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Abstract Microswimmers are self‐propelled particles that navigate fluid environments, offering significant potential for applications in environmental pollutant decomposition, biosensing, and targeted drug delivery. Their performance relies on engineered catalytic surfaces. Gold nanoclusters (AuNCs), with atomically precise structures, tunable optical properties, and high surface area‐to‐volume ratio, provide a new optimal catalyst for enhancing microswimmer propulsion. Unlike bulk gold or nanoparticles, AuNCs may deliver tunable photocatalytic activity and increased catalytic specificity, making them ideal co‐catalysts for hybrid microswimmers. For the first time, this study combines AuNCs with TiO₂/Cr₂O₃Janus microswimmers, combining the unique properties of both materials. This hybrid system capitalizes on the tuned optical properties of AuNCs and their role as co‐catalysts with TiO₂, driving enhanced photocatalytic performance under ultraviolet (UV) excitation. Using motion analysis, it is shown that the AuNC‐microswimmers exhibit significantly greater propulsion and mean squared displacement (MSD) as compared to controls. These findings suggest that the integration of nanoclusters with semiconductor materials enables state of the art, light‐switchable microswimmers. These AuNC‐microswimmer systems may thus offer new opportunities for environmental catalysis and other applications, providing precise control over catalytic and motile behaviors at the microscale. 

Abstract Active colloidal microcrystallites capable of generating flow patterns around or through their porous network are introduced, which in combination with “free microspheres,” create self‐assembled active clusters with multiple moving parts. Fluid flow draws microspheres within a microcrystallite's local environment toward—and aggregate at—the edge of the microcrystallite, where the previously translational movement transitions to continuous spinning. These experiments show that the spinning frequency decreases with an increase in diameter and that when the center of mass of a spinning particle is shifted off‐center—here Janus spheres—a time‐varying angular frequency is observed. Weight‐anisotropy also leads to a particularly intriguing phenomenon, which manifests as the spontaneous realignment of the rotational axis to a preferential direction; this effect is attributed to a gravitropic self‐correcting mechanism. Thus, the dynamics of the self‐assembled active structure remains stable over long time periods, despite being subjected to significant noise, for example, Brownian forces. 

Abstract Self‐propelled colloids are primed to become scaled up, nano‐ and microscale inorganic analogues of molecular motors and machines. In order to advance toward the ambitious goal of employing such active particles to form genuine man‐made small scale machinery, a significantly diversified library of particle types, capable of a wide range of motive behaviors, must be available. Here, it is shown that the dynamics of photoactivated, self‐phoretic particles can be engineered by targeted design of metal–semiconductor heterojunctions. This effect is demonstrated with three different microswimmers consisting of an elongated semiconducting tail made from anatase titanium dioxide; all three of which would otherwise be identical absent vapor‐deposited coatings of gold at different locations on the tails. The specific location of the heterojunction determines the swimming behavior for each type. Although here only one shape and material combination is focused upon, engineering active particles with site‐specific metal–semiconductor heterojunctions is a general technique for achieving desired kinematic behavior in active colloidal matter.