Catalytic Janus particles rely on chemical decomposition to self-propel and have displayed enormous potential for targeted drug delivery and cellular penetration. Catalytic propulsion mechanisms are limiting, however, with fuel requirements and specialized fluid properties being necessary to achieve propulsion. We have improved the dynamic propulsion of catalytic Janus particles by functionalizing flagellar filaments to one of their hemispheres. Flagellated Janus particles, torqued by rotating magnetic fields, swim along their rotation axis using the explicit chirality and flexibility of flagella, mimicking flagellar rotation of live bacteria. Depending on the working fluid, flagellated Janus particles can propel using either catalytic or swimming propulsion. We demonstrate experimentally that flagellated Janus particles behave predictably under the two actuation modes and can precisely follow trajectories under closed-loop feedback control. Flagellated Janus particles were demonstrated to swim in both Newtonian and shear-thickening fluids. These are the first Janus particles developed that can be propelled interchangeably between catalytic and flagellar swimming propulsion, allowing two distinct propulsion mechanisms for future use within in vivo operations.

An analysis of heterogeneously flagellated microswimmers inside viscous fluids is presented. Flagella harvested from Salmonella typhimurium were isolated, repolymerized, and functionalized to have biotin at their ends, allowing for chemical attachment along the surfaces of avidin-coated microparticles. Assembled microswimmers were rotated under incremental magnetic field frequencies, in saline and methylcellulose solutions, to baseline their velocity responses. A mean square displacement analysis revealed that rotating microswimmers exhibited anomalous diffusive behavior at small time scales in each fluid and had increased diffusivity compared with the non-rotating cases. Flagellated microswimmers had decreased diffusivity when compared with non-flagellated microparticles in Brownian conditions. Microswimmers were demonstrated to perform selected trajectories under proportional feedback control with reasonable accuracy. Finally, microswimmer propulsion was shown to be heavily influenced by the handedness of the rotating magnetic fields, with frequency induced reversals of swimming direction observed under clockwise rotation; this effect was determined to be the result of flagellar bundling and unbundling.

A variety of volatile organic compounds (VOCs) are produced and emitted by the human body every day. The identity and concentration of these VOCs reflect an individual’s metabolic condition. Information regarding the production and origin of VOCs, however, has yet to be congruent among the scientific community. This review article focuses on the recent investigations of the source and detection of biological VOCs as a potential for noninvasive discrimination between healthy and diseased individuals. Analyzing the changes in the components of VOC profiles could provide information regarding the molecular mechanisms behind disease as well as presenting new approaches for personalized screening and diagnosis. VOC research has prioritized the study of cancer, resulting in many research articles and reviews being written on the topic. This review summarizes the information gained about VOC cancer studies over the past 10 years and looks at how this knowledge correlates with and can be expanded to new and upcoming fields of VOC research, including neurodegenerative and other noninfectious diseases. Recent advances in analytical techniques have allowed for the analysis of VOCs measured in breath, urine, blood, feces, and skin. New diagnostic approaches founded on sensor-based techniques allow for cheaper and quicker results, and we compare their diagnostic dependability with gas chromatography- and mass spectrometry-based techniques. The future of VOC analysis as a clinical practice and the challenges associated with this transition are also discussed and future research priorities are summarized.