Biocompatible amphiphilic Janus nanoparticles with enhanced interfacial properties for colloidal surfactants.

Emulsions in which water droplets are dispersed in fluorocarbon oil phase (W/F emulsions) serve as effective means to encapsulate bioactives and precisely execute reactions in confined space due to the gas permeability, chemical inertness, and biocompatibility offered by the continuous phase. While molecular surfactants consisting of perfluorinated polyether (PFPE) and polyethylene glycol (PEG) have been used to stabilize these emulsions, these surfactants cannot effectively prevent coalescence and cross-contamination between the neighboring droplets. Herein, we present Janus nanoparticles (F-SiO-PEG) as biocompatible colloidal surfactants to achieve excellent stability in W/F emulsions. By utilizing monolayered wax colloidosomes as templates, we show that Janus silica nanoparticles with two distinctive surface wetting properties can be synthesized in high purity. Moreover, we demonstrate that additional PEGylation of these Janus particles allows these colloidal surfactants to strongly adhere at the W/F interface, granting excellent emulsion stability compared to the equivalent randomly functionalized nanoparticles and prevent non-specific adsorption of proteins. As the strategy outlined in this work is general, we anticipate that it can be further extended to prepare Janus particles with tailored interfacial properties for biomedical, cosmetics, and pharmaceutical applications involving emulsions.