Controlled Evaluation of Silver Nanoparticle Dissolution Using Atomic Force MicroscopyEPA Grant Number: FP917474
Title: Controlled Evaluation of Silver Nanoparticle Dissolution Using Atomic Force Microscopy
Investigators: Kent, Ronald Douglas
Institution: Virginia Polytechnic Institute and State University
EPA Project Officer: Cobbs-Green, Gladys M.
Project Period: August 1, 2012 through July 31, 2015
Project Amount: $126,000
RFA: STAR Graduate Fellowships (2012) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Fellowship - Environmental Engineering
The goal of this research is to acquire comprehensive kinetic data of silver nanoparticle (AgNP) dissolution that can be used in future assessments examining AgNP fate, transport and toxicity. The objective of this study is to quantify the effects of (1) surface coatings, (2) particle size and shape, (3) solution chemistry, and (4) reduced sulfur on the dissolution rates of un-aggregated AgNPs. An underlying hypothesis of this project is that aggregation hinders AgNP dissolution, so it is expected that the rate data obtained will represent the upper limit of AgNP dissolution for a specified condition.
Nanosphere lithography (NSL) will be used to fabricate uniform arrays of AgNPs on glass substrates. NSL is a versatile, inexpensive and highthroughput lithographic technique that enables creation of periodic nano- and micro-particle arrays and facilitates control over particle size, shape and interparticle spacing for a number of different materials and substrates. AgNPs produced by NSL are immobilized on the substrate to prevent aggregation. Following production, particle arrays will be functionalized with various surface coatings that commonly are used to stabilize AgNP suspensions, such as citrate and PVP. The prepared samples will be placed in solutions of varying pH, temperature, inorganic salt concentrations and organic matter concentrations. Particular emphasis will be given to inorganic and organic sulfides because of their high affinity for silver. Changes in particle height and morphology will be monitored over time by atomic force microscopy (AFM) to obtain a direct measure of AgNP dissolution rates in units of nm/d. Additional techniques, such as X-ray photoelectron spectroscopy and Raman spectroscopy, will be used to provide further information about the reactions occurring at the AgNP surfaces.
Preliminary experiments have demonstrated that the proposed method can successfully measure dissolution rates in units of nm/d with high precision, and a strong correlation has been shown between chloride concentration and AgNP dissolution rate. Future experimentation will yield important information regarding other influential variables. Regression models generated from the experimental data will provide a convenient method for calculating dissolution rates to predict the persistence of AgNPs in a specified environment. It is expected that the results will be applicable to a wide range of environments, from natural waters to biological fluids. The novel experimental approach overcomes many of the limitations of more traditional techniques and can potentially be extended to other nanomaterials as well; thus, this project may provide a pattern for future studies on the environmental fate of nanomaterials.
Potential to Further Environmental/Human Health Protection
This research will produce comprehensive information about AgNP dissolution that will be invaluable for rapidly assessing and managing the risks of AgNPs, which is paramount for protection of public health and the environment. Toxicity studies and exposure modeling will both benefit from this information since AgNP dissolution is linked intimately to both topics. Data collected from this project will assist in the sustainable application of AgNPs by revealing how size, shape or surface coating can either enhance or diminish particle inertness or persistence.