a, Assembly between multivalent dsRBD and siRNA–targeting-ligand bioconjugates, resulting in cargo loading with precisely controlled stoichiometry and highly accessible targeting ligands. b, Oligomerization of dsRBD–azide on eight-arm DBCO–PEG via copper-free click chemistry. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) indicates that increasing molar ratio of dsRBD over PEG eventually leads to saturated PEGylation (formation of octamer). c, Separation of dsRBD octamer from excess dsRBD using Superdex 200 size-exclusion chromatography. d, Titration of varying amounts of dsRBD octamer (from left to right: 0, 1.25, 2.5, 5, 10, 15, 20 and 40 pmol) with a fixed quantity (20 pmol) of fluorescein amidite-labelled siRNA. RNP8 is obtained at molar ratio 16/1 and 8/1 (second and third lanes from the left). More dsRBD octamer leads to unsaturated octamer with smaller gel shifts (fourth to eighth lanes). Additional fine titration studies near ratio 8 can be found in Supplementary Fig. 4. e, Stability of RNP8 in 50% mouse serum at 37 °C. Dissociated siRNA is quantified against the pure siRNA band (first lane). Quantitative dot plot of the gel band fluorescence intensities is shown in Supplementary Fig. 5. The dissociation is slow with a half-life of approximately 18 h. f, TEM micrograph of RNP8 stained by uranyl formate showing uniform and compact nanoparticles. g, Selected raw images of seven representative RNP8 particles. Raw images are shown in the upper row, and the corresponding low-pass filter processed and masked noise-reduced images are shown in the middle and bottom rows, respectively.