Aptamers are single-stranded DNA (or RNA) molecules selected from millions of possible sequences for their aptitude to bind a specific target. Developed originally as an alternative to antibodies for biotech applications, they have recently found application in sensors and in the treatment of age-related macular degeneration.
Researchers have now very cleverly combined liposome packaging and aptamer targeting to direct chemotherapy (e.g. cisplatin) to tumour cells (e.g. breast cancer). All the known advantages of DNA aptamers apply (non immunogenic, easier to produce and handle than antibodies), and on top of that one gets the chance to call back the attack if it goes wrong, by injecting antisense DNA.
Read my story in Chemistry World (free access to all).
Earlier pieces about aptamers include Chemical Origami (Chem. World 2006, restricted), as well as a chapter in The birds, the bees and the platypuses. I've also reviewed a book about aptamers, review should appear soon.