Synthesis of silver nanoparticles using methanol and dichloromethane extracts of Pulicaria gnaphalodes (Vent.) Boiss. aerial parts

Silica-based nanosystems against antibiotic-resistant bacteria and pathogenic viruses

Today, with the intensity of antibiotic abuse and self-medication, the need for the use of novel systems with high efficiency and biosafety for targeted drug delivery against antibiotic-resistant bacteria and their infections should be highly considered by researchers. Silica-based nanosystems with unique physicochemical properties such as large surface area, tuneable pore diameter, drug loading capacity, controlled particle size/morphology, and good biocompatibility are attractive candidates against antibiotic-resistant bacteria and pathogenic viruses. They can be loaded with antiviral and antimicrobial drugs or molecules through their exclusive internal porous structures or different surface linkers. In this context, smart nanosystems can be produced via suitable surface functionalization/modification with a variety of functional groups to act against different clinical pathogenic microbes or viruses, offering great opportunities for controlling and treating various infections. However, important criteria such as the ability to degrade, biocompatibility, biodegradability, cytotoxicity, stability, clearance from targeted organs should be systematically analysed to develop nanosystems or nanocarriers with high efficiency and multifunctionality. Herein, recent advancements pertaining to the application of silica-based nanosystems against antibiotic-resistant bacteria and pathogenic viruses are deliberated, focussing on important challenges and future perspectives.

Ag/Ag3PO4 Nanoparticle-Decorated Hydroxyapatite Functionalized Calcium Carbonate: Ultrasound-Assisted Sustainable Synthesis, Characterization, and Antimicrobial Activity

Silver nanoparticles are usually prepared by the reduction of silver cations through chemical and non-sustainable procedures that involve the use of reducing chemical agents. Therefore, many efforts have been made in the search for sustainable alternative methods. Among them, an ultrasound-assisted procedure could be a suitable and sustainable method to afford well-dispersed and nanometric silver particles. This paper describes a sustainable, ultrasound-assisted method using citrate as a reducing agent to prepare silver@hydroxyapatite functionalized calcium carbonate composites. For comparison, an ultrasound-assisted reduction was performed in the presence of NaBH₄. The composites obtained in the presence of these two different reducing agents were compared in terms of nanoparticle nature, antimicrobial activity, and cytotoxic activity. The nanoparticle nature was investigated by several techniques, including X-ray powder diffraction, field-emission scanning electron microscopy, transmission electron microscopy, UV-Vis spectroscopic measurements, and X-ray photoemission spectroscopy. Nanoparticles with a predominance of Ag or Ag₃PO₄ were obtained according to the type of reducing agent used. All composites were tested for antimicrobial and antibiofilm activities against Gram-positive and Gram-negative (Staphylococcus aureus and Pseudomonas aeruginosa, respectively) bacteria and for cytotoxicity towards human skin keratinocytes and human fibroblasts. The nature of the nanoparticles, Ag or Ag₃PO₄, and their predominance seemed to affect the in vitro silver release and the antimicrobial and antibiofilm activities. The composites obtained by the citrate-assisted reduction gave rise to the best results.

Antibacterial activity of green gold and silver nanoparticles using ginger root extract

Recent studies demonstrated that the speed of synthesis, biocompatibility, and antimicrobial activity of gold (Au) and silver (Ag) metals is enhanced when biosynthesized in nano-sized particles. In the present study, Au- and Ag-based nanoparticles (NPs) were synthesized via a biological process using aqueous Ginger root extract and characterized by various spectroscopic methods. The NPs have hexagonal and spherical shapes. The average particle size for Au and Ag NPs was 20 and 15 nm, respectively. The dynamic light scattering (DLS) technique has shown that the zeta potential values of synthesized NPs were 4.8 and - 7.11 mv, respectively. Gas chromatography-mass spectrometry (GC-MS) analysis of Ginger root extract revealed 25 compounds. The synthesized NPs showed significant activity against Staphylococcus aureus and Escherichia (E). coli in vitro, with IC50 and IC90 values for Au and Ag NPs, respectively, noted to be 7.5 and 7.3 µg/ml and 15 and 15.2 µg/ml for both bacterial strains. The protein leakage level was tremendous and morphological changes occurred in bacteria treated with biosynthesized NPs. These results suggest that the biosynthesized metallic NPs have the suitable potential for application as antibacterial agents with enhanced activities.

Application of Response Surface Methodology for Optimization of Nanosized Zinc Oxide Synthesis Conditions by Electrospinning Technique

Zinc oxide (ZnO) is a well-known semiconductor material due to its excellent electrical, mechanical, and unique optical properties. ZnO nanoparticles are widely used for the industrial-scale manufacture of microelectronic and optoelectronic devices, including metal oxide semiconductor (MOS) gas sensors, light-emitting diodes, transistors, capacitors, and solar cells. This study proposes optimization of synthesis parameters of nanosized ZnO by the electrospinning technique. A Box–Behnken design (BB) has been applied using response surface methodology (RSM) to optimize the selected electrospinning and sintering conditions. The effects of the applied voltage, tip-to-collector distance, and annealing temperature on the size of ZnO particles were successfully investigated. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images confirm the formation of polyvinylpyrrolidone-zinc acetate (PVP-ZnAc) fibers and nanostructured ZnO after annealing. X-ray diffraction (XRD) patterns indicate a pure phase of the hexagonal structure of ZnO with high crystallinity. Minimal-sized ZnO nanoparticles were synthesized at a constant applied potential of 16 kV, with a distance between collector and nozzle of 12 cm, flow rate of 1 mL/h, and calcination temperature of 600 °C. The results suggest that nanosized ZnO with precise control of size and morphology can be fabricated by varying electrospinning conditions, precursor solution concentration, and sintering temperature.

Application of Response Surface Methodology for Optimizing the Therapeutic Activity of ZnO Nanoparticles Biosynthesized from Aspergillus niger

In this study, the biosynthesis of zinc oxide nanoparticles using Aspergillus niger (A/ZnO-NPs) is described. These particles have been characterized by UV-Vis spectrum analysis, X-ray powder diffraction, field emission scanning electron microscopy, and transmission electron microscopy. To use this biosynthesized nanoparticle as an antiproliferative and antimicrobial agent, the IC₅₀ value against the breast cancer cell line and inhibition zone against Escherichia coli were used to optimize the effect of two processing factors including dose of filtrate fungi cell and temperature. The biosynthesized A/ZnO-NPs had an absorbance band at 320 nm and spherical shapes. The mean particles size was 35 nm. RSM (response surface methodology) was utilized to investigate the outcome responses. The Model F-value of 12.21 and 7.29 implies that the model was significant for both responses. The contour plot against inhibition zone for temperature and dose showed that if the dose increases from 3.8 to 17.2 µg/mL, the inhibition zone increases up to 35 mm. As an alternative to chemical and/or physical methods, biosynthesizing zinc oxide NPs through fungi extracts can serve as a more facile and eco-friendly strategy. Additionally, for optimization of the processes, the outcome responses in the biomedical available test can be used in the synthesis of ZnO-NPs that are utilized for large-scale production in various medical applications.

A review on the green and sustainable synthesis of silver nanoparticles and one-dimensional silver nanostructures

The significance of silver nanostructures has been growing considerably, thanks to their ubiquitous presence in numerous applications, including but not limited to renewable energy, electronics, biosensors, wastewater treatment, medicine, and clinical equipment. The properties of silver nanostructures, such as size, size distribution, and morphology, are strongly dependent on synthesis process conditions such as the process type, equipment type, reagent type, precursor concentration, temperature, process duration, and pH. Physical and chemical methods have been among the most common methods to synthesize silver nanostructures; however, they possess substantial disadvantages and short-comings, especially compared to green synthesis methods. On the contrary, the number of green synthesis techniques has been increasing during the last decade and they have emerged as alternative routes towards facile and effective synthesis of silver nanostructures with different morphologies. In this review, we have initially outlined the most common and popular chemical and physical methodologies and reviewed their advantages and disadvantages. Green synthesis methodologies are then discussed in detail and their advantages over chemical and physical methods have been noted. Recent studies are then reviewed in detail and the effects of essential reaction parameters, such as temperature, pH, precursor, and reagent concentration, on silver nanostructure size and morphology are discussed. Also, green synthesis techniques used for the synthesis of one-dimensional (1D) silver nanostructures have been reviewed, and the potential of alternative green reagents for their synthesis has been discussed. Furthermore, current challenges regarding the green synthesis of 1D silver nanostructures and future direction are outlined. To sum up, we aim to show the real potential of green nanotechnology towards the synthesis of silver nanostructures with various morphologies (especially 1D ones) and the possibility of altering current techniques towards more environmentally friendly, more energy-efficient, less hazardous, simpler, and cheaper procedures.

Antimicrobial and Antihypercholesterolemic Activities of Pulicaria gnaphalodes

Multidrug resistance has increased globally in the communities. Bacterial infections associated with health care have weakened the existing antimicrobial therapy and demand the search for alternative therapies. In the present investigation, the medicinal plant Pulicaria gnaphalodes from Quetta, Pakistan, has been screened for antimicrobial potential. In vitro antimicrobial efficacy of P gnaphalodes extracts (methanol and ethanol) was quantitatively evaluated on the basis of zone of inhibition against different bacteria and minimum inhibitory concentration (MIC). In vivo, antihypercholesterolemic activity is determined in different rat groups. The results of the study indicated that the ethanol extract of P gnaphalodes showed maximum zone of inhibition for Bacillus subtilis of 12.1 ± 1.1 mm from all others. The methanol extract showed maximum zone of inhibition for Staphylococcus aureus of 11.9 ± 1.0 mm and rifampicin showed maximum zone of inhibition of 23.1 ± 0.9 mm. The results of ethanol and methanol extract of P gnaphalodes against different bacteria revealed that this plant has greater antimicrobial activity. However, the plant extract shows nonsignificant antihypercholesterolemic activity. The extract of this plant can be utilized as medicine to inhibit several infections caused by some bacterial pathogens found in human body.

Biosynthesis of AgNPs by B. maydis and its antifungal effect against Exserohilum turcicum

In the present study, Bipolaris maydis was used to synthesise silver nanoparticles (AgNPs). Several parameters that influence the synthesis of AgNPs such as fungus age, the concentration of Ag nitrate (AgNO₃), and incubation time were explored to find the optimum synthesis condition. Furthermore, the antifungal activity of AgNPs against Exserohilum turcicum was determined by measuring inhibition zone diameter, colony formation, and conidia germination. The optimal biosynthesis system included fungus age of 7 days, 8 mM AgNO₃, and an incubation time of 120 h. Under these conditions, synthesised NPs were near round, and the average particle size was about 21 nm. At the experiment, the diameter of the inhibition zone reached a maximum of 8 mM AgNO₃ and 72 h. In addition, the inhibition rate of colony and conidia reached 83.39 and 100%, respectively, with 200 μg/ml AgNPs. The results offer a novel pathway for phytopathogen control and make it likely to develop new eco-friendly antimicrobial.

Recent Progress in Rapid Sintering of Nanosilver for Electronics Applications

Recently, nanosilver pastes have emerged as one of the most promising high temperature bonding materials for high frequency and high power applications, which provide an effective lead-free electronic packaging solution instead of high-lead and gold-based solders. Although nanosilver pastes can be sintered at lower temperature compared to bulk silver, applications of nanosilver pastes are limited by long-term sintering time (20⁻30 min), relative high sintering temperature (>250 °C), and applied external pressure, which may damage chips and electronic components. Therefore, low temperature rapid sintering processes that can obtain excellent nanosilver joints are anticipated. In this regard, we present a review of recent progress in the rapid sintering of nanosilver pastes. Preparation of nanosilver particles and pastes, mechanisms of nanopastes sintering, and different rapid sintering processes are discussed. Emphasis is placed on the properties of sintered joints obtained by different sintering processes such as electric current assisted sintering, spark plasma sintering, and laser sintering, etc. Although the research on rapid sintering processes for nanosilver pastes has made a great breakthrough over the past few decades, investigations on mechanisms of rapid sintering, and the performance of joints fabricated by pastes with different compositions and morphologies are still far from enough.

A review on green synthesis of silver nanoparticles and their applications

Development of reliable and eco-accommodating methods for the synthesis of nanoparticles is a vital step in the field of nanotechnology. Silver nanoparticles are important because of their exceptional chemical, physical, and biological properties, and hence applications. In the last decade, numerous efforts were made to develop green methods of synthesis to avoid the hazardous byproducts. This review describes the methods of green synthesis for Ag-NPs and their numerous applications. It also describes the comparison of efficient synthesis methods via green routes over physical and chemical methods, which provide strong evidence for the selection of suitable method for the synthesis of Ag-NPs.