No abstract

Manipulation and navigation of micro and nanoswimmers in different fluid environments can be achieved by chemicals, external fields, or even motile cells. Many researchers have selected magnetic fields as the active external actuation source based on the advantageous features of this actuation strategy such as remote and spatiotemporal control, fuel-free, high degree of reconfigurability, programmability, recyclability, and versatility. This review introduces fundamental concepts and advantages of magnetic micro/nanorobots (termed here as “MagRobots”) as well as basic knowledge of magnetic fields and magnetic materials, setups for magnetic manipulation, magnetic field configurations, and symmetry-breaking strategies for effective movement. These concepts are discussed to describe the interactions between micro/nanorobots and magnetic fields. Actuation mechanisms of flagella-inspired MagRobots (i.e., corkscrew-like motion and traveling-wave locomotion/ciliary stroke motion) and surface walkers (i.e., surface-assisted motion), applications of magnetic fields in other propulsion approaches, and magnetic stimulation of micro/nanorobots beyond motion are provided followed by fabrication techniques for (quasi-)spherical, helical, flexible, wire-like, and biohybrid MagRobots. Applications of MagRobots in targeted drug/gene delivery, cell manipulation, minimally invasive surgery, biopsy, biofilm disruption/eradication, imaging-guided delivery/therapy/surgery, pollution removal for environmental remediation, and (bio)sensing are also reviewed. Finally, current challenges and future perspectives for the development of magnetically powered miniaturized motors are discussed.

Beyond graphene, transitional metal dichalcogenides, and black phosphorus, there are other layered materials called metal thiophosphites (MPS), which are recently attracting the attention of scientists. Here we present the synthesis, structural and morphological characterization, magnetic properties, electrochemical performance, and the calculated density of states of different layered metal thiophosphite materials with a general formula MPS, and as a result of varying the metal component, we obtain CrPS, MnPS, FePS, CoPS, NiPS, ZnPS, CdPS, GaPS, SnPS, and BiPS. SnPS, ZnPS, CdPS, GaPS, and BiPS exhibit only diamagnetic behavior due to core electrons. By contrast, trisulfides with M = Mn, Fe, Co, and Ni, as well as CrPS, are paramagnetic at high temperatures and undergo a transition to antiferromagnetic state on cooling. Within the trisulfides series the Néel temperature characterizing the transition from paramagnetic to antiferromagnetic phase increases with the increasing atomic number and the orbital component enhancing the total effective magnetic moment. Interestingly, in terms of catalysis NiPS, CoPS, and BiPS show the highest efficiency for hydrogen evolution reaction (HER), while for the oxygen evolution reaction (OER) the highest performance is observed for CoPS. Finally, MnPS presents the highest oxygen reduction reaction (ORR) activity compared to the other MPS studied here. This great catalytic performance reported for these MPS demonstrates their promising capabilities in energy applications.

2D materials are at the forefront of materials research, advancing in applications for biomedical and bio/sensing. We elucidate properties of 2D materials beyond graphene that are relevant to those applications, as well as their correlation with toxicity.

Blackp hosphorus is al ayered material that is sensitive to the surrounding atmosphere.T his is generally considered as ad isadvantage,e specially when compared to more stable layered compounds,s uch as graphite or MoS 2 . This sensitivity is now turned into an advantage.Avapor sensor that is based on layered black phosphorus and uses electrochemical impedance spectroscopya st he detection method is presented;t he device selectively detects methanol vapor.The impedance phase measured at aconstant frequency is used as adistinctive parameter for the selective quantification of methanol, and increases with the methanol concentration. The low detection limit of 28 ppm is well below the approved exposure limit of 200 ppm. The results are highly reproducible, and the vapor sensor is shown to be very selective in the presence of other vapors and to have long-term stability.

Black phosphorus is an emerging layered material. Its nanoparticles show an increased bandgap when compared to bulk materials and they are typically fabricated by ultrasonication of macroscopic black phosphorus crystals. Here we fabricate black phosphorus nanoparticles (BP NPs) by solution based electrochemical exfoliation with bipolar electrodes, which induces opposite potentials on the opposite ends of black phosphorus macroparticles thereby leading to its decomposition into nanoparticles. BP NPs have enhanced catalytic effect on the hydrogen evolution reaction (HER) relative to black phosphorus macroparticles. We utilize black phosphorus nanoparticles as electrocatalytic tags in a competitive immunoassay for rabbit immunoglobulin G (IgG) detection. The detection signal is produced via nanoimpacts of the BP NPs followed by HER catalysis.

Transition metal carbides, known as MXenes, are generated via the selective etching of "A" layers from their layered, ternary parent compounds, MAX phases, where M corresponds to early d-transition metal, A being a main group sp-element from either Group 13 or 14 and carbon or nitrogen being denoted by X. MXenes are being recognized as a new and uprising class of 2D materials with extraordinary physical and electrochemical properties. The huge specific surface area and outstanding electrical conductivity of MXenes, make them ideal candidates for sensing and energy applications. Herein, we demonstrated the successful incorporation of pristine MXene, Ti 3 C 2 produced via HF etching and subsequent delamination with TBAOH, as a transducer platform toward the development of a second generation electrochemical glucose biosensor. Chronoamperometric studies demonstrate that the proposed biosensing system exhibits high selectivity and excellent electrocatalytic activity toward the detection of glucose, spanning over wide linear ranges of 50−27 750 μM and possess a low limit of detection of 23.0 μM. The findings reported in this study conceptually proves the probable applications of pristine MXenes toward the field of biosensors and pave ways for the future developments of highly selective and sensitive electrochemical biosensors for biomedical and food sampling applications.

Two-dimensional transition metal dichalcogenides (TMDs) have been in the spotlight for their intriguing properties, including a tunable band gap and fast heterogeneous electron-transfer (HET) rate. Understandably, they are especially attractive in the field of electrochemical biosensors. In this article, HET capabilities of various TMDs (MoS, MoSe, WS, and WSe) within group VI chemically exfoliated via t-BuLi intercalation are studied and these capabilities are used in the second generation electrochemical glucose biosensor. Strikingly, tungsten dichalcogenides (WS and WSe) exhibit superior HET properties compared to that of their molybdenum counterparts (MoS and MoSe). When incorporated into second generation glucose biosensors, WS and WSe generated a higher electrochemical responses than that of MoS and MoSe, following the same trend as expected. The commendable performance by WX is attributed to the dominance of 1T phase, revealed by characterization data. The developed and optimized 1T WX-based biosensor achieved analytical requirements of selectivity, wide linear ranges, as well as low limits of detection and quantification. The outstanding electrochemical performances of WS and WSe are to be recognized, adding on to the fact that they are not decorated with any metal nanoparticles. This is imperative to showcase the real potential of two-dimensional TMDs in electrochemical biosensors.