Revealing the Importance of Aging, Environment, Size and Stabilization Mechanisms on the Stability of Metal Nanoparticles: A Case Study for Silver Nanoparticles in a Minimally Defined and Complex Undefined Bacterial Growth Medium.

Ilse De Leersnyder,Pieter Vermeir,Leen De Gelder,Isabel Van Driessche

doi:10.3390/nano9121684

Ilse De Leersnyder, Pieter Vermeir + Show 2 more

Open Access

https://doi.org/10.3390/nano9121684

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Journal: Nanomaterials	Publication Date: Nov 25, 2019
Citations: 31	License type: CC BY 4.0

Affiliation: Ghent University

Abstract

Although the production and stabilization of metal nanoparticles (MNPs) is well understood, the behavior of these MNPs (possible aggregation or disaggregation) when they are intentionally or unintentionally exposed to different environments is a factor that continues to be underrated or overlooked. A case study is performed to analyze the stability of silver nanoparticles (AgNPs)—one of the most frequently used MNPs with excellent antibacterial properties—within two bacterial growth media: a minimally defined medium (IDL) and an undefined complex medium (LB). Moreover, the effect of aging, size and stabilization mechanisms is considered. Results clearly indicate a strong aggregation when AgNPs are dispersed in IDL. Regarding LB, the 100 nm electrosterically stabilized AgNPs remain stable while all others aggregate. Moreover, a serious aging effect is observed for the 10 nm electrostatically stabilized AgNPs when added to LB: after aggregation a restabilization effect occurs over time. Generally, this study demonstrates that the aging, medium composition (environment), size and stabilization mechanism—rarely acknowledged as important factors in nanotoxicity studies—have a profound impact on the AgNPs stabilization and should gain more attention in scientific research.

Highlights

The world has seen an exponential rise in the applications of metal nanoparticles (MNPs), leading to an increasing interest of researchers from different scientific disciplines [1,2]
This dilution was made in their solvent—2 mM NaC solution for the NaC stabilized AgNPs and ultra-pure water (Milli Q®, Merck) for the PVP and branched polyethyleneimine (BPEI) stabilized AgNPs, in an IDL medium or in an LB medium
Reporting of the hydrodynamic diameter of an aggregate alone seems incorrect to us due to the complexity of aggregation processes that can lead to more polydispersity and the formation of non-spherical aggregates of which size cannot be defined by one value

Summary

Introduction

The world has seen an exponential rise in the applications of metal nanoparticles (MNPs), leading to an increasing interest of researchers from different scientific disciplines [1,2]. Macromolecules, like the polyvinylpyrrolidone (PVP) polymer can sterically stabilize MNPs by attaching to the surface and form a ‘brush-like’ layer. This layer reduces the degree of freedom when the particles approach each other, leading to an energetic unfavorable state whereby the particles repel and remain stabilized. When the charge of the repulsive electrostatic forces is strong enough to overcome attractive Van de Waals forces, the MNPs are stabilized. A last option of stabilization is through electrosteric repulsion by the addition of a polyelectrolyte—like branched polyethyleneimine (BPEI) This stabilization mechanism is a combination of steric stabilizing polymers with charged groups [3,4,5,6,7]

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