Phototaxis is commonly observed in motile photosynthetic microorganisms. For example, green algae are capable of swimming towards a light source (positive phototaxis) to receive more energy for photosynthesis, or away from a light source (negative phototaxis) to avoid radiation damage or to hide from predators. Recently, with the aim of applying nanoscale machinery to biomedical applications, various inorganic nanomotors based on different propulsion mechanisms have been demonstrated. The only method to control the direction of motion of these self-propelled micro/nanomotors is to incorporate a ferromagnetic material into their structure and use an external magnetic field for steering. Here, we show an artificial microswimmer that can sense and orient to the illumination direction of an external light source. Our microswimmer is a Janus nanotree containing a nanostructured photocathode and photoanode at opposite ends that release cations and anions, respectively, propelling the microswimmer by self-electrophoresis. Using chemical modifications, we can control the zeta potential of the photoanode and program the microswimmer to exhibit either positive or negative phototaxis. Finally, we show that a school of microswimmers mimics the collective phototactic behaviour of green algae in solution.

Two-dimensional atomic crystals, such as two-dimensional oxides, have attracted much attention in energy storage because nearly all of the atoms can be exposed to the electrolyte and involved in redox reactions. However, current strategies are largely limited to intrinsically layered compounds. Here we report a general strategy that uses the surfaces of water-soluble salt crystals as growth templates and is applicable to not only layered compounds but also various transition metal oxides, such as hexagonal-MoO3, MoO2, MnO and hexagonal-WO3. The planar growth is hypothesized to occur via a match between the crystal lattices of the salt and the growing oxide. Restacked two-dimensional hexagonal-MoO3 exhibits high pseudocapacitive performances (for example, 300 F cm−3 in an Al2(SO4)3 electrolyte). The synthesis of various two-dimensional transition metal oxides and the demonstration of high capacitance are expected to enable fundamental studies of dimensionality effects on their properties and facilitate their use in energy storage and other applications.

Over the last decades, scientists have endeavored to develop nanoscopic machines and envisioned that these tiny machines could be exploited in biomedical applications and novel material fabrication. Here, a visible-/near-infrared light-driven nanomotor based on a single silicon nanowire is reported. The silicon nanomotor harvests energy from light and propels itself by the self-electrophoresis mechanism. Due to the high efficiency, the silicon nanowire can be readily driven by visible and near-infrared illumination at ultralow light intensity (≈3 mW cm ). The experimental study and numerical simulation also show that the detailed structure around the concentrated reaction center determines the migration behavior of the nanomotor. Importantly, due to the optical resonance inside the silicon nanowire, the spectral response of the nanowire-based nanomotor can be readily modulated by the nanowire's diameter. Compared to other methods, light controlling potentially offers more freedom and flexibility, as light can be modulated not only with its intensity and direction, but also with the frequency and polarities. This nanowire motor demonstrates a step forward to harness the advantages of light, which opens up new opportunities for the realization of many novel functions such as multiple channels communication to nanorobots and controllable self-assembly.