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.

The extensive oxygen-group functionality of single-layer graphene oxide proffers useful anchor sites for chemical functionalization in the controlled formation of graphene architecture and composites. However, the physicochemical environment of graphene oxide and its single-atom thickness facilitate its ability to undergo conformational changes due to responses to its environment, whether pH, salinity, or temperature. Here, we report experimental and molecular simulations confirming the conformational changes of single-layer graphene oxide sheets from the wet or dry state. MD, PM6, and ab initio simulations of dry SLG and dry and wetted SLGO and electron microscopy imaging show marked differences in the properties of the materials that can explain variations in previously observed results for the pH dependent behavior of SLGO and electrical conductivity of chemically modified graphene-polymer composites. Understanding the physicochemical responses of graphene and graphene oxide architecture and performing selected chemistry will ultimately facilitate greater tunability of their performance.

Single-layer graphene oxides (SLGOs) undergo morphological changes depending on the pH of the system and may account for restricted chemical reactivity. Herein, SLGO may also capture nanoparticles through layering and enveloping when the pH is changed, demonstrating potential usefulness in drug delivery or waste material capture.

Despite the large efforts to prepare super paramagnetic iron oxide nanoparticles (MNPs) for biomedical applications, the number of FDA or EMA approved formulations is few. It is not known commonly that the approved formulations in many instances have already been withdrawn or discontinued by the producers; at present, hardly any approved formulations are produced and marketed. Literature survey reveals that there is a lack for a commonly accepted physicochemical practice in designing and qualifying formulations before they enter in vitro and in vivo biological testing. Such a standard procedure would exclude inadequate formulations from clinical trials thus improving their outcome. Here we present a straightforward route to assess eligibility of carboxylated MNPs for biomedical tests applied for a series of our core-shell products, i.e., citric acid, gallic acid, poly(acrylic acid) and poly(acrylic acid-co-maleic acid) coated MNPs. The discussion is based on physicochemical studies (carboxylate adsorption/desorption, FTIR-ATR, iron dissolution, zeta potential, particle size, coagulation kinetics and magnetization measurements) and involves in vitro and in vivo tests. Our procedure can serve as an example to construct adequate physico-chemical selection strategies for preparation of other types of core-shell nanoparticles as well.