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Abstract In this work we report an eco-friendly and low cost method for reducing and capping silver nanoparticles with a lyophilized extract from grape and orange wastes. The synthesis of silver nanoparticles (AgNPs) was monitored by UV–Vis spectroscopy and their characterization was carried out using Transmission Electron Microscopy (TEM), Diffuse Reflectance Infrared Spectroscopy (DRIFT) and X Ray Diffraction (XRD). The AgNPs were crystalline and spherical, with diameters from 3 to 14 nm and 5–50 nm for the nanoparticles obtained from the grape and orange extract, respectively. DRIFT spectroscopy suggested the involvement of various functional groups from extract secondary metabolites during nanoparticle synthesis and capping nanoparticles. The antimicrobial activity of AgNPs was tested against Escherichia coli O157:H7 and Listeria monocytogenes using the agar diffusion method and optical density (OD 600). Non-significant difference of L. monocytogenes growth inhibition was observed between AgNPs obtained from both extracts, demonstrating a 13.5 mm diameter growth inhibition at 100 μg/ml. For E. coli O157:H7, only the AgNPs obtained from the grape extract exhibited a dose-dependent antimicrobial activity showing a final OD of 0.42 at 100 μL. Highlights • Spherical AgNPs of 10–50 nm were prepared using extracts of orange and grape waste. • Phenolic compounds act as reductor and capping agents for AgNPs synthesis. • AgNPs showed antimicrobial activity against E.coli O157:H7 and L. monocytogenes. • Antimicrobial activity is size particle and concentration dependent. [ABSTRACT FROM AUTHOR]

In this work, silver nanoparticles (AgNPs) were synthesized solely using catechin (Ct), a natural polyphenol, then their effects on the growth and metabolism of Aspergillus niger GM13 were investigated using 7.5 and 15 ppm of nanoparticles. AgNPs-Ct, induced physio-metabolic changes activating different stress compensation mechanisms that affect the fungal growth and survival. In particular, 15 ppm of AgNPs-Ct leads to a reduction of 81% of the mycelia biomass. The stress responses in the presence of AgNPs-Ct were further determined by overall cell changes through the production of reactive oxygen species (ROS) by the fungal hyphae. The increase in ROS production confirmed cellular oxidative stress which, together with membrane damage, can be considered to be the main antifungal effect. Adaptative fungal responses during AgNPs-Ct treatment were linked to a high accumulation of trehalose, glycerol, citric and oxalic acid, and several important enzymes involved in the catabolism of nutrients for cell growth, such as acid phosphatase, Naphthol-ASBI phosphohydrolase. The exposure to AgNPs-Ct also triggers changes in the production of VOC derivating from the α- or β-oxidation of fatty acids as alcohols, aldehydes, alkanes, and acids. Herein, the antifungal effect of AgNPs-Ct is demonstrated, elucidating the impact on its physio-metabolic profile. • Surfactant-free AgNPs were synthesized in water exclusively using catechin (Ct). • AgNPs-Ct physio-metabolic effects on A. niger growth were monitored. • AgNPs-Ct induces a redox homeostasis imbalance and osmotic disequilibrium. • Adaptation and defense mechanisms of A. niger were evidenced. • AgNPs-Ct are sustainable emerging biocontrol agents with promising features. [ABSTRACT FROM AUTHOR]

A sustainable approach for the green synthesis of silver nanoparticles (AgNPs) using an aqueous extract of hyperpigmented tomato (Solanum lycopersicum L) skins (HTS) was described. AgNPs characterization and catalytic activity in the degradation of methylene blue were reported. The influence of some experimental parameters on synthesis, such as green extract concentration, pH, microwave irradiation time, as well as stabilization time, was investigated. HTS extract was initially characterized regarding its reducing potential, Fourier Transform Infrared (FTIR) molecular fingerprinting and 1H NMR metabolite profiling and then used as a reducing-stabilizing agent for the green synthesis of AgNPs. Furthermore, a comparative study, with chemically synthetized AgNPs, was carried out and the catalytic activity of synthesized nanoparticles in the reduction of methylene blue was studied by UV–visible spectrophotometer. Obtained AgNPs were analyzed by ultraviolet–visible spectroscopy, FTIR, scanning electron microscopy and electrochemical analyses (cyclic and anodic stripping voltammetry). In general, obtained AgNPs were spherical in shape, with a diameter ranging from 21 to 93 nm, and very stable over time. Interestingly, a red shift of the surface plasmon resonance of green nanoparticles was observed as the volume of the HTS extract increased. Lastly, an improved catalytic activity in the reduction of methylene blue was detected in the case of green synthesized nanoparticles, with respect to those conventionally produced. • Hyperpigmented tomato skins were used for silver nanoparticles production. • Hyperpigmented tomato skin extracts were analyzed by spectroscopic and chromatographic analyses. • Reducing sugars are the major reducing components in the extracts. • Obtained silver nanoparticles were fully characterized. • Green nanoparticles showed better catalytic properties than chemically synthetized counterparts. [ABSTRACT FROM AUTHOR]