Stamped multilayer graphene laminates for disposable in-field electrodes: application to electrochemical sensing of hydrogen peroxide and glucose.

A multi-step approach is described for the fabrication of multi-layer graphene-based electrodes without the need for ink binders or post-print annealing. Graphite and nanoplatelet graphene were chemically exfoliated using a modified Hummers' method and the dried material was thermally expanded. Expanded materials were used in a 3D printed mold and stamp to create laminate electrodes on various substrates. The laminates were examined for potential sensing applications using model systems of peroxide (H2O2) and enzymatic glucose detection. Within the context of these two assay systems, platinum nanoparticle electrodeposition and oxygen plasma treatment were examined as methods for improving sensitivity. Electrodes made from both materials displayed excellent H2O2 sensing capability compared to screen-printed carbon electrodes. Laminates made from expanded graphite and treated with platinum, detected H2O2 at a working potential of 0.3 V (vs. Ag/AgCl [0.1 M KCl]) with a 1.91 µM detection limit and sensitivity of 64 nA·µM-1·cm-2. Electrodes made from platinum treated nanoplatelet graphene had a H2O2 detection limit of 1.98 µM (at 0.3 V), and a sensitivity of 16.5 nA·µM-1·cm-2. Both types of laminate electrodes were also tested as glucose sensors via immobilization of the enzyme glucose oxidase. The expanded nanographene material exhibited a wide analytical range for glucose (3.7 µM to 9.9 mM) and a detection limit of 1.2 µM. The sensing range of laminates made from expanded graphite was slightly reduced (9.8 µM to 9.9 mM) and the detection limit for glucose was higher (18.5 µM). When tested on flexible substrates, the expanded graphite laminates demonstrated excellent adhesion and durability during testing. These properties make the electrodes adaptable to a variety of tests for field-based or wearable sensing applications. Graphical abstract Expanded graphite (eGR) and expanded nanoplatelet graphene (nGN) were chemically exfoliated, thermally expanded, and manually stamped into flexible multi-layer graphene laminate electrodes. Hydrogen peroxide amperometric testing of eGR laminates compared to nGN laminates and a screen printed carbon (SPC) electrode.

Platinum Nanoparticle Decorated SiO2 Microfibers as Catalysts for Micro Unmanned Underwater Vehicle Propulsion.

Micro unmanned underwater vehicles (UUVs) need to house propulsion mechanisms that are small in size but sufficiently powerful to deliver on-demand acceleration for tight radius turns, burst-driven docking maneuvers, and low-speed course corrections. Recently, small-scale hydrogen peroxide (H2O2) propulsion mechanisms have shown great promise in delivering pulsatile thrust for such acceleration needs. However, the need for robust, high surface area nanocatalysts that can be manufactured on a large scale for integration into micro UUV reaction chambers is still needed. In this report, a thermal/electrical insulator, silicon oxide (SiO2) microfibers, is used as a support for platinum nanoparticle (PtNP) catalysts. The mercapto-silanization of the SiO2 microfibers enables strong covalent attachment with PtNPs, and the resultant PtNP-SiO2 fibers act as a robust, high surface area catalyst for H2O2 decomposition. The PtNP-SiO2 catalysts are fitted inside a micro UUV reaction chamber for vehicular propulsion; the catalysts can propel a micro UUV for 5.9 m at a velocity of 1.18 m/s with 50 mL of 50% (w/w) H2O2. The concomitance of facile fabrication, economic and scalable processing, and high performance-including a reduction in H2O2 decomposition activation energy of 40-50% over conventional material catalysts-paves the way for using these nanostructured microfibers in modern, small-scale underwater vehicle propulsion systems.