Are Smaller Nanoparticles Always Better? Understanding the Biological Effect of Size-Dependent Silver Nanoparticle Aggregation Under Biorelevant Conditions

Abstract

Péter Bélteky,1,* Andrea Rónavári,1,* Dalma Zakupszky,1 Eszter Boka,1 Nóra Igaz,2 Bettina Szerencsés,3 Ilona Pfeiffer,3 Csaba Vágvölgyi,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*These authors contributed equally to this workCorrespondence: Zoltán KónyaDepartment of Applied and Environmental Chemistry, Faculty of Science and Informatics, University of Szeged, Rerrich Square 1, Szeged, H-6720, HungaryTel [phone]Email [email protected]: Silver nanoparticles (AgNPs) are one of the most commonly investigated nanomaterials, especially due to their biomedical applications. However, their excellent cytotoxic and antimicrobial activity is often compromised in biological media due to nanoparticle aggregation. In this work, the aggregation behavior and the related biological activity of three different samples of citrate capped silver nanoparticles, with mean diameters of 10, 20, and 50 nm, respectively, were examined.Methods: Following nanoparticle synthesis and characterization with transmission electron microscopy, their aggregation behavior under various pH values, NaCl, glucose, and glutamine concentrations, furthermore in cell culture medium components such as Dulbecco’s Modified Eagle’s Medium and fetal bovine serum, was assessed through dynamic light scattering and ultraviolet-visible spectroscopy.Results: The results indicated that acidic pH and physiological electrolyte content universally induce micron-scale aggregation, which can be mediated by biomolecular corona formation. Remarkably, larger particles demonstrated higher resistance against external influences than smaller counterparts. In vitro cytotoxicity and antimicrobial assays were performed by treating cells with nanoparticulate aggregates in differing stages of aggregation.Conclusion: Our results revealed a profound association between colloidal stability and toxicity of AgNPs, as extreme aggregation led to the complete loss of biological activity. The higher degree of aggregation resistance observed for larger particles had a significant impact on the in vitro toxicity, since such samples retained more of their activity against microbes and mammalian cells. These findings lead to the conclusion that aiming for the smallest possible nanoparticles might not be the best course of action, despite the general standpoint of the relevant literature.Keywords: seed-mediated growth, colloidal stability, size-dependent aggregation behavior, aggregation compromised toxicity

Keywords

• seed-mediated growth
• colloidal stability
• size-dependent aggregation behavior
• aggregation compromised toxicity