Additive manufacturing provides a unique tool for prototyping structures toward electrochemical sensing, due to its ability to produce highly versatile, tailored-shaped devices in a low-cost and fast way with minimized waste. Here we present 3D-printed graphene electrodes for electrochemical sensing. Ring- and disc-shaped electrodes were 3D-printed with a Fused Deposition Modeling printer and characterized using cyclic voltammetry and scanning electron microscopy. Different redox probes KFe(CN):KFe(CN), FeCl, ascorbic acid, Ru(NH)Cl, and ferrocene monocarboxylic acid) were used to assess the electrochemical performance of these devices. Finally, the electrochemical detection of picric acid and ascorbic acid was carried out as proof-of-concept analytes for sensing applications. Such customizable platforms represent promising alternatives to conventional electrodes for a wide range of sensing applications.

Photoactivated micromachines are at the forefront of the micro-and nanomotors field, as light is the main power source of many biological systems. Currently, this rapidly developing field is based on metal-containing segments, typically TiO 2 and precious metals. Herein, we present metal-free tubular micromotors solely based on graphitic carbon nitride, as highly scalable and low-cost micromachines that can be actuated by turning on/off the light source. These micromotors are able to move by a photocatalytic-induced bubble-propelled mechanism under visible light irradiation, without any metal-containing part or biochemical molecule on their structure. Furthermore, they exhibit interesting properties, such as a translucent tubular structure that allows the optical visualization of the O 2 bubble formation and migration inside the microtubes, as well as inherent fluorescence and adsorptive capability. Such properties were exploited for the removal of a heavy metal from contaminated water with the concomitant optical monitoring of its adsorption by fluorescence quenching. This multifunctional approach contributes to the development of metal-free bubble-propelled tubular micromotors actuated under visible light irradiation for environmental applications.

The first models of mesoporous ZnO/Pt Janus micromotors that show fuelfree and light-powered propulsion depending on the interface roughness are shown. Two models of ZnO semiconducting particles with distinct surface morphologies and pore structures are synthesized by self-aggregation of primary nanoparticles and nanosheets into nanoscale rough and smooth microparticles, respectively. The self-assembled nanosheet model (smooth) provides a large surface for the formation of a continuous Pt layer with strong adherence, whereas the discontinuous Pt species take place inside the inter-nanoparticles pores in the self-assembled nanoparticle model (rough). The effects of the interface, surface porosity, defect, and charge transfer on the light-powered motion for both well-designed mesoporous ZnO/Pt Janus micromotors are investigated and compared to find the underlying propulsion mechanisms. The degradation of two model pollutants is demonstrated as a proof-of-concept application of these carefully engineered Janus micromotors. In this work, it is shown that by discreet material fabrication together with semiconductor/metal interface charge transport interpretation, it would be possible to develop new light-driven Janus micromotors based on other photocatalysts containing active surfaces such as TiO 2 .

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Layered transition metal dichalcogenides (TMDs) have gained attention from the scientific community because of their extended range of applications. Molybdenum diselenide (MoSe) has been proven to be an efficient catalyst for the hydrogen evolution reaction (HER), having implications in the research of new catalysts for clean energy production. One way to produce large quantities of these materials involves the use of surfactants for liquid exfoliation. Herein, we investigate the effects of cationic, anionic, and nonionic surfactants within a concentration range on the heterogeneous electron transfer rates, electrocatalytic efficiency toward the HER of MoSe, and on the stability of the dispersions. We found that surfactants can have a detrimental effect on the electrocatalytic properties of the material when used above a concentration threshold. In some cases, high surfactant levels also had a negative effect on the stability of the material. This report serves to gain an understanding on how the way TMDs are prepared, processed, and stabilized can have dramatic effects on their efficiency toward HER, one of their most popular applications, and how choosing the appropriate surfactant type and concentration is crucial to gain in stability without compromising the intrinsic properties of the material.

The cathodic process in electrochemical water electrolyzers, the hydrogen evolution reaction (HER), is an extremely important reaction as it produces clean H2 gas that can be utilized in a fuel cell to create electricity as an energy source for the increasing energy consumption of today’s World. Transition metal dichalcogenide (TMD) materials have emerged as a competitor to Pt catalysts for the HER; however, the HER catalytic activity of TMD materials depends on various parameters including their fabrication route. Herein, we present a one-step powderless deposition growth process of 2H-MoS2 and 2H-WS2 materials on their native metals which serve directly as electrodes. The 2H phase TMDs were subsequently partially converted to the 1T-phase by a tert-butyllithium immersion treatment. The 2H and 2H/1T phase TMD foils were utilized for electrochemical hydrogen evolution, and we show that these TMD foils outperform or rival other MoS2 and WS2 materials in the literature fabricated by powder-based deposition/growth techniques. These findings highlight the importance of developing new scalable fabrication routes for HER catalysts in the race toward clean energy production.

Simple and sensitive assays for DNA detection still represent a highly pursued research area with important implications in biomedical-related sciences. Graphene oxide (GO) is a highly efficient quenching platform for fluorophore-tagged DNA, which is why its use for fluorescent sensing has been widespread over the past decade. GO-based biosensing systems frequently rely upon the isolation of biomolecule–material complexes prior to detection via hybridization-induced desorption of the fluorescent dye. Simple mix-and-read detection formats that do not require purification/isolation/wash steps are envisioned as promising schemes for decentralized analysis, with potential for commercial scalability. For GO-based mix-and-read assays, the aging process of the quenching material in aqueous media can be a crucial parameter affecting the analytical performance, which has so far not been addressed in the literature. To get this goal, top–down characterization microstructures to atomic levels is needed. Herein, we revisit GO as a well-known quenching system, aiming at a centrifugation-free, mix-and-read, no-wash format, toward the detection of an apolipoprotein-E-encoding DNA sequence as a model analyte. We look into the progression of GO aging in water medium through a top–down characterization and investigate the analytical performance of fresh versus aged dispersions in terms of hybridization-based detection. We found that aged GO, while still retaining a high quenching efficiency, undergoes morphological changes over time with concomitant detrimental effects on its analytical performance toward DNA detection.