From Concentrated Dispersion to Solid β-Cyclodextrin Polymer-Capped Silver Nanoparticle Formulation: A Trojan Horse Against Escherichia coli

Preparation of concentrated silver nanoparticles in water remains a challenge today. The intrinsic reactivity of silver, as well as the high surface energy of nanoparticles, make it difficult to handle them without altering their pristine properties. Herein, we report the preparation of concentrated silver nanoparticles (AgNPs) dispersion (2 mM; 1.5⋅10¹⁵ NPs/mL) by reducing Ag⁺ in-situ of a β-cyclodextrin-epichlorohydrin polymer (βCDP) as a capping agent. The prepared nanoparticles (AgNPs@βCDP) with a Surface Plasmon Resonance band at 396 nm, and a hydrodynamic diameter of 21.4 ±1.8 nm, retained both features after being precipitated and re-dispersed in water. The AgNPs core had a spherical morphology, with a 12.7 ±1.5 nm diameter in size, as determined by TEM. The AgNPs@βCDP showed outstanding bactericidal properties against Escherichia coli (MIC= 0.37 nM), one of the lowest ever achieved for silver nanoparticles. We suggest that the polymer acts as a Trojan horse with AgNPs as payload.