Our objective in this review article is to find out relevant information about methods of determination of antioxidant activity of silver nanoparticles. There are many studies dealing with mentioned problem and herein we summarize the knowledge about methods evaluating the antioxidant activity of silver nanoparticles reported so far. Many authors declare better antioxidant activity of silver nanoparticles compared to the extract used for synthesis of them. In this review, we focused on methods of antioxidant activity determination in detail to find out novel and perspective techniques to solve the general problems associated with the determination of antioxidant activity of silver nanoparticles.

A green synthetic route for the production of silver nanoparticles (AgNPs) using five different aqueous plant extracts, namely, Berberis vulgaris, Brassica nigra, Capsella bursa-pastoris, Lavandula angustifolia and Origanum vulgare, was investigated in this study. The present work demonstrates the influence of plant extract composition (antioxidant and total phenolic content) on the size and morphology of the produced AgNPs. The biosynthetic procedure was rapid and simple and was easily monitored via colour changes and ultraviolet and visible (UV-Vis) spectroscopy. Subsequently, measurement of zeta potential (ZP), photon cross-correlation spectroscopy (PCCS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) analysis were employed to characterise the as-synthesised nanoparticles. The XRD investigation confirmed the presence of Ag0 in the nanoparticles, and interactions between the bioactive compounds of the plants and the produced AgNPs were evident in the FTIR spectra. TEM indicated that the nanoparticles exhibited a bimodal size distribution, with the smaller particles being spherical and the larger having a truncated octahedron shape. In addition, the antimicrobial activity of the AgNPs was tested against five bacterial strains. All synthesised nanoparticles exhibited enhanced antimicrobial activity at a precursor concentration of 5 mM compared to the control substance, gentamicin sulphate, with the best results observed for AgNPs prepared with B. nigra and L. angustifolia extracts.

Mushrooms Basidiomycota have long been appreciated for their taste, flavour, desirable aroma, texture, nutraceutical and medicinal attributes. Honey mushrooms (Armillaria mellea) are edible mushroom generally used in traditional oriental medicine. The aim of this study was to examine extracts from the fruiting bodies of these mushrooms. The content of the components with antioxidant properties, such as total phenols, total flavonoids, β-carotene, lycopene and β-glucans were determined by spectrophotometric methods. The results obtained showed that the water extracts contained higher levels of total phenols and total flavonoids (367.1 and 548.5 mg.dm−3 gallic acid equivalent — GAE, respectively) in comparison with methanol extracts (108.2 and 113.4 mg.dm−3 GAE, respectively). Very low contents of β-carotene and lycopene were determined in the methanol extract (0.756 mg.g−1 dry weight and 0.05 mg.g−1 dry weight, respectively). Methanol extracts from the fruiting bodies of Honey mushrooms (Armillaria mellea) inhibited the uptake activity of 2,2-diphenylpicrylhydrazyl (DPPH) free radicals by 45 %. The IC50 (mg of compound, that inhibit 50 % of DPPH radicals) of methanol extract was below 10 mg.cm−3 (6.448 mg.cm−3), suggesting a high antioxidant potential of fruiting bodies of the Honey mushrooms Armillaria mellea.

This study shows mechanochemical synthesis as an alternative method to the traditional green synthesis of silver nanoparticles in a comparative manner by comparing the products obtained using both methodologies and different characterization methods. As a silver precursor, the most commonly used silver nitrate was applied and the easily accessible lavender (Lavandula angustofolia L.) plant was used as a reducing agent. Both syntheses were performed using 7 different lavender:AgNO3 mass ratios. The synthesis time was limited to 8 and 15 min in the case of green and mechanochemical synthesis, respectively, although a significant amount of unreacted silver nitrate was detected in both crude reaction mixtures at low lavender:AgNO3 ratios. This finding is of particular interest mainly for green synthesis, as the potential presence of silver nitrate in the produced nanosuspension is often overlooked. Unreacted AgNO3 has been removed from the mechanochemically synthesized samples by washing. The nanocrystalline character of the products has been confirmed by both X-ray diffraction (Rietveld refinement) and transmission electron microscopy. The latter has shown bimodal size distribution with larger particles in tens of nanometers and the smaller ones below 10 nm in size. In the case of green synthesis, the used lavender:AgNO3 ratio was found to have a decisive role on the crystallite size. Silver chloride has been detected as a side-product, mainly at high lavender:AgNO3 ratios. Both products have shown a strong antibacterial activity, being higher in the case of green synthesis, but this can be ascribed to the presence of unreacted AgNO3. Thus, one-step mechanochemical synthesis (without the need to prepare extract and performing the synthesis as separate steps) can be applied as a sustainable alternative to the traditional green synthesis of Ag nanoparticles using plants.

The prevalence of infectious diseases is becoming a worldwide problem, and antimicrobial drugs have long been used for prophylactic and therapeutic purposes, but bacterial resistance has creating serious treatment problems. The development of antibiotic resistance makes scientists around the world to seek new drugs that would be more effective. The use and search for drugs obtained from plants and other natural products have increased in recent years. It is well known that silver and its compounds have strong antibacterial activity. Silver, compared to the other metals, shows higher toxicity to microorganisms, while it exhibits lower toxicity to mammalian cells. The progress in the field of nanotechnology has helped scientists to look for new ways in the development of antibacterial drugs. Silver nanoparticles (AgNPs) are interesting for their wide range of applications, e.g. in pharmaceutical sciences, which include treatment of skin diseases (e.g. acne and dermatitis) and other infectious diseases (e.g. post-surgical infections). Various antibacterial aids, such as antiseptic sprays, have also been developed from AgNPs. In this chapter, we have focused on various synthesis methodologies of AgNPs, antibacterial properties, and the mechanism of action.

In this study we examined the dried fruiting bodies of Morchella esculenta, collected in the area of the coal and biomass based thermal power plant in Vojany from the nearby Bahoň marsh, in the Slovak Republic. The area is characterized by a high environmental burden, especially because of air pollutant emissions from the power plant operation. Twenty-three (23) chemical elements were found in the dried fruiting bodies after microwave-assisted sample preparation using an Inductively Coupled Plasma Mass Spectrophotometer ICP-MS AGILENT 7500c system. The mercury content was determined employing a special AMA 254 apparatus intended for the determination of Hg directly in dry powdered fruiting bodies without microwave digestion. The content of toxic elements expressed in mg.kg−1 DW (dry weight) were as follows: Hg 0.048—0.052 (RSD—Relative Standard Deviation = 4.80 %); Cd 4.543—6.169 (RSD = 3.35 %); Pb 0.261—0.291 (RSD = 2.67 %); As 0.455—0.469 (RSD = 5.79 %); Cr 1.585—1.616 (RSD = 2.33 %); and Ni 8.166—9.276 (RSD = 3.03 %). The contents of cadmium, nickel and mercury exceeded the hygiene limits, while the contents of arsenic and lead approached the hygiene limits. Due to the high levels of toxic elements, the fruiting bodies collected in the location are not suitable for culinary purposes. The mushroom Morchella esculenta acts as an accumulator of toxic elements from the environment in which it grows and can be considered as an indicator of environmental pollution.

Biosurfactants (BSs) are surface-active compounds produced by diverse microorganisms, including the genus Bacillus. These bioactive compounds possess biological activities such as antiadhesive, antimicrobial and antibiofilm effects that can lead to important applications in combating many infections. Based on these findings, we decided to investigate the antibiofilm activity of BSs from the marine Bacillus amyloliquefaciens against Staphylococcus aureus CCM 4223. Expression of biofilm-related genes was also evaluated using qRT-PCR. Isolated and partially purified BSs were identified and characterized by molecular tools and by UHPLC-DAD and MALDI-TOF/MS. Bacillus amyloliquefaciens 3/22, that exhibited surfactant activity evaluated by oil spreading assay, was characterized using the 16S rRNA sequencing method. Screening by PCR detected the presence of the sfp, srfAA, fenD and ituD genes, suggesting production of the lipopeptides (LPs) surfactin, fengycin and iturin. The above findings were further supported by the results of UHPLC-DAD and MALDI-TOF/MS. As quantified by the crystal violet method, the LPs significantly (p < 0.001) reduced biofilm formation of S. aureus in a dose-dependent manner and decreased expression of biofilm-related genes fnbA, fnbB, sortaseA and icaADBC operon. Data from our investigation indicate a promising therapeutic application for LPs isolated from B. amyloliquefaciens toward prevention of S. aureus biofilm infections.

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