Multicompartmental particles for combined imaging and siRNA delivery.

The controlled delivery of genetic material, such as genes, plasmids, or siRNA, holds great promise for the therapy of a number of debilitating diseases. [ 1–3 ] While the fundamental concept of permanent or temporary genetic manipulation has been widely embraced by the scientifi c community, severe concerns remain about the safe and effi cient transfer of the genetic material into human cells, where it needs to be released in order to interact with the cell nucleus. [ 1 , 2 , 4 ] In addition it is desirable, in many cases, to combine gene delivery with a secondary function, such as release of a chemotherapeutic agent or an imaging modality. The main delivery challenges fall broadly into two categories: fi rst, the cell membrane represents an effective barrier against the infl ux of foreign genetic material resulting in notoriously low transfection rates. Second, a host of nucleases exist in the human body, which cause rapid breakdown of any unprotected genetic material. A number of approaches have been developed to address these challenges including electroporation, [ 5 ] viral vectors, [ 6 , 7 ] cationic liposomal formulations, [ 1 ] and nanoparticles. [ 1 , 2 ]