Silver nanoparticles: aggregation behavior in biorelevant conditions and its impact on biological activity

Péter Bélteky,1 Andrea Rónavári,1,2 Nóra Igaz,2 Bettina Szerencsés,3 Ildikó Y Tóth,1 Ilona Pfeiffer,3 Mónika Kiricsi,2 Zoltán Kónya1,4 1Department of Applied and Environmental Chemistry, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary; 2Department of Biochemistry and Molecular Biology, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary; 3Department of Microbiology, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary; 4MTA-SZTE Reaction Kinetics and Surface Chemistry Research Group, Szeged, Hungary Purpose: The biomedical applications of silver nanoparticles (AgNPs) are heavily investigated due to their cytotoxic and antimicrobial properties. However, the scientific literature is lacking in data on the aggregation behavior of nanoparticles, especially regarding its impact on biological activity. Therefore, to assess the potential of AgNPs in therapeutic applications, two different AgNP samples were compared under biorelevant conditions.Methods: Citrate-capped nanosilver was produced by classical chemical reduction and stabilization with sodium citrate (AgNP@C), while green tea extract was used to produce silver nanoparticles in a green synthesis approach (AgNP@GTs). Particle size, morphology, and crystallinity were characterized using transmission electron microscopy. To observe the effects of the most important biorelevant conditions on AgNP colloidal stability, aggregation grade measurements were carried out using UV-Vis spectroscopy and dynamic light scatterig, while MTT assay and a microdilution method were performed to evaluate the effects of aggregation on cytotoxicity and antimicrobial activity in a time-dependent manner.Results: The aggregation behavior of AgNPs is mostly affected by pH and electrolyte concentration, while the presence of biomolecules can improve particle stability due to the biomolecular corona effect. We demonstrated that high aggregation grade in both AgNP samples attenuated their toxic effect toward living cells. However, AgNP@GT proved less prone to aggregation thus retained a degree of its toxicity.Conclusion: To our knowledge, this is the first systematic examination regarding AgNP aggregation behavior with simultaneous measurements of its effect on biological activity. We showed that nanoparticle behavior in complex systems can be estimated by simple compounds like sodium chloride and glutamine. Electrostatic stabilization might not be suitable for biomedical AgNP applications, while green synthesis approaches could offer new frontiers to preserve nanoparticle toxicity by enhancing colloidal stability. The importance of properly selected synthesis methods must be emphasized as they profoundly influence colloidal stability, and therefore biological activity. Keywords: colloidal stability, green synthesis, antimicrobial activity, cytotoxicity &nbsp

Biological activity of green-synthesized silver nanoparticles depends on the applied natural extracts: a comprehensive study

Andrea Rónavári,1,* Dávid Kovács,2,* Nóra Igaz,2,* Csaba Vágvölgyi,3 Imre Miklós Boros,2,4 Zoltán Kónya,1,5 Ilona Pfeiffer,3 Mónika Kiricsi2 1Department of Applied and Environmental Chemistry, 2Department of Biochemistry and Molecular Biology, 3Department of Microbiology, University of Szeged, 4Institute of Biochemistry, Biological Research Center of the Hungarian Academy of Sciences, 5MTA-SZTE Reaction Kinetics and Surface Chemistry Research Group, Szeged, Hungary *These authors contributed equally to this work Abstract: Due to obvious disadvantages of the classical chemical methods, green synthesis of metallic nanoparticles has attracted tremendous attention in recent years. Numerous environmentally benign synthesis methods have been developed yielding nanoparticles via low-cost, eco-friendly, and simple approaches. In this study, our aim was to determine the suitability of coffee and green tea extracts in green synthesis of silver nanoparticles as well as to compare the performance of the obtained materials in different biological systems. We successfully produced silver nanoparticles (C-AgNP and GT-AgNP) using coffee and green tea extracts; moreover, based on our comprehensive screening, we delineated major differences in the biological activity of C-AgNPs and GT-AgNPs. Our results indicate that although GT-AgNPs exhibited excellent antimicrobial activity against all the examined microbial pathogens, these particles were also highly toxic to mammalian cells, which limits their potential applications. On the contrary, C-AgNPs manifested substantial inhibitory action on the tested microbes but were nontoxic to human and mouse cells, indicating an outstanding capacity to discriminate between potential pathogens and mammalian cells. These results clearly show that the various green materials used for stabilization and for reduction of metal ions have a defining role in determining and fine-tuning the biological activity of the obtained nanoparticles. Keywords: green synthesis, silver nanoparticles, antimicrobial activity, toxicit

Biosynthesized silver and gold nanoparticles are potent antimycotics against opportunistic pathogenic yeasts and dermatophytes

Andrea Rónavári,1,2 Nóra Igaz,2 Mohana Krishna Gopisetty,2 Bettina Szerencsés,3 Dávid Kovács,2 Csaba Papp,3 Csaba Vágvölgyi,3 Imre Miklós Boros,2,4 Zoltán Kónya,1,5 Mónika Kiricsi,2 Ilona Pfeiffer3 1Department of Applied and Environmental Chemistry, 2Department of Biochemistry and Molecular Biology, 3Department of Microbiology, Faculty of Science and Informatics, University of Szeged, Szeged, 4Institute of Biochemistry, Biological Research Centre of the Hungarian Academy of Sciences, 5MTA-SZTE Reaction Kinetics and Surface Chemistry Research Group, Szeged, Hungary Background: Epidemiologic observations indicate that the number of systemic fungal infections has increased significantly during the past decades, however in human mycosis, mainly cutaneous infections predominate, generating major public health concerns and providing much of the impetus for current attempts to develop novel and efficient agents against cutaneous mycosis causing species. Innovative, environmentally benign and economic nanotechnology-based approaches have recently emerged utilizing principally biological sources to produce nano-sized structures with unique antimicrobial properties. In line with this, our aim was to generate silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) by biological synthesis and to study the effect of the obtained nanoparticles on cutaneous mycosis causing fungi and on human keratinocytes. Methods: Cell-free extract of the red yeast Phaffia rhodozyma proved to be suitable for nanoparticle preparation and the generated AgNPs and AuNPs were characterized by transmission electron microscopy, dynamic light scattering and X-ray powder diffraction. Results: Antifungal studies demonstrated that the biosynthesized silver particles were able to inhibit the growth of several opportunistic Candida or Cryptococcus species and were highly potent against filamentous Microsporum and Trichophyton dermatophytes. Among the tested species only Cryptococcus neoformans was susceptible to both AgNPs and AuNPs. Neither AgNPs nor AuNPs exerted toxicity on human keratinocytes. Conclusion: Our results emphasize the therapeutic potential of such biosynthesized nanoparticles, since their biocompatibility to skin cells and their outstanding antifungal performance can be exploited for topical treatment and prophylaxis of superficial cutaneous mycosis. Keywords: antifungal activity, biological synthesis, dermatophytes, opportunistic pathogenic yeasts, silver nanoparticles, toxicit

Estradiol-Based Salicylaldehyde (Thio)Semicarbazones and Their Copper Complexes with Anticancer, Antibacterial and Antioxidant Activities

A series of novel estradiol-based salicylaldehyde (thio)semicarbazones ((T)SCs) bearing (O,N,S) and (O,N,O) donor sets and their Cu(II) complexes were developed and characterized in detail by 1H and ¹³C nuclear magnetic resonance spectroscopy, UV–visible and electron paramagnetic resonance spectroscopy, electrospray ionization mass spectrometry and elemental analysis. The structure of the Cu(II)-estradiol-semicarbazone complex was revealed by X-ray crystallography. Proton dissociation constants of the ligands and stability constants of the metal complexes were determined in 30% (v/v) DMSO/H2O. Estradiol-(T)SCs form mono-ligand complexes with Cu(II) ions and exhibit high stability with the exception of estradiol-SC. The Cu(II) complexes of estradiol-TSC and its N,N-dimethyl derivative displayed the highest cytotoxicity among the tested compounds in MCF-7, MCF-7 KCR, DU-145, and A549 cancer cells. The complexes do not damage DNA according to both in vitro cell-free and cellular assays. All the Cu(II)-TSC complexes revealed significant activity against the Gram-positive Staphylococcus aureus bacteria strain. Estradiol-TSCs showed efficient antioxidant activity, which was decreased by complexation with Cu(II) ions. The exchange of estrone moiety to estradiol did not result in significant changes to physico-chemical and biological properties