Active self-assembly of colloidal machines with passive rotational parts via coordination of phoresis and osmosis.

The organization of microscopic objects into specific structures with movable parts is a prerequisite for building sophisticated micromachines with complex functions, as exemplified by their macroscopic counterparts. Here we report the self-assembly of active and passive colloids into micromachinery with passive rotational parts. Depending on the attachment of the active colloid to a substrate, which varies the degrees of free freedom of the assembly, colloidal machines with rich internal rotational dynamics are realized. Energetic analysis reveals that the energy efficiency increases with the degrees of freedom of the machine. The experimental results can be rationalized by the cooperation of phoretic interaction and osmotic flow encoded in the shape of the active colloid, which site-specifically binds and exerts a torque to passive colloids, supported by finite element calculations and mesoscale simulations. Our work offers a new design principle that utilizes nonequilibrium interfacial phenomena for spontaneous construction of multiple-component reconfigurable micromachinery.

Photoactive and Intrinsically Fuel Sensing Metal-Organic Framework Motors for Tailoring Collective Behaviors of Active-Passive Colloids.

Microorganisms display nonequilibrium predator-prey behaviors, such as chasing-escaping and schooling via chemotactic interactions. Even though artificial systems have revealed such biomimetic behaviors, switching between them by control over chemotactic interactions is rare. Here, a spindle-like iron-based metal-organic framework (MOF) colloidal motor which self-propels in glucose and H2 O2 , triggered by UV light is reported. These motors display intrinsic UV light-triggered fuel-dependent chemotactic interactions, which are used to tailor the collective dynamics of active-passive colloidal mixtures. In particular, the mixtures of active MOF motors with passive colloids exhibit distinctive "chasing-escaping" or "schooling" behaviors, depending on glucose or hydrogen peroxide being used as the fuel. The transition in the collective behaviors is attributed to an alteration in the sign of ionic diffusiophoretic interactions, resulting from a change in the ionic clouds produced. This study offers a new strategy on tuning the communication between active and passive colloids, which holds substantial potentials for fundamental research in active matter and practical applications in cargo delivery, chemical sensing, and particle segregation.

Cell-Mimic Directional Cargo Transportation in a Visible-Light-Activated Colloidal Motor/Lipid Tube System.

Active tether and transportation of cargoes on cytoskeletal highway enabled by molecular motors is key for accurate delivery of vesicles and organelles in the complex intracellular environment. Here, a hybrid system composed of colloidal motors and self-assembled lipid tubes is designed to mimic the subcellular traffic system in living cells. The colloidal motors, composed of gold-coated hematite, display light-activated self-propulsion tunable by the light intensity and the concentration of hydrogen peroxide fuel. Importantly, the motors show light-switchable binding with lipid cargoes and attachment to the lipid tubes, whereby the latter act as the motor highways. Upon assembly, the colloidal motor/lipid tube system demonstrates directional delivery of lipid vesicles, emulating intracellular transportation. The assembly and function of the hybrid system are rationalized by a cooperative action of light-triggered electrophoretic and hydrodynamic effects, supported by finite element analysis. A synthetic analog of the biological protein motor/cytoskeletal filament system is realized for the manipulation and delivery of different matter at the microscale, which is expected to be a promising platform for various applications in materials science, nanotechnology, microfluidics, and synthetic biology.

Inorganic-Organic Hybrid Copolymeric Colloids as Multicolor Emission, Fuel-Free, UV- and Visible-Light-Actuated Micropumps.

Light-actuated micromachines are of enormous interest due to their ability to harvest light for triggering catalytic reactions to acquire free energy for mechanical work. This work presents an inorganic-organic hybrid copolymeric poly(cyclotriphosphazene-co-barbituric acid) colloid, which displays multiwavelength excited emission and catalytic activities, exploiting the unique structural, chemical, and optical features of inorganic heterocyclic ring hexachlorocyclotriphosphazene and organic co-monomer barbituric acid. Specifically, this work reveals particle-resolved unusual multicolor emission under excitation with the same or different wavelengths of light using fluorescence microscopy. The result is rationalized by density functional theory studies. In this work, the authors find that emission is coincident with fluorometric measurements, and the photocatalytic properties are anticipated from the overall band structure. This work also demonstrates the use of these colloids as micropumps, which can be remotely activated by UV, blue, and green lights under fuel-free conditions, and ascribe the behavior to ionic diffusiophoresis arising from light-triggered generation of H+ and other charged species. This work offers a new class of polymeric colloids with multiple-wavelength excited emission and catalytic activities, which is expected to open new opportunities in the design of fuel-free, photo-actuated micromachines and active systems.

Light-Activated Fuel-Free Janus Metal Organic Framework Colloidal Motors for the Removal of Heavy Metal Ions.

Light-powered fuel-free colloidal motors possess significant potential for practical applications ranging from nanomedicine to environmental remediation. However, current light-powered colloidal motors often require the incorporation of expensive metals or high concentrations of toxic chemical fuels, which is a severe limitation for their practical applications. Integrating highly ordered and porous materials with a large surface area into colloidal motors is a promising strategy for upsurging their self-propelled speed and adsorption, which will benefit many applications. Here, highly efficient, fuel-free, and light-activated metal organic framework (MOF)-3-trimethoxysilyl propyl methacrylate Janus colloidal motors with a hierarchical morphology are reported. These colloidal motors can be driven by UV or visible light, with a self-propelled speed tuned by the light intensity. The speed can be further enhanced by morphology optimization or by the addition of H2O2 as a fuel. The colloidal motors display a superior efficiency in removing heavy metal ions of Hg, which is up to ∼90% within 40 min from the contaminated water, attributed to their high surface area, hierarchical morphology, large number of active sites, and high mobility. This work not only offers a facile approach to incorporate a versatile MOF family into the design of fuel-free and light-powered Janus colloidal motors, but also demonstrates their potential for real-life applications such as environmental remediation.

Morphology Control of Novel Cross-Linked Ferrocenedimethanol Derivative Cyclophosphazenes: From Microspheres to Nanotubes and Their Enhanced Physicochemical Performances.

Polyphosphazenes have grabbed focal attention in materials research due to their structural diversity, intrinsic backbone stability, and capability to form hybrid molecules. Herein, for the first time, we report morphology-controlled cross-linked hybrid nanotubes and microspheres composed of a novel iron-containing poly(ferrocenedimethano)cyclotriphosphazene synthesized via a facile polycondensation between 1,1'-ferrocenedimethanol and hexachlorocyclotriphosphazene. The morphology was tuned by introducing two sets of mixed solvent systems that are tetrahydrofuran:acetonitrile and acetone:toluene mixtures, for the growth of nanotubes and microspheres, respectively. A growth mechanism for nanotubes and microspheres has been proposed. The nanotubes exhibited intrinsic paramagnetic properties (saturation magnetization of 53 emu/g and coercivity of 19.6) and fluorescence emission (2450 au) as compared to microspheres owing to their remarkable cross-linked structure. Both nanotubes and microspheres demonstrated significant potential to absorb negatively charged hazardous methyl orange dye, and their adsorption capacities came out under the range of 880-2235 and 737-2125 mg g-1, respectively. This facile fabrication route is anticipated to open a new window for structural manipulation of other metal-containing polymers for improved physicochemical properties.