Chemically powered micro- and nanomotors are small devices that are self-propelled by catalytic reactions in fluids. Taking inspiration from biomotors, scientists are aiming to find the best architecture for self-propulsion, understand the mechanisms of motion, and develop accurate control over the motion. Remotely guided nanomotors can transport cargo to desired targets, drill into biomaterials, sense their environment, mix or pump fluids, and clean polluted water. This Review summarizes the major advances in the growing field of catalytic nanomotors, which started ten years ago.

In this tutorial review we describe the recent progress on catalytic microtubular engines fabricated by rolled-up nanotech on polymers. We summarize the technical aspects of the technology and the basic principles that cause the catalytic microengines to self-propel in fuel solutions. The control over speed, directionality and interactions of the microengines to perform tasks such as cargo transportation is also discussed. We compare this technology to other fabrication techniques of catalytic micro-/nanomotors and outline challenges and opportunities for such engines in future studies. Since rolled-up nanotech on polymers can easily integrate almost any type of inorganic material, huge potential and advanced performance such as high speed, cargo delivery, motion control, and dynamic assembly are foreseen--ultimately promising a practical way to construct versatile and intelligent catalytic tubular microrobots.

Achieving control over the directionality of active colloids is essential for their use in practical applications such as cargo carriers in microfluidic devices. So far, guidance of spherical Janus colloids was mainly realized using specially engineered magnetic multilayer coatings combined with external magnetic fields. Here we demonstrate that step-like submicrometre topographical features can be used as reliable docking and guiding platforms for chemically active spherical Janus colloids. For various topographic features (stripes, squares or circular posts), docking of the colloid at the feature edge is robust and reliable. Furthermore, the colloids move along the edges for significantly long times, which systematically increase with fuel concentration. The observed phenomenology is qualitatively captured by a simple continuum model of self-diffusiophoresis near confining boundaries, indicating that the chemical activity and associated hydrodynamic interactions with the nearby topography are the main physical ingredients behind the observed behaviour.

We describe the use of catalytically self-propelled microjets (dubbed micromotors) for degrading organic pollutants in water via the Fenton oxidation process. The tubular micromotors are composed of rolled-up functional nanomembranes consisting of Fe/Pt bilayers. The micromotors contain double functionality within their architecture, i.e., the inner Pt for the self-propulsion and the outer Fe for the in situ generation of ferrous ions boosting the remediation of contaminated water.The degradation of organic pollutants takes place in the presence of hydrogen peroxide, which acts as a reagent for the Fenton reaction and as main fuel to propel the micromotors. Factors influencing the efficiency of the Fenton oxidation process, including thickness of the Fe layer, pH, and concentration of hydrogen peroxide, are investigated. The ability of these catalytically self-propelled micromotors to improve intermixing in liquids results in the removal of organic pollutants ca. 12 times faster than when the Fenton oxidation process is carried out without catalytically active micromotors. The enhanced reaction–diffusion provided by micromotors has been theoretically modeled. The synergy between the internal and external functionalities of the micromotors, without the need of further functionalization, results into an enhanced degradation of nonbiodegradable and dangerous organic pollutants at small-scale environments and holds considerable promise for the remediation of contaminated water.

Recently a significant amount of attention has been paid towards the development of man‐made synthetic catalytic micro‐ and nanomotors that can mimic biological counterparts in terms of propulsion power, motion control, and speed. However, only a few applications of such self‐propelled vehicles have been described. Here the magnetic control of self‐propelled catalytic Ti/Fe/Pt rolled‐up microtubes (microbots) that can be used to perform various tasks such as the selective loading, transportation, and delivery of microscale objects in a fluid is shown; for instance, it is demonstrated for polystyrene particles and thin metallic films (“nanoplates”). Microbots self‐propel by ejecting microbubbles via a platinum catalytic decomposition of hydrogen peroxide into oxygen and water. The fuel and surfactant concentrations are optimized obtaining a maximum speed of 275 µm s−1 (5.5 body lengths per second) at 15% of peroxide fuel. The microbots exert a force of around 3.77 pN when transporting a single 5 µm diameter particle; evidencing a high propulsion power that allows for the transport of up to 60 microparticles. By the introduction of an Fe thin film into the rolled‐up microtubes, their motion can be fully controlled by an external magnetic field.

The development of synthetic nanomotors for technological applications in particular for life science and nanomedicine is a key focus of current basic research. However, it has been challenging to make active nanosystems based on biocompatible materials consuming nontoxic fuels for providing self-propulsion. Here, we fabricate self-propelled Janus nanomotors based on hollow mesoporous silica nanoparticles (HMSNPs), which are powered by biocatalytic reactions of three different enzymes: catalase, urease, and glucose oxidase (GOx). The active motion is characterized by a mean-square displacement (MSD) analysis of optical video recordings and confirmed by dynamic light scattering (DLS) measurements. We found that the apparent diffusion coefficient was enhanced by up to 83%. In addition, using optical tweezers, we directly measured a holding force of 64 ± 16 fN, which was necessary to counteract the effective self-propulsion force generated by a single nanomotor. The successful demonstration of biocompatible enzyme-powered active nanomotors using biologically benign fuels has a great potential for future biomedical applications.

We fabricated self-powered colloidal Janus motors combining catalytic and magnetic cap structures, and demonstrated their performance for manipulation (uploading, transportation, delivery) and sorting of microobjects on microfluidic chips. The specific magnetic properties of the Janus motors are provided by ultrathin multilayer films that are designed to align the magnetic moment along the main symmetry axis of the cap. This unique property allows a deterministic motion of the Janus particles at a large scale when guided in an external magnetic field. The observed directional control of the motion combined with extensive functionality of the colloidal Janus motors conceptually opens a straightforward route for targeted delivery of species, which are relevant in the field of chemistry, biology, and medicine.

A new biohybrid micro-robot is developed by capturing bovine sperm cells inside magnetic microtubes that use the motile cells as driving force. These micro-bio-robots can be remotely controlled by an external magnetic field. The performance of micro-robots is described in dependence on tube radius, cell penetration, and temperature. The combination of a biological power source and a microdevice is a compelling approach to the development of new microrobotic devices with fascinating future applications.