Potential impact of natural organic ligands on the colloidal stability of silver nanoparticles

Abstract

Interaction of natural organic matter (NOM) with engineered nanoparticles (NPs) determine NP fate, transport, and environmental persistence. However, the effect of NOM chemical composition, structure, and concentration on aggregation kinetics and dissolution behavior of silver nanoparticles (AgNPs) are still poorly understood because of heterogeneity and variability in NOM and AgNP properties. Here, aggregation behavior of citrate-coated silver nanoparticles (cit-AgNPs with a z-average diameter of 18nm) was investigated in the presence of l-cysteine (l-cys) and N-acetyl l-cysteine (NAL-cys) using UV-vis spectroscopy. We also investigated the effect of Suwannee River fulvic acid (SRFA) and a NOM isolated from the Yukon River (YRNOM) on the stability of cit-AgNPs. The dissolution of cit-AgNPs decreased with increased L-cys and NAL-cys concentration from 0 to 10μM. The critical coagulation concentration (CCC) of cit-AgNPs decreased in the presence of l-cys and increased in the presence of NAL-cys. Similarly, l-cys destabilizes cit-AgNPs in the presence of SRFA. The differences in the stability of cit-AgNPs in the presence of l-cys and NAL-cys can be attributed to the differences in the functional groups in these two cysteine molecules. l-cys has both negatively charged carboxylic group and a positively charged amine group, resulting in bridging between different particles. NAL-cys is a derivative of cysteine wherein an acetyl group is attached to the nitrogen atom thus shielding the positive charge on the amine group and therefore eliminating the bridging interaction mechanism. SRFA and YRNOM enhanced the stability of cit-AgNPs and increased the CCC value to higher counter ion concentrations. The concentration of SRFA (1-5mgL) did not affect the CCC, whereas the increased concentration of YRNOM increased the CCC of cit-AgNPs to high Na concentrations likely due to increased sorption of higher molecular weight compounds on the surface of cit-AgNPs. The outcome of this study suggests the importance of understanding the molecular properties of NOM (e.g. functional groups and molecular weight) in determining cit-AgNP environmental behaviors.

Constraints and Priorities for Conducting Experimental Exposures of Marine Organisms to Microplastics

“…In the rich environment of marine salts, specific ions might have specific chemical interactions with surface groups and thus neutralize particle charges (Hofmeister, 1888). In addition, Afshinnia et al (2018) reported that natural colloids from the medium (e.g., humic substances) could influence the charge of the particles, suppressing the positive charge and enhancing the negative one, depending on both the point zero charge (pzc) of the particles and the pH of the solution. An ecocorona can favor the adhesion of the particles to each other or instead reduce their flocculation in accordance with new surface affinities (Yu et al, 2017).…”

The toxicity of coated silver nanoparticles to the alga Raphidocelis subcapitata

“…The behaviour of NPs in test systems is not predictable using the traditional methods of partitioning and bioavailability [22,66]. The stability of organic-coated AgNPs in biological media has received significant attention in the last few years in nanotechnology and toxicology studies [3,84]. Similar to the observations made in this study, other toxicological studies also have shown that aggregation, dissolution, change in NP characteristics and culture media influence the bioavailability of NPs and hence, play an important role in determining toxicity [37,86,106].…”

Effect of polymer coating composition on the aggregation rates of Ag nanoparticles in NaCl solutions and seawaters

“…The values of the effective aggregation rates and fractal structure parameters could, in principle, be obtained in the laboratory from aggregation experiments performed in synthetic solutions, as explained below. Several important contributions have been recently presented on the effect of natural dissolved organic matter (DOM) on the stability behaviour of NPs in samples representative of environmental conditions (Afshinnia et al, 2018;Baalousha et al, 2013a;Ellis et al, 2016) However, the specific role of the organic coating composition in the interactions of NPs with DOM still remains largely unknown.…”