Method validation and characterization of stress degradation products of azelastine hydrochloride using LC-UV/PDA and LC-Q/TOF-MS studies

RATIONALE

Azelastine HCl is a second-generation H1 -receptor antagonist approved by the US Food and Drug Administration (US FDA) for treating seasonal allergic rhinitis and non-allergic vasomotor rhinitis. This study encompasses the validation of a liquid chromatography-ultra violet photo diode array (LC-UV/PDA) method for the drug and its extension to liquid chromatography/quadrupole time-of-flight mass spectrometry (LC-Q/TOF-MS) studies for identification and characterization of various stress degradation products of the drug.

METHODS

Stress degradation of azelastine HCl was undertaken under the International Council for Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) prescribed conditions of hydrolytic, photolytic, oxidative, and thermal stress. The degraded drug solutions were analyzed using Ultra Performance Liquid Chromatography (UPLC) employing a C18 (100 × 4.6 mm; 2.6 μ, Kinetex) column by isocratic elution. Detection wavelength was 241 nm. The degradation products were identified and characterized using UPLC-MS/TOF studies, and an attempt was made to isolate one of the degradation products by solvent extraction.

RESULTS

The drug was found to significantly degrade under acidic/alkaline/neutral photolytic, oxidative, and alkaline hydrolytic conditions. Six degradation products (I-VI) were identified through LC-Q/TOF-MS studies that were adequately resolved from the drug with the developed UPLC method. All degradation products (I-VI) were ionized in the total ion chromatogram (TIC) in the LC-MS studies, and these were identified and characterized, and the degradation pathway of the drug was postulated. One of the oxidation products isolated from the degraded drug solution was characterized through differential scanning calorimetry, Fourier-transform infrared spectroscopy, and nuclear magnetic resonance spectral data.

CONCLUSIONS

Six degradation products generated from stress degradation studies on azelastine HCl were adequately resolved through LC-UV/PDA studies followed by method validation. These were successfully identified and characterized through LC-Q/TOF-MS studies, and the degradation pathways for the generation of these products from the drug have been postulated.

Targeted color design of silver-gold alloy nanoparticles

This research article focuses on the targeted color design of silver-gold alloy nanoparticles (NPs), employing a multivariate optimization approach. NP synthesis involves interconnected process parameters, making independent variation challenging. Data-based property-process relationships are established to optimize optical properties effectively. We define a color target, employ a green chemical co-reduction method at room temperature and optimize process parameters accordingly. The CIEL*a*b* color space (Commission Internationale de l'Éclairage - International Commission on Illumination) and Euclidean distances facilitate accurate color matching to establish the property-process relationship. Concurrently, theoretical Mie calculations explore the structure-property relationship across particle sizes, concentrations, and molar gold contents. The theoretically optimal structure agrees very well with experimental particle structures at the property-process relationship's optimum. The data-driven property-process relationship provides valuable insights into the formation mechanism of a complex particle system, sheds light on the role of relevant process parameters and allows to evaluate the practically available property space. Model validation beyond the original grid demonstrates its robustness, yielding colors close to the target. Additionally, Design of Experiments (DoE) methods reduce experimental work by threefold with slight accuracy trade-offs. Our novel methodology for targeted color design demonstrates how data-based methods can be utilized alongside structure-property relationships to unravel property-process relationships in the design of complex nanoparticle systems and paves the way for future developments in targeted property design.

In situ reduction of Ag nanoparticles using okra polysaccharides for the preparation of flexible multifunctional sensors

This paper reports the fabrication of flexible films loaded with Ag nanoparticles (Ag NPs) and annotated as POPA films from polyvinyl alcohol, okra polysaccharides, phytic acid, and AgNO3 via an in situ reduction and solution-casting method. The prepared films exhibit strain, temperature, and humidity sensing. As a flexible strain sensor, the POPA sensor has a wide strain sensing range (1-250 %), and fast response/recovery (0.22/0.28 s), while as a temperature sensor, it senses the human body temperature and exhibits excellent temperature sensitivity (TCR = -1.401 % °C-1) and good linearity (R2 = 0.994) in the temperature range of 30-55 °C. Additionally, in the relative humidity (RH) of range 35-95 %, the POPA humidity sensor outputs stable electrical signals during adsorption and desorption. Moreover, it exhibits low hysteresis values (3.19 % RH) and good linearity (R2 = 0.989) for the detection of breathing rates during different human body states. Consequently, the POPA sensor exhibits good stability, repeatability, and reversibility for strain, temperature, and humidity sensing. The designed multifunctional POPA sensor thus holds great potential for its application in flexible wearable devices and electronics.

Silver Nanoparticle Synthesis in Glycerol by Low-Pressure Plasma-Driven Electrolysis: The Roles of Free Electrons and Photons

Low-temperature plasmas in and in contact with liquids have emerged as a catalyst-free approach for the selective, electrode-free, and green synthesis of novel materials. For the synthesis of nanomaterials, short-lived solvated electrons have been proposed to be the critical reducing species, while the role of ultraviolet (UV) photons from plasma is less explored. Here, we demonstrate that UV radiation contributes ∼70% of the integral plasma effect in synthesizing silver (Ag) nanoparticles within a glycerol solution. We suggest that the UV radiation causes C-H bond cleavage of the glycerol molecules, with an experimentally and theoretically determined threshold photon energy of only 5 eV. The photon-induced dissociation leads to the formation of glycerol fragmentation radicals, causing the reduction of Ag+ ions to Ag neutrals, enabling nanoparticle formation in the liquid phase.

Novel Size-Tunable and Straightforward Ultra-Small Nanoparticle Synthesis in a Varying Concentration Range of Glycerol as a Green Reducing Solvent

Despite all the possibilities available so far for the synthesis of nanoparticles (NPs), synthesizing ultra-small (<10 nm) monodispersed particles is still demanding. Getting a particular size with a straightforward method is a trial-and-error approach. To explore this prospective, in the current study, we have introduced a protocol which offers a varying concentration range of glycerol to successfully generate the NPs of repeatable and consistent particle size in each synthesis, thus giving an alternative from lengthy tentative preparations and/or testing protocols. Since synthesizing controlled sized nanoparticles in aqueous medium is somewhat difficult as the balance of particle growth and nucleation is challenging to control, herein, we used a polyol method with glycerol both as a solvent medium as well as reducing species for silver nitrate, as an example model ion source, to execute the nanoparticle synthesis. In order to maintain the stability of the synthesized NPs, polyvinylpyrolidone (PVP) was added as a stabilizer. The synthesis, monodispersity, and stability were confirmed using techniques such as UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and X-ray powder diffraction (XRD), while morphological analysis and ultra-small size validation were conducted using TEM, SEM, and AFM. Interestingly, in the various concentrations of glycerol solution used (10-100%), we have observed a tunable linear size range to obtain ultra-small nanoparticles (<10 nm) up to 60% glycerol, while further increasing the glycerol component increased the size approximately to ∼160 nm, providing tunable properties in this synthesis procedure. Hence, this study provides a distinct possibility to obtain ultra-small nanoparticles with a tunable size feature for further applications in numerous fields.

Surfactant-Free Colloidal Syntheses of Gold-Based Nanomaterials in Alkaline Water and Mono-alcohol Mixtures

Gold nanoparticles (Au NPs) and gold-based nanomaterials combine unique properties relevant for medicine, imaging, optics, sensing, catalysis, and energy conversion. While the Turkevich-Frens and Brust-Schiffrin methods remain the state-of-the-art colloidal syntheses of Au NPs, there is a need for more sustainable and tractable synthetic strategies leading to new model systems. In particular, stabilizers are almost systematically used in colloidal syntheses, but they can be detrimental for fundamental and applied studies. Here, a surfactant-free synthesis of size-controlled colloidal Au NPs stable for months is achieved by the simple reduction of HAuCl₄ at room temperature in alkaline solutions of low-viscosity mono-alcohols such as ethanol or methanol and water, without the need for any other additives. Palladium (Pd) and bimetallic Au _x Pd _y NPs, nanocomposites and multimetallic samples, are also obtained and are readily active (electro)catalysts. The multiple benefits over the state-of-the-art syntheses that this simple synthesis bears for fundamental and applied research are highlighted.

Green room temperature synthesis of silver-gold alloy nanoparticles

Metallic alloy nanoparticles (NPs) exhibit interesting optical, electrical and catalytic properties, dependent on their size, shape and composition. In particular, silver-gold alloy NPs are widely applied as model systems to better understand the syntheses and formation (kinetics) of alloy NPs, as the two elements are fully miscible. Our study targets product design via environmentally friendly synthesis conditions. We use dextran as the reducing and stabilizing agent for the synthesis of homogeneous silver-gold alloy NPs at room temperature. Our approach is a one-pot, low temperature, reaction-controlled, green and scalable synthesis route of well-controlled composition and narrow particle size distribution. The composition over a broad range of molar gold contents is confirmed by scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy (STEM-EDX) measurements and auxiliary inductively coupled plasma-optical emission spectroscopy measurements (ICP-OES). The distributions of the resulting particles in size and composition are obtained from multi-wavelength analytical ultracentrifugation using the optical back coupling method and further confirmed by high-pressure liquid chromatography. Finally, we provide insight into the reaction kinetics during the synthesis, discuss the reaction mechanism and demonstrate possibilities for scale-up by a factor of more than 250 by increasing the reactor volume and NP concentration.

An investigation of the allylation cascade reactions of substituted indigos

In a continuation of the exploration of indigo cascade reactions, a series of -OMe, -Ph, -Br and -NO₂ substituted indigos 1a-i were synthesised to probe electronic effects upon the outcome of allylation cascade reactions. When indigos 1a-i in the presence of base were reacted with allyl bromide, spiroindolinepyridoindolones 17-25 (36-75%) were obtained as the major products in each case, marking a shift in outcome relative to that previously reported for unsubstituted indigo. In electron-rich derivatives (-OMe, -Ph), C-allylspiroindolinepyridoindolediones 26-29 (3-11%) were also isolated, which are most likely formed via a Claisen rearrangement of the respective spiroindolinepyridoindolones 18-21. Additionally, the isolation of diallylbiindolone 16, oxazinobiindole 30 and N,N'-diallyl-3,3'-bis(allyloxy)biindole 31 each represented novel polyheterocyclic derivatives, providing intriguing new mechanistic insights, reaction pathways and in the case of 30 the first common heterocyclic skeletal outcome shared in both allylation and propargylation cascade reactions of indigo.

Chemical Insights into the Formation of Colloidal Iridium Nanoparticles from In Situ X-ray Total Scattering: Influence of Precursors and Cations on the Reaction Pathway

Iridium nanoparticles are important catalysts for several chemical and energy conversion reactions. Studies of iridium nanoparticles have also been a key for the development of kinetic models of nanomaterial formation. However, compared to other metals such as gold or platinum, knowledge on the nature of prenucleation species and structural insights into the resultant nanoparticles are missing, especially for nanoparticles obtained from Ir_xCl_y precursors investigated here. We use in situ X-ray total scattering (TS) experiments with pair distribution function (PDF) analysis to study a simple, surfactant-free synthesis of colloidal iridium nanoparticles. The reaction is performed in methanol at 50 °C with only a base and an iridium salt as precursor. From different precursor salts─IrCl₃, IrCl₄, H₂IrCl₆, or Na₂IrCl₆─colloidal nanoparticles as small as Ir_∼55 are obtained as the final product. The nanoparticles do not show the bulk iridium face-centered cubic (fcc) structure but show decahedral and icosahedral structures. The formation route is highly dependent on the precursor salt used. Using IrCl₃ or IrCl₄, metallic iridium nanoparticles form rapidly from Ir_xCl_y^n- complexes, whereas using H₂IrCl₆ or Na₂IrCl₆, the iridium nanoparticle formation follows a sudden growth after an induction period and the brief appearance of a crystalline phase. With H₂IrCl₆, the formation of different Ir_n (n = 55, 55, 85, and 116) nanoparticles depends on the nature of the cation in the base (LiOH, NaOH, KOH, or CsOH, respectively) and larger particles are obtained with larger cations. As the particles grow, the nanoparticle structure changes from partly icosahedral to decahedral. The results show that the synthesis of iridium nanoparticles from Ir_xCl_y is a valuable iridium nanoparticle model system, which can provide new compositional and structural insights into iridium nanoparticle formation and growth.

In situ synthesis of Ag/Ag2O-cellulose/chitosan nanocomposites via adjusting KOH concentration for improved photocatalytic and antibacterial applications

This work proposed a facile way to construct cellulose/chitosan-loaded Ag/Ag₂O nanocomposite films (ACC) from alkali/urea solution by increasing the content of alkali KOH in the solvent. The saturated alkali and hydroxyl groups of the cellulose and chitosan chains were accelerated to convert AgNO₃ to Ag⁰. Ag₂O served as nuclei to lower the energy barrier. The formation of Ag/Ag₂O nanoparticles (NPs) endowed the cellulose bio-reduced Ag composites with multifunction and stronger photocatalytic activity. Ag/Ag₂O NPs with the diameter of 139-360 nm were uniformly dispersed in the composite films, resulting in superior mechanical properties (64.6 MPa) and thermal stability. Almost 92 % of methyl orange was degraded under UV-irradiation within 40 min by ACC. After 3 runs of degradation, the photocatalytic abilities of ACC remained. Moreover, the films exhibited good antibacterial activities. The width of inhibition zones around ACC reached 9.2-12 mm and 8.6-10.4 mm for S. aureus and E. coli. The strategy provided a new avenue to construct multifunctional cellulose/chitosan materials for various applications, such as wastewater treatment, and electrocatalysis.

Dual action of pyroligneous acid in the eco-friendly synthesis of bactericidal silver nanoparticles

In the present study, we demonstrate that pyroligneous acid (PA), also known as wood vinegar, functions efficiently as both reducing and stabilizing agent in the synthesis of silver nanoparticles (AgNPs). The synthesis and stabilization of AgNPs take place in the following fashion: 1) in alkaline environment, oxygenated species (phenols in the present case) contained in PA reduce silver ions to metallic silver; 2) acetic acid, abundantly present in PA, adsorb onto the AgNPs conferring electrostatic stabilization. This mechanism is supported by GC-MS and RAMAN analysis, with the former revealing the compounds lacking in PA after nanoparticle synthesis and the latter demonstrating acetic acid adsorbed on the nanoparticles. The AgNPs produced via this method were quite stable up to 150 days (zeta potential = -56 mV). The AgNPs were then found to inhibit the growth of Escherichia coli and Staphylococcus aureus. Concerning PA, we showed that it displays bactericidal properties only under acidic conditions. This study contributes to the development of more environmentally benign routes to produce nanomaterials.

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Pyroligneous acid as reducing and stabilizing agent to produce silver nanoparticles.

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No hazardous chemicals employed in the synthesis of the nanoparticles.

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Pyroligneous acid displays bactericidal activity only under acidic conditions.

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Mitigation of the environmental impact of pyrolysis gasses.

A combination therapy strategy for treating antibiotic resistant biofilm infection using a guanidinium derivative and nanoparticulate Ag(0) derived hybrid gel conjugate

Bacteria organized in biofilms show significant tolerance to conventional antibiotics compared to their planktonic counterparts and form the basis for chronic infections. Biofilms are composites of different types of extracellular polymeric substances that help in resisting several host-defense measures, including phagocytosis. These are increasingly being recognized as a passive virulence factor that enables many infectious diseases to proliferate and an essential contributing facet to anti-microbial resistance. Thus, inhibition and dispersion of biofilms are linked to addressing the issues associated with therapeutic challenges imposed by biofilms. This report is to address this complex issue using a self-assembled guanidinium-Ag(0) nanoparticle (AD-L@Ag(0)) hybrid gel composite for executing a combination therapy strategy for six difficult to treat biofilm-forming and multidrug-resistant bacteria. Improved efficacy was achieved primarily through effective biofilm inhibition and dispersion by the cationic guanidinium ion derivative, while Ag(0) contributes to the subsequent bactericidal activity on planktonic bacteria. Minimum Inhibitory Concentration (MIC) of the AD-L@Ag(0) formulation was tested against Acinetobacter baumannii (25 μg mL-1), Pseudomonas aeruginosa (0.78 μg mL-1), Staphylococcus aureus (0.19 μg mL-1), Klebsiella pneumoniae (0.78 μg mL-1), Escherichia coli (clinical isolate (6.25 μg mL-1)), Klebsiella pneumoniae (clinical isolate (50 μg mL-1)), Shigella flexneri (clinical isolate (0.39 μg mL-1)) and Streptococcus pneumoniae (6.25 μg mL-1). Minimum bactericidal concentration, and MBIC50 and MBIC90 (Minimum Biofilm Inhibitory Concentration at 50% and 90% reduction, respectively) were evaluated for these pathogens. All these results confirmed the efficacy of the formulation AD-L@Ag(0). Minimum Biofilm Eradication Concentration (MBEC) for the respective pathogens was examined by following the exopolysaccharide quantification method to establish its potency in inhibition of biofilm formation, as well as eradication of mature biofilms. These effects were attributed to the bactericidal effect of AD-L@Ag(0) on biofilm mass-associated bacteria. The observed efficacy of this non-cytotoxic therapeutic combination (AD-L@Ag(0)) was found to be better than that reported in the existing literature for treating extremely drug-resistant bacterial strains, as well as for reducing the bacterial infection load at a surgical site in a small animal BALB/c model. Thus, AD-L@Ag(0) could be a promising candidate for anti-microbial coatings on surgical instruments, wound dressing, tissue engineering, and medical implants.

Green Synthesis of Ag NPs Using Ustilago maydis as Reducing and Stabilizing Agent

Ustilago maydis (UM) is a fungus that grows naturally on Zea mays; it reduces the corn yields, and thus, it represents huge economic loss; however, it can be used as an exotic food, and in the present work, it is successfully used as a reducing and stabilizing agent for the preparation of silver nanoparticles (Ag NPs) due to its content of amino acids and biosurfactants. The effects of the concentration of UM aqueous extract, pH, and sunlight on the particle size, surface plasmon resonance, stability, and morphology of Ag NPs obtained by green synthesis were evaluated. A green reduction was observed only in presence of UM, and colloidal Ag NPs were obtained with or without the presence of sunlight; nevertheless, continuous sunlight exposure greatly increased the reaction rate. Ag NPs tend to increase in size from 153 nm to 1400 nm at a higher pH and a greater amount of UM, and also, UM tends to stabilize the Ag NPs preventing their agglomeration according to measurement of zeta potential (−10.75 ± 0.84 mV) and SEM observation; furthermore, surface plasmon resonances were more intense between 400 and 480 nm of wavelength adding greater amount of UM. This study concludes that UM not only reduces AgNO3 but also acts as stabilizer of Ag NPs.

Optimized colloidal growth of hexagonal close-packed Ag microparticles and their stability under catalytic conditions

The colloidal synthesis of hcp silver microparticles is optimized by tuning the chemical reduction kinetics and the surface stabilization during synthesis.

Green Synthesis of Metallic Nanoparticles Using Some Selected Medicinal Plants from Southern Africa and Their Biological Applications

The application of metallic nanoparticles (MNPs), especially that of silver, gold, cobalt, and zinc as antimicrobial, anticancer, drug delivery, contrast, and bioimaging agents has transformed the field of medicine. Their functions, which are attributed to their physicochemical properties, have gained prominence in various technological fields. Although MNPs can be produced via rigorous physical and chemical techniques, in recent years, a biological approach utilizing natural materials has been developed. With the increasing enthusiasm for safe and efficient nanomaterials, the biological method incorporating microorganisms and plants is preferred over physical and chemical methods of nanoparticle synthesis. Of these bio-entities, plants have received great attention owing to their capability to reduce and stabilize MNPs in a single one-pot protocol. South Africa is home to ~10% of the world's plant species, making it a major contributor to the world's ecological scenery. Despite the documented contribution of South African plants, particularly in herbal medicine, very few of these plants have been explored for the synthesis of the noble MNPs. This paper provides a review of some important South African medicinal plants that have been utilized for the synthesis of MNPs. The enhanced biological properties of the biogenic MNPs attest to their relevance in medicine. In this endeavour, more of the African plant biodiversity must be explored for the synthesis of MNPs and be validated for their potential to be translated into future nanomedicine.

Green synthesis of antibacterial and cytotoxic silver nanoparticles by Piper nigrum seed extract and development of antibacterial silver based chitosan nanocomposite

In the present study, we have used seed extract of P. nigrum as an effective reducing agent for the synthesis of silver nanoparticles (Ag NPs) and silver based chitosan nanocomposite (Ag/CS NC). The silver nanoparticles were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and Fourier transform infrared spectroscopy (FTIR). The appearance of a surface plasmon resonance (SPR) peak located at 430 nm reveals the formation of silver nanoparticles. The TEM analysis indicates that the attained silver nanoparticles were mostly in spherical shapes with sizes ranging between 15 and 38 nm. The high resolution liquid chromatography with mass spectroscopy (HR-LCMS) analysis was performed to screen the phytochemical constituents of P. nigrum seed extract. The silver nanoparticles synthesized by P. nigrum seed extract exhibited effective antibacterial activity against Bacillus subtilis (B. subtilis) and Escherichia coli (E. coli). In addition, the silver nanoparticles showed potent cytotoxicity against hazardous human cancer cell lines MDA-MB-231, PANC-1, SKOV-3, PC-3 and Hela. The observation of bright spots in the TEM dark field images represents the presence of Ag in CS suspension. Besides, the Ag/CS NC coated cotton fabric substantially showed remarkable antibacterial activity against B. subtilis and E. coli.

Gold Nanoparticles Synthesized Using Extracts of Cyclopia intermedia, Commonly Known as Honeybush, Amplify the Cytotoxic Effects of Doxorubicin

Cyclopia intermedia (C. intermedia) is an indigenous South African shrub used to prepare the popular medicinal honeybush (HB) tea. This plant contains high levels of mangiferin (MGF), a xanthonoid that was reported to have numerous biological activities, including anti-tumor activity. MGF and extracts that contain high concentrations of MGF, such as extracts from Mangifera indica L. or mango have been used to synthesize gold nanoparticles (AuNPs) using green nanotechnology. It has previously been shown that when AuNPs synthesized from M. indica L. extracts are used in combination with doxorubicin (DOX) and Ayurvedic medicine, the anti-tumor effects appear to be augmented. It has also been demonstrated that MGF used in combination with DOX resulted in enhanced anti-tumor effects. In this study, C. intermedia (HB) and MGF were used to synthesize HB-AuNPs and MGF-AuNPs, respectively. The physicochemical properties of the AuNPs were characterized by the UV-Visible Spectroscopy (UV-Vis), dynamic light scattering (DLS), Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction spectroscopy (XRD) and high-resolution transmission electron microscopy (HR-TEM). The cytotoxicity of HB-AuNPs and MGF-AuNPs were assessed on human colon (Caco-2), prostate (PC-3) and glioblastoma (U87) cancer cells; as well as normal breast epithelial (MCF-12A) cells using the MTT assay. Both HB-AuNPs and MGF-AuNPs demonstrated relatively low cytotoxicity in these cells. However, when these nanoparticles were used in combination with DOX, the cytotoxicity of DOX was significantly augmented.

Biosynthesis, Characterization, and Biological Activities of Procyanidin Capped Silver Nanoparticles

In this study, procyanidin dimers and Leucosidea sericea total extract (LSTE) were employed in the synthesis of silver nanoparticles (AgNPs) and characterized by ultraviolet-visible (UV-Visible) spectroscopy, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), and dynamic light scattering (DLS) techniques. AgNPs of about 2–7 nm were obtained. DLS and stability evaluations confirmed that the AgNPs/procyanidins conjugates were stable. The formed nanoparticles exhibited good inhibitory activities against the two enzymes studied. The IC₅₀ values against the amylase enzyme were 14.92 ± 1.0, 13.24 ± 0.2, and 19.13 ± 0.8 µg/mL for AgNPs coordinated with LSTE, F1, and F2, respectively. The corresponding values for the glucosidase enzyme were 21.48 ± 0.9, 18.76 ± 1.0, and 8.75 ± 0.7 µg/mL. The antioxidant activities were comparable to those of the intact fractions. The AgNPs also demonstrated bacterial inhibitory activities against six bacterial species. While the minimum inhibitory concentrations (MIC) of F1-AgNPs against Pseudomonas aeruginosa and Staphylococcus aureus were 31.25 and 15.63 µg/mL respectively, those of LSTE-AgNPs and F2-AgNPs against these organisms were both 62.50 µg/mL. The F1-AgNPs demonstrated a better bactericidal effect and may be useful in food packaging. This research also showed the involvement of the procyanidins as reducing and capping agents in the formation of stable AgNPs with potential biological applications.

Physico-chemical characterisation of the fraction of silver (nano)particles in pristine food additive E174 and in E174-containing confectionery

Silver (E174) is authorised as a food additive in the EU. The unknown particle size distribution of E174 is a specific concern for the E174 risk assessment. This study characterised the fraction of silver (nano)particles in 10 commercially available pristine E174 food additives and 10 E174-containing products by transmission electron microscopy (TEM) and single-particle inductively coupled plasma-mass spectrometry (spICP-MS). TEM analysis showed that all samples contained micrometre-sized flakes and also a fraction of (nano)particles. Energy-dispersive X-ray spectroscopy (EDX) and electron diffraction confirmed that the (nano)particles and micrometre-sized flakes consisted of silver. A higher amount of (nano)particles was observed in the products than in the food additives. In addition, the surface of the micrometre-sized flakes was rougher in products. The median of the minimum external dimension, assessed as minimal Feret diameter, of the fraction of (nano)particles determined by quantitative TEM analysis was 11 ± 4 nm and 18 ± 7 nm (overall mean ± standard deviation), for food additives and products, respectively. Similar size distributions were obtained by spICP-MS and TEM, considering the limit of detection of spICP-MS. The median of the equivalent spherical diameter of the fraction of (nano)particles determined by spICP-MS was 19 ± 4 nm and 21 ± 2 nm (overall mean ± standard deviation), for food additives and products, respectively. In all samples, independent of the choice of technique, the nano-sized particles represented more than 97% (by number) of the silver particles, even though the largest mass of silver was present as flakes.

Green Synthesis of Silver Nanoparticles with Size Distribution Depending on Reducing Species in Glycerol at Ambient pH and Temperatures

With an increase in biodiesel demand, a large surplus of glycerol is expected, and there is interest regarding the usage of glycerol as a value-added product. One such idea is to use glycerol as a "green solvent" to replace petroleum-based organic solvents. Glycerol is nontoxic to humans, and its vapor pressure is sufficiently high for the chemical reaction to be performed at high temperatures under ambient atmospheric pressures. Its dielectric constant is between those of water and organic solvents, and it dissolves widely varying materials, spanning between salts and organic molecules. Metal nanoparticles have been known to be synthesized in glycerol within limited experimental conditions, including high temperatures, alkaline pH conditions, and the irradiance of ultraviolet light. Herein, we report that silver nanoparticles have been formed in glycerol under completely green conditions (e.g., room temperature, neutral pH conditions, and without irradiance of ultraviolet light). We suggest that aldehydes and free radicals are generated in glycerol, which is operating as reducing species.

A Simple Drop-and-Dry Approach to Grass-Like Multifunctional Nanocoating on Flexible Cotton Fabrics Using In Situ-Generated Coating Solution Comprising Titanium-Oxo Clusters and Silver Nanoparticles

Multifunctional nanocoatings have been of central importance in various technological fields, yet their fabrication, especially on flexible substrates, still remains a persistent challenge to date. We herein demonstrate a mild single-step drop-and-dry approach to the in situ growth of hierarchical grass-like nanostructures on flexible cotton fabrics. A precursor solution comprising titanium-oxo clusters [Ti₁₈MnO₃₀(OEt)₂₀(MnPhen)₃] (Phen = 1,10-phenanthroline) and AgNO₃ is employed wherein Ag⁺ cations are in situ-reduced to silver nanoparticles (AgNPs). Drop-casting onto cotton fabrics under mild conditions induces the in situ growth of the heterogeneous grass-like assembly, and each constituent nanofibrous 'grass leaf' incorporates AgNPs both on the surface and embedded in the interior. The hierarchical morphology and heterogeneous composition of these grass-like nanostructures impart the coated cotton fabrics with enhanced antibacterial properties, robust hydrophobicity, and UV-blocking capability, which are features desired in textile materials but lacking in natural cotton.

Mild Homogeneous Synthesis of Gold Nanoparticles through the Epoxide Route: Kinetics, Mechanisms, and Related One-Pot Composites

A new one-pot homogeneous methodology at room temperature to obtain Au nanoparticles (AuNP) on the basis of the epoxide route is presented. The proposed method takes advantage of the homogenous generation of OH^- moieties driven by epoxide ring-opening, mediated by chloride nucleophilic attack. Once reached alkaline conditions, the reducing medium allows the quantitative formation of AuNP under well-defined kinetic control. A stabilizing agent, such as polyvinylpyrrolidone (PVP) or cetyltrimethylammonium chloride (CTAC), is required to maintain the AuNP stable. Meanwhile their presence dramatically affects the reduction kinetics and pathway, as demonstrated by the evolution of the UV/Vis spectra, small-angle X-ray scattering (SAXS) patterns, and pH value along the reaction. In the presence of PVP nanogold spheroids are obtained following a similar reduction mechanism as that observed for control experiments in the absence of PVP. However, if CTAC is employed a stable complex with Au^III is formed, leading to a different reaction pathway and resulting in ellipsoidal-like shaped AuNP. Moreover, the proposed methodology allows stabilize the growing AuNP, by coupling their formation with nonalkoxidic sol-gel reactions, leading to nanocomposite gels with embedded metallic nanoparticles. The epoxide route thus offers a versatile scenario for the one-pot preparation of new metal nanoparticles-inorganic/hybrid matrices nanocomposites with valuable optical properties.

In Situ Ligand-Directed Growth of Gold Nanoparticles in Biological Tissues

Fundamental understandings and precise control of nanoparticle growth in the complex biological environment are crucial to broadening their potential applications in tissue imaging. Herein, we report that glutathione (GSH), a widely used capping ligand for precise control of the size of gold nanoparticle (AuNP) down to single-atom level in test tubes, can also be used to direct the selective growth of the AuNPs in the mitochondria of renal tubule cells as well as hippocampus cells in the tissues. Precise control of this growth process can lead to the formation of both ultrasmall AuNPs with near-infrared luminescence and large plasmonic AuNPs. The observed selective growth of the AuNPs is likely due to unique GSH storage function of the mitochondria. Using a different ligand, β-glucose thiol, we also found that the brush border of the intestine for glucose absorption became the major site for the growth of luminescent AuNPs. These findings suggest that selective growth of AuNPs in the biological tissues can indeed be directed with specific ligands, opening up a new avenue to tissue labeling and future development of artificial bionano hybrid systems.

Gold nanoparticle-carboxymethyl cellulose nanocolloids for detection of human immunodeficiency virus type-1 (HIV-1) using laser light scattering immunoassay

It is estimated that over 100 million people have been infected with human immunodeficiency virus (HIV-1) resulting in approximately 30 million deaths globally. Herein, we designed and developed novel nano-immunoconjugates using gold nanoparticles (AuNPs) and carboxymethylcellulose (CMC) biopolymer, which performed simultaneously as an eco-friendly in situ reducing agent and surface stabilizing ligand for the aqueous colloidal process. These AuNPs-CMC nanocolloids were biofunctionalized with the gp41 glycoprotein receptor (AuNPs-CMC-gp41) or HIV monoclonal antibodies (AuNPs-CMC_PolyArg-abHIV) for detection using the laser light scattering immunoassay (LIA). These AuNPs-CMC bioengineered nanoconjugates were extensively characterized by morphological and physicochemical methods, which demonstrated the formation of spherical nanocrystalline colloidal AuNPs with the average size from 12 to 20 nm and surface plasmon resonance peak at 520 nm. Thus, stable nanocolloids were formed with core-shell nanostructures composed of AuNPs and biomacromolecules of CMC-gp41, which were cytocompatible based on in vitro cell viability results. The AuNPs-CMC-gp41 nanoconjugates were tested against HIV monoclonal antibodies conjugates (AuNPs-CMC_PolyArg-abHIV) using the light scattering immunoassay (LIA) where they behaved as active nanoprobes for the detection at nM level of HIV-1 antigenic proteins. This strategy offers a novel nanoplatform for creating bioprobes using green nanotechnology for the detection of HIV-1 and other virus-related diseases.

Synthesis of Colloidal Metal Nanocrystals: A Comprehensive Review on the Reductants

There is a growing interest in controlling the synthesis of colloidal metal nanocrystals and thus tailoring their properties toward various applications. In this context, choosing an appropriate combination of reagents (e.g., salt precursor, reductant, capping agent, and stabilizer) plays a pivotal role in enabling the synthesis of metal nanocrystals with diversified sizes, shapes, and structures. Here we present a comprehensive review that highlights one of the key reagents for the synthesis of metal nanocrystals via chemical reduction: the reductants. We start with a brief introduction to the compounds commonly employed as reductants in the colloidal synthesis of metal nanocrystals by showing their oxidation half-reactions and the corresponding oxidation potentials. Then we offer specific examples pertaining to the controlled synthesis of metal nanocrystals, followed by some fundamental aspects covering the general mechanisms of metal ion reduction based on the Marcus Theory. Afterwards, we present a case-by-case discussion on a wide variety of reductants, including their major properties, reduction mechanisms, and additional effects on the final products. We illustrate these aspects by selecting key examples from the literature and paying close attention to the underlying mechanism in each case. At the end, we conclude by summarizing the highlights of the review and providing some perspectives on future directions.

Carboxylate Functional Groups Mediate Interaction with Silver Nanoparticles in Biofilm Matrix

Biofilms causing medical conditions or interfering with technical applications can prove undesirably resistant to silver nanoparticle (AgNP)-based antimicrobial treatment, whereas beneficial biofilms may be adversely affected by the released silver nanoparticles. Isolated biofilm matrices can induce reduction of silver ions and stabilization of the formed nanosilver, thus altering the exposure conditions. We thus study the reduction of silver nitrate solution in model experiments under chemically defined conditions as well as in stream biofilms. Formed silver nanoparticles are characterized by state-of-the art methods. We find that isolated biopolymer fractions of biofilm organic matrix are capable of reducing ionic Ag, whereas other isolated fractions are not, meaning that biopolymer fractions contain both reducing agent and nucleation seed sites. In all of the investigated systems, we find that silver nanoparticle-biopolymer interface is dominated by carboxylate functional groups. This suggests that the mechanism of nanoparticle formation is of general nature. Moreover, we find that glucose concentration within the biofilm organic matrix correlates strongly with the nanoparticle formation rate. We propose a simple mechanistic explanation based on earlier literature and the experimental findings. The observed generality of the extracellular polymeric substance/AgNP system could be used to improve the understanding of impact of Ag+ on aqueous ecosystems, and consequently, to develop biofilm-specific medicines and bio-inspired water decontaminants.

On the synergy between silver nanoparticles and doxycycline towards the inhibition of Staphylococcus aureus growth

In a previous paper (RSC Adv., 2015, 5, 66886–66893), we showed that the combination of silver nanoparticles (NanoAg) with doxycycline (DO) culminated in an increased bactericidal activity towards E. coli. Herein we further investigated the metabolic changes that occurred on Staphylococcus aureus upon exposure to NanoAg with the help of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) coupled with multivariate data analysis. It has been discovered that the combination of DO with NanoAg produced metabolic changes in S. aureus that were not simply the overlap of the treatments with DO and NanoAg separately. Our results suggest that DO and NanoAg act synergistically to impede protein synthesis by the bacteria.

Silver nanoparticles conjugated with doxycycline act synergistically to halt S. aureus growth via inhibition of protein synthesis.

In situ synthesis of silver nanoparticles on the surface of PDMS with high antibacterial activity and biosafety toward an implantable medical device

We developed a straightforward method to fabricate antibacterial silicon films via the in situ synthesis of silver nanoparticles (AgNPs) on a polydimethylsiloxane (PDMS) film. To grow AgNPs attached on the film, AgNP seeds were synthesized through the reduction of silver ions electrostatically bound to hydroxyl groups formed on the surface of the film after treatment with air plasma. In the growth reaction, silver ions were reduced on the seeds of AgNPs by sodium citrate in a solution of AgNO3, which allowed for the formation of AgNPs with sizes of up to ~ 500 nm, which The formed AgNPs on the films were characterized using UV-vis spectrophotometer, scattering electron microscope and induced coupled mass spectrometer. The amount of AgNPs was estimated to be less than 0.05% of the total film weight. Even though it was coated with a small amount of AgNPs, the PDMS film exhibited reduction of E. coli and S. aureus with values of log10 4.8 and log10 5.7, respectively. The biosafety of the AgNP-attached PDMS film was examined by contact of cells with the film or film eluent. Counting of viable cells revealed no significant cytotoxicity of the in situ-fabricated AgNPs on the PDMS film.

Direct one-pot synthesis of cinnamaldehyde immobilized on gold nanoparticles and their antibiofilm properties

The objective of the present study was to develop a one-pot strategy to synthesis gold nanoparticle complexes using cinnamaldehyde, a potent antibiofilm agent which in its free form, exhibits high volatility and unstable nature. Hence, we developed cinnamaldehyde gold nanoparticles (CGNPs) in a single step to overcome the limitations of free cinnamaldehyde. Furthermore, reduction abilities of cinnamaldehyde under different experimental conditions, that is, varying precursor concentrations of cinnamaldehyde and gold, metal salts, pH, temperature, and light sources, were investigated. UV-vis spectroscopy, transmission electron microscopy, attenuated total reflectance Fourier transform infrared spectroscopy, and dynamic light-scattering measurements revealed that heat influenced the nanoparticle formation in the presence of cinnamaldehyde, and as produced cinnamaldehyde immobilized on gold nanoparticles were spherical, monodispersed, and stable by surface charge. CGNPs containing 0.01% cinnamaldehyde by weight exhibited effective biofilm inhibition of up to >80% against Gram positive bacteria (methicillin-sensitive and -resistant strains of Staphylococcus aureus, MSSA and MRSA, respectively) and Gram negative (Escherichia coli and Pseudomonas aeruginosa) and a fungus Candida albicans. In addition, CGNPs attenuated the virulence of C. albicans by inhibiting hyphae formation. Based on observations of their antibiofilm effects and confocal microscopy findings, CGNPs caused biofilm damage by direct contact. Thus, cinnamaldehyde appears to be a promising reduction material for the eco-friendly, one-pot synthesis of CGNPs with excellent antibiofilm activity.

Environmentally friendly and facile synthesis of Rh nanoparticles at room temperature by alkaline ethanol solution and their application for ethanol electrooxidation

A facile, fact and green synthetic route was developed to prepare Rh nanoparticles at room temperature.

Antimicrobial dependence of silver nanoparticles on surface plasmon resonance bands against Escherichia coli

This study presents a simple and trouble-free method for determining the antimicrobial properties of silver nanoparticles (AgNPs) based on the surface plasmon resonance (SPR) bands. AgNPs were prepared by chemical reduction method using silver nitrates as a metallic precursor and formaldehyde (HCHO) as a reducing agent and capped by polyethylene glycol. Effects of several processing variables on the size and shape of AgNPs were monitored using an ultraviolet–visible spectrophotometer based on their SPR bands. The formed particles showing various particle shapes and full width at half maximum (FWHM) were tested against Escherichia coli by surface spreading using agar plates containing equal amounts of selected AgNPs samples. The NPs exhibited higher antimicrobial properties; however, monodispersed spherical NPs with narrow FWHM were more effective against E. coli growth. The NPs prepared are promising candidates in diverse applications such as antimicrobial agents in the food and biomedical industries.

A step ahead towards the green synthesis of monodisperse gold nanoparticles: the use of crude glycerol as a greener and low-cost reducing agent

Crude glycerol obtained directly from transesterification reaction was employed as a low-cost and greener reducing agent to prepare monodisperse AuNPs (∼8 nm).