The rapid growth of research in electrochemistry in the last decade has resulted in a significant advancement in exploiting electrochemical strategies for assessing biological substances. Among these, amino acids are of utmost interest due to their key role in human health. Indeed, an unbalanced amino acid level is the origin of several metabolic and genetic diseases, which has led to a great need for effective and reliable evaluation methods. This review is an effort to summarize and present both challenges and achievements in electrochemical amino acid sensing from the last decade (from 2010 onwards) to show where limitations and advantages stem from. In this review, we place special emphasis on five well-known electroactive amino acids, namely cysteine, tyrosine, tryptophan, methionine and histidine. The recent research and achievements in this area and significant performance metrics of the proposed electrochemical sensors, including the limit of detection, sensitivity, stability, linear dynamic range(s) and applicability in real sample analysis, are summarized and presented in separate sections. More than 400 recent scientific studies were included in this review to portray a rich set of ideas and exemplify the capabilities of the electrochemical strategies to detect these essential biomolecules at trace and even ultra-trace levels. Finally, we discuss, in the last section, the remaining issues and the opportunities to push the boundaries of our knowledge in amino acid electrochemistry even further.

Spinel‐structured transition metal (TM) oxides have shown great potential as a sustainable alternative to platinum group metal‐based electrocatalysts. Among them, high‐entropy oxides (HEOs) with multiple TM‐cation sites are suitable for engineering octahedral redox‐active centers to enhance the catalyst reactivity. This paper reports on the preparation of electrospun (Cr _1/5 Mn _1/5 Fe _1/5 Co _1/5 Ni _1/5 ) ₃ O ₄ nanofibers (NFs) and their evaluation as electrocatalysts. Its main aim is to unveil the nanostructural features that play a key role in the alkaline oxygen evolution reaction. Differing calcination temperature (300−800 °C) and duration (2 or 4 h) leads to different morphology of the NFs, crystallinity of the oxide, density of defects, and cation distribution in the lattice, which reflect in different electrocatalytic behaviors. The best performance (overpotential and Tafel slope at 10 mA cm ⁻² : 325 mV and 40 mV dec ⁻¹ , respectively) pertains to the NFs calcined at 400 °C for 2 h. To gain a deeper understanding of their electrocatalytic properties, the pristine NFs are investigated by a combination of analytical techniques. In particular, broadband electric spectroscopy reveals that the mobility of oxygen vacancies in the best electrocatalyst is associated to very fast local dielectric relaxations of metal coordination octahedral geometries and experimentally demonstrates the key role of O‐deficient octahedra.

The development of fast and reliable gas sensors is a pressing and growing problem for environmental monitoring due to the presence of pollutants in the atmosphere. Among all gases, particular attention is devoted to NO, which can cause serious health problems. WO₃ nanorods represent promising candidates for this purpose due to their high electrical stability and low cost of production. Here, the hydrothermal synthesis of WO₃ nanorods is reported, in addition to the realization of a chemo-resistive NO sensor. NO-sensing tests were performed at different temperatures (250–400 °C) and under different gas concentrations (250–2500 ppm), and NO response and recovery curves were also modeled by using the Langmuir adsorption theory by highlighting the NO-sensing mechanism of the WO₃ nanorods. An interaction occurred at the surface between NO and the adsorbed oxygen ions, thus clarifying the NO-reducing behavior. The fast response and recovery times open the route for the development of fast NO sensors based on WO₃.