Capillary origami as a new method for obtaining folded structures with interior nanoparticle coating

•Capillary origami is used to coat inside of 3D enclosures with nanoparticles.•First method to form a 3D structure while coating with nanoparticles.•Iron-oxide and gold nanoparticle coated folded surfaces were obtained.•Surfaces in triangular, rectangular and cubic forms were achieved.•Particle distribution with respect to the surface orientation is studied. We introduce capillary origami as a new method to obtain 3D enclosures with coated nanoparticles on their inner surfaces. When a liquid droplet that contains nanoparticles is placed on the surface of a thin and flexible membrane, the membrane folds around the droplet. As the droplet evaporates nanoparticles deposit on folded surfaces and eventually a 3D enclosure is obtained. In this study, both magnetic iron-oxide (Fe3O4) and gold (Au) nanoparticles are used and it is shown that with both types of nanoparticles the enclosures remain closed after the complete evaporation of the droplet. It is also demonstrated that the magnetic nanoparticles can be concentrated at a chosen location on the folded geometry by using a magnet during evaporation. The origami based coating method is applied on different geometries and distribution of nanaparticles depending on the surface orientation is quantified. As part of the study, the capillary origami behavior of liquids with and without nanoparticles is compared. [Display omitted]