Compared with conventional analytical techniques, electroanalytical technologies offer continuous, fast, and reliable detection with portable, wearable, and reagentless devices. In this thesis, novel electrochemical sensors and actuators were developed and designed to fulfill specific needs for personal health management, sports performance, and environmental monitoring, and to find alternatives for conventional techniques. In the first part of the thesis, wearable electrochemical biosensors were developed for real-time lactate measurement in sweat towards personalized health management and sports performance assessment. By coupling the lactate oxidase-based sensing element and permselective diffusion membrane, the interference of other sweat components while controlling lactate diffusion was investigated, and precise lactate detection in the physiological lactate concentration range (1 – 50 mM) was achieved. Embedded into fully wearable on-body platforms, the wearable lactate biosensors exhibited a response time of <90 s, good stability, low interference from other sweat components, and good reliability during prolonged continuous use. Comprehensive on-body validation with elite athletes demonstrated a strong correlation of sweat lactate measurement with mainstream blood lactate assay and other physiological indicators of physical exertion, indicating the effectiveness of using the developed lactate biosensors as wearable health diagnostic and performance monitoring tools. In the second part, portable and reagentless electrochemical instruments were developed for the in-situ detection of dissolved inorganic phosphate (DIP) in environmental waters, a key water pollutant causing eutrophication. An integrated actuator-sensor platform was established based on polyaniline (PANI)-based proton pumps and electrochemically controlled molybdate ion delivery, which were combined to form detectable phosphomolybdate complexes within a confined thin-layer electrochemical cell. The device operated reagentless and reliably quantified the DIP concentration from 0.1 to 20 µM in complex matrices such as seawater, and the results were compared with traditional chromatographic analysis. As its compact size and good functionality, the device should be well-suited for routine deployment in aquatic environments and could significantly improve the capability of decentralized water quality monitoring. In the third part, the capabilities and applications of PANI-based electrochemical actuators were further explored. The related application of this actuator was explicitly extended towards reagentless acidification strategies. Bulk experiments showed that the PANI-coated stainless-steel meshes could effectively and sustainably acidify large volumes of water samples without any acid reagents for potential reuse in portable environmental remediation devices. At the same time, the microscale behavior of a confined actuator was investigated using scanning electrochemical microscopy (SECM), and the relationship between polymer morphology and localized proton-pumping performance was elucidated to guide the further rational tuning of polymer-based actuators for more localized proton release. Such actuators would be valuable tools for miniaturized electrochemical actuators. Overall, this thesis has advanced the development of portable, wearable, and reagentless electrochemical sensing and actuation technologies and demonstrated their profound potential in personal health monitoring, sports performance assessment, and environmental protection through novel analytical approaches.

Jämfört med konventionella analytiska tekniker erbjuder elektroanalytiska teknologier kontinuerlig, snabb och tillförlitlig detektion med portabla, bärbara och reagensfria analysenheter. I denna avhandling har nya elektrokemiska sensorer och aktuatorer utvecklats och designats för att uppfylla specifika behov inom personanpassad hälsovård, sportprestanda och miljöövervakning. I den första delen av avhandlingen utvecklades bärbara elektrokemiska biosensorer för on-demand, realtidsmätning av laktat i svett för personanpassad hälsovård och bedömning av sportprestanda. Genom att koppla ihop det laktatoxidasbaserade avkänningselementet och det permslektiva diffusionsmembranet minimerades krossinterferens från andra komponenter i svett, och precis detektion av laktat inom det fysiologiska intervallet för laktat (1 – 50 mM) uppnåddes. När de integrerades i fullt bärbara kroppsburna plattformar visade de bärbara laktatbiosensorerna en responstid på <90 s, god stabilitet, låg interferens från andra svettkomponenter och god tillförlitlighet under långvarig kontinuerlig användning. Omfattande validering på elitidrottare visade stark korrelation mellan svettlaktatmätningar och etablerade blodlaktattester samt andra fysiologiska indikatorer på fysisk ansträngning, vilket bekräftar effektiviteten av att använda de utvecklade laktatbiosensorerna som bärbara verktyg för hälso-diagnostik och prestandaövervakning.  I den andra delen utvecklades portabla och reagensfria elektrokemiska analysenheter för in situ-detektion av upplöst oorganiskt fosfat (DIP), en av de mest relevanta föroreningar i vatten som orsakar övergödning. En integrerad aktuator-sensorplattform etablerades där polyanilin (PANI)-baserade protonpumpar och elektrokemiskt styrd molybdatjonsleverans kombinerades för att bilda detekterbara fosfomolybdatskomplex inom en begränsad elektrokemisk tunnskiktscell. Enheten fungerade helt reagensfritt och kvantifierade pålitligt DIP-koncentrationen från 0,1 till 20 µM i komplexa matriser såsom havsvatten, och resultaten validerades med traditionell kromatografisk analys. Tack vare sin kompakta storlek och goda funktionalitet bör enheten vara väl lämpad för rutinmässig användning i vattenmiljöer och möjliggör för framtida decentraliserade mätningar av DIP för övervakning av vattenkvalitet. I den tredje delen undersöktes ytterligare tillämpningar av PANI-baserade elektrokemiska aktuatorer inom reagensfria försurningsstrategier. Bulkexperiment visade att de PANI-belagda stålnätselektroder effektivt och hållbart kunde försura stora volymer av vattenprover utan tillsats av syrereagenser för potentiell återanvändning i portabla miljöskyddande detektionsenheter. Samtidigt undersöktes aktuatorns mikrostruktir med skannande elektrokemisk mikroskopi (SECM), och sambandet mellan polymermorfologi och protonpumps-prestanda klarlades för att guida ytterligare rationell justering av polymerbaserade aktuatorer för använding inom försurningsstrategier. Sådana aktuatorer skulle vara värdefulla verktyg för miniatyriserade elektrokemiska aktorer.  Sammanfattningsvis har denna avhandling avancerat utvecklingen av portabla, bärbara och reagensfria elektrokemiska avkännings- och aktutorteknologier och demonstrerat deras djupgående potential inom personanpassad hälsoövervakning, bedömning av sportprestanda och miljöskydd genom nya analytiska tillvägagångssätt.

This study examined the anaerobic release of phosphorus (P) from two different Baltic Sea sediments (B and F), focusing on the impact of initial concentration of externally introduced waste-derived volatile fatty acids (VFA) as the carbon source, temperature, pH, and mixing conditions. The first batch bioreactor set was operated to demonstrate the effect of VFA on anaerobic P release at different concentrations (1000–10000 mg/L as COD) at 20 °C. A notable P release of up to 15.85 mg/L PO4–P was observed for Sediment B at an initial carbon concentration of 10000 mg COD/L. However, VFA consumption in the bioreactors was minimal or no subsequent. The second batch bioreactor set was carried out to investigate the effect of temperature (20 °C-35 °C), pH (5.5, 7.0 and 8.5) and mixing conditions on P release by introducing lower initial carbon concentration (1000 mg COD/L) considering the potential risk for VFA accumulation in the bioreactors. Maximum P releases of 4.4 mg/L and 3.5 mg/L were for Sediment B and Sediment F, respectively. Two-way ANOVA tests revealed that the operation time and pH and their interactions were statistically significant (p < 0.05) for both sediments while the effect of mixing was not statistically significant. Most of the sulfate was reduced during batch bioreactor operation and Desulfomicobiaceae became dominant among other sulfate-reducing bacteria (SRB) possibly shows the importance of SRB in terms of anaerobic P release. This study gives an insight into future implementations of phosphorus mining from eutrophic environment under anaerobic conditions.

The analysis of many environmental and clinical samples requires the modification of the original pH, which is conventionally carried out by manual/automatic addition of acid, base, or buffering reagents. In the case of decentralized measurements, often, this approach is not plausible. Instead, reagentless alternatives, such as electrochemically activated in-situ pH adjustments, are suitable. Herein, we present a method for electrochemical, reversible pH modulation of thin-layer samples (<100 µm thickness) using the co-polymer poly(aniline-co-o-aminophenol) (PANOA). The PANOA's electropolymerization strategy was optimized considering the proton exchange properties in the final material. Thus, limiting the maximum anodic potential to 0.85 V and with the number of cyclic scans being ≤150), the optimal pH modulation capabilities were observed. The reversible proton exchange properties of PANOA were quantified by monitoring the pH inside the thin-layer sample (volume of 0.6 µL), which was defined by a 3D-printed microfluidic cell and a pH-sensor placed in a face planar configuration to the PANOA film. A pH value in the range of 2–4 can repeatably be reached in the samples in 3 min, purely by an electrochemical means and without the addition of external reagents. The concept has been demonstrated to acidify samples at environmental pH (artificial samples and Seawater). The outcomes suggest that the family of polyaniline-co-polymers are interesting to be explored and utilized for electrochemically based pH modulation strategies, if careful considerations are taken regarding their electropolymerization process. Overall, such materials could contribute to the development of continuous, decentralized measuring devices requiring acidification for the formal detection of environmental markers, such as nutrients, carbon species speciation and alkalinity, among others.

The aim of this study was recovery of phosphorus (P) from marine sediment, and our results revealed the influence of P release from the sediment stimulated with different types and concentrations of carbon sources. During the 15-day anaerobic operation, the sediments stimulated with 1 g/L propionic acid and glucose exhibited more prominent effects compared to other trials, with 5.98 mg/L and 6.44 mg/L of P released, respectively, with a total solid content of 4 %. Notably, the excessive addition of carbon sources was shown to can partially inhibit P release. As microbial activity intensified, P was utilized for microbial synthesis, resulting in a decreased P in the supernatant. For example, in glucose-fed systems with concentrations of 5 g/L and 10 g/L, the P concentration decreased from 5 mg/L on Day 3 to approximately 3 mg/L on Day 15. The sequencing results indicated distinct evolutions within different carbon source-fed systems over the 15-day operations. Feeding high concentrations of glucose resulted in rapid enrichment of fermentative bacteria under anaerobic conditions, while sulfate-reducing bacteria promoted P release in volatile fatty acids-fed systems. Metabolic analysis revealed that carbon sources not only influence gene expression in different systems, but also impact the metabolic pathways involved in nutrient cycling, which can be interrelated. For example, a significant positive correlation was observed between the abundance of P and sulfur cycling functional genes (phoD, cysD).

In the last decade, sport performance assessment has significantly transformed due to the appearance of disruptive technologies. Subjective pen and paper notations have evolved into advanced wearable sensing systems that acquire performance-related data. The selection of adequate performance metric variables always causes a debate in sport physiology, and this becomes more relevant once new biochemical indicators are proposed, such as sweat lactate. Here, we analyze the correlation of real-time sweat lactate, obtained with a validated wearable biosensor, with the typical physiological parameters often recorded in sports laboratories (e.g., blood lactate, Borg scale for the rating of perceived exertion, heart rate, power output, blood glucose, and respiratory quotient). We found that the heart rate, power output, Borg scale, and blood lactate relate to sweat lactate in independent individuals during cycling activity. Hence, we demonstrate the potential to associate non-invasive, quantitative, and personalized analysis with sport practice.

Invited for this month ' s cover are the collaborating groups of Prof. Cuartero and Prof. Crespo at KTH and UCAM universities with the participation of Dalarna University. The cover picture shows a wearable biosensor for the digitalization of lactate in sweat during sport activity. The biosensor is integrated into a microfluidic system for continue lactate monitoring, producing reliable real-time profiles. It was found out that real-time sweat lactate assessment is a potential proxy of personalized training strategies in sports such as cycling." More information can be found in the Research Article by Maria Cuartero, GastonA. Crespo, and co-workers.

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.

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.

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.