Wearable lactate sensors for sweat analysis are highly appealing for both the sports and healthcare fields. Electrochemical biosensing is the approach most widely used for lactate determination, and this technology generally demonstrates a linear range of response far below the expected lactate levels in sweat together with a high influence of pH and temperature. In this work, we present a novel analytical strategy based on the restriction of the lactate flux that reaches the enzyme lactate oxidase, which is immobilized in the biosensor core. This is accomplished by means of an outer plasticized polymeric layer containing the quaternary salt tetradodecylammonium tetrakis(4-chlorophenyl) borate (traditionally known as ETH500). Also, this layer prevents the enzyme from being in direct contact with the sample, and hence, any influence with the pH and temperature is dramatically reduced. An expanded limit of detection in the millimolar range (from 1 to 50 mM) is demonstrated with this new biosensor, in addition to an acceptable response time; appropriate repeatability, reproducibility, and reversibility (variations lower than 5% for the sensitivity); good resiliency; excellent selectivity; low drift; negligible influence of the flow rate; and extraordinary correlation (Pearson coefficient of 0.97) with a standardized method for lactate detection such as ion chromatography (through analysis of 22 sweat samples collected from 6 different subjects performing cycling or running). The developed lactate biosensor is suitable for on-body sweat lactate monitoring via a microfluidic epidermal patch additionally containing pH and temperature sensors. This applicability was demonstrated in three different body locations (forehead, thigh, and back) in a total of five on-body tests while cycling, achieving appropriate performance and validation. Moreover, the epidermal patch for lactate sensing is convenient for the analysis of sweat stimulated by iontophoresis in the subjects' arm, which is of great potential toward healthcare applications.

The chemical digitalization of sweat using wearable sensing interfaces is an attractive alternative to traditional blood-based protocols in sports. Although sweat lactate has been claimed to be a relevant biomarker in sports, an analytically validated wearable system to prove that has not yet been developed. We present a fully integrated sweat lactate sensing system applicable to in situ perspiration analysis. The device can be conveniently worn in the skin to monitor real-time sweat lactate during sports, such as cycling and kayaking. The novelty of the system is threefold: advanced microfluidics design for sweat collection and analysis, an analytically validated lactate biosensor based on a rational design of an outer diffusion-limiting membrane, and an integrated circuit for signal processing with a custom smartphone application. The sensor covering the range expected for lactate in sweat (1-20 mM), with appropriate sensitivity (−12.5 ± 0.53 nA mM-1), shows an acceptable response time (<90 s), and the influence of changes in pH, temperature, and flow rate are neglectable. Also, the sensor is analytically suitable with regard to reversibility, resilience, and reproducibility. The sensing device is validated through a relatively high number of on-body tests performed with elite athletes cycling and kayaking in controlled environments. Correlation outcomes between sweat lactate and other physiological indicators typically accessible in sports laboratories (blood lactate, perceived exhaustion, heart rate, blood glucose, respiratory quotient) are also presented and discussed in relation to the sport performance monitoring capability of continuous sweat lactate.

We present a methodology for the detection of dissolved inorganic phosphorous (DIP) in seawater using an electrochemically driven actuator-sensor system. The motivation for this work stems from the lack of tangible solutions for the in situ monitoring of nutrients in water systems. It does not require the addition of any reagents to the sample and works under mild polarization conditions, with the sample confined to a thin-layer compartment. Subsequent steps include the oxidation of polyaniline to lower the pH, the delivery of molybdate via a molybdenum electrode, and the formation of an electroactive phosphomolybdate complex from DIP species. The phosphomolybdate complex is ultimately detected by either cyclic voltammetry (CV) or square wave voltammetry (SWV). The combined release of protons and molybdate consistently results in a sample pH < 2 as well as a sufficient excess of molybdate, fulfilling the conditions required for the stoichiometric detection of DIP. The current of the voltammetric peak was found to be linearly related to DIP concentrations between 1 and 20 μM for CV and 0.1 and 20 μM for SWV, while also being selective against common silicate interference. The analytical application of the system was demonstrated by the validated characterization of five seawater samples, revealing an acceptable degree of difference compared to chromatography measurements. This work paves the way for the future DIP digitalization in environmental waters by in situ electrochemical probes with unprecedented spatial and temporal resolution. It is expected to provide real-time data on anthropogenic nutrient discharges as well as the improved monitoring of seawater restoration actions.

Polyaniline (PANI) has shown substantial interest in analytical chemistry as an electrochemical proton pump for pH modulation in water and soil systems. In this work, we present a reagent-free electrochemical setup employing 3D PANI-coated stainless steel (PANI-SS) mesh arrays, which enable efficient pH control in both bulk and small-volume aqueous samples at the milliliter scale. The custom-designed electrochemical cell with a total volume of 40 mL featured multiple PANI-SS meshes as working electrodes, a screen-printed carbon counter electrode, and an Ag/AgCl reference electrode. The 3D mesh architecture substantially enhanced the electroactive surface area, allowing rapid and scalable proton delivery. A single PANI-SS mesh can release ~3 µmol of protons within 200 s at 0.4 V, lowering the pH of an unbuffered 40 mL NaCl solution from ~5.3 to ~4.3. By further increasing the number of meshes to four, the pH decreased to 3.36 in unbuffered solution and 3.89 in brackish water, respectively. In addition, we explore the applicability of the PANI mesh system to selectively acidify samples containing 5% sediment to a targeted pH of 4-5, which is crucial for certain bioreaction uses. These performances demonstrated the system’s ability to provide effective proton transfers, achieving significant acidification without the use of chemical reagents. Moreover, with excellent reversibility and ability to be electrochemically regenerated using diluted acidic mining leachates, PANI-SS meshes offer a sustainable alternative to the traditional acidification concept using conventional acids, aligning with the principles of circular chemistry. Therefore, the obtained results are crucial for the future development of similar PANI-based systems in their applications as efficient and environmentally friendly electrochemical proton pumps.

Electrochemical proton pumps based on conductive polymers provide a promising route for localized pH modulation in analytical and environmental applications. In this work, we present a comparative study of polyaniline (PANI) and its copolymer, poly(aniline-co-o-aminophenol) (PANOA), focusing on their structural, morphological, and electrochemical properties, which are relevant to their proton pumping performance. The local microscopic variations in their surface topography, morphology and conductivity are studied by employing scanning electrochemical microscope (SECM), while detailed characterization using scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) reveals significant differences in films’ porosity, stability, and doping behavior that directly influences their acidification efficiency and spatial proton distribution. PANI films with a porous, swelling-prone structure enable broad and intense proton release, but also complicate precise pH monitoring. In contrast, PANOA films demonstrate compact and morphologically stable structures, offering more localized and controllable pH modulation. To resolve the local proton gradients generated by these films, we employ a PANI-based ultramicroelectrode (UME) pH sensor integrated into a SECM platform, enabling micrometer-scale resolution of pH changes near the film surface. This approach offers a novel methodology for investigating interfacial proton dynamics and contributes to a deeper understanding of how polymer structure influences proton pump functionality. The dual application of PANI polymer as both a proton pump and a pH sensor demonstrates its versatility, providing valuable insights into the design of next-generation electrochemical platforms for pH modulation.