Silver nanoparticles: various methods of synthesis, size affecting factors and their potential applications–a review

Recent progression of cyanobacteria and their pharmaceutical utility: an update

Cyanobacteria (blue-green algae) are Gram-negative photosynthetic eubacteria that are found everywhere. This largest group of photosynthetic prokaryotes is rich in structurally novel and biologically active compounds; several of which have been utilized as prospective drugs against cancer and other ailments, as well. Consequently, the integument of nanoparticles-synthetic approaches in cyanobacterial extracts should increase pharmacological activity. Moreover, silver nanoparticles (AgNPs) are small materials with diameters below 100 nm that are classified into different classes based on their forms, sizes, and characteristics. Indeed, the biosynthesized AgNPs are generated with a variety of organisms, algae, plants, bacteria, and a few others, for the medicinal purposes, as the bioactive compounds of curio and some proteins from cyanobacteria have the potentiality in the treatment of a wide range of infectious diseases. The critical focus of this review is on the antimicrobial, antioxidant, and anticancer properties of cyanobacteria. This would be useful in the pharmaceutical industries in the future drug development cascades.Communicated by Ramaswamy H. Sarma.

Temperature Estimation during Pulsed Laser Sintering of Silver Nanoparticles

During the thermal sintering of metal nanoparticles (NPs) the process temperature plays the most important role in the outcome of the sintering results and the selection of a suitable substrate. Here, temperature calculation during pulsed laser sintering of silver (Ag) nanoparticles (NPs) inkjet-printed on glass substrates is presented. During the pulsed laser sintering of Ag NPs, a minimum line resistivity less than twice the bulk silver resistivity was obtained within around 52 s under a laser power of 276 mW. The temperature field during the pulsed laser sintering of Ag NPs was estimated via a three-dimensional numerical model in which a temperature-dependent thermal conductivity of Ag NPs was adopted. An algorithm for treating the thermal conductivity of the heated Ag NPs in a region by a previous laser shot was devised for the improvement of the temperature field estimation. A maximum temperature of approximately 204 °C over the Ag NPs line was obtained with a 276 mW laser power and a scanning speed of 135 μm/s.

Polymeric Dental Nanomaterials: Antimicrobial Action

This review aims to describe and critically analyze studies published over the past four years on the application of polymeric dental nanomaterials as antimicrobial materials in various fields of dentistry. Nanoparticles are promising antimicrobial additives to restoration materials. According to published data, composites based on silver nanoparticles, zinc(II), titanium(IV), magnesium(II), and copper(II) oxide nanoparticles, chitosan nanoparticles, calcium phosphate or fluoride nanoparticles, and nanodiamonds can be used in dental therapy and endodontics. Composites with nanoparticles of hydroxyapatite and bioactive glass proved to be of low efficiency for application in these fields. The materials applicable in orthodontics include nanodiamonds, silver nanoparticles, titanium(IV) and zinc(II) oxide nanoparticles, bioactive glass, and yttrium(III) fluoride nanoparticles. Composites of silver nanoparticles and zinc(II) oxide nanoparticles are used in periodontics, and nanodiamonds and silver, chitosan, and titanium(IV) oxide nanoparticles are employed in dental implantology and dental prosthetics. Composites based on titanium(IV) oxide can also be utilized in maxillofacial surgery to manufacture prostheses. Composites with copper(II) oxide nanoparticles and halloysite nanotubes are promising materials in the field of denture prosthetics. Composites with calcium(II) fluoride or phosphate nanoparticles can be used in therapeutic dentistry for tooth restoration.

Current Methods for Synthesis and Potential Applications of Cobalt Nanoparticles: A Review

Cobalt nanoparticles (CoNPs) are promising nanomaterials with exceptional catalytic magnetic, electronic, and chemical properties. The nano size and developed surface open a wide range of applications of cobalt nanoparticles in biomedicine along with those properties. The present review assessed the current environmentally friendly synthesis methods used to synthesize CoNPs with various properties, such as size, zeta potential, surface area, and magnetic properties. We systematized several methods and provided some examples to illustrate the synthetic process of CoNPs, along with the properties, the chemical formula of obtained CoNPs, and their method of analysis. In addition, we also looked at the potential application of CoNPs from water purification cytostatic agents against cancer to theranostic and diagnostic agents. Moreover, CoNPs also can be used as contrast agents in magnetic resonance imaging and photoacoustic methods. This review features a comprehensive understanding of the synthesis methods and applications of CoNPs, which will help guide future studies on CoNPs.

In Situ Growth of Silver Nanoparticles on Chitosan Matrix for the Synthesis of Hybrid Electrospun Fibers: Analysis of Microstructural and Mechanical Properties

A viable alternative for the next generation of wound dressings is the preparation of electrospun fibers from biodegradable polymers in combination with inorganic nanoparticles. A poly(vinyl alcohol)-chitosan-silver nanoparticles (PVA-CTS-Ag NPs) system has been developed for antimicrobial and wound healing applications. Here, the preparation of PVA-CTS-Ag electrospun fibers using a two-step process is reported in order to analyze changes in the microstructural, mechanical, and antibacterial properties and confirm their potential application in the biomedical field. The Ag nanoparticles were well-dispersed into the chitosan matrix and their cubic structure after the electrospinning process was also retained. The Ag NPs displayed an average diameter of ~33 nm into the CTS matrix, while the size increased up to 213 nm in the PVA-CTS-Ag(NPs) fibers. It was observed that strong chemical interactions exist between organic (CTS) and inorganic phases through nitrogenous groups and the oxygen of the glycosidic bonds. A defect-free morphology was obtained in the PVA-CTS-Ag NPs final fibers with an important enhancement of the mechanical properties as well as of the antibacterial activity compared with pure PVA-CTS electrospun fibers. The results of antibacterial activity against E. coli and S. aureus confirmed that PVA-CTS-Ag(NPs) fibers can be potentially used as a material for biomedical applications.

Characterization, cytotoxicity, and genotoxicity properties of novel biomediated nanosized-silver by Egyptian Streptomyces roseolus for safe antimicrobial applications

Multi-drug resistant bacteria are not effectively managed with current treatments, making it a serious global problem. Therefore, there is an essential need for finding new antimicrobial agents. In this regard, silver nanoparticles (Ag-NPs) have been projected as a new generation of antimicrobial agents. Ag-NPs were biomediated by Egyptian Streptomyces roseolus for the first time, which was molecularly identified using 16S rRNA sequencing under accession no. MT071505. Biosynthesized Ag-NPs were characterized using UV-Vis spectroscopy, XRD, TEM, FTIR, and DLS. FTIR analysis confirmed the presence of different bioactive functional groups, such as N-H, C-H, C-O-C, C-NH2, and C=O acting as bioreducing/stabilizing agents for Ag-NPs. Ag-NPs exhibited antimicrobial activity against some multi-drug resistant Gram-positive and Gram-negative pathogens. MBC of Ag-NPs against Listeria monocytogenes and Klebsiella pneumonia were 0.195 and 0.048 mg/mL, respectively, with a tolerance level of 2 confirming its biocidal effect. SEM imaging of Ag-NPs-treated L. monocytogenes and K. pneumonia showed shrunk destroyed cells after 6 h of treatment. Biosynthesized Ag-NPs exhibited IC50 of < 0.3 and 8.21 mg/mL, on normal Human Skin Fibroblast, and Blood Lymphocytes, respectively. IC50 values were significantly higher than its MBC values, with no harmful cytotoxic effect, thus can be safely applied at its biocidal concentration. For biosafety purposes, the genotoxicity of biosynthesized Ag-NPs was assessed using Comet assay for the first time on Blood Lymphocytes, with zero-tail and 100% head intensity indicating non-genotoxic effect. An ecofriendly biomediated synthesis of Ag-NPs was described with easy scale-up, non-toxic by-products, so, it can be recommended as a powerful-safe antimicrobial agent.

Silver Nanoparticles for Conductive Inks: From Synthesis and Ink Formulation to Their Use in Printing Technologies

Currently, silver nanoparticles have attracted large interest in the photonics, electrics, analytical, and antimicrobial/biocidal fields due to their excellent optical, electrical, biological, and antibacterial properties. The versatility in generating different sizes, shapes, and surface morphologies results in a wide range of applications of silver nanoparticles in various industrial and health-related areas. In industrial applications, silver nanoparticles are used to produce conductive inks, which allows the construction of electronic devices on low-cost and flexible substrates by using various printing techniques. In order to achieve successful printed patterns, the necessary formulation and synthesis need to be engineered to fulfil the printing technique requirements. Additional sintering processes are typically further required to remove the added polymers, which are used to produce the desired adherence, viscosity, and reliable performance. This contribution presents a review of the synthesis of silver nanoparticles via different methods (chemical, physical and biological methods) and the application of silver nanoparticles under the electrical field. Formulation of silver inks and formation of conductive patterns by using different printing techniques (inkjet printing, screen printing and aerosol jet printing) are presented. Post-printing treatments are also discussed. A summary concerning outlooks and perspectives is presented at the end of this review.

Preparing Copper Nanoparticles and Flexible Copper Conductive Sheets

Nanotechnology is used in a wide range of fields, including medicine, cosmetics, and new material development, and is one of the most popular technologies in the field of flexible electronic products. For the present work, the chemical reduction method with environmentally friendly reducing agents was used to synthesize copper nanoparticles (CuNPs) with good dispersibility. The CuNPs were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and ultraviolet-visible spectrophotometry (UV-vis). After the CuNPs were formed, the solvent, polymers, and additives were added to form copper ink. Finally, the prepared copper inks were applied to flexible polyethylene terephthalate (PET) substrate under low sintering temperature and the effects of sintering time and different concentrations of sintering agent on resistivity were investigated. The results show that the copper nanoparticles synthesized by secondary reduction were smaller, more uniform, and better dispersed than those formed by primary reduction. Ethylene glycol has reducing effects under high temperatures; therefore, the CuNPs formed using the mixed solvent were small and well dispersed. The copper ink was applied on the PET substrate, treated with a formic acid aqueous solution, and sintered at 130 °C for 60 min, and its resistivity was about 1.67 × 10-3 Ω cm. The proposed synthesizing method is expected to have potential applications in the flexible electronic products field.

Nano drug delivery in intracellular bacterial infection treatments

The present work aimed to review the potential mechanisms used by macrophages to kill intracellular bacteria, their entrance to the cell, and mechanisms of escape of cellular immunity and applications of various nanoparticles. Since intracellular bacteria such as Mycobacterium and Brucella can survive in host cells and can resist the lethal power of macrophages, they can cause chronic disease or recur in 10-30% of cases in improved patients Nano drug-based therapeutics are promising tools for treating intracellular bacteria and preventing recurrence of the disease caused by these bacteria. In addition, among their unique features, we can mention the small size and the ability of these compounds to purposefully reach the target location.

Solid-State Preparation of Metal and Metal Oxides Nanostructures and Their Application in Environmental Remediation

Nanomaterials have attracted much attention over the last decades due to their very different properties compared to those of bulk equivalents, such as a large surface-to-volume ratio, the size-dependent optical, physical, and magnetic properties. A number of solution fabrication methods have been developed for the synthesis of metal and metal oxides nanoparticles, but few solid-state methods have been reported. The application of nanostructured materials to electronic solid-state devices or to high-temperature technology requires, however, adequate solid-state methods for obtaining nanostructured materials. In this review, we discuss some of the main current methods of obtaining nanomaterials in solid state, and also we summarize the obtaining of nanomaterials using a new general method in solid state. This new solid-state method to prepare metals and metallic oxides nanostructures start with the preparation of the macromolecular complexes chitosan·Xn and PS-co-4-PVP·MXn as precursors (X = anion accompanying the cationic metal, n = is the subscript, which indicates the number of anions in the formula of the metal salt and PS-co-4-PVP = poly(styrene-co-4-vinylpyridine)). Then, the solid-state pyrolysis under air and at 800 °C affords nanoparticles of M°, M_xO_y depending on the nature of the metal. Metallic nanoparticles are obtained for noble metals such as Au, while the respective metal oxide is obtained for transition, representative, and lanthanide metals. Size and morphology depend on the nature of the polymer as well as on the spacing of the metals within the polymeric chain. Noticeably in the case of TiO₂, anatase or rutile phases can be tuned by the nature of the Ti salts coordinated in the macromolecular polymer. A mechanism for the formation of nanoparticles is outlined on the basis of TG/DSC data. Some applications such as photocatalytic degradation of methylene by different metal oxides obtained by the presented solid-state method are also described. A brief review of the main solid-state methods to prepare nanoparticles is also outlined in the introduction. Some challenges to further development of these materials and methods are finally discussed.

Effect of Ag Nanoparticles on Denitrification and Microbial Community in a Paddy Soil

The extensive application of Ag nanoparticles (AgNPs) in industry, agriculture, and food processing areas increases the possibility of its release and accumulation to agroecosystem, but the effects of AgNPs to denitrification and the microbial community in paddy ecosystems are still poorly studied. In this study, microcosmic simulation experiments were established to investigate the response of soil denitrification to different levels of AgNPs (i.e., 0.1, 1, 10, and 50 mg/kg) in a paddy soil. Real-time quantitative PCR and high-throughput sequencing were conducted to reveal the microbial mechanism of the nanometer effect. The results showed that, though 0.1–10 mg/kg AgNPs had no significant effects on denitrification rate and N₂O emission rate compared to CK and bulk Ag treatments, 50 mg/kg AgNPs significantly stimulated more than 60% increase of denitrification rate and N₂O emission rate on the 3rd day (P < 0.05). Real-time quantitative PCR revealed that 50 mg/kg AgNPs significantly decreased the abundance of 16S bacterial rRNA gene, nirS/nirK, cnorB, and nosZ genes, but it did not change the narG gene abundance. The correlation analysis further revealed that the cumulative N₂O emission was positively correlated with the ratio of all the five tested denitrifying genes to bacterial 16S rRNA gene (P < 0.05), indicating that the tolerance of narG gene to AgNPs was the key factor of the increase in denitrification in the studied soil. High-throughput sequencing showed that only the 50-mg/kg-AgNP treatment significantly changed the microbial community composition compared to bulk Ag and CK treatments. The response of microbial phylotypes to AgNPs suggested that the most critical bacteria which drove the stimulation of 50 mg/kg AgNPs on N₂O emission were Firmicutes and β-proteobacteria, such as Clotridiales, Burkholderiales, and Anaerolineales. This study revealed the effects of AgNPs to denitrification in a paddy ecosystem and could provide a scientific basis for understanding of the environmental and toxicological effects of Ag nanomaterials.

Facile Synthesis of Silver Nanoparticles and Preparation of Conductive Ink

In the scientific industry, sustainable nanotechnology has attracted great attention and has been successful in facilitating solutions to challenges presented in various fields. For the present work, silver nanoparticles (AgNPs) were prepared using a chemical reduction synthesis method. Then, a low-temperature sintering process was deployed to obtain an Ag-conductive ink preparation which could be applied to a flexible substrate. The size and shape of the AgNPs were characterized by ultraviolet–visible spectrophotometry (UV-Vis) and transmission electron microscopy (TEM). The experiments indicated that the size and agglomeration of the AgNPs could be well controlled by varying the reaction time, reaction temperature, and pH value. The rate of nanoparticle generation was the highest when the reaction temperature was 100 °C within the 40 min reaction time, achieving the most satisfactorily dispersed nanoparticles and nanoballs with an average size of 60.25 nm at a pH value of 8. Moreover, the electrical resistivity of the obtained Ag-conductive ink is controllable, under the optimal sintering temperature and time (85 °C for 5 min), leading to an optimal electrical resistivity of 9.9 × 10⁻⁶ Ω cm. The results obtained in this study, considering AgNPs and Ag-conductive ink, may also be extended to other metals in future research.

Antimicrobial ‘inks’ for 3D printing: block copolymer-silver nanoparticle composites synthesised using supercritical CO2

A new synthetic methodology to produce polymer-AgNP composite microparticles using scCO2 is presented. These microparticle possessed long-lived antimicrobial activity and were tested for compatibility in the Laser Sintering 3D printing process.

Synthesis, characterization and anticancer activities of silver nanoparticles from the leaves of Datura stramonium L

In recent years, a wide range of studies has pointed out the role of nanoparticles as reservoirs of therapeutics for several diseases, including cancer. Nowadays, cancer research is focused on the development of novel treatment approaches to fight this dreadful disorder. Based on the evidential research and applications of nanoparticles, it is expected that green synthesized nanoparticles may show a prominent role, especially in the biomedical field. The present work is centered on the preparation and characterization of silver nanoparticles (Ag-NPs) from the aqueous (AQ) extract and non-alkaloidal (NA) fraction of Datura stramonium leaves and to evaluate their anticancer potential against mammalian cell lines. The biogenic Ag-NPs are characterized by UV-vis spectra, FTIR DLS, UV-Vis, SEM, and TEM. SEM and TEM analysis reveals the spherical morphology of NPs. The Ag-NPs exhibit cytotoxicity against various mammalian cell lines (A549, HCT-116, PANC-1, SHSY5Y, and U87), which indicate that the AQ and NA based NPs are highly potent to cause cancer cell death. To the best of our knowledge, the present report, for the first time, describes the green synthesis of Ag-NPs from the NA fraction of the D. stramonium and provides pieces of evidence for its anticancer potential.

Graphitic Carbon Nitride as a Platform for the Synthesis of Silver Nanoclusters

Graphitic carbon nitride (CN) synthetized by the thermal polycondensation of melamine at 550 °C for 4 h was further exfoliated by heating at 500 °C for 3 h. Silver cations were adsorbed on the exfoliated graphitic carbon nitride (CNE) and then reduced by sodium borohydride forming silver nanoclusters (NCs) with a size of less than 1 nm. The NCs were located on the CNE surface and did not change the CNE properties except for its pore size distribution and thereby specific surface area (SSA). The Ag NCs were able to collect the photoinduced electrons of CNE and thus reduce their recombination with the holes. It was also documented by the increase in the CNE photocatalytic activity in terms of the degradation of antibiotic Ofloxacin. This study demonstrates the ability of CNE to serve as a platform for a simple and fast synthesis of Ag NCs without any stabilizing compounds.

Synthesis of Chitosan-Silver Nanoparticle Composite Spheres and Their Antimicrobial Activities

Synthesis of silver nanoparticles–chitosan composite particles sphere (AgNPs-chi-spheres) has been completed and its characterization was fulfilled by UV–vis spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and zetasizer nano. UV–vis spectroscopy characterization showed that AgNPs-chi-spheres gave optimum absorption at a wavelength of 410 nm. The XRD spectra showed that the structure of AgNPs-chi-spheres were crystalline and spherical. Characterization by SEM showed that AgNPs-chi-spheres, with the addition of 20% of NaOH, resulted in the lowest average particle sizes of 46.91 nm. EDX analysis also showed that AgNPs-chi-spheres, with the addition of a 20% NaOH concentration, produced particles with regular spheres, a smooth and relatively nonporous structure. The analysis using zetasizer nano showed that the zeta potential value and the polydispersity index value of the AgNPs-chi-sphere tended to increase with an increased NaOH concentration. The results of the microbial activity screening showed that the AgNP-chi-Spheres with highest concentration of NaOH, produced the highest inhibition zone diameters against S. aureus, E. coli, and C. albicans, with inhibition zone diameters of 19.5, 18.56, and 12.25 nm, respectively.

Room-Temperature One-Step Synthesis of Silver/Reduced Graphene Oxide Nanocomposites as an Excellent Microwave Absorber

The present study is focused on room-temperature synthesis carried out by reduction of an aqueous silver nitrate (AgNO₃) and AgNO₃/graphene oxide (GO) dispersion using a low-cost commercial Fehling B solution in one step to form silver quantum dots (Ag QDs) and their Ag/reduced graphene oxide (Ag/RGO) nanocomposites and their characterization. The crystallinity, surface chemistry, structural, and morphological studies indicated the formation of crystalline small-sized quasispherical-functionalized Ag particles distributed uniformly on the surface of RGO. The conductivity measurements further showed an improvement in the conductivity of Ag/RGO nanocomposites as compared to neat Ag QDs. Our findings showed that Ag/RGO nanocomposites prepared by using 0.055 wt % of GO exhibited a total enhanced electromagnetic interference (EMI)-shielding efficiency (SE_T) of ∼39.2-42.3 dB (2-8 GHz) with a maximum value of ∼43.8 dB at 7. 5 GHz due to conduction loss, an interconnected conducting network, and a synergistic effect, and it followed an absorption mechanism. Furthermore, this superior absorption-dominated shielding conferred reflection loss (R_L) in the range of -79 to -82.5 dB with a R_L minima of -88 dB at 7.5 GHz, considering an effective absorption bandwidth of ∼6 GHz with 99.9% absorptivity. It is anticipated that Ag/RGO nanocomposites prepared in one step at room temperature could find potential EMI-shielding applications.

Sustainable Synthesis of Silver Nanoparticles Using Marine Algae for Catalytic Degradation of Methylene Blue

Herein, Sargassum coreanum (marine algae)-mediated silver nanoparticles (AgNPs) were successfully synthesized by a simple reduction method. The synthesized AgNPs were characterized using ultraviolet-visible spectroscopy, attenuated total reflection Fourier transformed infrared spectroscopy, X-ray diffractometry, field emission scanning electron microscopy (FESEM) with energy-dispersive X-ray (EDX) spectroscopy, and high-resolution transmission electron microscopy (HR-TEM) analysis. The acquired colloidal AgNPs were strongly absorbed around 420 nm and displayed brown color under visible light. The XRD pattern of AgNPs exposed their face-centered cubic geometry along with crystalline nature. The HRTEM images of synthesized AgNPs confirmed the mean particle size of 19 nm with a distorted spherical shape, and the calculated interlayer distance (d-spacing value) was about 0.24 nm. Further, the catalytic degradation of methylene blue using sodium borohydride and AgNPs was monitored using UV–vis spectroscopy. The result revealed that AgNPs performed as a superior catalyst, which completely degraded MB in 20 min. The rate constant for MB degradation was calculated to be 0.106 min−1, demonstrating that the marine algae-mediated AgNPs had outstanding catalytic activity. This approach is easy and environmentally benign, which can be applied for environmental-based applications such as dye degradation and pollutant detoxification.

Antibacterial activity and characteristics of silver nanoparticles biosynthesized from Carduus crispus

In recent years’ synthesis of metal nanoparticle using plants has been extensively studied and recognized as a non-toxic and efficient method applicable in biomedical field. The aim of this study is to investigate the role of different parts of medical plant Carduus crispus on synthesizing silver nanoparticles and characterize the produced nanoparticle. Our study showed that silver nanoparticles (AgNP) synthesized via whole plant extract exhibited a blue shift in absorption spectra with increased optical density, which correlates to a high yield and small size. Also, the results of zeta potential, X-ray diffraction, photon cross-correlation spectroscopy analysis showed the surface charge of − 54.29 ± 4.96 mV (AgNP-S), − 42.64 ± 3.762 mV (AgNP-F), − 46.02 ± 4.17 mV (AgNP-W), the crystallite size of 36 nm (AgNP-S), 13 nm (AgNP-F), 14 nm (AgNP-W) with face-centered cubic structure and average grain sizes of 145.1 nm, 22.5 nm and 99.6 nm. Another important characteristic, such as elemental composition and constituent capping agent has been determined by energy-dispersive X-ray spectroscopy and Fourier transform infrared. The silver nanoparticles were composed of ~ 80% Ag, ~ 15% K, and ~ 7.5% Ca (or ~ 2.8% P) elements. Moreover, the results of the FTIR measurement suggested that the distinct functional groups present in both AgNP-S and AgNP-F were found in AgNP-W. The atomic force microscopy analysis revealed that AgNP-S, AgNP-F and AgNP-W had sizes of 131 nm, 33 nm and 70 nm respectively. In addition, the biosynthesized silver nanoparticles were evaluated for their cytotoxicity and antibacterial activity. At 17 µg/ml concentration, AgNP-S, AgNP-F and AgNP-W showed very low toxicity on HepG2 cell line but also high antibacterial activity. The silver nanoparticles showed antibacterial activity on both gram-negative bacterium Escherichia coli (5.5 ± 0.2 mm to 6.5 ± 0.3 mm) and gram-positive bacterium Micrococcus luteus (7 ± 0.4 mm to 7.7 ± 0.5 mm). Our study is meaningful as a first observation indicating the possibility of using special plant organs to control the characteristics of nanoparticles.

Gold and Silver Nanoparticle-Based Colorimetric Sensors: New Trends and Applications

Gold and Silver nanoparticles (AuNPs and AgNPs) are perfect platforms for developing sensing colorimetric devices thanks to their high surface to volume ratio and distinctive optical properties, particularly sensitive to changes in the surrounding environment. These characteristics ensure high sensitivity in colorimetric devices. Au and Ag nanoparticles can be capped with suitable molecules that can act as specific analyte receptors, so highly selective sensors can be obtained. This review aims to highlight the principal strategies developed during the last decade concerning the preparation of Au and Ag nanoparticle-based colorimetric sensors, with particular attention to environmental and health monitoring applications.

Comparison of the Antimicrobial and Hemolytic Activities of Various Forms of Silver (Ions, Nanoparticles, Bioconjugates) Stabilized in a Zeolite Matrix

A quantitative and qualitative comparison of the antimicrobial and hemolytic activities of silver in various states, in the form of ions, nanoparticles, and bioconjugates with the antimicrobial protein lysozyme stabilized in an inert zeolite matrix, has been carried out. A synthetic zeolite with a β structure was chosen as a zeolite matrix. Using the ion-exchange method, the method of chemical reduction, and treating the matrix with a silver hydrosol with specified characteristics, samples of zeolites with the same silver content in various forms (Ag⁺, Ag° - Ag°/Lyz) in the amounts of 0.8 and 5 wt % have been synthesized. The samples obtained were studied by a complex of physicochemical research methods: X-ray diffraction, UV absorption spectroscopy, low-temperature nitrogen adsorption, electron microscopy, and atomic absorption. Antimicrobial activity was assessed against antibiotic-resistant Gram-negative microbe (e.g., Escherichia coli ML-35, Pseudomonas aeruginosa 522/17 MDR, Klebsiella pneumoniae ESBL 344) and Gram-positive microbe (e.g., Staphylococcus aureus 1399/17). The hemolytic activity in relation to human erythrocytes was estimated. The results obtained showed significant antimicrobial activity with a simultaneously high hemolytic activity of ionic silver. Silver nanoparticles have a lower level of antimicrobial activity and toxicity. Bioconjugates of silver nanoparticles and lysozyme showed an optimal combination of antimicrobial properties and lack of hemolytic activity.

Anti-bacterial activity of gold nanocomposites as a new nanomaterial weapon to combat photogenic agents: recent advances and challenges

Gold nanocomposites are being widely used in numerous biomedical applications owing to their excellent stability and miniaturization. Gold nanocomposites are notable because of their flexibility of functionalization and synthesis, ease of detection, and low toxicity. Cost-effectiveness, long-term stability, non-cytotoxicity, and biocompatibility are the main aspects of ideal nanocomposites. Antibacterial nanocomposites are being developed extensively in the food industry, environmental applications, and biological and medical devices. This review focuses on the applications of metal-based nanoparticles, mainly gold nanoparticles (AuNPs), as antibacterial agents in medical approaches. Additionally, the antibacterial mechanisms of AuNPs and their roles in fighting antibiotic-resistant microorganisms are highlighted in the present review.

Ecofriendly preparation of silver nanoparticles-based nanocomposite stabilized by polysaccharides with antibacterial, antifungal and antiviral activities

In the present work, sustainable and green method was used to prepare silver nanoparticles (Ag-NPs), followed with incorporation into tertiary nanocomposite consisted of starch, oxidized cellulose and ethyl cellulose. The prepared tertiary silver-nanocomposite (Ag-NC) was fully characterized via instrumental analysis (UV-vis, FT-IR, XRD, SEM, EDX and TEM) and evaluated for antibacterial, antifungal, and antiviral activities. Ag-NC significantly suppressed growth of tested bacterial strains (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Bacillus subtilis)  as compared with controls. Antifungal activity revealed that the prepared tertiary Ag-NC has a promising antifungal activity towards unicellular (Candida albicans) and multicellular fungi  ( Aspergillus niger, A. terreus, A. flavus and A. fumigatus). In same line, both Ag-NC and free Ag-NPs have shown a dose-dependent reduction in Vero cell line with maximum non-toxic dose at 6.25 and 12.5 μg/mL, respectively. Both Ag-NPs and Ag-NC exhibited antiviral effects against Herpes simplex virus, Adenovirus and Coxsackie B virus in a dose-dependent manner. Combined treatment of Ag-NPs incorporated into tertiary nanocomposite based on starch, oxidized cellulose and ethyl cellulose opens new possibilities to be more efficient nanomaterials for preventing microbial growth. In conclusion, the prepared tertiary Ag-NC has a promising antibacterial, antifungal as well as antiviral activities.

Synthesis, Characterization, and Photocatalytic Activities of Graphene Oxide/metal Oxides Nanocomposites: A Review

Sustainable water processing techniques have been extensively investigated and are capable of improving water quality. Among the techniques, photocatalytic technology has shown great potential in recent years as a low cost, environmentally friendly and sustainable technology. However, the major challenge in the industrial development of photocatalyst technology is to develop an ideal photocatalyst which must have high photocatalytic activity, a large specific surface area, harvest sunlight and shows recyclability. Keeping these views, the present review highlighted the synthesis approaches of graphene/metal oxide nanocomposite, characterization techniques and their prominent applications in photocatalysis. Various parameters such as photocatalyst loading, structure of photocatalyst, temperature, pH, effect of oxidizing species and wavelength of light were addressed which could affect the rate of degradation. Moreover, the formation of intermediates during photo-oxidation of organic pollutants using these photocatalysts is also discussed. The analysis concluded with a synopsis of the importance of graphene-based materials in pollutant removal. Finally, a brief overview of the problems and future approaches in the field is also presented.

Plant response to silver nanoparticles: a critical review

Although several metal ions/metal nanoparticles (NPs) are toxic to both plants and animals, some of them are used as nutrients and growth promoters. Plants exposed to silver nanoparticles (Ag-NPs) have shown both beneficial and harmful effects. All concentrations of Ag-NPs are not effective for a given plant because any excess can block the passage of essential nutrients. Regulated treatment of plants by Ag-NPs may enhance their overall growth and development. It has been noticed that Ag-NPs decrease the mass of edible plants (Cucurbita pepo, Allium cepa, cabbage, and lettuce) and vegetables, but they also induce the germination of seeds in many cases. NPs interact with proteins, enzymes, and carbohydrates influencing the total biomass, root, and shoot growth of plants. Also, Ag-NPs act as an ethylene inhibitor and activate the antioxidants in onions. Their substantial quantity becomes deposited in onion leaves and bulbs. Size and concentration are the two major factors responsible for the increase/decrease of plant growth and biomass. Plants make adaptations to reduce the toxicity caused by Ag-NPs. In some cases, Ag-NPs induce root elongation and increase chlorophyll, carbohydrate, proteins, rate of photosynthesis and inhibit the biosynthesis of ethylene. This review article provides a comprehensive overview of both the beneficial and adverse effects of Ag-NPs on germination, growth, development, physiological, and biochemical characteristics of a wide range of edible and crop plants. We have also critically discussed: the chemistry, toxicity, uptake, translocation, and accumulation of Ag-NPs in plant systems.

A Review on Silver Nanoparticles: Classification, Various Methods of Synthesis, and Their Potential Roles in Biomedical Applications and Water Treatment

Recent developments in nanoscience have appreciably modified how diseases are prevented, diagnosed, and treated. Metal nanoparticles, specifically silver nanoparticles (AgNPs), are widely used in bioscience. From time to time, various synthetic methods for the synthesis of AgNPs are reported, i.e., physical, chemical, and photochemical ones. However, among these, most are expensive and not eco-friendly. The physicochemical parameters such as temperature, use of a dispersing agent, surfactant, and others greatly influence the quality and quantity of the synthesized NPs and ultimately affect the material’s properties. Scientists worldwide are trying to synthesize NPs and are devising methods that are easy to apply, eco-friendly, and economical. Among such strategies is the biogenic method, where plants are used as the source of reducing and capping agents. In this review, we intend to debate different strategies of AgNP synthesis. Although, different preparation strategies are in use to synthesize AgNPs such as electron irradiation, optical device ablation, chemical reduction, organic procedures, and photochemical methods. However, biogenic processes are preferably used, as they are environment-friendly and economical. The review covers a comprehensive discussion on the biological activities of AgNPs, such as antimicrobial, anticancer anti-inflammatory, and anti-angiogenic potentials of AgNPs. The use of AgNPs in water treatment and disinfection has also been discussed in detail.

Polyvinyl-Pyrrolidone-Coated Silver Nanoparticles-The Colloidal, Chemical, and Biological Consequences of Steric Stabilization under Biorelevant Conditions

(1) Background: Several properties of silver nanoparticles (AgNPs), such as cytotoxic, anticancer, and antimicrobial activities, have been subjects of intense research; however, important aspects such as nanoparticle aggregation are generally neglected, although a decline in colloidal stability leads to a loss of the desired biological activities. Colloidal stability is affected by pH, ionic strength, or a plethora of biomolecules that interact with AgNPs under biorelevant conditions. (2) Methods: As only a few studies have focused on the relationship between aggregation behavior and the biological properties of AgNPs, here, we have systematically evaluated this issue by completing a thorough analysis of sterically (via polyvinyl-pyrrolidone (PVP)) stabilized AgNPs that were subjected to different circumstances. We assessed ultraviolet-visible light absorption, dynamic light scattering, zeta potential measurements, in vitro cell viability, and microdilution assays to screen both colloidal stability as well as bioactivity. (3) Results: The results revealed that although PVP provided outstanding biorelevant colloidal stability, the chemical stability of AgNPs could not be maintained completely with this capping material. (4) Conclusion: These unexpected findings led to the realization that stabilizing materials have more profound importance in association with biorelevant applications of nanomaterials than just being simple colloidal stabilizers.

Photochemical Synthesis of Gold and Silver Nanoparticles-A Review

Nanomaterials have supported important technological advances due to their unique properties and their applicability in various fields, such as biomedicine, catalysis, environment, energy, and electronics. This has triggered a tremendous increase in their demand. In turn, materials scientists have sought facile methods to produce nanomaterials of desired features, i.e., morphology, composition, colloidal stability, and surface chemistry, as these determine the targeted application. The advent of photoprocesses has enabled the easy, fast, scalable, and cost- and energy-effective production of metallic nanoparticles of controlled properties without the use of harmful reagents or sophisticated equipment. Herein, we overview the synthesis of gold and silver nanoparticles via photochemical routes. We extensively discuss the effect of varying the experimental parameters, such as the pH, exposure time, and source of irradiation, the use or not of reductants and surfactants, reagents' nature and concentration, on the outcomes of these noble nanoparticles, namely, their size, shape, and colloidal stability. The hypothetical mechanisms that govern these green processes are discussed whenever available. Finally, we mention their applications and insights for future developments.

Biodirected Synthesis of Silver Nanoparticles Using Aqueous Honey Solutions and Evaluation of Their Antifungal Activity against Pathogenic Candida Spp

Silver nanoparticles (AgNPs) were synthesized using aqueous honey solutions with a concentration of 2%, 10%, and 20%-AgNPs-H2, AgNPs-H10, and AgNPs-H20. The reaction was conducted at 35 °C and 70 °C. Additionally, nanoparticles obtained with the citrate method (AgNPs-C), while amphotericin B (AmB) and fluconazole were used as controls. The presence and physicochemical properties of AgNPs was affirmed by analyzing the sample with ultraviolet-visible (UV-Vis) and fluorescence spectroscopy, scanning electron microscopy (SEM), and dynamic light scattering (DLS). The 20% honey solution caused an inhibition of the synthesis of nanoparticles at 35 °C. The antifungal activity of the AgNPs was evaluated using opportunistic human fungal pathogens Candida albicans and Candida parapsilosis. The antifungal effect was determined by the minimum inhibitory concentration (MIC) and disc diffusion assay. The highest activity in the MIC tests was observed in the AgNPs-H2 variant. AgNPs-H10 and AgNPs-H20 showed no activity or even stimulated fungal growth. The results of the Kirby-Bauer disc diffusion susceptibility test for C. parapsilosis strains indicated stronger antifungal activity of AgNPs-H than fluconazole. The study demonstrated that the antifungal activity of AgNPs is closely related to the concentration of honey used for the synthesis thereof.

Silver Nanoparticles and Their Antibacterial Applications

Silver nanoparticles (AgNPs) have been imposed as an excellent antimicrobial agent being able to combat bacteria in vitro and in vivo causing infections. The antibacterial capacity of AgNPs covers Gram-negative and Gram-positive bacteria, including multidrug resistant strains. AgNPs exhibit multiple and simultaneous mechanisms of action and in combination with antibacterial agents as organic compounds or antibiotics it has shown synergistic effect against pathogens bacteria such as Escherichia coli and Staphylococcus aureus. The characteristics of silver nanoparticles make them suitable for their application in medical and healthcare products where they may treat infections or prevent them efficiently. With the urgent need for new efficient antibacterial agents, this review aims to establish factors affecting antibacterial and cytotoxic effects of silver nanoparticles, as well as to expose the advantages of using AgNPs as new antibacterial agents in combination with antibiotic, which will reduce the dosage needed and prevent secondary effects associated to both.

A Brief Overview of Antimicrobial Nanotextiles Prepared by In Situ Synthesis and Deposition of Silver Nanoparticles on Cotton

Antimicrobial nanotextiles are prepared by coating or deposition of the biocides such as organic compounds or nanoparticles on the textile fibers. The deposition of silver nanoparticles (AgNPs) on textiles has received increased attention due to their well-known antimicrobial properties. Recently, the technique of in situ synthesis and deposition of AgNPs on cotton is being used frequently to prepare antimicrobial nanotextiles. The technique involves complexation of the Ag⁺ ions in cotton fibers followed by their reduction to generate the particles. This in situ synthesis and deposition approach provides several advantages over the post synthesis deposition or grafting process. In this brief overview, we have presented basic information about different biocides used to prepare antimicrobial nanotextiles and highlighted the importance of in situ synthesis and deposition of AgNPs on cotton to prepare the antimicrobial nanotextiles. The recent achievements in this field and future challenges that need to be addressed are presented.

Ag-Based Synergistic Antimicrobial Composites. A Critical Review

The emerging problem of the antibiotic resistance development and the consequences that the health, food and other sectors face stimulate researchers to find safe and effective alternative methods to fight antimicrobial resistance (AMR) and biofilm formation. One of the most promising and efficient groups of materials known for robust antimicrobial performance is noble metal nanoparticles. Notably, silver nanoparticles (AgNPs) have been already widely investigated and applied as antimicrobial agents. However, it has been proposed to create synergistic composites, because pathogens can find their way to develop resistance against metal nanophases; therefore, it could be important to strengthen and secure their antipathogen potency. These complex materials are comprised of individual components with intrinsic antimicrobial action against a wide range of pathogens. One part consists of inorganic AgNPs, and the other, of active organic molecules with pronounced germicidal effects: both phases complement each other, and the effect might just be the sum of the individual effects, or it can be reinforced by the simultaneous application. Many organic molecules have been proposed as potential candidates and successfully united with inorganic counterparts: polysaccharides, with chitosan being the most used component; phenols and organic acids; and peptides and other agents of animal and synthetic origin. In this review, we overview the available literature and critically discuss the findings, including the mechanisms of action, efficacy and application of the silver-based synergistic antimicrobial composites. Hence, we provide a structured summary of the current state of the research direction and give an opinion on perspectives on the development of hybrid Ag-based nanoantimicrobials (NAMs).

Green synthesis of bio-functionalized nano-particles for the application of copper removal - characterization and modeling studies

Green technology for the synthesis of nanoparticles has gained momentum due to its cost-effectiveness and eco-friendly nature. In this research study, silver nanoparticles (AgNps) were synthesized using an eco-friendly biological method involving the use of marine algae, Halimeda gracilis. The surface properties of the synthesized silver nanoparticles were studied using UV-visible spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy methods. During the synthesis of nano particles, the parameters namely temperature (30 °C to 90 °C), pH (6-10), silver nitrate (AgNO₃) concentration (1-3 mg/ml) and quantity of algal extract (1-3 ml) were optimized to improve the production of AgNPs. The application of the synthesized silver nanoparticles for the adsorptive removal of copper from aqueous and industrial wastewater was investigated. Intra-particle diffusion mechanism was identified to be controlling step in metal removal. Regeneration of sorbent was carried out using 2.0 M HCl and the reusability was verified for 6 cycles. A removal efficiency of copper (64.8%) from electroplating wastewater demonstrated the industrial application potential of the synthesized silver nanoparticles.

Characterizing the Role of Biologically Relevant Fluid Dynamics on Silver Nanoparticle Dependent Oxidative Stress in Adherent and Suspension In Vitro Models

Silver nanoparticles (AgNPs) are being employed in numerous consumer goods and applications; however, they are renowned for inducing negative cellular consequences including toxicity, oxidative stress, and an inflammatory response. Nanotoxicological outcomes are dependent on numerous factors, including physicochemical, biological, and environmental influences. Currently, NP safety evaluations are carried out in both cell-based in vitro and animal in vivo models, with poor correlation between these mechanisms. These discrepancies highlight the need for enhanced exposure environments, which retain the advantages of in vitro models but incorporate critical in vivo influences, such as fluid dynamics. This study characterized the effects of dynamic flow on AgNP behavior, cellular interactions, and oxidative stress within both adherent alveolar (A549) and suspension monocyte (U937) models. This study determined that the presence of physiologically relevant flow resulted in substantial modifications to AgNP cellular interactions and subsequent oxidative stress, as assessed via reactive oxygen species (ROS), glutathione levels, p53, NFκB, and secretion of pro-inflammatory cytokines. Within the adherent model, dynamic flow reduced AgNP deposition and oxidative stress markers by roughly 20%. However, due to increased frequency of contact, the suspension U937 cells were associated with higher NP interactions and intracellular stress under fluid flow exposure conditions. For example, the increased AgNP association resulted in a 50% increase in intracellular ROS and p53 levels. This work highlights the potential of modified in vitro systems to improve analysis of AgNP dosimetry and safety evaluations, including oxidative stress assessments.

Mechanism of Producing Metallic Nanoparticles, with an Emphasis on Silver and Gold Nanoparticles, Using Bottom-Up Methods

Bottom-up nanoparticle (NP) formation is assumed to begin with the reduction of the precursor metallic ions to form zero-valent atoms. Studies in which this assumption was made are reviewed. The standard reduction potential for the formation of aqueous metallic atoms-E0(Mn+aq/M0aq)-is significantly lower than the usual standard reduction potential for reducing metallic ions Mn+ in aqueous solution to a metal in solid state. E0(Mn+aq/M0solid). E0(Mn+aq/M0aq) values are negative for many typical metals, including Ag and Au, for which E0(Mn+aq/M0solid) is positive. Therefore, many common moderate reduction agents that do not have significantly high negative reduction standard potentials (e.g., hydrogen, carbon monoxide, citrate, hydroxylamine, formaldehyde, ascorbate, squartic acid, and BH4-), and cannot reduce the metallic cations to zero-valent atoms, indicating that the mechanism of NP production should be reconsidered. Both AgNP and AuNP formations were found to be multi-step processes that begin with the formation of clusters constructed from a skeleton of M+-M+ (M = Ag or Au) bonds that is followed by the reduction of a cation M+ in the cluster to M0, to form Mn0 via the formation of NPs. The plausibility of M+-M+ formation is reviewed. Studies that suggest a revised mechanism for the formation of AgNPs and AuNPs are also reviewed.

BSA/Silver Nanoparticle-Loaded Hydrogel Film for Local Photothermal Treatment of Skin Cancer

PURPOSE

To develop a hydrogel film containing bovine serum albumin (BSA)-coated silver nanoparticles (BSA/AgNP) and evaluate its applicability for topical photothermal treatment (PTT) of skin cancer.

METHODS

BSA/AgNP-loaded hydrogel films were prepared and their swelling, bioadhesive, mechanical, and photothermal properties were characterized in vitro and in vivo.

RESULTS

The synthesized BSA/AgNP exhibited a narrow size distribution with good size stability and, notably, possessed great photothermal activity that could stably maintain through repetitive laser irradiation. The BSA/AgNP-loaded hydrogel films showed favorable swelling, bioadhesive, tensile, and photothermal properties. Based on these results, when tested the anti-cancer effects in B16F10 s.c. tumor-bearing mice, the PTT with the topical treatment of BSA/AgNP-loaded hydrogel films could significantly inhibit the tumor growth by a single treatment with no apparent toxicity.

CONCLUSIONS

Overall, the results of this study demonstrated that the BSA/AgNP-loaded hydrogel films may serve as an effective but safe topical PTT agent for the treatment of skin cancer.

Endophytic Bacteria Enterobacter hormaechei Fabricated Silver Nanoparticles and Their Antimicrobial Activity

Antimicrobial resistance (AMR), one of the greatest issues for humankind, draws special attention to the scientists formulating new drugs to prevent it. Great emphasis on the biological synthesis of silver nanoparticles (AgNPs) for utilization in single or combinatorial therapy will open up new avenues to the discovery of new antimicrobial drugs. The purpose of this study was to synthesize AgNPs following a green approach by using an endophytic bacterial strain, Enterobacter hormaechei, and to assess their antimicrobial potential against five pathogenic and four multidrug-resistant (MDR) microbes. UV-Vis spectroscopy, fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), and zeta potential (ζ) were used to characterize the synthesized AgNPs. Endophytic E. hormaechei-mediated AgNPs (Eh-AgNPs) were represented by a strong UV-Vis absorbance peak at 418 nm within 5 min, forming spherical and polydispersed nanoparticles in the size range of 9.91 nm to 92.54 nm. The Eh-AgNPs were moderately stable with a mean ζ value of -19.73 ± 3.94 mV. The presence of amine, amide, and hydroxyl functional groups was observed from FTIR analysis. In comparison to conventional antibiotics, the Eh-AgNPs were more effective against Bacillus cereus (ATCC 10876) and Candida albicans (ATCC 10231), exhibiting 9.14 ± 0.05 mm and 8.24 ± 0.05 mm zones of inhibition (ZOIs), respectively, while displaying effective inhibitory activity with ZOIs ranging from 10.98 ± 0.08 to 13.20 ± 0.07 mm against the MDR bacteria. Eh-AgNP synthesis was rapid and eco-friendly. The results showed that Eh-AgNPs are promising antimicrobial agents that can be used in the development and formulation of new drugs to curb the menace of antimicrobial resistance in pathogenic and MDR microbes.