CHANGES IN ENSEMBLE MORPHOLOGY OF DISSOLVING PROTEIN-STABILIZED SILVER NANOPARTICLES
Matthew N. Martin1,2, Robert I. MacCuspie1, Vincent A. Hackley1, Andrew J. Allen1
1 Material Measurement Laboratory, NIST, Gaithersburg, MD 20899-8520
2 Materials Science and Engineering Department, University of Maryland, College Park, MD 20742-2115
Typically, aqueous silver nanoparticles are stabilized electrostatically with citrate molecules or with common commercial polymers like Polyvinylpyrroliodone (PVP) . However, at high acid concentrations, such as those found in stomach acid (pH~1), these coatings cannot protect silver nanoparticles from the outside environment. Thus, to study silver nanoparticle dissolution at low pH, covalently bound proteins like bovine-serum albumin (BSA) and thiolated polyethyleneglycol (PEG) are needed.
We present results showing quantitative dissolution of BSA-, PEG-, PVP-, and citrate-coated silver nanoparticles in nitric acid concentrations down to pH 0.3. Synchrotron-based small-angle X-ray scattering (SAXS), ultraviolet-visible extinction spectroscopy (UV-vis), dynamic light scattering (DLS), and transmission electron microscopy (TEM) were used to characterize the particles. SAXS, UV-vis, and DLS were useful for determining the dissolution and aggregation rates of particles at varying acid concentrations, and TEM revealed information about how acid breaches a nanoparticle surface coating, thus initiating dissolution.
 R.I. MacCuspie, K. Rogers, M. Patra, Z. Suo, A.J. Allen, M.N. Martin and V.A. Hackley; “Challenges for physical characterization of silver nanoparticles under pristine and environmentally relevant conditions,” J. Environ. Monit., 13, 1212-1226 (2011).