Influence of glucose, sucrose, and dextran coatings on the stability and toxicity of silver nanoparticles

Construction, characterization and application of locust bean gum/Phyllanthus reticulatus anthocyanin - based plasmonic silver nanocomposite for sensitive detection of ferrous ions

Iron is a transition metal of tremendous eco-physiological significance. This work aimed at constructing a simple plasmonic Ag-nanocomposite (LBG/PRAg-NC) based on locust bean gum and Phyllanthus reticulatus anthocyanin in a sustainable manner for the optical detection of ferrous ions (Fe²⁺) in aqueous solution. LBG/PRAg-NC was prepared via a green chemistry route and thoroughly characterized for its physico-chemical and plasmonic attributes. Successful synthesis of LBG/PRAg-NC under room temperature with Phyllanthus reticulatus anthocyanin as reductant and locust bean gum as stabilizer was accomplished within 15 min. LBG/PRAg-NC exhibited small size (∼8.04 nm), spherically shaped nanosilver, with good colloidal dispersion, stability and prominent SPR absorption peak at 420 nm. XPS analysis revealed the existence of both Ag⁰ and Ag ⁺ species embedded in the biopolymer support. Furthermore, LBG/PRAg-NC was highly selective for Fe²⁺ as opposed to other interferents including Fe³⁺. The presence of Fe²⁺ engendered a redox oxidation of the analyte by the Ag⁺ species, prompting a rapid, concentration dependent increase in color and SPR absorption band intensity of LBG/PRAg-NC colloidal solution. In aqueous solution, the probe displayed a good linear range for Fe²⁺ (0.1-100 μM), and a low detection limit (LOD of 0.38 μM). The obtained detection limit is much lower than the guideline limit of Fe²⁺ content in drinking water, ∼5 μM. Additionally, the probe was successfully applied in determination of Fe²⁺ in aqueous solutions of apple juice, iron supplement tablet, and tap water, with commendable analytical performances. Therefore, our research findings demonstrate a facile, efficacious, cost-effective, and eco-friendly approach for the sustainable synthesis of plasmonic Ag-nanocomposites based solely on locust bean gum and Phyllanthus reticulatus anthocyanin. Importantly, these results validate the capacity of plasmonic Ag-nanocomposite constructed via green chemistry route as a simple, rapid, and selective probe for effective monitoring of trace amounts of Fe²⁺ in aqueous environment.

Nanotechnology-General Aspects: A Chemical Reduction Approach to the Synthesis of Nanoparticles

The role of nanotechnology is increasingly important in our society. Through it, scientists are acquiring the ability to understand the structure and properties of materials and manipulate them at the scale of atoms and molecules. Nanomaterials are at the forefront of the rapidly growing field of nanotechnology. The synthesis of nanostructured materials, especially metallic nanoparticles, has attracted tremendous interest over the past decade due to their unique properties, making these materials excellent and indispensable in many areas of human activity. These special properties can be attributed to the small size and large specific surface area of nanoparticles, which are very different from those of bulk materials. Nanoparticles of different sizes and shapes are needed for many applications, so a variety of protocols are required to produce monodisperse nanoparticles with controlled morphology. The purpose of this review is firstly to introduce the reader to the basic aspects related to the field of nanotechnology and, secondly, to discuss metallic nanoparticles in greater detail. This article explains the basic concepts of nanotechnology, introduces methods for synthesizing nanoparticles, and describes their types, properties, and possible applications. Of many methods proposed for the synthesis of metal nanoparticles, a chemical reduction is usually preferred because it is easy to perform, cost-effective, efficient, and also allows control of the structural parameters through optimization of the synthesis conditions. Therefore, a chemical reduction method is discussed in more detail-each factor needed for the synthesis of nanoparticles by chemical reduction is described in detail, i.e., metal precursors, solvents, reducing agents, and stabilizers. The methods that are used to characterize nanomaterials are described. Finally, based on the available literature collection, it is shown how changing the synthesis parameters/methods affects the final characteristics of nanoparticles.

How similar is the antibacterial activity of silver nanoparticles coated with different capping agents?†

Silver nanoparticles (AgNPs) represent one of the most commercialised metal nanomaterials, with an extensive number of applications that span from antimicrobial products to electronics. Bare AgNPs are very susceptible to aggregation, and capping agents are required for their protection and stabilisation. The capping agents can endow new characteristics which can either improve or deteriorate AgNPs (bio)activity. In the present work, five different capping agents were studied as stabilizing agents for AgNPs: trisodium citrate (citrate), polyvinylpyrrolidone (PVP), dextran (Dex), diethylaminoethyl-dextran (Dex^DEAE) and carboxymethyl-dextran (Dex^CM). The properties of the AgNPs were studied using a set of methods, including transmission electron microscopy, X-ray diffraction, thermogravimetric analysis and ultraviolet-visible and infrared spectroscopy. Coated and bare AgNPs were also tested against Escherichia coli, methicillin-resistance Staphylococcus aureus and Pseudomonas aeruginosa to analyse their capacity to suppress bacterial growth and eradicate biofilms of clinically relevant bacteria. The results showed that all the capping agents endow long-term stability for the AgNPs in water; however, when the AgNPs are in bacterial culture media, their stability is highly dependent on the capping agent properties due to the presence of electrolytes and charged macromolecules such as proteins. The results also showed that the capping agents have a substantial impact on the antibacterial activity of the AgNPs. The AgNPs coated with the Dex and Dex^CM were the most effective against the three strains, due to their better stability which resulted in the release of more silver ions, better interactions with the bacteria and diffusion into the biofilms. It is hypothesized that the antibacterial activity of capped AgNPs is governed by a balance between the AgNPs stability and their ability to release silver ions. Strong adsorption of capping agents like PVP on the AgNPs endows higher colloidal stability in culture media; however, it can decrease the rate of Ag⁺ release from the AgNPs and reduce the antibacterial performance. Overall, this work presents a comparative study between different capping agents on the properties and antibacterial activity of AgNPs, highlighting the importance of the capping agent in their stability and bioactivity.

Nanosilver antibacterial activity is governed by a balance between the nanosilver stability and their ability to release/dope Ag⁺ to solution.

Interfacial charge transfer complex formation between silver nanoparticles and aromatic amino acids

The optical properties of surface-modified silver nanoparticles (Ag NPs) with aromatic amino acids tryptophan (Trp) and histidine (His) were examined using the cluster model for density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. Also, the redistribution of electronic charges upon chemisorption of ligand molecules onto silver's surfaces is determined. The obtained theoretical data, on one side, undoubtedly indicate the the formation of an interfacial charge transfer (ICT) complex between silver and this type of ligand, and, on the other side, partial oxidation of surface silver atoms accompanied by an increase of electron density in ligand molecules. The ICT complex formation, based on noble metal nanoparticles, has never been reported previously to the best of our knowledge. The experimental spectroscopic measurements support the theoretical data. A new absorption band in the visible spectral range appears upon surface modification of Ag NPs, and, when exposed to air, oxidation of surface-modified Ag NPs is significantly faster than the oxidation of the unmodified ones.

A review on contemporary nanomaterial-based therapeutics for the treatment of diabetic foot ulcers (DFUs) with special reference to the Indian scenario

Diabetes mellitus (DM) is a predominant chronic metabolic syndrome, resulting in various complications and high mortality associated with diabetic foot ulcers (DFUs). Approximately 15-30% of diabetic patients suffer from DFUs, which is expected to increase annually. The major challenges in treating DFUs are associated with wound infections, alterations to inflammatory responses, angiogenesis and lack of extracellular matrix (ECM) components. Furthermore, the lack of targeted therapy and efficient wound dressings for diabetic wounds often results in extended hospitalization and limb amputations. Hence, it is essential to develop and improve DFU-specific therapies. Nanomaterial-based innovative approaches have tremendous potential for preventing and treating wound infections of bacterial origin. They have greater benefits compared to traditional wound dressing approaches. In this approach, the physiochemical features of nanomaterials allow researchers to employ different methods for diabetic wound healing applications. In this review, the status and prevalence of diabetes mellitus (DM) and amputations due to DFUs in India, the pathophysiology of DFUs and their complications are discussed. Additionally, nanomaterial-based approaches such as the use of nanoemulsions, nanoparticles, nanoliposomes and nanofibers for the treatment of DFUs are studied. Besides, emerging therapeutics such as bioengineered skin substitutes and nanomaterial-based innovative approaches such as antibacterial hyperthermia therapy and gene therapy for the treatment of DFUs are highlighted. The present nanomaterial-based techniques provide a strong base for future therapeutic approaches for skin regeneration strategies in the treatment of diabetic wounds.