Fig. 6: Microassembly of multisized building blocks using optical tweezers.

a SEM image of a 3D pyramid assembled from streptavidin-coated 1 µm polystyrene spheres and biotin-coated 2 µm polystyrene spheres. The small spots are defects resulting from metal coating for SEM imaging. Inset: 3D layout of the structure, with green spheres corresponding to a biotin-functionalized coating and blue spheres corresponding to a streptavidin-functionalized coating. b Series of bright-field optical microscope images at varying elevations to capture the planes that contain the 2 µm PS spheres. c Series of epifluorescence microscope images obtained using a Texas Red filter set, captured for the same field of view and elevations as shown in b. These images demonstrate the pink-fluorescent nature of the 2 µm building blocks.