Nanoparticles of double-stranded nucleic acid complexed about a complexing agent such as the melamine derivatives of formulae I and II, preferably forming a trimeric nucleic acid complex. In alternative embodiments, polyarginine or a polymer of Gln and Asn further complexed with the double-stranded nucleic acid complex. In a preferred embodiment, the ds nucleic acid is a double stranded RNA having 15 to 30 base pairs suitable for RNA interference. In another aspect of the invention, a ds RNA is produced in which all of the uridines are changed to 5-methyluridine. Preferably, the resultant ds RNAs have 15 to about 30 base pairs and are suitable for RNA interference.