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.Electronic supplementary materialThe online version of this article (doi:10.1007/s11051-016-3565-0) contains supplementary material, which is available to authorized users.
Highlights
Nanomaterials (NMs) have received increasing attention due to their distinctive physicochemical properties at nanosize (Adeleye et al 2016; Kim et al 2010; Lohse and Murphy 2012), especially for their medical application potential, as multi-drug resistant pathogens become ever more frequent (Meredith et al 2015; MoronesRamirez et al 2013; Piddock 2012; Sprenger and Fukuda 2016)
The formation of uncoated AgNPs is controlled by the aggregative growth of small AgNPs (Polte et al 2012; Van Hyning et al 2001), but aggregation of the NPs can lead to the failure of synthesis (Mulfinger et al 2007)
Uncoated AgNPs were aggregated by Ca(NO3)2, and a concentration of 2 mM was sufficient to induce the formation of large AgNPs clusters
Summary
Nanomaterials (NMs) have received increasing attention due to their distinctive physicochemical properties at nanosize (Adeleye et al 2016; Kim et al 2010; Lohse and Murphy 2012), especially for their medical application potential, as multi-drug resistant pathogens become ever more frequent (Meredith et al 2015; MoronesRamirez et al 2013; Piddock 2012; Sprenger and Fukuda 2016). Silver nanoparticles (AgNPs) are widely used nanomaterials due to their toxic effects on microorganisms (Chaloupka et al 2010; Eckhardt et al 2013; Morones-Ramirez et al 2013). The antibacterial activities of AgNPs are generally thought to be indirectly mediated by the release of silver ions (Ag?) (Leclerc and Wilkinson 2014; Shen et al 2015; Xiu et al 2012), but some studies have suggested nanoparticles themselves can play a direct role in toxicity to bacteria In ultracentrifugation, precipitating the tiny nanoparticles requires large centrifugal forces and long running times (Mostowfi et al 2009), which might be problematic when AgNPs continuously release Ag? Emerging techniques such as single particle inductively coupled plasma mass spectrometry (SPICP-MS) and asymmetrical flow field-flow fractionation coupled with inductively coupled plasma mass spectrometry (AF4-ICP-MS) are complex to operate and standardize (Mitrano et al 2012; Pace et al 2012)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
