Rapid Iodine Sensing on Mechanically Treated Carbon Nanofibers.

In this work, we report on a rapid, efficient electrochemical iodine sensor based on mechanically treated carbon nanofiber (MCNF) electrodes. The electrode’s highly graphitic content, unique microstructure, and the presence of nitrogen heteroatoms in its atomic lattice contribute to increased heterogeneous electron transfer and improved kinetics compared to conventional pyrolytic carbons. The electrode demonstrates selectivity for iodide ions in the presence of both interfering agents and high salt concentrations. The sensor exhibits clinically relevant limits of detection of 0.59 µM and 1.41 µM, in 1X PBS and synthetic urine, respectively, and a wide dynamic range between 5 µM and 700 µM. These results illustrate the advantages of the material’s unique electrochemical properties for iodide sensing, in addition to its simple, inexpensive fabrication. The reported iodine sensor eliminates the need for specimen processing, revealing its aptitude for applications in point-of-care diagnostics.

Nitrogen-Rich Polyacrylonitrile-Based Graphitic Carbons for Hydrogen Peroxide Sensing.

Catalytic substrate, which is devoid of expensive noble metals and enzymes for hydrogen peroxide (H2O2), reduction reactions can be obtained via nitrogen doping of graphite. Here, we report a facile fabrication method for obtaining such nitrogen doped graphitized carbon using polyacrylonitrile (PAN) mats and its use in H2O2 sensing. A high degree of graphitization was obtained with a mechanical treatment of the PAN fibers embedded with carbon nanotubes (CNT) prior to the pyrolysis step. The electrochemical testing showed a limit of detection (LOD) 0.609 µM and sensitivity of 2.54 µA cm-2 mM-1. The promising sensing performance of the developed carbon electrodes can be attributed to the presence of high content of pyridinic and graphitic nitrogens in the pyrolytic carbons, as confirmed by X-ray photoelectron spectroscopy. The reported results suggest that, despite their simple fabrication, the hydrogen peroxide sensors developed from pyrolytic carbon nanofibers are comparable with their sophisticated nitrogen-doped graphene counterparts.

Fabrication of Multilayered Composite Nanofibers Using Continuous Chaotic Printing and Electrospinning: Chaotic Electrospinning.

Multi-material and multilayered micro- and nanostructures are prominently featured in nature and engineering and are recognized by their remarkable properties. Unfortunately, the fabrication of micro- and nanostructured materials through conventional processes is challenging and costly. Herein, we introduce a high-throughput, continuous, and versatile strategy for the fabrication of polymer fibers with complex multilayered nanostructures. Chaotic electrospinning (ChE) is based on the coupling of continuous chaotic printing (CCP) and electrospinning, which produces fibers with an internal multi-material microstructure. When a CCP printhead is used as an electrospinning nozzle, the diameter of the fibers is further scaled down by 3 orders of magnitude while preserving their internal structure. ChE enables the use of various polymer inks for the creation of nanofibers with a customizable number of internal nanolayers. Our results showcase the versatility and tunability of ChE to fabricate multilayered structures at the nanoscale at high throughput. We apply ChE to the synthesis of unique carbon textile electrodes composed of nanofibers with striations carved into their surface at regular intervals. These striated carbon electrodes with high surface areas exhibit 3- to 4-fold increases in specific capacitance compared to regular carbon nanofibers; ChE holds great promise for the cost-effective fabrication of electrodes for supercapacitors and other applications.

Using chaotic advection for facile high-throughput fabrication of ordered multilayer micro- and nanostructures: continuous chaotic printing.

This paper introduces the concept of continuous chaotic printing, i.e. the use of chaotic flows for deterministic and continuous extrusion of fibers with internal multilayered micro- or nanostructures. Two free-flowing materials are coextruded through a printhead containing a miniaturized Kenics static mixer (KSM) composed of multiple helicoidal elements. This produces a fiber with a well-defined internal multilayer microarchitecture at high-throughput (>1.0 m min-1). The number of mixing elements and the printhead diameter determine the number and thickness of the internal lamellae, which are generated according to successive bifurcations that yield a vast amount of inter-material surface area (∼102 cm2 cm-3) at high resolution (∼10 µm). This creates structures with extremely high surface area to volume ratio (SAV). Comparison of experimental and computational results demonstrates that continuous chaotic 3D printing is a robust process with predictable output. In an exciting new development, we demonstrate a method for scaling down these microstructures by 3 orders of magnitude, to the nanoscale level (∼150 nm), by feeding the output of a continuous chaotic 3D printhead into an electrospinner. The simplicity and high resolution of continuous chaotic printing strongly supports its potential use in novel applications, including-but not limited to-bioprinting of multi-scale layered biological structures such as bacterial communities, living tissues composed of organized multiple mammalian cell types, and fabrication of smart multi-material and multilayered constructs for biomedical applications.

Study of the electrostatic jet initiation in near-field electrospinning.

HYPOTHESIS: The electrostatic initiation of a jet from the meniscus of a polymeric solution is a key step in near-field electrospinning (NFES), however this process is not sufficiently understood to determine a criterion for the critical emitter voltage triggering the jet, nor to optimize the electrodes. It is expected that the jet initiation in NFES is similar to that in cone-jet electrosprays, and can be described with a first principles model. EXPERIMENTS: The electrostatic jet initiation of an SU-8 polymeric solution is studied with two different electrode geometries to quantify the initiation parameters and illustrate the optimization of the electric field. A first-principles model is developed to predict and analyze the initiation. FINDINGS: Two jet emission mechanisms are identified: one in which the jet is ejected from a free-standing conical meniscus; and one resulting from the contact of the meniscus with the collector, as it evolves from a spherical to a conical shape. Both are triggered by a critical emitter potential. The former produces the thinnest jets with a diameter that depends on the properties of the fluid, while the latter is an alternative to existing mechanical initiation methods. The model reproduces well the experimental phenomena including the critical voltage.

Graphitizing Non-graphitizable Carbons by Stress-induced Routes.

Graphitic carbons' unique attributes have attracted worldwide interest towards their development and application. Carbon pyrolysis is a widespread method for synthesizing carbon materials. However, our understanding of the factors that cause differences in graphitization of various pyrolyzed carbon precursors is inadequate. We demonstrate how electro-mechanical aspects of the synthesis process influence molecular alignment in a polymer precursor to enhance its graphitization. Electrohydrodynamic forces are applied via electrospinning to unwind and orient the molecular chains of a non-graphitizing carbon precursor, polyacrylonitrile. Subsequently, exerting mechanical stresses further enhances the molecular alignment of the polymer chains during the formative crosslinking phase. The stabilized polymer precursor is then pyrolyzed at 1000 °C and characterized to evaluate its graphitization. The final carbon exhibits a uniformly graphitized structure, abundant in edge planes, which translates into its electrochemical kinetics. The results highlight the significance of physical synthesis conditions in defining the structure and properties of pyrolytic carbons.