Improved hybrid-shelled perfluorocarbon microdroplets as ultrasound- and laser-activated phase-change platform

Hypothesis: We propose significant improvements to perfluorocarbon microdroplets, conferring them colloidal stability, chemical versatility, and size control. Decafluoropentane cores are stabilized by biocompatible interfaces - either a monolayer of the cationic surfactant dimethyldioctadecylammonium bromide (DDAB) or a double shell obtained by adding crosslinked dextran methacrylate as further coating - and functionalised with gold nanoparticles. We hypothesize that this formulation enables dual, acoustic (ADV) and optical (ODV) vaporisation of microdroplets into microbubbles, yielding a versatile "phase-change" theranostic platform. Experiments: Microdroplets synthesis is optimized by high-speed homogenization methodology. Functionalisation with gold nanoparticles is achieved by electrostatic decoration. The colloidal suspension is characterised by the concerted use of dynamic light scattering, electrophoresis, and confocal microscopy, to assess microdroplets' stability. Additional structural details are provided by small-angle X-ray scattering. We analysed the ultrasound- and laser-stimulated transition into microbubbles and characterised their response to ultrasound by acoustic spectroscopy. Findings: Hybrid-shelled microdroplets were produced at high density, with narrow diameter distribution (~1 µm). The highly charged surface and the long hydrocarbon tails of DDAB protruding within the core provide high stability. The elastomeric dextran layer at the water interface allows obtaining stable cavitating microbubbles by ADV exhibiting interesting viscoelastic features. The presence of gold nanoparticles unlocks the opto-thermal microdroplet vaporisation.