The concentration-dependent aggregation of Ag NPs induced by cystine

Abstract

Cystine is widely used in cell culture media. Cysteine, the reduced form of cystine, is widely used to scavenge dissolved Ag in eco-toxicological studies to differentiate dissolved vs. nanoparticle uptake and toxicity. However, little is known about the impact of cysteine and cystine on the aggregation behavior of Ag NPs, in particular as a function of Ag NP concentration. Herein, we investigate how cystine (0-300μM) affects the stability of citrate-, polyvinylpyrrolidone-, and polyethylene glycol-coated silver nanoparticles (cit-Ag NPs, PVP-Ag NPs and PEG-Ag NPs, respectively) with and without Suwannee River fulvic acid (SRFA) as a function of Ag NPs concentration using UV-vis spectroscopy at environmentally and ecotoxicologically relevant Ag NP concentrations (ca. 125-1000μgL(-1)). The results demonstrate, for the first time, the concentration-dependent aggregation of cit-Ag NPs in the presence of cystine with a shift in the critical coagulation concentration (CCC) to lower cystine concentrations at lower cit-Ag NP concentrations. At the highest cit-Ag NP concentration (1000μgL(-1)), reaction limited aggregation was only observed and no CCC was measured. SRFA slowed the aggregation of cit-Ag NPs by cystine and aggregation occurred in reaction limited aggregation (RLA) regime only. No CCC value was measured in the presence of SRFA. Cystine replaces citrate, PVP and PEG coatings, resulting in aggregation of both electrostatically and sterically stabilized Ag NPs. These findings are important in understanding the factors determining the behavior of Ag NPs in cell culture media. Also due to the similarity between cystine and cysteine, these results are important in understanding the uptake and toxicity of Ag NPs vs. Ag ions, and suggest that the reduction of the toxicity of Ag NPs in the presence of cysteine could be due to a combined effect of scavenging Ag(+) ions and Ag NP aggregation in the presence of cysteine.

Aggregation and sedimentation of shattered graphene oxide nanoparticles in dynamic environments: a solid-body rotational approach

“…13,14 Once they have entered aquatic environments, aggregation of such particles can significantly affect their functionality and transport behaviour, particularly in aqueous and porous media. 4,5,15 Despite the existence of many studies on homo-and hetero-aggregation of various nanoparticles (NP), 14,[16][17][18][19][20][21] and abundant reports on the impacts of various factors on the aggregation behaviour of these NP, [22][23][24][25][26] it still remains a problem of how system dynamics modify aggregation. It is particularly of paramount importance in groundwater (GW) transport to understand how complex multi-cascade processes of advective and diffusive transport, [27][28][29][30] tortuosity in porous media, 31 and the arrival of aggregates from upgradient pores 32,33 impact the aggregation behaviour of NP.…”

Effect of nanomaterial and media physicochemical properties on nanomaterial aggregation kinetics

“…For instance, the CCC for citrate-Ag NMs decreases with the increased concentration of carbonate and phosphate anions in the medium, which was ascribed to the sorption of phosphate and carbonate anions on the surface of citrate-Ag NMs, and the concurrent reduction in the magnitude of Ag NM zeta potential 81,83 . Addition of cystine to citrate-Ag NMs results in NM concentration-dependent shift in the CCC, where the CCC of cystine decreases with the decrease in Ag NM concentration 77 . At lower Ag NM concentrations, lower concentration of cystine is required to fully cover and destabilize Ag NMs 77 .…”

“… The polymer should be strongly adsorbed to the particle surface. Desorption or replacement of the surface coating by molecules/ligands with high affinity to particle surface could compromise NM stability 77 .…”

“…wan der Waals and electrostatic repulsion). However, several NMs have high affinity to media constituents such as anions 62,89 and small organic compounds 77 . In such circumstances, the attachment efficiency and the CCC values are strongly dependent on NM concentration, in particular at low, environmentally relevant NM concentrations 77 .…”

“…However, several NMs have high affinity to media constituents such as anions 62,89 and small organic compounds 77 . In such circumstances, the attachment efficiency and the CCC values are strongly dependent on NM concentration, in particular at low, environmentally relevant NM concentrations 77 . This is because at lower NM concentrations, less total surface area is available, and thus chemical sorption of anions, and bio-and geo-molecules on the surface of NMs is more significant.…”