primarily achieved by the surface activity of the monomers in the presence of micelles. To ensure the maximum potential of surface activity of monomers in morphology control, a micellar phase is required. This account specifically focuses on the crystal growth control by the surface active monomers of conventional surfactants and that of water soluble polymers. It also distinguishes the mechanisms involved in the shape control driven by the micellar phase of micelle forming polymers, their role as nanoreactors, micellar stability, and micellar transitions from the monomeric phase. The fundamental basis of the crystal growth control by the surface active agents holds the key of using other non-convectional surface active species like proteins, carbohydrates, and bioactive polymers to achieve morphology control bionanomaterials for their specific biological applications.

An injectable supramolecular hydrogel hybridized with silver nanoparticles for antibacterial application

Silver nanoparticles (AgNPs) show long-lasting and broad-spectrum antibacterial activity. Herein, PEGylated AgNPs were prepared in situ by complexing AgNO₃ with the random copolymer of poly(ethylene glycol) methyl ether methacrylate (PEGMA) and polyacrylic acid via electrostatic interaction followed by in situ reduction. AgNP hybrid supramolecular hydrogels were thus prepared through host-guest inclusion between PEGMA side chains and α-cyclodextrins in aqueous solution. The hydrogels were physically cross-linked by both pseudopolyrotaxane crystallization and AgNPs, which showed temperature responsiveness and self-healing properties. By hybridizing AgNPs, the hydrogels showed excellent antibacterial properties against S. aureus and E. coli bacteria as well as low cytotoxicity and have potential applications as injectable antibacterial materials.

Zinc oxide/silver bimetallic nanoencapsulated in PVP/PCL nanofibres for improved antibacterial activity

The anti-infection ability and skin regeneration are important aspects on the progress of wound healing, which needs an ideal wound dressing that not only resists bacteria but also promotes skin regeneration. In this study, zinc oxide/silver/polyvinylpyrrolidone/polycaprolactone (ZnO/Ag/PVP/PCL) nanofibres were prepared through electrospinning. Firstly, zinc oxide nanoparticles (ZnONPs) and silver nanoparticle (AgNPs) were synthesized respectively. Secondly, the two nanoparticles were mixed with polyvinylpyrrolidone (PVP) and polycaprolactone (PCL) to obtain the nanofibres. The results of scanning electron microscopy (SEM) showed that ZnONPs and AgNPs were 40.07 ± 9.70 nm and 37.46 ± 12.02 nm, respectively. After electrospinning, the nanofibres were 368.22 ± 123.96 nm in diameter. Infrared spectroscopy revealed that ZnONPs/AgNPs bimetallic nanomaterials were physically embedded in the nanofibres. The antibacterial effects against Staphylococcus aureus and Escherichia coli of ZnO/Ag/PVP/PCL nanofibres were significantly better than these of the single metal material-loaded nanofibres. More importantly, the combination of ZnO and Ag reduced the cytotoxicity of ZnO/Ag/PVP/PCL bimetallic nanofibres toward fibroblasts. These findings demonstrated that ZnO/Ag/PVP/PCL bimetallic nanofibres should be of greater interest than the single metal nanomaterial-loaded nanofibres in inhibiting growth of bacteria.