Double Emulsion-Templated Nanoparticle Colloidosomes with Selective Permeability
Original entry by Sagar Bhandari, APPHY 225 Fall 2010
Double Emulsion-Templated Nanoparticle Colloidosomes with Selective Permeability, Daeyeon Lee, David A. Weitz , Advanced Materials Volume 20, Issue 18, pages 3498–3503, September 17, 2008
emulsion, nanoparticles, colloidosomes, permeability
In this paper, the authors demonstrate that nanoparticle colloidosomes with selective permeability can be prepared from monodisperse double emulsions as templates instead of using the conventional water-in-oil emulsion. The monodisperse water-in-oil-in-water double emulsions with a core shell geometry are prepared using glass capillary microfluidic devices. Hydrophobic silica nanoparticles are used to create the colloidosome shells by dispersing them in the oil shell and after stabilization removing the oil solvent. The size of the colloidosomes can be controlled since the size of emulsions dimension can be precisely tuned by independently controlling the flow rates of each fluid phase. Their microfluidic device combines a flow focusing and coflowing geometry as shown in Fig 1 (a). This kind of geometry results in hydrodynamic flow focusing of three different fluid streams at the orifice of the collection tube and leads to the formation of double emulsions. Silicon nano partciles are used in oil phase to stabilize the double emulsion. After the nanoparticle stabilized double emulsions are collected, the oil phase is removed by evaporation, leading to the formation of nanoparticle colloidosomes through dense packing of nanoparticles as shown in Figure 1(b).The double emulsions so generated are very monodisperse as evidenced by the hexagonal close packing of the drops, illustrated by optical and fluorescence microscopy images in Figure 1(c) and (d),respectively.
Colloidosomes with shell thicknesses ranging from 100nm to 10mm were created by controlling the dimension of the double emulsions and the volume fraction of nanoparticles in the oil phase. Magnetically responsive composite colloidosomes can also be prepared by suspending Fe3O4 magnetic nanoparticles along with hydrophobic silica nanoparticles in the oil phase.
The selective permeability of these colloidosomes is demonstrated by exposing them to aqueous solutions of fluorescence probes with different molecular weights. The permeation of fluorescence probes into the interior of the colloidosomes is detected by confocal laser scanning microscopy (CLSM). This was demonstrated by showing that Calcein,a low weight moelcule , freely diffuses into the interior of SiO2 nanoparticle colloidosomes as shown in Figure 2(a)while FITC-dextran, a higher wieght molecule cannot diffuse into the interior of the colloidosomes in Figure 2(b).