This paper describes the design and characterization of an open-source universal wireless electrochemical detector (UWED). This detector interfaces with a smartphone (or a tablet) using Bluetooth Low Energy protocol; the smartphone provides (i) a user interface for receiving the experimental parameters from the user and visualizing the result in real-time, and (ii) a proxy for storing, processing, and transmitting the data and experimental protocols. This approach simplifies the design, and decreases both the size and the cost of the hardware; it also makes UWED adaptable to different types of analyses by simple modification of the software. The UWED can perform the most common electroanalytical techniques of potentiometry, chronoamperometry, cyclic voltammetry, and square wave voltammetry, with results closely comparable to benchtop commercial potentiostats. Although the operating ranges of electrical current and voltage of UWED (±1.5 V, ± 180 µA) are more limited than most benchtop commercial potentiostats, its functional range is sufficient for most electrochemical analyses in aqueous solutions. Because UWED is simple, small in size, assembled from inexpensive components, and completely wireless, it offers new opportunities for the development of affordable diagnostics, sensors, and wearable devices. All the files and details required for fabrication of UWED are provided as supporting materials, including: (i) designs for the electrical circuits and a list of all necessary components, (ii) the layout of the printed circuit board, (iii) the firmware of the microcontroller, and (iv) the code for the software for the smartphone.

To test the hypothesis that an abiotic Earth and its inert atmosphere could form chemically reactive carbon- and nitrogen-containing compounds, we designed a plasma electrochemical setup to mimic lightning-induced electrochemistry under steady-state conditions of the early Earth. Air-gap electrochemical reactions at air–water–ground interfaces lead to remarkable yields, with up to 40 moles of carbon dioxide being reduced into carbon monoxide and formic acid, and 3 moles of gaseous nitrogen being fixed into nitrate, nitrite, and ammonium ions, per mole of transmitted electrons. Interfaces enable reactants (e.g., minerals) that may have been on land, in lakes, and in oceans to participate in radical and redox reactions, leading to higher yields compared to gas-phase-only reactions. Cloud-to-ground lightning strikes could have generated high concentrations of reactive molecules locally, establishing diverse feedstocks for early life to emerge and survive globally.

Benzalkonium (BA⁺) chloride is one of the most common preservatives used in prescription-based and over-the-counter eye drops. Knowing the concentration of BA⁺ in eye drops is important for both quality control (at the pharmaceutical preparation stage) and human health (ocular toxicity has been linked to BA⁺ use). This paper describes the design and fabrication of a benzalkonium-selective potentiometric sensor for the determination of BA⁺ in ophthalmic solutions. The sensor is composed of a 3D-printed ion-selective membrane (ISM) that selectively measures BA⁺ in the presence of potentially interfering ions routinely found in ophthalmic formulations (i.e., Mg²⁺, Ca²⁺, Na⁺ and K⁺). The 3D printed BA⁺-ion-selective electrodes (ISEs) produced a Nernstian response of 55 mV/Decade across a range of 1.0 mM to 31.0 μM BA⁺ along with an LOD of 8 μM, which covers the relevant concentration range found in ophthalmic solutions. The 3D printed BA⁺-ISEs proved to be highly stable with an average drift of 205 μV/hr. Successful measurement of BA⁺ in diluted ophthalmic solutions was completed from 100–500 μM. The mass production capability afforded by 3D-printing offers a unique and intriguing fabrication protocol for developing low-cost sensors which could be incorporated quickly and seamlessly by pharmaceutical companies or community-based pharmacies.