“We have been working on nonviral gene delivery - the method of transferring foreign genes or plasmid DNA into cells using nonviral means - for a decade,” Kam Leong told nanotechweb.org. “We use polycationic polymers to condense DNA into nanoparticles that can be taken up by cells, and deliver these DNA nanoparticles to different tissues in vivo.” But the efficiency of this kind of gene delivery is poor. “One of the challenges is to control the characteristics of the DNA nanoparticles, in terms of size and how the DNA is entrapped,” explained Leong. “We thought that these [metallic] nanorods would be potentially attractive carriers for delivery of DNA into cells because of the control of the nanorods’ size and composition.”

Leong and colleagues made the bifunctional gold/nickel nanorods by electrodeposition into the cylindrical 100 nm diameter pores of an alumina membrane. They deposited a 100 nm thick layer of gold and 100 nm of nickel before etching away the alumina template. Then the researchers functionalized the nanorods by attaching DNA plasmids to the nickel segments and transferrin, a cell-targeting protein, to the gold segments. To do this they used molecular linkages that bind selectively to either gold or nickel.

“[The different metallic segments] allow for the attachment of biofunctionalities to the nanorods in a spatially defined manner,” explained Leong. The researchers say they could also add extra segments to the nanorods and bind additional functionalities, such as an endosomolytic agent, to them, or add magnetic segments so that they could manipulate the nanorods with an external magnetic field.

In vitro and in vivo experiments showed promising results for the gene-delivery system. According to Leong, the obvious application for the technique is in genetic immunization. “Plasmid DNA encoding the antigen can be delivered by these nanorods in conjunction with a gene gun, which can shoot the nanorods into the dermal tissue,” he said.

Now, the researchers, who reported their work in Nature Materials, plan to improve the efficiency with which the nanorods deliver genes.