Autonomously Propelled Motors for Value-Added Product Synthesis and Purification

Thread-Like Radical-Polymerization via Autonomously Propelled (TRAP) Bots

Micromotor-mediated synthesis of thread-like hydrogel microstructures in an aqueous environment is presented. The study utilizes a catalytic micromotor assembly (owing to the presence of a Pt layer), with an on-board chemical reservoir (i.e., polymerization mixture), toward thread-like radical-polymerization via autonomously propelled bots (i.e., TRAP bots). Synergistic coupling of catalytically active Pt layer, together with radical initiators (H₂ O₂ and FeCl₃ (III)), and PEGDA monomers preloaded into the TRAP bot, results in the polymerization of monomeric units into elongated thread-like hydrogel polymers coupled with self-propulsion. Interestingly, polymer generation via TRAP bots can also be triggered in the absence of hydrogen peroxide for cellular/biomedical application. The resulting polymeric hydrogel microstructures are able to entrap living cells (NIH 3T3 fibroblast cells), and are easily separable via a centrifugation or magnetic separation (owing to the presence of a Ni layer). The cellular biocompatibility of TRAP bots is established via a LIVE/DEAD assay and MTS cell proliferation assay (7 days observation). This is the first study demonstrating real-time in situ hydrogel polymerization via an artificial microswimmer, capable of enmeshing biotic/abiotic microobjects in its reaction environment, and lays a strong foundation for advanced applications in cell/tissue engineering, drug delivery, and cleaner technologies.

Micromotors for drug delivery in vivo: The road ahead

Autonomously propelled/externally guided micromotors overcome current drug delivery challenges by providing (a) higher drug loading capacity, (b) localized delivery (less toxicity), (c) enhanced tissue penetration and (d) active maneuvering in vivo. These microscale drug delivery systems can exploit biological fluids, as well as exogenous stimuli, like light-NIR, ultrasound and magnetic fields (or a combination of these), towards propulsion/drug release. Ability of these wireless drug carriers towards localized targeting and controlled drug release, makes them a lucrative candidate for drug administration in complex microenvironments (like solid tumors or gastrointestinal tract). In this report, we discuss these microscale drug delivery systems for their therapeutic benefits under in vivo setting and provide a design-application rationale towards greater clinical significance. Also, a proof-of-concept depicting 'microbots-in-a-capsule' towards oral drug delivery has been discussed.

Lab-on-a-micromotor: catalytic Janus particles as mobile microreactors for tailored synthesis of nanoparticles

Catalytic Janus micromotors encapsulating Cd2+ or citrate are used here as mobile microreactors for "on the fly" CdS quantum dot and gold nanoparticle synthesis. Micromotor navigation in microliter "reagent solutions" results in the generation of the corresponding nanoparticles inside the micromotor body with high yield and negligible waste generation. Nanoparticle generation can be attributed to convective diffusion of reagents into the moving reactor body. "On-demand" modulation of nanoparticle size and catalytic activities can be achieved by judicious control of the motion behavior of the microreactor. The use of confined reagents in connection with such enhanced movement allows for efficient operation in very low (less than 800 μL) volumes. The new microreactors developed here hold considerable promise for reactions in aqueous environments for novel synthetic schemes in different sites along with multiplexed capabilities for a myriad of catalytic reactions.

Sensitive Monitoring of Enterobacterial Contamination of Food Using Self-Propelled Janus Microsensors

Food poisoning caused by bacteria is a major cause of disease and death worldwide. Herein we describe the use of Janus micromotors as mobile sensors for the detection of toxins released by enterobacteria as indicators of food contamination. The micromotors are prepared by a Pickering emulsion approach and rely on the simultaneous encapsulation of platinum nanoparticles for enhanced bubble-propulsion and receptor-functionalized quantum dots (QDs) for selective binding with the 3-deoxy-d-manno-oct-2-ulosonic acid target in the endotoxin molecule. Lipopolysaccharides (LPS) from Salmonella enterica were used as target endotoxins, which upon interaction with the QDs induce a rapid quenching of the native fluorescence of the micromotors in a concentration-dependent manner. The micromotor assay can readily detect concentrations as low as 0.07 ng mL^-1 of endotoxin, which is far below the level considered toxic to humans (275 μg mL^-1). Micromotors have been successfully applied for the detection of Salmonella toxin in food samples in 15 min compared with several hours required by the existing Gold Standard method. Such ultrafast and reliable approach holds considerable promise for food contamination screening while awaiting the results of bacterial cultures in a myriad of food safety and security defense applications.

Bionic Manufacturing: Towards Cyborg Cells and Sentient Microbots

Bio-inspired engineering applies biological design principles towards developing engineering solutions but is not practical as a manufacturing paradigm. We advocate 'bionic manufacturing', a synergistic fusion of biotic and abiotic components, to transition away from bio-inspiration toward bio-augmentation to address current limitations in bio-inspired manufacturing.

Biosensing Strategy for Simultaneous and Accurate Quantitative Analysis of Mycotoxins in Food Samples Using Unmodified Graphene Micromotors

A high-performance graphene-based micromotor strategy for simultaneous, fast, and reliable assessment of two highly concerning mycotoxins (fumonisin B1 (FB1) and ocratoxin A (OTA)) has successfully been developed. The assay principle is based on the selective recognition from aptamers to the target mycotoxins and further "on-the-move" fluorescence quenching of the free aptamer in the outer layer of unmodified reduced graphene (rGO; sensing layer) micromotors. Template-prepared rGO/platinum nanoparticles (PtNPs) tubular micromotors were synthesized rapidly and inexpensively by the direct electrodeposition within the conical pores of a polycarbonate template membrane. The new wash-free approach offers using just 1 μL of sample, a simultaneous and rapid "on-the-fly" detection (2 min) with high sensitivity (limits of detection of 7 and 0.4 ng/mL for OTA and FB1, respectively), and high selectivity. Remarkable accuracy (E_r < 5%) during the mycotoxin determination in certified reference material as well as excellent quantitative recoveries (96-98%) during the analysis of food samples were also obtained. The excellent results obtained allow envisioning an exciting future for the development of novel applications of catalytic micromotors in unexplored fields such as food safety diagnosis.

Autonomously propelled microscavengers for precious metal recovery

We report biogenic micromotor design consisting of porous chalky elongated tubes (∼60 μm length) coated with Fe–Pt for dual functionality i.e. metallic gold formation and rapid isolation.

Ultrafast Nanocrystals Decorated Micromotors for On-Site Dynamic Chemical Processes

CdS-polyaniline-Pt and ZnS-polyaniline-Pt micromotors have been synthesized and characterized. The nanocrystals are generated "in situ" during the template electrosynthesis of the micromotors while being simultaneously trapped in the polymeric network, generating a hybrid structure. The presence of nanocrystal "edges" in the inner polyaniline layer result in a rough Pt catalytic surface and enhanced electron transfer for highly efficient bubble propulsion at remarkable speeds of over 2500 μm/s. The incorporation of CdS and ZnS nanocrystals impart several attractive functions, including cation-exchange based chemical transformation capabilities and enhanced photocatalytic performance. The remarkable ion-exchange properties of ZnS-polyaniline (PANI)-Pt micromotors are illustrated for the cation exchange of heavy metals cations. The superior photocatalytic performance of CdS-PANI-Pt micromotors is used for the enhanced photocatalytic oxidation of bisphenol A. Such self-propelled micromotors act as highly efficient dynamic platforms that offer significantly shorter and more efficient processes as compared with common static operations. The attractive properties of these micromotors will pave the way for diverse sensing, decontamination, energy generation, or electronic applications.