Preparation and characterization of stable monodisperse silver nanoparticles via photoreduction

Drying-Induced Flash Nanoprecipitation in a Sessile Drop: A Route to Synthesize Polymeric Nanoparticles

Flash nanoprecipitation is a simple and scalable method to produce nanoparticles by rapid mixing of a polymer solution with an antisolvent. High-speed mixing devices for the continuous synthesis of polymeric nanoparticles and drug-encapsulated nanoparticles have been designed. In this work, we demonstrate a different approach to induce flash nanoprecipitation using the differential evaporation of solvents in a sessile drop. To show proof of concept, we use polymethyl-methacrylate (PMMA) dissolved in a tetrahydrofuran (THF)-water mixture as a model system. A sessile drop of the polymer solution is allowed to dry under controlled conditions. The sessile drops of the PMMA-THF-water ternary mixture are observed to dry in the constant radius mode. As THF in the drop evaporates faster than water, PMMA supersaturates and precipitates as nanoparticles. Although coffee-ring formation is well-studied in the drying of colloidal suspensions, this work demonstrates the formation of nanoparticles in situ due to a change of solvent quality and subsequent deposition of particles at the pinned contact line. Using the theory of drying of binary solutions, we calculate the temporal variation of composition. The drying paths passing through the low-concentration branch of the binodal give rise to nanoparticles, whereas those passing through the high-concentration branch yield porous films. Spherical polymeric nanoparticles in the size range of 250-700 nm were synthesized using this technique starting from drops with different initial polymer concentration. The method is a cost-effective (no high-speed mixing is required) and scalable alternative to conventional flash nanoprecipitation for synthesizing polymeric nanoparticles for potential applications in drug delivery, diagnostics, and polymer recycling.

Preparation of cellulose-based wipes treated with antimicrobial and antiviral silver nanoparticles as novel effective high-performance coronavirus fighter

Coronaviruses (CoV) are a large family of viruses that cause illness ranging from the common cold to more severe diseases such as Middle East Respiratory Syndrome (MERS-CoV) and Severe Acute Respiratory Syndrome (SARS-CoV). We succeeded in preparing disinfectant cellulose-based wipes treated with antimicrobial and antiviral silver nanoparticles to be used for prevention of contamination and transmission of several pathogenic viruses and microbes to human in critical areas such as hospitals and healthcare centers especially coronavirus. In this work, the antimicrobial and antiviral activities of silver nanoparticles (AgNPs) prepared with four different techniques were investigated for the utilization as a disinfectant for cellulose-based wipes. These four methods are namely; 1) trisodium citrate with cotton yarn as a reducing agent, 2) preparing AgNP's using aqueous solution of PVA in the presence of glucose, 3) trisodium citrate with cotton fabric as a reducing agent, and 4) photochemical reaction of polyacrylic acid and silver nitrate solution. Polyester/viscose blended spunlace nonwoven fabrics as cellulose based fabrics were treated with the prepared silver nanoparticles to be used as surfaces disinfection wipes. The properties of the nonwoven fabrics were examined including thickness, tensile strength in dry and wet conditions in both machine direction (MD) and cross-machine direction (CMD), bursting strength, air permeability, water permeability and surface wettability. Characterization of the AgNPs was carried out in terms of UV-VIS spectroscopy, TEM, SEM, and Zeta potential analysis. The assessment of AgNPs active solutions for antimicrobial and antiviral activities was evaluated. The results obtained from the analyses of the AgNPs samples prepared with different techniques showed good uniformity and stability of the particles, as well uniform coating of the AgNPs on the fibers. Additionally, there is a significant effect of the AgNPs preparation method on their disinfectant performance that proved its effectiveness against coronavirus (MERS-CoV), S. aureus and B. subtilis as Gram-positive bacteria, E. coli and P. mirabilis as Gram-negative bacteria, A. niger and C. albicans fungi.

Progress in controlling the synthesis of atomically precise silver nanoclusters

This short review was designed to summarize the advances in synthesis methods of silver nanoclusters.

Bactericidal and Cytotoxic Properties of Silver Nanoparticles

Silver nanoparticles (AgNPs) can be synthesized from a variety of techniques including physical, chemical and biological routes. They have been widely used as nanomaterials for manufacturing cosmetic and healthcare products, antimicrobial textiles, wound dressings, antitumor drug carriers, etc. due to their excellent antimicrobial properties. Accordingly, AgNPs have gained access into our daily life, and the inevitable human exposure to these nanoparticles has raised concerns about their potential hazards to the environment, health, and safety in recent years. From in vitro cell cultivation tests, AgNPs have been reported to be toxic to several human cell lines including human bronchial epithelial cells, human umbilical vein endothelial cells, red blood cells, human peripheral blood mononuclear cells, immortal human keratinocytes, liver cells, etc. AgNPs induce a dose-, size- and time-dependent cytotoxicity, particularly for those with sizes ≤10 nm. Furthermore, AgNPs can cross the brain blood barrier of mice through the circulation system on the basis of in vivo animal tests. AgNPs tend to accumulate in mice organs such as liver, spleen, kidney and brain following intravenous, intraperitoneal, and intratracheal routes of administration. In this respect, AgNPs are considered a double-edged sword that can eliminate microorganisms but induce cytotoxicity in mammalian cells. This article provides a state-of-the-art review on the synthesis of AgNPs, and their applications in antimicrobial textile fabrics, food packaging films, and wound dressings. Particular attention is paid to the bactericidal activity and cytotoxic effect in mammalian cells.

The role of adatoms in chloride-activated colloidal silver nanoparticles for surface-enhanced Raman scattering enhancement

Chloride-capped silver nanoparticles (Cl-AgNPs) allow for high-intensity surface-enhanced Raman scattering (SERS) spectra of cationic molecules to be obtained (even at nanomolar concentration) and may also play a key role in understanding some fundamental principles behind SERS. In this study, we describe a fast (<10 min) and simple protocol for obtaining highly SERS-active colloidal silver nanoparticles (AgNPs) with a mean diameter of 36 nm by photoconversion from AgCl precursor microparticles in the absence of any organic reducing or capping agent. The resulting AgNPs are already SERS-activated by the Cl^- ions chemisorbed onto the metal surface where the chloride concentration in the colloidal solution is 10^-2 M. Consequently, the enhanced SERS spectra of cationic dyes (e.g., crystal violet or 9-aminoacridine) demonstrate the advantages of Cl-AgNPs compared to the as-synthesized AgNPs obtained by standard Ag⁺ reduction with hydroxylamine (hya-AgNPS) or citrate (cit-AgNPs). The results of SERS experiments on anionic and cationic test molecules comparing Cl-AgNPs, hya-AgNPs and cit-AgNPs colloids activated with different amounts of Cl^- and/or cations such as Ag⁺, Mg²⁺ or Ca²⁺ can be explained within the understanding of the adatom model - the chemisorption of cationic analytes onto the metal surface is mediated by the Cl^- ions, whereas ions like Ag⁺, Mg²⁺ or Ca²⁺ mediate the electronic coupling of anionic species to the silver metal surface. Moreover, the SERS effect is switched on only after the electronic coupling of the adsorbate to the silver surface at SERS-active sites. The experiments presented in this study highlight the SERS-activating role played by ions such as Cl^-, Ag⁺, Mg²⁺ or Ca²⁺, which is a process that seems to prevail over the Raman enhancement due to nanoparticle aggregation.

The Pros and Cons of the Use of Laser Ablation Synthesis for the Production of Silver Nano-Antimicrobials

Silver nanoparticles (AgNPs) are well-known for their antimicrobial effects and several groups are proposing them as active agents to fight antimicrobial resistance. A wide variety of methods is available for nanoparticle synthesis, affording a broad spectrum of chemical and physical properties. In this work, we report on AgNPs produced by laser ablation synthesis in solution (LASiS), discussing the major features of this approach. Laser ablation synthesis is one of the best candidates, as compared to wet-chemical syntheses, for preparing Ag nano-antimicrobials. In fact, this method allows the preparation of stable Ag colloids in pure solvents without using either capping and stabilizing agents or reductants. LASiS produces AgNPs, which can be more suitable for medical and food-related applications where it is important to use non-toxic chemicals and materials for humans. In addition, laser ablation allows for achieving nanoparticles with different properties according to experimental laser parameters, thus influencing antibacterial mechanisms. However, the concentration obtained by laser-generated AgNP colloids is often low, and it is hard to implement them on an industrial scale. To obtain interesting concentrations for final applications, it is necessary to exploit high-energy lasers, which are quite expensive. In this review, we discuss the pros and cons of the use of laser ablation synthesis for the production of Ag antimicrobial colloids, taking into account applications in the food packaging field.

Development of Ag/AgX (X = Cl, I) nanoparticles toward antimicrobial, UV-protected and self-cleanable viscose fibers

In situ synthesis of Ag/AgX nanoparticles (NPs) onto viscose fibers adds new functionalities and broadens their applications. In this study, Ag/AgX (X = Cl, I) NPs were in situ synthesized onto viscose fibers to impart brilliant colors, UV-protection, antimicrobial, self-cleaning, and photocatalytic properties. The AgX NPs were deposited on the fibers by ultrasonic irradiation, while Ag-NPs were formed by photoreduction of excess Ag⁺ ions under UV irradiation. The Ag/AgX NPs-loaded onto viscose fibers endowed with pale yellow for Ag/AgI and pale purple/violet for Ag/AgCl. The colored viscose fibers showed excellent antimicrobial activity against Escherichia coli (gram-negative), Staphylococcus aureus (Gram positive), and Candida Albican. The Ag/AgX/viscose fiber also showed excellent photocatalytic and self-cleaning activity toward degradation of methylene blue.

Synthesis and antibacterial characterization of sustainable nanosilver using naturally-derived macromolecules

Greener nanosynthesis utilizes fewer amounts of materials, water, and energy; while reducing or replacing the need for organic solvents. A novel approach is presented using naturally-derived flavonoids including Quercetin pentaphosphate (QPP), Quercetin sulfonic acid (QSA) and Apigenin Triphosphate (ATRP). These water soluble, phosphorylated flavonoids were utilized both as reducing agent and stabilizer. The synthesis was achieved at room temperature using water as a solvent and it requires no capping agents. The efficiency of the resulting silver nanoparticle synthesis was compared with naturally-occurring flavonoid such as Quercetin (QCR). Results show that QCR reduced Ag(+) faster followed by QPP, QSA and ATRP respectively. This is the first evidence of direct utilization of QCR for synthesis of silver nanoparticles (AgNPs) in water. The percentage conversion of Ag(+) to Ag(0) was determined to be 96% after 35min. The synthesized nanoparticles were characterized using Transmission electron microscopy (TEM), Energy dispersive absorption spectroscopy (EDS), UV-vis spectroscopy, High resolution TEM (HR-TEM) with selected area electron diffraction (SAED). The particle sizes ranged from 2 to 80nm with an average size of 22nm and in the case of ATRP, the nanoparticle shapes varied from spherical to hexagonal with dispersed particle size ranging from 2 to 30nm. Crystallinity was confirmed by XRD and the SAED of (111), (200), and the fringes observed in HRTEM images. Results were in agreement with the UV resonance peaks of 369-440nm. The particles also exhibit excellent antibacterial activity against Staphylococcus epidermidis, Escherichia coli and Citrobacter freundii in water.

Adsorption of Silver Nanoparticles onto Different Surface Structures of Chitin/Chitosan and Correlations with Antimicrobial Activities

Size-controlled spherical silver nanoparticles (Ag NPs) can be simply prepared by autoclaving mixtures of glass powder containing silver with glucose. Moreover, chitins with varying degrees of deacetylation (DDAc < 30%) and chitosan powders and sheets (DDAc > 75%) with varying surface structure properties have been evaluated as Ag NP carriers. Chitin/chitosan-Ag NP composites in powder or sheet form were prepared by mixing Ag NP suspensions with each of the chitin/chitosan-based material at pH 7.3, leading to homogenous dispersion and stable adsorption of Ag NPs onto chitin carriers with nanoscale fiber-like surface structures, and chitosan carriers with nanoscale porous surface structures. Although these chitins exhibited mild antiviral, bactericidal, and antifungal activities, chitin powders with flat/smooth film-like surface structures had limited antimicrobial activities and Ag NP adsorption. The antimicrobial activities of chitin/chitosan-Ag NP composites increased with increasing amounts of adsorbed Ag NPs, suggesting that the surface structures of chitin/chitosan carriers strongly influence adsorption of Ag NPs and antimicrobial activities. These observations indicate that chitin/chitosan-Ag NPs with nanoscale surface structures have potential as antimicrobial biomaterials and anti-infectious wound dressings.

Comparative study of antimicrobial activity of AgBr and Ag nanoparticles (NPs)

The diverse mechanism of antimicrobial activity of Ag and AgBr nanoparticles against gram-positive and gram-negative bacteria and also against several strains of candida was explored in this study. The AgBr nanoparticles (NPs) were prepared by simple precipitation of silver nitrate by potassium bromide in the presence of stabilizing polymers. The used polymers (PEG, PVP, PVA, and HEC) influence significantly the size of the prepared AgBr NPs dependently on the mode of interaction of polymer with Ag⁺ ions. Small NPs (diameter of about 60–70 nm) were formed in the presence of the polymer with low interaction as are PEG and HEC, the polymers which interact with Ag⁺ strongly produce nearly two times bigger NPs (120–130 nm). The prepared AgBr NPs were transformed to Ag NPs by the reduction using NaBH₄. The sizes of the produced Ag NPs followed the same trends – the smallest NPs were produced in the presence of PEG and HEC polymers. Prepared AgBr and Ag NPs dispersions were tested for their biological activity. The obtained results of antimicrobial activity of AgBr and Ag NPs are discussed in terms of possible mechanism of the action of these NPs against tested microbial strains. The AgBr NPs are more effective against gram-negative bacteria and tested yeast strains while Ag NPs show the best antibacterial action against gram-positive bacteria strains.

Facile Precursor for Synthesis of Silver Nanoparticles Using Alkali Treated Maize Starch

Silver nanoparticles were prepared by using alkali treated maize starch which plays a dual role as reducer for AgNO3 and stabilizer for the produced AgNPs. The redox reaction which takes a place between AgNO3 and alkali treated starch was followed up and controlled in order to obtain spherical shaped silver nanoparticles with mean size 4-6 nm. The redox potentials confirmed the principle role of alkali treatment in increasing the reducibility of starch macromolecules. The measurements of reducing sugars at the end of reaction using dinitrosalicylic acid reagent (DNS) were carried out in order to control the chemical reduction reaction. The UV/Vis spectra show that an absorption peak, occurring due to surface plasmon resonance (SPR), exists at 410 nm, which is characteristic to yellow color of silver nanoparticles solution. The samples have been characterized by transmission electron microscopy (TEM), which reveal the nanonature of the particles.

Preparation of carboxylated Ag nanoparticles as a coating material for medical devices and control of antibacterial activity

Carboxyl group-donated silver (Ag) nanoparticles for coating on medical devices were prepared by a two-phase reduction system in situ. AgNO3 was the Ag ion source, tetraoctylammonium bromide [N(C8H17)4Br] the phase-transfer agent, sodium tetrahydroborate (NaBH4) the reducing agent and 10-carboxy-1-decanthiol (C11H22O2S, CDT) the capping agent. The characterizations of the Ag nanoparticles were conducted by diffuse reflectance Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric differential thermal analysis (TG/DTA) and transmission electron microscope. With CDT capped on Ag nanoparticles, we found that the band around 3,100 cm(-1) was attributed to COO-H stretching vibration, two adsorptions at 2,928 and 2,856 cm(-1) to C-H symmetric/anti-symmetric stretching vibration, and at 1,718 cm(-1) to C=O stretching vibration in the FT-IR spectra. The organic components of the carboxylated Ag nanoparticles were 5.8-25.9 wt%, determined by TG/DTA. The particle sizes of the carboxylated Ag nanoparticles were well controlled by the addition of the capping agent, CDT, into the reaction system. The antimicrobial activity of the Ag nanoparticles covered with different contents of CDT against E. coli was evaluated. Smaller-size Ag nanoparticles showed higher antibacterial activity, which depended on a surface area that attached easily to a microorganism cell membrane.

Impact of metallic and metal oxide nanoparticles on wastewater treatment and anaerobic digestion

Metallic and metal oxide nanomaterials have been increasingly used in consumer products (e.g. sunscreen, socks), the medical and electronic industries, and environmental remediation. Many of them ultimately enter wastewater treatment plants (WWTPs) or landfills. This review paper discusses the fate and potential effects of four types of nanoparticles, namely, silver nanoparticles (AgNPs), nano ZnO, nano TiO2, and nano zero valent iron (NZVI), on waste/wastewater treatment and anaerobic digestion. The stabilities and chemical properties of these nanoparticles (NPs) result in significant differences in antimicrobial activities. Analysis of published data of metallic and metal oxide NPs suggests that oxygen is often a prerequisite for the generation of reactive oxygen species (ROS) for AgNPs and NZVI, while illumination is necessary for ROS generation for nano TiO2 and nano ZnO. Furthermore, such nanoparticles are capable of being oxidized or dissolved in water and can release metal ions, leading to metal toxicity. Therefore, AgNPs and nano TiO2 are chemically stable NPs that have no adverse effects on microbes under anaerobic conditions. Although the toxicity of nanomaterials has been studied intensively under aerobic conditions, more research is needed to address their fate in anaerobic waste/wastewater treatment systems and their long-term effects on the environment.

In situ approach induced growth of highly monodispersed Ag nanoparticles within free standing PVA/PVP films

Ag nanoparticles supported within polyvinyl alcohol (PVA)/polyvinyl pyrrolidone (PVP) films have been successfully synthesized using novel in situ method. PVA and PVP acted as stabilizer and polyol reductant, respectively. The successful incorporation of silver nanoparticles in PVA/PVP matrix was confirmed by UV-Vis spectroscopy, X-ray diffraction (XRD), transmission electron microscope (TEM) and Fourier transform infrared (FTIR) spectroscopy. It was found that PVA/PVP-stabilized silver nanocomposite film revealed the presence of well-dispersed and spherical silver nanoparticles with an average diameter of 30 nm, while the particle sizes were reduced as the PVP percentage increased. A possible formation mechanism of Ag nanoparticles is also proposed in this article.

A Facile Method for the Synthesis of Silver Nanoparticles in the Presence of Sodium Phosphate

A facile method for the synthesis of silver nanoparticles (NPs) has been developed by using sodium phosphate (Na3PO4) as stabilizing agents and glucose the reducing agent, respectively. The obtained silver NPs have been characterized by X-ray diffraction (XRD), UV-visible spectroscopy (UV-vis) and transmission electron microscopy (TEM). It was found that in the presence of sodium phosphate, silver NPs with different morphologies and sizes were obtained. The formation mechanism of diverse silver NPs was studied preliminarily.

Role of base in the formation of silver nanoparticles synthesized using sodium acrylate as a dual reducing and encapsulating agent

The formation mechanism of Ag nanoparticles (NPs) synthesized with a wet-chemical reduction method using sodium acrylate as a dual reducing and capping agent was investigated with various analytical techniques. The time course of the state of the reaction solution was investigated using UV-vis and XAFS spectroscopies which showed that the NP formation rate increased with increasing concentration of sodium hydroxide (NaOH). The detailed kinetic analyses reveal that both the reduction rate of Ag ions and the nucleation rate of Ag NPs are dramatically increased with increasing NaOH concentration. XANES analyses imply that another reaction pathway via alternative Ag(+) species, such as Ag(OH)(x), was developed in the presence of NaOH. Consequently, NaOH is found to play an important role not only in creating specific intermediates in the reduction of Ag(+) to Ag(0), but also in accelerating the reduction and nucleation rates by enhancing the oxidation of sodium acrylate, thereby increasing the rate of formation of the Ag NPs.

Murraya Koenigii leaf-assisted rapid green synthesis of silver and gold nanoparticles

A facile bottom-up 'green' and rapid synthetic route using Murraya Koenigii leaf extract as reducing and stabilizing agent produced silver nanoparticles at ambient conditions and gold nanoparticles at 373 K. The nanoparticles were characterized using UV-vis, transmission electron microscopy (TEM), X-ray diffraction (XRD) and FTIR analysis. This method allows the synthesis of well-dispersed silver and gold nanoparticles having size ∼10 nm and ∼20 nm, respectively. Silver nanoparticles with size ∼10 nm having symmetric SPR band centered at 411 nm is obtained within 5 min of addition of the extract to the solution of AgNO3 at room temperature. Nearly spherical gold nanoparticles having size ∼20 nm with SPR at 532 nm is obtained on adding the leaf extract to the boiling solution of HAuCl4. Crystallinity of the nanoparticles is confirmed from the high-resolution TEM images, selected area electron diffraction (SAED) and XRD patterns. From the FTIR spectra it is found that the biomolecules responsible for capping are different in gold and silver nanoparticles. A comparison of the present work with the author's earlier reports on biosynthesis is also included.

Mangifera indica leaf-assisted biosynthesis of well-dispersed silver nanoparticles

The use of various parts of plants for the synthesis of nanoparticles is considered as a green technology as it does not involve any harmful chemicals. The present study reports a facile and rapid biosynthesis of well-dispersed silver nanoparticles. The method developed is environmentally friendly and allows the reduction to be accelerated by changing the temperature and pH of the reaction mixture consisting of aqueous AgNO3 and Mangifera Indica leaf extract. At a pH of 8, the colloid consists of well-dispersed triangular, hexagonal and nearly spherical nanoparticles having size ∼20 nm. The UV-vis spectrum of silver nanoparticles gave surface plasmon resonance (SPR) at 439 nm. The synthesized nanocrystals were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Water soluble organics present in the leaf are responsible for the reduction of silver ions. This green method provides faster synthesis comparable to chemical methods and can be used in areas such as cosmetics, foods and medical applications.

Nanosilver as a new generation of nanoproduct in biomedical applications

Nanosilver (NS), comprising silver nanoparticles, is attracting interest for a range of biomedical applications owing to its potent antibacterial activity. It has recently been demonstrated that NS has useful anti-inflammatory effects and improves wound healing, which could be exploited in developing better dressings for wounds and burns. The key to its broad-acting and potent antibacterial activity is the multifaceted mechanism by which NS acts on microbes. This is utilized in antibacterial coatings on medical devices to reduce nosocomial infection rates. Many new synthesis methods have emerged and are being evaluated for NS production for medical applications. NS toxicity is also critically discussed to reflect on potential concerns before widespread application in the medical field.