Inspired by the machines that have changed the world through their autonomous functions, scientists have focused their attention on performing similar functions at the micro/nanoscale. The motility of these micro/nanomachines (micro/nanomotors) offers enormous opportunities for cargo delivery, biodetection, and environmental and biomedical applications. Among the various geometries of micro/nanomotors, a tubular shape provides asymmetric inner and outer surfaces, where the inner wall hosts chemical reactions that supply the moving power and the outer wall can be modified for specific chemical and biological functions. This review describes the concept of tubular micro/nanomotors, including their basic principles, fabrication methods and control over their motion. With the assistance of catalytic reactions, tubular micro/nanomotors can generate a powerful thrust force to navigate in complex natural and in vitro environments. Modification of the tubular micro/nanomotors allows the motors to capture, transport, and release selected cargos on demand. In addition, their application in sensing and decontamination benefits from their collection behavior and self‐mixing effect. Furthermore, noncatalytic reaction‐driven tubular micro/nanomotors, such as redox‐based and biohybrid tubular micro/nanomotors, provide new possibilities for practical in vivo applications. The state‐of‐the‐art tubular micro/nanomotors could offer a promising platform for various applications, e.g., lab‐on‐chip devices and in vivo theranostics.

The motion of catalytic tubular micromotors are driven by the oxygen bubbles generated from chemical reaction and is influenced by the resistance from the liquid environment. Herein, we fabricated a rolled‐up graphene tubular micromotor, in which the graphene layer was adopted as the outmost surface. Due to the hydrophobic property of the graphene layer, the fabricated micromotor performed a motion pattern that could escape from the attraction from the bubbles. In addition, Escherichia coli and Staphylococcus culture experiments proved that the graphene outer surface displays antibacterial property. Considering the bubble‐avoiding and antibacterial properties, the rolled‐up graphene tubular micromotor holds great potential for various applications such as in vivo drug delivery and biosensors.

specific surface area. [1,2] The nontrivial band structure of graphene near the Fermi level enables a series of appealing phenomena, e.g., the anomalous quantum Hall effect, [3] ultrahigh electron mobility, [4] and superior thermal conductivity, [5] rendering it a promising candidate for the next generation of micro/nanoelectronic devices. With respect to its current status and future perspectives, it is of great significance to fully explore the tunability of the properties of graphene by various methods, e.g., doping, [6] gating, [7] and strain engineering. [8,9] Among these approaches, strain engineering is capable of altering the lattice symmetry of graphene, thus tuning its electronic band structure, [10,11] which could be superior in the bandgap opening, [12] conductance modulation, [13,14] and the formation of strong magnetic field. [15] For a realistic graphene-integrated optoelectronic device in an on-chip manner, such as optical modulators, [16] silicongraphene photodetectors, [17,18] and broadband polarizer, [19] strain engineering is desired in order to provide a flexible approach for tuning the electrical structure of graphene. However, developed strain-tuning methods, such as the deformation of flexible substrates, [20,21] piezoelectric substrate actuation, [22] and pressurized blisters, [23] are hardly compatible with onchip applications. Particularly, using the rolling method as a reliable approach for both optimal yields and effective strain manipulation [24][25][26] suggests direct and precise tuning with target morphologies and thus their mechanical properties. [27] Based on rolling geometry, the corresponding strain states in graphene can be designed and accurately realized, as summarized in Figure 1, where the tensile strain in graphene could be introduced through the transfer process of graphene onto conventional semiconductors. [28,29] However, compressive strain in graphene is seldom reported because the critical compressive strain for buckling is several orders of magnitude smaller than the critical tensile strain for fracturing. [30] Furthermore, for a few compressive strain cases, it is essential to explore the fundamental physics of out-of-plane deformation, which often occurs during the compression process.On the other hand, the innovative 3D architecture based on 2D graphene and graphene oxide enables morphologyengineered performance, such as strong mechanical properties, On-chip strain engineering is highly demanded in 2D materials as an effective route for tuning their extraordinary properties and integrating consistent functionalities toward various applications. Herein, rolling technique is proposed for strain engineering in monolayer graphene grown on a germanium substrate, where compressive or tensile strain could be acquired, depending on the designed layer stressors. Unusual compressive strains up to 0.30% are achieved in the rolled-up graphene tubular structures. The subsequent phonon hardening under compressive loading is observed through straininduced Raman G band splittin...

We demonstrate hyperbolic metamaterials (HMMs) on a curved surface for an efficient outcoupling of nonradiative modes, which lead to an enhanced spontaneous emission. Those high-wavevector plasmonic modes can propagate along the curved structure and emit into the far field, realizing a directional light emission with maximal fluorescent intensity. Detailed simulations disclose a high Purcell factor and a spatial power distribution in the curved HMM, which agrees with the experimental result. Our work presents remarkable enhancing capability in both the Purcell factor and emission intensity, which could suggest a unique structure design in metamaterials for potential application in, e.g., high-speed optical sensing and communications.

Exploring micromotors with outstanding propulsion efficiency is of great importance for aspects ranging from enhancement of performance to realization of applications. Improvements in propulsion efficiency lead to a lower fuel requirementand broadens the potential application areas for higher environment compatibility. In this article, a tubular micromotor with catalytic nanoparticle superlattices is fabricated through a simple epitaxial assembly method. A high surface-to-volume ratio due to the use of catalytic nanoparticles, a carbon outer layer and cooperative propulsion of multitubes enables the micromotor to move in biocompatible environment with a low concentration of fuel. In addition, magnetic nanoparticles are integrated into the micromotor to offer effective control of the direction of movement by using a magnetic field. This work provides a simple and low-cost fabrication method for a micromotor with high performance, which is expected to meet practical demands.