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

Laser-induced graphene electrodes for electrochemical ion sensing, pesticide monitoring, and water splitting

Laser-induced graphene (LIG) has shown to be a scalable manufacturing route to create graphene electrodes that overcome the expense associated with conventional graphene electrode fabrication. Herein, we expand upon initial LIG reports by functionalizing the LIG with metallic nanoparticles for ion sensing, pesticide monitoring, and water splitting. The LIG electrodes were converted into ion-selective sensors by functionalization with poly(vinyl chloride)-based membranes containing K⁺ and H⁺ ionophores. These ion-selective sensors exhibited a rapid response time (10-15 s), near-Nernstian sensitivity (53.0 mV/dec for the K⁺ sensor and - 56.6 mV/pH for the pH sensor), and long storage stability for 40 days, and were capable of ion monitoring in artificial urine. The pesticide biosensors were created by functionalizing the LIG electrodes with the enzyme horseradish peroxidase and displayed a high sensitivity to atrazine (28.9 nA/μM) with negligible inference from other common herbicides (glyphosate, dicamba, and 2,4-dichlorophenoxyacetic acid). Finally, the LIG electrodes also exhibited a small overpotential for hydrogen evolution reaction and oxygen evolution reaction. The oxygen evolution reaction tests yielded overpotentials of 448 mV and 995 mV for 10 mA/cm² and 100 mA/cm², respectively. The hydrogen evolution reaction tests yielded 35 mV and 281 mV for the corresponding current densities. Such a versatile LIG platform paves the way for simple, efficient electrochemical sensing and energy harvesting applications.

Unravelling the cooperative role of lattice strain on MnO2/TiO2 and MnO2/ZnO catalysts for the fast decomposition of hydrogen peroxide

The rate of decomposition of hydrogen peroxide was directly correlated with lattice strain, as derived from strain calculations.

Synergistic effect between La–Ni bimetallic oxides for the efficient decomposition of hydrogen peroxide

La–Ni bimetallic oxides with pure composition and well-crystalline structures were prepared, which showed high catalytic activities toward H₂O₂ decomposition.

Electrochemical Glucose Sensors Enhanced by Methyl Viologen and Vertically Aligned Carbon Nanotube Channels

Freestanding, vertically aligned carbon nanotubes (VACNTs) were patterned into 16 μm diameter microchannel arrays for flow-through electrochemical glucose sensing. Non-enzymatic sensing of glucose was achieved by the chemical reaction of glucose with methyl viologen (MV) at an elevated temperature and pH (0.1 M NaOH), followed by the electrochemical reaction of reduced-MV with the VACNT surface. The MV sensor required no functionalization (including no metal) and was able to produce on average 3.4 electrons per glucose molecule. The current density of the MV sensor was linear with both flow rate and glucose concentration. Challenges with interference chemicals were mitigated by operating at a low potential of -0.2 V vs Ag/AgCl. As a comparison, enzymatic VACNT sensors with platinum nano-urchins were functionalized with glucose oxidase by covalent binding (1-ethyl-3-(-3-dimethylaminopropyl)carbodiimide/ N-hydroxysuccinimide) or by polymer entrapment [poly(3,4-ethylene-dioxythiophene)] and operated in phosphate buffered saline. With normalization by the overall cross-sectional area of the flow (0.713 cm²), the sensitivity of the MV, enzyme-in-solution, and covalent sensors were 45.93, 18.77, and 1.815 mA cm^-2 mM^-1, respectively. Corresponding limits of detection were 100, 194, and 311 nM glucose. The linear sensing ranges for the sensors were 250 nM to 200 μM glucose for the MV sensor, 500 nM to 200 μM glucose for the enzyme-in-solution sensor, and 1 μM to 6 mM glucose for the covalent sensor. The flow cell and sensor cross-sectional area were scaled down (0.020 cm²) to enable detection from 200 μL of glucose with MV by flow injection analysis. The sensitivity of the small MV sensor was 5.002 mA cm^-2 mM^-1, with a limit of detection of 360 nM glucose and a linear range up to at least 150 μM glucose. The small MV sensor has the potential to measure glucose levels found in 200 μL of saliva.

Mechanism and Kinetics of Hydrogen Peroxide Decomposition on Platinum Nanocatalysts

The decomposition of H₂O₂ to H₂O and O₂ catalyzed by platinum nanocatalysts controls the energy yield of several energy conversion technologies, such as hydrogen fuel cells. However, the reaction mechanism and rate-limiting step of this reaction have been unsolved for more than 100 years. We determined both the reaction mechanism and rate-limiting step by studying the effect of different reaction conditions, nanoparticle size, and surface composition on the rates of H₂O₂ decomposition by three platinum nanocatalysts with average particle sizes of 3, 11, and 22 nm. Rate models indicate that the reaction pathway of H₂O₂ decomposition is similar for all three nanocatalysts. Larger particle size correlates with lower activation energy and enhanced catalytic activity, explained by a smaller work function for larger platinum particles, which favors chemisorption of oxygen onto platinum to form Pt(O). Our experiments also showed that incorporation of oxygen at the nanocatalyst surface results in a faster reaction rate because the rate-limiting step is skipped in the first cycle of reaction. Taken together, these results indicate that the reaction proceeds in two cyclic steps and that step 1 is the rate-limiting step. Step 1: Pt + H₂ O₂ → H₂ O + Pt( O). Step 2: Pt( O) + H₂ O₂ → Pt + O₂ + H₂ O. Overall: 2 H₂ O₂ → O₂ + 2 H₂ O. Establishing relationships between the properties of commercial nanocatalysts and their catalytic activity, as we have done here for platinum in the decomposition of H₂O₂, opens the possibility of improving the performance of nanocatalysts used in applications. This study also demonstrates the advantage of combining detailed characterization and systematic reactivity experiments to understand property-behavior relationships.

Neuro-Nano Interfaces: Utilizing Nano-Coatings and Nanoparticles to Enable Next-Generation Electrophysiological Recording, Neural Stimulation, and Biochemical Modulation

Neural interfaces provide a window into the workings of the nervous system-enabling both biosignal recording and modulation. Traditionally, neural interfaces have been restricted to implanted electrodes to record or modulate electrical activity of the nervous system. Although these electrode systems are both mechanically and operationally robust, they have limited utility due to the resultant macroscale damage from invasive implantation. For this reason, novel nanomaterials are being investigated to enable new strategies to chronically interact with the nervous system at both the cellular and network level. In this feature article, the use of nanomaterials to improve current electrophysiological interfaces, as well as enable new nano-interfaces to modulate neural activity via alternative mechanisms, such as remote transduction of electromagnetic fields are explored. Specifically, this article will review the current use of nanoparticle coatings to enhance electrode function, then an analysis of the cutting-edge, targeted nanoparticle technologies being utilized to interface with both the electrophysiological and biochemical behavior of the nervous system will be provided. Furthermore, an emerging, specialized-use case for neural interfaces will be presented: the modulation of the blood-brain barrier.

Utility of PEGylated dithiolane ligands for direct synthesis of water-soluble Au, Ag, Pt, Pd, Cu and AuPt nanoparticles

The ability of small PEGylated dithiolane molecules to produce a variety of metallic nanoparticles directly in water is highlighted here.