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Electric energy is generated when water droplets slide down electrodes coated with a hydrophobic dielectric layer. The principle of energy generation needs to be clarified for the optimization and scalable design of the energy‐harvesting system. In this study, it is shown that droplet energy harvesting is the reverse phenomenon of voltage‐driven droplet actuation or electrowetting‐on‐dielectric (EWOD). For this reverse EWOD, the interfacial energy difference generated between the three‐phase contact line of the advancing and receding part of the droplet is the cause of the generation of electric energy. To prove the effect of interfacial energy on energy harvesting, the wetting property of the dielectric layer is controlled by nanopatterning while maintaining the chemical properties. The width and gap of the electrodes and the droplet size determine whether the harvested voltage waveform is monophasic or biphasic. The energy conversion efficiency is determined by the wetting properties of the surface, and the maximum value is as high as 40%.

Extracellular vesicles (EVs) have emerged as novel biomarkers and therapeutic material. However, the small size (~200 nm) of EVs makes efficient separation challenging. Here, a physical/chemical stress-free separation of EVs based on diffusion through a nanoporous membrane chip is presented. A polycarbonate membrane with 200 nm pores, positioned between two chambers, functions as the size-selective filter. Using the chip, EVs from cell culture media and human serum were separated. The separated EVs were analyzed by nanoparticle tracking analysis (NTA), scanning electron microscopy, and immunoblotting. The experimental results proved the selective separation of EVs in cell culture media and human serum. Moreover, the diffusion-based separation showed a high yield of EVs in human serum compared to ultracentrifuge-based separation. The EV recovery rate analyzed from NTA data was 42% for cell culture media samples. We expect the developed method to be a potential tool for EV separation for diagnosis and therapy because it does not require complicated processes such as immune, chemical reaction, and external force and is scalable by increasing the nanoporous membrane size.