Stable Full-Inkjet-Printed Solid-State Ag/AgCl Reference Electrode.

With a growing demand for the availability of inexpensive, simple, and rapid prototyped devices, the prospect of miniaturization of the reference electrodes using printing techniques becomes promising. A stable and reusable full-inkjet-printed solid-state reference electrode (IPRE) was developed. The reference electrode was fully produced by consecutive inkjet printing of several layers. Ag ink was printed and chlorinated by NaClO printing, forming a Ag/AgCl pseudoreference electrode. Then a surface protection by printing a Cl--saturated polyvinyl butyral membrane finally gave a reference electrode that demonstrated an outstanding performance comparable to commercial ones. This full inkjet printing fabrication strategy will improve the viability of producing low-cost miniaturized reference electrodes with interest in many electrochemical sensor-dependent areas.

Versatile Three-Dimensional-Printed Platform for Nitrite Ion Analyses Using a Smartphone with Real-Time Location.

Nitrogen-based chemicals represent one of the most important family of compounds in freshwater and marine ecosystems. The nitrogen cycle is responsible for spreading nitrogen compounds all over the environment in an equilibrium manner. Mankind's industrial activities have harshly contributed to the disruption of the nitrogen cycle and its consequences have severely affected Earth's ecosystems. Tracking the chemicals involved in the nitrogen cycle have become a crucial point in fighting against eutrophication and global water acidification. A smartphone readout-based system has been developed to determine the concentration of nitrite ion (the nitrogen compound that possess higher toxicity) in environmental samples. The device was fabricated by means of three-dimensional printing to allow easy design modification to fit any smartphone. Moreover, the system took advantage of the less explored potential of ambient light sensor contained within the smartphones. Finally, "ALSens" application was developed to be used by nontrained personnel to not only determine nitrite ion concentration but also to automatically send relevant parameters (analyte, day, hour, location, and concentration) of the assay for tracking purposes to an open online database, allowing a worldwide mapping of nitrite ion concentration. Considering the devastating implications of nitrogen cycle disruption, these systems for nitrite ion screening will suddenly become a standard global monitoring approach.

Inkjet-Printed Sulfide-Selective Electrode.

Inkjet printing technology has emerged as an alternative manufacturing method for low-cost production of electrodes. Despite significant progress, there is still a lack in the production of ion-selective electrodes. Herein, the two-step fabrication of the first inkjet-printed sulfide-selective electrode (IPSSE) is described. The two-step fabrication consists of printing a silver electrode followed by an electrochemical deposition of sulfide to produce a second kind electrode (Ag/Ag2S). The performance of this novel device was tested using potentiometric measurements. Nernstian response (-29.4 ± 0.3 mV·decade-1) was obtained within concentrations of 0.03-50 mM with a response time of ∼3 s. Furthermore, river/sea-spiked environmental samples and samples from a bioreactor for sulfate reduction to sulfide were measured and compared against a commercial sensor giving no significant differences. The IPSSE described in this work showed good reproducibility and durability during daily measurements over 15 days without any special storage conditions. Considering all the current challenges in inkjet-printed ion-selective electrodes, this different fabrication approach opens a new perspective for mass production of all-solid state ion-selective electrodes.