(369b) Stability of Engineered Nanoparticles In Aqueous Systems: Elucidating the Roles of Capping Agents and Natural Organic Matter

The rapid development of novel nanomaterials and their incorporation into consumer products has not been paralleled with an equal effort investigating the possible environmental implications.  Increasingly, the properties of engineered nanoparticles (ENPs) are tailored for specific applications through the use of organic capping agents.  Furthermore, when released into the environment it is probably that ENPs will interact with natural organic matter (NOM).  The objective of this work is to develop an improved understanding of the roles of synthetic capping agents and NOM in controlling the aggregation of engineered nanoparticles (ENPs) in aquatic environmental systems. Using a suite of ligand-stabilized gold nanoparticles (AuNPs) and various NOM isolates, the specific aims of the project are to: (1) Correlate the physicochemical properties of capping agents with interactions between capped ENPs in aquatic systems; and (2) Correlate the physicochemical properties of capping agents and NOM with interactions between capped ENPs and NOM in aquatic systems.  ENP stability with respect to aggregation is being assessed using the zeta potential and aggregation rates measured using time-resolved dynamic light scattering. Results indicate that NOM is adsorbed onto the AuNP surfaces, alterning surface charge and providing stability with respect to aggregation.  Different classes of NOM stabilize AuNPs to different extents.  The specific mechanisms of NOM-AuNP interactions are being probed using advanced surface and solution phases spectroscopic techniques (e.g., fluorescence, Raman, and EDX). By using a group of well-characterized ENPs that vary only with respect to their surface functionality, we aim to correlate environmental behavior with ENP properties in structure-activity type relationships. For example, results indicate that the stabilizing effects of NOM are related to the molecular weight of the specific NOM fractions.  This work will provide an improved ability to predict environmental fate based on NP characteristics and yield the feedback necessary for the design of safer nanomaterials.