Uniform fluorescent photonic crystal supraballs generated from nanocrystal-loaded hydrogel microspheres

We report an alternative strategy for fabricating fluorescent photonic crystal (PC) supraballs using CdTe nanocrystal (NC) loaded hydrogel microspheres via a simple microfluidic device. Firstly, monodispersed hydrogel microspheres with poly(styrene-co-acrylic acid) (PS-co-PAA) cores and poly(acrylic acid-co-2-hydroxyethyl methacrylate) (PAA-co-PHEMA) shells were controllably prepared by seeded copolymerization. Then, with the help of stimulus-responsive behavior of the hydrogel microspheres, the CdTe NCs (ca. 4.3 nm) were physically entrapped in them to form CdTe/microgel hybrid latexes. Finally, we have successfully fabricated uniform fluorescent PC supraballs using CdTe/microgel hybrid latexes as the discontinuous phase and methysilicone oil as the continuous phase in a microfluidic assembly. The combination of electronic confinement, originating from the CdTe NCs, and photon confinement, due to the periodic dielectric structure of the long- range ordered hydrogel microsphere arrays, has been realized in these fluorescent PC supraballs. In addition, by measuring the changes of CdTe NCs leakage concentration at different pH values, we have found PC supraballs display good pH- triggered release behavior.