We recommend to dissolve the single stranded RNA in 1X TE buffer (prepared under RNase-free conditions(10 mM TrisCl, pH7.5, 0.1 mM EDTA). This buffers the pH and chelates metal ions that can contribute to RNA degradation. RNase-free water is also acceptable. Duplex RNA (siRNA) comes lyophilized from 10 mM Tris-HCL, pH 8.0, 20 mM NaCl, 1 mM EDTA. Resuspending in the appropriate amount of water to bring the RNA conc. to 20 µM will reconstitute the buffer to the same.