title: New, rapid method to measure dissolved silver concentration in silver nanoparticle suspensions by aggregation combined with centrifugation.
abstract: It is unclear whether the antimicrobial activities of silver nanoparticles (AgNPs) are exclusively mediated by the release of silver ions (Ag+) or, instead, are due to combined nanoparticle and silver ion effects. Therefore, it is essential to quantify dissolved Ag in nanosilver suspensions for investigations of nanoparticle toxicity. We developed a method to measure dissolved Ag in Ag+/AgNPs mixtures by combining aggregation of AgNPs with centrifugation. We also describe the reproducible synthesis of stable, uncoated AgNPs. Uncoated AgNPs were quickly aggregated by 2 mM Ca2+, forming large clusters that could be sedimented in a low-speed centrifuge. At 20,100g, the sedimentation time of AgNPs was markedly reduced to 30 min due to Ca2+-mediated aggregation, confirmed by the measurements of Ag content in supernatants with graphite furnace atomic absorption spectrometry. No AgNPs were detected in the supernatant by UV-Vis absorption spectra after centrifuging the aggregates. Our approach provides a convenient and inexpensive way to separate dissolved Ag from AgNPs, avoiding long ultracentrifugation times or Ag+adsorption to ultrafiltration membranes.
authors.affiliation: Institute of Microbiology and Infection, School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT UK.
authors.forename: Feng
authors.identifier: 0000-0001-5187-3336
authors.initials: F
authors.lastname: Dong
authors.affiliation: School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT UK.
authors.forename: Eugenia
authors.initials: E
authors.lastname: Valsami-Jones
authors.affiliation: Institute of Microbiology and Infection, School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT UK.
authors.forename: Jan-Ulrich
authors.initials: JU
authors.lastname: Kreft
keywords: Aggregation; Centrifugation; Environmental and health effects; Nanotoxicology; Sedimentation; Separation; Silver nanoparticles