We designed a 3D DNA origami nanoparticle with a relatively flat structure and an affinity to the DNA condensate, which are expected to be suitable properties for stabilizing the DNA condensate interface. The 3D DNA origami had the shape of a hollow hexagonal prism (28 nm in side length, 8 nm in height) (Figures and). The 3D DNA origami has two types of single-stranded DNAs (ssDNAs) named condensate-binding tag and origami-connecting tag. To coat a DNA condensate with 3D DNA origami, a 'binder' binds a condensate-binding tag of the 3D DNA origami with an origami-binding motif in the DNA condensate (Figures and). The binding valence of 3D DNA origami is tunable from 0 to 40 by changing the number of the condensate-binding tags (Figure ). After the coating, the input of a 'connector' can connect the 3D DNA origami by the hybridization of the connector with origami-connecting tags (Figures (ii) and S4), changing the solidity of the DNA origami coating. The generation and purification of the 3D DNA origami were explained in the Experimental Section and Tables S2-S5.