Cysteine-Induced Modifications of Zero-valent Silver Nanomaterials: Implications for Particle Surface Chemistry, Aggregation, Dissolution, and Silver Speciation

Abstract

The persistence of silver nanoparticles in aquatic environments and their subsequent impact on organisms depends on key transformation processes, which include aggregation, dissolution, and surface modifications by metal-complexing ligands. Here, we studied how cysteine, an amino acid representative of thiol ligands that bind monovalent silver, can alter the surface chemistry, aggregation, and dissolution of zero-valent silver nanoparticles. We compared nanoparticles synthesized with two coatings, citrate and polyvinylpirrolidone (PVP), and prepared nanoparticle suspensions (approximately 8 μM total Ag) containing an excess of cysteine (400 μM). Within 48 h, up to 47% of the silver had dissolved, as indicated by filtration of the samples with a 0.025-μm filter. Initial dissolution rates were calculated from the increase of dissolved silver concentration when particles were exposed to cysteine and normalized to the available surface area of nanoparticles in solution. In general, the rates of dissolution were almost 3 times faster for citrate-coated nanoparticles relative to PVP-coated nanoparticles. Rates tended to be slower in solutions with higher ionic strength in which the nanoparticles were aggregating. Xray absorption spectroscopy analysis of the particles suggested that cysteine adsorbed to silver nanoparticles surfaces through the formation of Ag(+I)sulfhydryl bonds. Overall, the results of this study highlight the importance of modifications by sulfhydrylcontaining ligands that can drastically influence the long-term reactivity of silver nanoparticles in the aquatic environment and their bioavailability to exposed organisms. Our findings demonstrate the need to consider multiple interlinked transformation processes when assessing the bioavailability, environmental risks, and safety of nanoparticles, particularly in the presence of metalbinding ligands.

Antibacterial activity of silver nanoparticles: A surface science insight

“…These soluble species can then diffuse toward the target cells, where further thiol-exchange with bio-molecules can lead to their anti-microbial action. In 2013, Gondikas et al [100] showed that a high concentration of cysteine (50 molar equivalent toward Ag) lead to a high dissolution rate of Ag NPs compared to a system without thiols (Fig. 5D).…”

“…Notably, in the case of bound cysteine (where the thiol-thiolate group is not involved in the protonation state), the pH has to be chosen so that the system is not zwitterionic (and thus neutral) to have an increased solubility. This effect can explain the difference in the dissolution of cysteine-coated Ag NPs [65,100,102,103], as they are performed at different pH. A study of the impact of soluble thiols on the dissolution of NPs, and notably in substoichiometric conditions, remains to our knowledge still to be done.…”

Transformations of silver nanoparticles in wastewater effluents: links to Ag bioavailability

“…In addition, the physiological state of the cell will influence the dynamics of interaction with either the NP or the species originating from it. Once the NP or related transformed species interact with a physiologically active site on the cell surface, they may affect the cell metabolism and disrupt the cellular homeostasis [35]. If the interaction is strong enough to overwhelm the stress responses, which arise due to a disruption in homeostasis, a toxic outcome will ensue [36].…”

“…If the interaction is strong enough to overwhelm the stress responses, which arise due to a disruption in homeostasis, a toxic outcome will ensue [36]. The bioavailability of a NP can be inferred by characterizing a biological end-point; these biological end-points will be different for different organisms (e.g., algae, bacteria, and fish) and may include metal bioaccumulation (sorption or uptake), photosynthetic activity, motility, respiration and growth [35]. show that Ag bioaccumulation was largely due to the ionic forms of the metal.…”

Transport of PVP-coated Silver Nanoparticles in Saturated Porous Media

“…일반적으로 실제 환경에 존재하는 다양한 환경변수(이온의 종류와 농도, pH, 자연 유기물, 입자상 물질 등)는 나노물질의 거동에 영향을 미 치는 것으로 알려져 있다 (Chen and Elimelech, 2007;Domingos et al, 2009;Jassby et al, 2012;Gondikas et al, 2012). 이전 연구결과에 따르면 은나노는 낮은 이온강 도 또는 자연유기물이 존재하는 수환경 조건에서 비교적 안정하게 존재하지만, 이온강도가 증가됨에 따라 응집속 도가 증가되고 토양 흡착량도 증가하는 것으로 알려져 있 다 (Bae et al, 2013;Huynh and Chen, 2011 (Pol et al, 2002;Tombacz and Szekeres, 2004;Cornelis et al, 2013;Liu, 2014;Zhou et al, 2012).…”