In vitro selection of RNA sequences that mediate the formation of iron oxide nanoparticles

RNA sequences have been discovered to mediate the formation of magnetic cobalt-doped iron oxide nanoparticles. RNA in vitro selection with magnetic field partitioning was used to evolve an initial library of ∼10 14 unique RNA sequences. Both native and imidazolyl modified RNA combinatorial libraries were subjected to the selection pressure. After eight rounds of the selection, imidazolyl modified and native, families of active RNA sequences were identified. The iron oxide nanoparticles were formed at room temperature and neutral pH, and at low metal precursor concentration (FeCl2 150 muM, CoCl2 37.5 muM). The RNA concentration was significantly lower (0.9 muM), yet crystalline iron oxide nanoparticles were formed rapidly (1 minute) and with a narrow size distribution (2.9 +/- 0.9 nm, 2.7 +/- 0.5 nm for imidazolyl modified and native isolate respectively). The average iron to cobalt ratio was determined to be 28:1 for the modified RNA isolates and 21:1 for native RNA isolates.;The material synthesis was proven RNA and sequence dependant. The isolate I2_96 truncation experiments showed that after shortening the isolate I2_96 and A5 sequences at the 3' ends the RNA still retained its activity in mediating the formation of magnetic iron oxide nanoparticles. However the synthesized nanoparticles were smaller and the overall yield of the product was lower than for the full length sequence.;Various analytical techniques were employed in effort to identify the composition of the synthesized material. It was concluded that the synthesized material was a magnetic iron oxide doped with cobalt; either magnetite (Fe 3O4), maghemite (gamma-Fe2O3) or a mixture of those.;In effort to generate more material the isolate A5, recovered from a native RNA in vitro selection, was genetically encoded into E. coli. The resulting bacteria produced A5 RNA and when grown in presence of 1 mM of FeCl2 and 0.1 mM of sodium citrate they generated spherical, iron containing nanoparticles, about 3 nm in size.