Fluorescent polyurethane nanocapsules prepared via inverse miniemulsion: surface functionalization for use as biocarriers.

The functionalization of well-defined PU nanocapsules with an aqueous core prepared by performing a polyaddition at the interface of inverse (water-in-oil) miniemulsion droplets is demonstrated. The miniemulsion technique involving the nanoreactor concept allows one to obtain an encapsulation efficiency as high as 90% within the nanocapsules. A pH independent fluorescent dye is used as a model system for the aqueous core. By varying the molar ratio of the diol to the diisocyanate at a fixed surfactant concentration, the shell thickness of the nanocapsules can be finely tuned. The carboxy- and amino-functionalized surface of the nanocapsules can be tailored by an in-situ carboxymethylation reaction and by physical adsorption of a cationic polyelectrolyte, i.e. PAEMA or PEI. The increased uptake of amino-functionalized fluorescent nanocapsules by HeLa cells clearly demonstrates the potential of the functionalized nanocapsules to be successfully exploited as biocarriers.