Figure 2: 3D reconstruction of two representative DNA-nanogold conjugates by IPET.

(a) The OpNS samples of DNA-nanogold conjugates were imaged using ET from a series of tilt angles (from −60° to +60° at 1.5° intervals). Three targeted particles (yellow circled) with their orthogonal views are indicated by the linked dashed arrows in the three selected ET tilt micrographs. The relative tilt angles are indicated in each image, and the axis of the tilt is vertical to the images. (b) Nine representative tilt images of the first targeted individual particle are displayed in the first column from the left (SNR of DNA portion: ∼0.31). Using IPET, the tilt images (after CTF correction) were gradually aligned to a common centre for 3D reconstruction via an iterative refinement process. The projections of the intermediate and final 3D reconstructions at the corresponding tilt angles are displayed in the next four columns according to their corresponding tilt angles. (c) Final IPET 3D density map of the targeted individual particle (SNR of DNA portion: ∼2.44). (d) The final 3D density map and its overlaid 3D density maps (final map in blue and its reversed map in gold) indicated the overall conformation of the DNA-nanogold conjugates. (e) The FSC analyses under including (black line) and excluding (red line) nanogold portions (two density maps reconstructed from odd and even numbers of tilt images) revealed that the resolutions of the IPET 3D density map were both ∼14.7 Å. (f–i) The 3D density map of a second individual DNA-nanogold conjugate was reconstructed from the tilt images (SNR of DNA portion: ∼0.56) using IPET. The FSC analysis showed that the 3D reconstruction resolution (SNR of DNA portion: ∼3.26) was ∼17.1 Å. Scale bars=20 nm (a) and 10 nm (d,h).