| 1. |
- Fuoco, Tiziana, PhD, 1986-, et al.
(author)
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Capturing the Real-Time Hydrolytic Degradation of a Library of Biomedical Polymers by Combining Traditional Assessment and Electrochemical Sensors
- 2021
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 22:2, s. 949-960
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Journal article (peer-reviewed)abstract
- We have developed an innovative methodology to overcome the lack of techniques for real-time assessment of degradable biomedical polymers at physiological conditions. The methodology was established by combining polymer characterization techniques with electrochemical sensors. The in vitro hydrolytic degradation of a series of aliphatic polyesters was evaluated by following the molar mass decrease and the mass loss at different incubation times while tracing pH and L-lactate released into the incubation media with customized miniaturized electrochemical sensors. The combination of different analytical approaches provided new insights into the mechanistic and kinetics aspects of the degradation of these biomedical materials. Although molar mass had to reach threshold values for soluble oligomers to be formed and specimens' resorption to occur, the pH variation and L-lactate concentration were direct evidence of the resorption of the polymers and indicative of the extent of chain scission. Linear models were found for pH and released L-lactate as a function of mass loss for the Llactide-based copolymers. The methodology should enable the sequential screening of degradable polymers at physiological conditions and has potential to be used for preclinical material's evaluation aiming at reducing animal tests.
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| 2. |
- Kendir Cakmak, Ece, et al.
(author)
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How to develop a bio-based phosphorus mining strategy for eutrophic marine sediments: Unlocking native microbial processes for anaerobic phosphorus release
- 2024
-
In: Chemosphere. - : Elsevier BV. - 0045-6535 .- 1879-1298. ; 358
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Journal article (peer-reviewed)abstract
- 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.
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| 3. |
- Miras, Marina, et al.
(author)
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Analytical Tool for Quality Control of Irrigation Waters via a Potentiometric Electronic Tongue
- 2023
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In: Chemosensors. - : MDPI AG. - 2227-9040. ; 11:7
-
Journal article (peer-reviewed)abstract
- A potentiometric electronic tongue (ET) for the analysis of well and ditch irrigation water samples is herein proposed. The sensors' array is composed of six ion-selective electrodes based on plasticized polymeric membranes with low selectivity profiles, i.e., the membranes do not contain any selective receptor. The sensors differ between them in the type of ion-exchanger (sensors for cations or anions) and the plasticizer used in the membrane composition, while the polymeric matrix and the preparation protocol were maintained. The potentiometric response of each sensor towards the main cations (Na+, K+, Ca2+, Mg2+) and anions (HCO3-, Cl-, SO42-, NO3-) expected in irrigation water samples was characterized, revealing a fast response time (<50 s). A total of 19 samples were analyzed with the sensor array at optimized experimental conditions, but, also, a series of complementary analytical techniques were applied to obtain the exact ion composition and conductivity to develop a trustable ET. The principal component analysis of the final potential values of the dynamic response observed with each sensor in the array allows for the differentiation between most of the samples in terms of quality. Furthermore, the ET was treated with a linear multivariate regression method for the quantitative determination of the mentioned ions in the irrigation water samples, revealing rather good prediction of Mg2+, Na+, and Cl- concentrations and acceptable results for the rest of ions. Overall, the ET is a promising analytical tool for irrigation water quality, exceeding traditional characterization approaches (conductivity, salinity, pH, cations, anions, etc.) in terms of overhead costs, versatility, simplicity, and total time for data provision.
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| 4. |
- Aref, Mohaddeseh, et al.
(author)
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Potentiometric pH Nanosensor for Intracellular Measurements: Real-Time and Continuous Assessment of Local Gradients
- 2021
-
In: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 93:47, s. 15744-15751
-
Journal article (peer-reviewed)abstract
- We present a pH nanosensor conceived for single intracellular measurements. The sensing architecture consisted of a two-electrode system evaluated in the potentiometric mode. We used solid-contact carbon nanopipette electrodes tailored to produce both the indicator (pH nanosensor) and reference electrodes. The indicator electrode was a membrane-based ion-selective electrode containing a receptor for hydrogen ions that provided a favorable selectivity for intracellular measurements. The analytical features of the pH nanosensor revealed a Nernstian response (slope of -59.5 mV/pH unit) with appropriate repeatability and reproducibility (variation coefficients of <2% for the calibration parameters), a fast response time (<5 s), adequate medium-term drift (0.7 mV h(-)(1)), and a linear range of response including physiological and abnormal cell pH levels (6.0-8.5). In addition, the position and configuration of the reference electrode were investigated in cell-based experiments to provide unbiased pH measurements, in which both the indicator and reference electrodes were located inside the same cell, each of them inside two neighboring cells, or the indicator electrode inside the cell and the reference electrode outside of (but nearby) the studied cell. Finally, the pH nanosensor was applied to two cases: (i) the tracing of the pH gradient from extra-to intracellular media over insertion into a single PC12 cell and (ii) the monitoring of variations in intracellular pH in response to exogenous administration of pharmaceuticals. It is anticipated that the developed pH nanosensor, which is a label-free analytical tool, has high potential to aid in the investigation of pathological states that manifest in cell pH misregulation, with no restriction in the type of targeted cells.
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| 5. |
- Chen, Chen, et al.
(author)
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Portable All-in-One Electrochemical Actuator-Sensor System for the Detection of Dissolved Inorganic Phosphorus in Seawater
- 2023
-
In: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 95:8, s. 4180-4189
-
Journal article (peer-reviewed)abstract
- 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.
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| 6. |
- Colozza, Noemi, et al.
(author)
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Insights into Tripodal Tris(pyrazolyl) Compounds as Ionophores for Potentiometric Ammonium Ion Sensing
- 2022
-
In: ChemElectroChem. - : Wiley. - 2196-0216. ; 9:18
-
Journal article (peer-reviewed)abstract
- The decentralisation of accurate determination of the ammonium ion (NH4+) is relevant for environmental monitoring (i. e., nitrogen cycle) and certain clinical applications (e. g., kidney and liver diseases). Potentiometric ionophore-based sensors are one alternative for these purposes in terms of versatile implementation, though the potassium ion (K+) is known to be a major source of interference. We herein investigate the use of three different tripodal tris(pyrazolyl) compounds derived from 1,3,5-triethylbenzene as NH4+ ionophores. A complete set of potentiometric experiments together with theoretical simulations reveals suitable analytical performance while demonstrating a suppression of the K+ interference given the formation of an adequate cavity in the ionophore to host NH4+ over K+ in the membrane environment. The results support the use of these electrodes in the analytical detection of NH4+ in a wide range of samples with variable contents.
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| 7. |
- Cuartero, Maria, PhD, 1984-
(author)
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Electrochemical sensors for in-situ measurement of ions in seawater
- 2021
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In: Sensors and actuators. B, Chemical. - : Elsevier BV. - 0925-4005 .- 1873-3077. ; 334
-
Journal article (peer-reviewed)abstract
- In the current water monitoring panorama, certain benefits are expected to arise when the modus operandum of analysis shifts from sampling-based to purely in-situ approaches. Since the appearance of the first submersible conductivity-temperature-depth (CTD) probe in the 80 s, clear efforts to move towards decentralized strategies have been reported in the literature, with some having even been brought to the stage of fruitful commercialization. Among the portfolio of available analytical techniques, only a handful of approaches offer clear potential for implementation in submersible devices, in terms of adequate analytical features, autonomy, feasibility of miniaturization, and ease of portability. Electrochemical sensors have demonstrated excellent characteristics for this purpose, particularly in the detection of ions. The present review analyses electrochemical sensors that have shown an aptitude for in-situ measurements of ions, including trace metals, nutrients, and carbon species in seawater. The previous 5 years have been selected as the main period for review, although in some instances comment is made upon earlier contributions to the field or commercialized devices, where these are deemed to exemplify crucial technological advancements. There is a notable lack of electrochemical sensors being deployed in in-situ applications, and this scarcity is even more stark when seawater is considered: only a very few cases have been demonstrated under such challenging conditions. With the aim of providing inspiration towards genuine advances in the field of in-situ seawater analysis, this work also highlights some laboratory scale research as well as studies concerning other environmental waters than seawater.
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| 8. |
- Cuartero, Maria, PhD, 1984-, et al.
(author)
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Potentiometric Electronic Tongue for Quantitative Ion Analysis in Natural Mineral Waters
- 2022
-
In: Sensors. - : MDPI. - 1424-8220. ; 22:16
-
Journal article (peer-reviewed)abstract
- The present paper addresses the development and use of a new potentiometric electronic tongue for both qualitative and quantitative characterization of natural mineral waters. The electronic tongue is particularly related to the conductivity and ion content of/in the water sample. The analytical system is based on six ion-selective electrodes whose membranes are formulated to provide either cationic or anionic response and considering plasticizers with different dielectric constants (bis(2-ethylhexyl) sebacate, 2-nitrophenyl octyl ether or tricresylphosphate), while keeping the polymeric matrix, i.e., poly(vinyl chloride). Notably, the absence of any ionophore in the membrane provides a general response profile, i.e., no selectivity toward any special ion, which is convenient for the realization of an effective electronic tongue. The dynamic response of the tongue toward water samples of different chemical compositions and geographical locations has been obtained. At the optimized experimental conditions, the tongue presents acceptable repeatability and reproducibility (absence of hysteresis). The principal component analysis of the final potential values observed with the six electrodes allows for the differentiation and classification of the samples according to their conductivity, which is somehow related to the mineralization. Moreover, quantitative determination of the six main ions in the water samples (i.e., chloride, nitrate, hydrogen carbonate, sulfate, sodium, calcium, and magnesium) is possible by means of a simple linear calibration (and cross-validation) model.
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| 9. |
- Garcia-Guzman, Juan Jose, et al.
(author)
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Microneedle based electrochemical (Bio)Sensing : Towards decentralized and continuous health status monitoring
- 2021
-
In: TrAC. Trends in analytical chemistry. - : Elsevier BV. - 0165-9936 .- 1879-3142. ; 135
-
Research review (peer-reviewed)abstract
- Microneedle (MN) based electrochemical (bio)sensing has become a growing field within the discipline of analytical chemistry as a result of its unique capacity for continuous, decentralized health status monitoring. There are two significant advantages to this exclusive feature: i) the ability to directly analyze interstitial fluid (ISF), a body fluid with a similar enough composition to plasma (and blood) to be considered a plentiful source of information related to biologically relevant molecules and biomarkers; and ii) the capacity to overcome some of the major limitations of blood analysis including painful extraction, high interferant concentrations, and incompatibility with diagnosis of infants (and especially newborns). Recent publications have demonstrated important advancements in electrochemical MN sensor technology, among which are included new MN fabrication methods and various modification strategies, providing different architectures and allowing for the integration of electronics. This versatility highlights the undeniable need for interdisciplinary efforts towards tangible progress in the field. In a context evidently dominated by glucose sensing, which is slowly being expanded towards other analytes, the following crucial questions arise: to what extent are electrochemical MN (bio)sensors a reliable analytical tool for continuous ISF monitoring? Which is the best calibration protocol to be followed for in vivo assays? Which strategies can be employed to protect the sensing element during skin penetration? Is there an appropriate validation methodology to assess the accuracy of electrochemical MN (bio)sensors? How significant is the distinction between successful achievements in the laboratory and the real commercial feasibility of products? This paper aims to reflect on those previous questions while reviewing the progress of electrochemical MN (bio)sensors in the last decade with a focus on the analytical aspects. Overall, we describe the current state of electrochemical MN (bio)sensors, the benefits and challenges associated to ISF monitoring, as well as key features (and bottlenecks) regarding its implementation for in vivo assays.
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| 10. |
- Garcia-Guzman, Juan Jose, et al.
(author)
-
Toward In Vivo Transdermal pH Sensing with a Validated Microneedle Membrane Electrode
- 2021
-
In: ACS Sensors. - : American Chemical Society (ACS). - 2379-3694. ; 6:3, s. 1129-1137
-
Journal article (peer-reviewed)abstract
- We present herein the most complete characterization of microneedle (MN) potentiometric sensors for pH transdermal measurements for the time being. Initial in vitro assessment demonstrated suitable analytical performances (e.g., Nernstian slope, linear range of response from 8.5 to 5.0, and fast response time) in both buffer media and artificial interstitial fluid (ISF). Excellent repeatability and reproducibility together with adequate selectivity and resiliency facilitate the appropriateness of the new pH MN sensor for transdermal ISF analysis in healthcare. The ability to resist skin insertions was evaluated in several ex vivo setups using three different animal skins (i.e., chicken, pork, and rat). The developed pH MN sensor was able to withstand from 5 to 10 repetitive insertions in all the skins considered with a minimal change in the calibration graph (<3% variation in both slope and intercept after the insertions). Ex vivo pH measurements were validated by determining the pH with the MN sensor and a commercial pH electrode in chicken skin portions previously conditioned at several pH values, obtaining excellent results with an accuracy of <1% and a precision of <2% in all cases. Finally, pH MN sensors were applied for the very first time to transdermal measurements in rats together with two innovative validation procedures: (i) measuring subcutaneous pH directly with a commercial pH microelectrode and (ii) collecting ISF using hollow MNs and then the pH measurement of the sample with the pH microelectrode. The pH values obtained with pH MN sensors were statistically more similar to subcutaneous measurements, as inferred by a paired sample t-test at 95% of confidence level. Conveniently, the validation approaches could be translated to other analytes that are transdermally measured with MN sensors.
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| 11. |
- Gil, R. L., et al.
(author)
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Addressing the Detection of Ammonium Ion in Environmental Water Samples via Tandem Potentiometry-Ion Chromatography
- 2022
-
In: ACS Measurement Science Au. - : American Chemical Society (ACS). - 2694-250X. ; 2:3, s. 199-207
-
Journal article (peer-reviewed)abstract
- An analytical methodology for detecting ammonium ion (NH4+) in environmental water through potentiometry-ion chromatography (IC) in tandem is presented here. A multielectrode flow cell is implemented as a potentiometric detector after chromatographic separation of cations in the sample. The electrodes are fabricated via miniaturized all-solid-state configuration, using a nonactin-based plasticized polymeric membrane as the sensing element. The overall analytical setup is based on an injection valve, column, traditional conductometric detector, and new potentiometric detector (in that order), permitting the characterization of the analytical performance of the potentiometric detector while validating the results. The limit of detection was found to be ca. 3 × 10-7 M NH4+ concentration after linearization of the potentiometric response, and intra- and interelectrode variations of <10% were observed. Importantly, interference from other cations was suppressed in the tandem potentiometry-IC, and thus, the NH4+ content in fresh- and seawater samples from different locations was successfully analyzed. This analytical technology demonstrated a great potential for the reliable monitoring of NH4+ at micromolar levels, in contrast to the conductivity detector and previously reported NH4+ potentiometric sensors functioning in batch mode or even coupled with IC. Additionally, the suitability of the potentiometric cell for selective multi-ion analysis in the same sample, i.e., Na+, NH4+, and K+ in water, has been proven.
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| 12. |
- Liu, Yujie, et al.
(author)
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Semi-empirical treatment of ionophore-assisted ion-transfers in ultrathin membranes coupled to a redox conducting polymer
- 2021
-
In: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 388, s. 138634-
-
Journal article (peer-reviewed)abstract
- Applying spectroelectrochemistry to all-solid-state electrodes composed of poly(3-octylthiophene) (POT) and an ultrathin ion-selective membrane on top, it is possible to monitor the dynamic charge transfer (CT) in POT when this event is coupled to ion transfers (ITs) promoted by the absence/presence of a se-lective ionophore in the membrane. Herein, we report on a combination of empirical and theoretical ev-idence revealing that different molar ratios of the ionophore and the cation exchanger in the membrane result in the modulation of non-assisted and assisted ITs of different stoichiometries. This occurs upon the same anodic voltammetric scan. The use of the developed theory together with Sigmoidal & minus;Boltzmann fittings of the experimental dynamic absorbance observed in the POT film permits calculating voltammo-grams with different ITs. An easy semi-empirical treatment additionally provides the calculation of bind-ing constants related to the assisted transfers. Furthermore, the approach is suitable for both preferred and non-preferred ions by the ionophore, which additionally leads to the estimation of the selectivity profile of the POT-membrane system. The extra discovery about the number of electrons associated to the CT in the POT film is expected to propitiate further research towards maximizing peak resolution in the voltammetric experiments. In this context, the developed theory would help in future steps to-wards the prediction of voltammetric responses for multi-ionophore membranes backside contacted with new redox materials, prospecting hence new electrodes for multi-ion detection with optimized analytical features.
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| 13. |
- Liu, Yujie, et al.
(author)
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Spectroelectrochemical Evidence of Interconnected Charge and Ion Transfer in Ultrathin Membranes Modulated by a Redox Conducting Polymer
- 2020
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In: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 92:20, s. 14085-14093
-
Journal article (peer-reviewed)abstract
- Previous publications have demonstrated the tuning of ion-transfer (IT) processes across ion-selective membranes (ISMs) with thicknesses in the nanometer order by modulating the oxidation state of a film of a conducting polymer, such as poly(3-octylthiophene) [POT], that is in back-side contact. Attempts on the theoretical description of this charge transfer (CT)-IT system have considered the Nernst equation for the CT, while there is no empirical evidence confirming this behavior. We present herein the first experimental characterization of the CT in POT films involved in different CT-IT systems. We take advantage of the absorbance change in the POT film while being oxidized, to monitor the CT linked to nonassisted and assisted ITs at the sample-ISM interface, from one to three ionophores, therefore promoting a change in the nature and number of the ITs. The CT is visualized as an independent sigmoid in different potential ranges according to the assigned IT. Herein, we have proposed a simple calculation of the empirical CT utilizing the mathematical Sigmoidal-Boltzmann model. The identification of the physical meaning of the mathematical definition of CT opens up new possibilities for the design of sensors with superior analytical features (mainly in terms of selectivity) and the calculation of apparent binding constants in the ISM.
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| 14. |
- Liu, Yujie, et al.
(author)
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Spectroelectrochemistry with Ultrathin lon-Selective Membranes : Three Distinct Ranges for Analytical Sensing
- 2022
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In: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 94:25, s. 9140-9148
-
Journal article (peer-reviewed)abstract
- We present spectroelectrochemical sensing of the potassium ion (K+) at three very distinct analytical ranges-nanomolar, micromolar, and millimolar-when using the same ion-selective electrode (ISE) but interrogated under various regimes. The ISE is conceived in the all-solid-state format: an ITO glass modified with the conducting polymer poly(3-octylethiophene) (POT) and an ultrathin potassium-selective membrane. The experimental setup is designed to apply a potential in a three-electrode electrochemical cell with the ISE as the working electrode, while dynamic spectral changes in the POT film are simultaneously registered. The POT film is gradually oxidized to POT+, and this process is ultimately linked to K+ transfer at the membrane-sample interface, attending to electroneutrality requirements. The spectroelectrochemistry experiment provides two signals: a voltammetric peak and a transient absorbance response, with the latter of special interest because of its correspondence with the generated charge in the POT and thus with the ionic charge expelled from the membrane. By modifying how the ion analyte (K+ but also others) is initially accumulated into the membrane, we found three ranges of response for the absorbance: 10-950 nM for an accumulation-stripping protocol, 0.5-10 mu M in diffusion-controlled cyclic voltammetry, and 0.5-32 mM with thin-layer cyclic voltammetry. This wide response range is a unique feature, one that is rare to find for a sensor and indeed for any analytical technique. Accordingly, the developed sensor is highly appealing for many analytical applications, especially considering the versatility of samples and ion analytes that may be spotted.
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| 15. |
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| 16. |
- Liu, Yujie, 1995-, et al.
(author)
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Voltammetric Ion-Selective Electrodes in Thin-Layer Samples : Absolute Detection of Ions Using Ultrathin Membranes
- 2024
-
In: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 96:3, s. 1147-1155
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Journal article (peer-reviewed)abstract
- Calibration-free sensors are generally understood as analytical tools with no need for calibration apart from the initial one (i.e., after its fabrication). However, an "ideal" and therefore "more restricted" definition of the concept considers that no calibration is necessary at all, with the sensor being capable of directly providing the analyte concentration in the sample. In the electroanalysis field, investigations have been directed to charge-based readouts (i.e., coulometry) that allow for concentration calculation via the Faraday Law: The sample volume must be precisely defined and the absoluteness of the electrochemical process in which the analyte is involved must be ensured (i.e., the analyte in the sample is similar to 100% converted/transported). Herein, we report on the realization of calibration-free coulometric ISEs based on ultrathin ion-selective membranes, which is demonstrated for the detection of potassium ions (K+). In essence, the K+ transfer at the membrane-sample interface is modulated by the oxidation state of the conducting polymer underlying the membrane. The accumulation/release of K+ to/from the membrane is an absolute process owing to the confinement of the sample to a thin-layer domain (thickness of <100 mu m). The capacity of the membrane expressed in charge is fixed to ca. 18 mu C, and this dictates the detection of micromolar levels of K+ present in ca. 5 mu L sample volume. The system is interrogated with cyclic voltammetry to obtain peaks related to the K+ transfer that can be treated charge-wise. The conceptual and technical innovative steps developed here made the calibration-free detection of K+ possible in artificial and real samples with acceptable accuracy (<10% difference compared with the results obtained from a current-based calibration and ion chromatography). The charge-based analysis does not depend on temperature and appeared to be repetitive, reproducible, and reversible in the concentration range from 1 to 37.5 mu M, with an average coulometry efficiency of 96%.
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| 17. |
- Molina Osorio, Andres, et al.
(author)
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Evidence of transient potentials in ion-selective electrodes based on thin-layer ion-exchange membranes
- 2024
-
In: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 484
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Journal article (peer-reviewed)abstract
- Polymeric membranes with ion-exchange properties have found numerous applications in water treatment, dialysis, energy storage, chemical sensors, and bio-interfaces, among others. Notably, it is common to operate under non-equilibrium conditions while pursuing specific features (e.g., current generation) through an electron-to-ion mechanism. To maximize the final performance, it is crucial to understand the role of each interface within the system, which becomes complex when the device is tailored with several materials and films. This is the case for ion sensors based on thin membranes in backside contact with a redox active conducting polymer. Herein, we investigate such a system operating under a charge transfer mechanism, which features electroneutrality maintenance as the main driving force upon application of a linear sweep potential. This potential is modeled as being unequally distributed among the various system interfaces. Our results demonstrate and quantify the existence of a transient membrane potential at the membrane-electrolyte interface, owing to the implementation of a strategical measurement point on the buried membrane side and connected to a built-in electrometer for the exclusive acquisition of the potential difference at such an interface. The transient membrane potential was found to be <1 % of the total applied potential, meaning that the ion-transfer process at the electrolyte-membrane interface is less energetically costly that the electron transfer and doping processes occurring at the conducting polymer side. This small contribution can be potentiated by increasing the ion-exchange capacity of the membrane, which indirectly enlarges the system current and serves as a strategy for increasing the efficiency of the device.
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| 18. |
- Molina Osorio, Andres, et al.
(author)
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Modelling electrochemical modulation of ion release in thin-layer samples
- 2021
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In: JOURNAL OF ELECTROANALYTICAL CHEMISTRY. - : Elsevier BV. - 1572-6657. ; 903, s. 115851-
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Journal article (peer-reviewed)abstract
- In this work, we present a model based on the finite element approach to describe the electrochemically controlled release of ions from a redox-active film into a sample confined to a thin-layer spatial domain. The model includes the effect of interfacial charge transfer kinetics and 1D-diffusion treatment for an electron transfer-ion transfer (ET-IT) coupled reaction. More in detail, the oxidation of the redox-active film (ET) involves an ion release to an aqueous phase (IT). The dynamic concentration of the released ion is calculated when the ET-IT reaction proceeds under potentiostatic control, and the effect of the thickness of each phase (i.e., film or aqueous) on the diffusion profile is analyzed. The model is experimentally validated for the particular case in which oxidation of a thin film of polyaniline (PANI, 10 mu m in thickness) is linked to the release of protons from the film into an electrolyte solution. The proton release produces certain pH changes in the electrolyte that are monitored by a pH sensor located at 330 mu m from the PANI film. The charge associated with the proton release is related to the dynamic concentration of protons in the electrolyte through pH-coulograms that agree with the theoretical predictions. Overall, the model can reproduce the general behavior of the experimental proton pump and provides key insights into the functioning mechanism of electrochemical systems where redox and ion transfer reactions are coupled.
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| 19. |
- Molinero Fernandez, Agueda, et al.
(author)
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In Vivo Transdermal Multi-Ion Monitoring with a Potentiometric Microneedle-Based Sensor Patch
- 2023
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In: ACS Sensors. - : American Chemical Society (ACS). - 2379-3694. ; 8:1, s. 158-166
-
Journal article (peer-reviewed)abstract
- Microneedle sensor technology offers exciting opportunities for decentralized clinical analyses. A novel issue puts forward herein is to demonstrate the uniqueness of membrane-based microneedles to accomplish real-time, on-body monitoring of multiple ions simultaneously. The use of multi-ion detection is clinically relevant since it is expected to provide a more complete and reliable assessment of the clinical status of a subject concerning electrolyte disorders and others. We present a microneedle system for transdermal multiplexed tracing of pH, Na+, K+, Ca2+, Li+, and Cl-. The device consists of an array of seven solid microneedles externally modified to provide six indicator electrodes, each selective for a different ion, and a common reference electrode, all integrated into a wearable patch read in a potentiometric mode. We show in vitro measurements at the expected clinical levels, resulting in a fast response time, excellent reversibility and repeatability, and adequate selectivity. Close-to-Nernstian sensitivity, sufficient stability and resiliency to skin penetration guarantee the sensor's success in transdermal measurements, which we demonstrate through ex vivo (with pieces of rat skin) and in vivo (on-body measurements in rats) tests. Accuracy is evaluated by comparison with gold standard techniques to characterize collected dermal fluid, blood, and serum. In the past, interstitial fluid (ISF) analysis has been challenging due to difficult sample collection and analysis. For ions, this has resulted in extrapolations from blood concentrations (invasive tests) rather than pure measurements in ISF. The developed microneedle patch is a relevant analytical tool to address this information gap.
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| 20. |
- Robayo Molina, Iván, et al.
(author)
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Usefulness of the Distribution of Relaxation Time Method in Electroanalytical Systems : The Case of Voltammetric Ion-Selective Electrodes
- 2023
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In: ACS Omega. - : American Chemical Society (ACS). - 2470-1343.
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Journal article (peer-reviewed)abstract
- Despite the distribution of relaxation time (DRT) method providing clear insights about processes that go unnoticed by traditional electrochemical impedance spectroscopy (EIS) analysis, it has not yet been adopted to solve electroanalytical systems. As an illustration case, we apply the DRT method to deconvolve EIS data from solid-state voltammetric ion-selective electrodes (ISEs). The main aim is to shed light on the underlying working mechanism across the different materials and interfaces, specifically, the doping of a conducting polymer when covered with a very thin (ca. 230 nm) permselective membrane. Although frequency-dependent AC measurements in EIS allow the separation of processes that contribute to the electrical signal, interpretation of the data is challenging. DRT may overcome this inconvenience by revealing a series of peaks corresponding to the predominant electrochemical processes, without any preknowledge on those. To demonstrate our hypothesis, we examine the conducting polymer poly(3-octylthiophene) (POT) linked to a membrane with sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (Na+TFPB-) as the cation exchanger, in which the lipophilic anionic part (TFPB-) is responsible for the POT doping when it gets electrochemically oxidized (POT+). The investigation of EIS data obtained under different conditions with the DRT method showed the occurrence of several processes. We have attributed two of these to two different conformational changes in the POT film in connection with p-type charge-transfer doping. Indeed, the kinetics is found to follow a Butler-Volmer behavior, with average charge transfers of 0.5 and 0.3 mol of electrons for each peak. Overall, we demonstrate the utility of the EIS-DRT tandem to separately study charge-transfer events that interconnect along the same (interfacial segmented) system, which cannot be reached by using classical electrochemical approaches. These kinds of insights are necessary for a more efficient design and high-level exploitation of voltammetric ISEs but also other electrochemical systems such as catalysts, batteries, and photovoltaic cells.
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| 21. |
- Steininger, Fabian, et al.
(author)
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Imaging Sample Acidification Triggered by Electrochemically Activated Polyaniline
- 2022
-
In: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 94:40, s. 13647-13651
-
Journal article (peer-reviewed)abstract
- In this letter, we demonstrate 2D acidification of samples at environmental and physiological pH with an electrochemically activated polyaniline (PANI) mesh. A novel sensor–actuator concept is conceived for such a purpose. The sample is sandwiched between the PANI (actuator) and a planar pH optode (sensor) placed at a very close distance (∼0.50 mm). Upon application of a mild potential to the mesh, in contrast to previously reported acidification approaches, PANI releases a significant number of protons, causing an acid–base titration in the sample. This process is monitored in time and space by the pH optode, providing chemical imaging of the pH decrease along the dynamic titration via photographic acquisition. Acidification of samples at varying buffer capacity has been investigated: the higher the buffer capacity, the more time (and therefore proton charge) was needed to reach a pH of 4.5 or even lower. Also, the ability to map spatial differences in buffer capacity within a sample during the acid–base titration was unprecedentedly proven. The sensor–actuator concept could be used for monitoring certain analytes in samples that specifically require acidification pretreatment. Particularly, in combination with different optodes, dynamic mapping of concentration gradients will be accessible in complex environmental samples ranging from roots and sediments to bacterial aggregates.
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| 22. |
- Van Hoovels, Kevin, et al.
(author)
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Can Wearable Sweat Lactate Sensors Contribute to Sports Physiology?
- 2021
-
In: ACS Sensors. - : American Chemical Society (ACS). - 2379-3694. ; 6:10, s. 3496-3508
-
Research review (peer-reviewed)abstract
- The rise of wearable sensors to measure lactate content in human sweat during sports activities has attracted the attention of physiologists given the potential of these "analytical tools" to provide real-time information. Beyond the assessment of the sensing technology per se, which, in fact, has not rigorously been validated yet in controlled conditions, there are many open questions about the true usefulness of such wearable sensors in real scenarios. On the one hand, the evidence for the origin of sweat lactate (e.g., via the sweat gland, derivation from blood, or other alternative mechanisms), its high concentration (1-25 mM or even higher) compared to levels in the blood, and the possible correlation between different biofluids (particularly blood) is rather contradictory and generates vivid debate in the field. On the other hand, it is important to point out that accurate detection of sweat lactate is highly dependent on the procedure used to collect and/or reach the fluid, and this can likely explain the large discrepancies reported in the literature. In brief, this paper provides our vision of the current state of the field and a thoughtful evaluation of the possible reasons for present controversies, together with an analysis of the impact of wearable sweat lactate sensors in the physiological context. Finally, although there is not yet overwhelming scientific evidence to provide an unequivocal answer to whether wearable sweat lactate sensors can contribute to sports physiology, we still understand the importance to bring this challenging question up-front to create awareness and guidance in the development, validation, and implementation of wearable sensors.
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| 23. |
- Wang, Qianyu, et al.
(author)
-
Electrochemical biosensor for glycine detection in biological fluids
- 2021
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In: Biosensors & bioelectronics. - : Elsevier BV. - 0956-5663 .- 1873-4235. ; 182
-
Journal article (peer-reviewed)abstract
- We present herein the very first amperometric biosensor for the quantitative determination of glycine in diverse biological fluids. The biosensor is based on a novel quinoprotein that catalyzes the oxidation of glycine with high specificity. This process is coupled to the redox conversion of Prussian blue in the presence of hydrogen peroxide originating from the enzymatic reaction. The optimized tailoring of the biosensor design consists of the effective encapsulation of the quinoprotein in a chitosan matrix with the posterior addition of an outer Nafion layer, which is here demonstrated to suppress matrix interference. This is particularly important in the case of ascorbic acid, which is known to influence the redox behavior of the Prussian blue. The analytical performance of the biosensor demonstrates fast response time (<7 s), acceptable reversibility, reproducibility, and stability (<6% variation) as well as a wide linear range of response (25?500 ?M) that covers healthy (and even most unhealthy) physiological levels of glycine in blood/serum, urine and sweat. A total of 6 real samples from healthy patients and animals were analyzed: two serum, two urine and two sweat samples. The results were validated via commercially available fluorescence kit, displaying discrepancy of less than 9% in all the samples. The unique analytical features and effortless preparation of the new glycine biosensor position it at the forefront of current technologies towards decentralized clinical applications and sport performance monitoring.
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| 24. |
- Wang, Qianyu, et al.
(author)
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Intradermal Glycine Detection with a Wearable Microneedle Biosensor : The First In Vivo Assay
- 2022
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In: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 94:34, s. 11856-11864
-
Journal article (peer-reviewed)abstract
- Glycine (GLY) is gaining importance in medical diagnoses due to its relationship with multiple physiological functions. Today, GLY is exclusively analyzed using instrumentation centralized in clinical labs, and a tangible point-of-care tool that gathers real-time data from the patient for effective and fast evaluations is lacking. Relevant clinical advances are expected as soon as the rapid provision of both punctual and continuous measurements is possible. In that context, this work presents a microneedle (MN)-based biosensor for intradermal GLY detection in interstitial fluid (ISF). The MN tip is externally tailored to detect GLY levels through the hydrogen peroxide formed in its reaction with a quinoprotein-based GLY oxidase enzyme. The analytical performance of the MN biosensor indicates a fast response time (<7 s); acceptable reversibility, reproducibility, and stability; as well as a wide linear range of response (25-600 μM) that covers the physiological levels of GLY in ISF. The MN biosensor conveniently exhibits high selectivity for GLY over other compounds commonly found in ISF, and the response is not influenced by temperature, pH, or skin insertions. Validated intradermal measurements of GLY were obtained at the in vitro (with pieces of rat skin), ex vivo (on-body tests of euthanized rats) and in vivo (on-body tests of anesthetized rats) levels, demonstrating its ability to produce accurate physiological data. The developed GLY MN biosensor is skin-wearable and provides reliable, real-time intradermal GLY measurements in ISF by means of a minimally invasive approach.
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| 25. |
- Wiorek, Alexander, et al.
(author)
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Imaging of CO2 and Dissolved Inorganic Carbon via Electrochemical Acidification–Optode Tandem
- 2023
-
In: ACS Sensors. - : American Chemical Society (ACS). - 2379-3694. ; 8:7, s. 2843-2851
-
Journal article (peer-reviewed)abstract
- Dissolved inorganic carbon (DIC) is a key component of the global carbon cycle and plays a critical role in ocean acidification and proliferation of phototrophs. Its quantification at a high spatial resolution is essential for understanding various biogeochemical processes. We present an analytical method for 2D chemical imaging of DIC by combining a conventional CO2 optode with localized electrochemical acidification from a polyaniline (PANI)-coated stainless-steel mesh electrode. Initially, the optode response is governed by local concentrations of free CO2 in the sample, corresponding to the established carbonate equilibrium at the (unmodified) sample pH. Upon applying a mild potential-based polarization to the PANI mesh, protons are released into the sample, shifting the carbonate equilibrium toward CO2 conversion (>99%), which corresponds to the sample DIC. It is herein demonstrated that the CO2 optode–PANI tandem enables the mapping of free CO2 (before PANI activation) and DIC (after PANI activation) in complex samples, providing high 2D spatial resolution (approx. 400 μm). The significance of this method was proven by inspecting the carbonate chemistry of complex environmental systems, including the freshwater plant Vallisneria spiralis and lime-amended waterlogged soil. This work is expected to pave the way for new analytical strategies that combine chemical imaging with electrochemical actuators, aiming to enhance classical sensing approaches via in situ (and reagentless) sample treatment. Such tools may provide a better understanding of environmentally relevant pH-dependent analytes related to the carbon, nitrogen, and sulfur cycles.
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| 26. |
- Wiorek, Alexander, et al.
(author)
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Polyaniline Films as Electrochemical-Proton Pump for Acidification of Thin Layer Samples
- 2019
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In: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 91:23, s. 14951-14959
-
Journal article (peer-reviewed)abstract
- Here, we provide the first experimental evidence of proton release from polyaniline (PANI) films subjected to anodic potentials at environmental pHs. We conducted an extensive characterization of unpolarized/polarized PANI films—synthesized by traditional sequential voltammetric scanning—by using spectroelectrochemistry, synchrotron radiation-X-ray photoelectron spectroscopy, near edge X-ray absorption fine structure, and potentiometric pH sensing in the vicinity of the PANI layer. This new insight enables the utilization of PANI as a proton pump, which is actively tuned through an electrochemical pulse, so as to controllably acidify well-confined thin layer samples. Furthermore, we demonstrate the analytical significance of this system by measuring the alkalinity of artificial and natural water samples by using two faced planar PANI electrodes, one working as a proton source and the other one as pH electrode. Finally, the impact of this approach is 2-fold: (i) all-solid-state electrode materials may be used with devisible consequences in miniaturized and implementable submersible probes, and (ii) rapid determination of alkalinity as compared to traditional approaches together with a versatility in pH adjustment in any kind of sample, among other applications.
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| 27. |
- Wiorek, Alexander, et al.
(author)
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Reagentless Acid–Base Titration for Alkalinity Detection in Seawater
- 2021
-
In: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 93:42, s. 14130-14137
-
Journal article (peer-reviewed)abstract
- Herein, we report on a reagentless electroanalytical methodology for automatized acid–base titrations of water samples that are confined into very thin spatial domains. The concept is based on the recent discovery from our group (Wiorek, A. Anal. Chem. 2019, 91, 14951−14959), in which polyaniline (PANI) films were found to be an excellent material to release a massive charge of protons in a short time, achieving hence the efficient (and controlled) acidification of a sample. We now demonstrate and validate the analytical usefulness of this approach with samples collected from the Baltic Sea: the titration protocol indeed acts as an alkalinity sensor via the calculation of the proton charge needed to reach pH 4.0 in the sample, as per the formal definition of the alkalinity parameter. In essence, the alkalinity sensor is based on the linear relationship found between the released charge from the PANI film and the bicarbonate concentration in the sample (i.e., the way to express alkalinity measurements). The observed alkalinity in the samples presented a good agreement with the values obtained by manual (classical) acid–base titrations (discrepancies <10%). Some crucial advantages of the new methodology are that titrations are completed in less than 1 min (end point), the PANI film can be reused at least 74 times over a 2 week period (<5% of decrease in the released charge), and the utility of the PANI film to even more decrease the final pH of the sample (pH ∼2) toward applications different from alkalinity detection. Furthermore, the acidification can be accomplished in a discrete or continuous mode depending on the application demands. The new methodology is expected to impact the future digitalization of in situ acid–base titrations to obtain high-resolution data on alkalinity in water resources.
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| 28. |
- Wiorek, Alexander, et al.
(author)
-
Selective Deionization of Thin-Layer Samples Using Tandem Carbon Nanotubes-Polymeric Membranes
- 2023
-
In: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 95:42, s. 15681-15689
-
Journal article (peer-reviewed)abstract
- Herein, we investigate the selective deionization (i.e., the removal of ions) in thin-layer samples (<100 mu m in thickness) using carbon nanotubes (CNTs) covered with an ionophore-based ion-selective membrane (ISM), resulting in a CNT-ISM tandem actuator. The concept of selective deionization is based on a recent discovery by our group (), where the activation of the CNT-ISM architecture is conceived on a mild potential step that charges the CNTs to ultimately generate the depletion of ions in a thin-layer sample. The role of the ISM is to selectively facilitate the transport of only one ion species to the CNT lattice. To estimate the deionization efficiency of such a process, a potentiometric sensor is placed less than 100 mu m away from the CNT-ISM tandem, inside a microfluidic cell. This configuration helped to reveal that the selective uptake of ions increases with the capacitance of the CNTs and that the ISM requires a certain ion-exchanger capacity, but this does not further affect its efficiency. The versatility of the concept is demonstrated by comparing the selective uptake of five different ions (H+, Li+, Na+, K+, and Ca2+), suggesting the possibility to remove any cation from a sample by simply changing the ionophore in the ISM. Furthermore, ISMs based on two ionophores proved to achieve the simultaneous and selective deionization of two ion species using the same actuator. Importantly, the relative uptake between the two ions was found to be governed by the ion-ionophore binding constants, with the most strongly bound ion being favored over other ions. The CNT-ISM actuator concept is expected to contribute to the analytical sensing field in the sense that ionic interferents influencing the analytical signal can selectively be removed from samples to lower traditional limits of detection.
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| 29. |
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| 30. |
- Wiorek, Alexander, et al.
(author)
-
Selective Ion Capturing via Carbon Nanotubes Charging
- 2022
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In: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 94:21, s. 7455-7459
-
Journal article (peer-reviewed)abstract
- We present a phenomenon consisting of the synergistic effects of a capacitive material, such as carbon nanotubes (CNTs), and an ion-selective, thin-layer membrane. CNTs can trigger a charge disbalance and propagate this effect into a thin-layer membrane domain under mildly polarization conditions. With the exceptional selectivity and the fast establishment of new concentration profiles provided by the thin-layer membrane, a selective ion capture from the solution is expected, which is necessarily linked to the charge generation on the CNTs lattice. As a proof-of-concept, we investigated an arrangement based on a layer of CNTs modified with a nanometer-sized, potassium-selective membrane to conform an actuator that is in contact with a thin-layer aqueous solution (thickness of 50 μm). The potassium ion content was fixed in the solution (0.1–10 mM range), and the system was operated for 120 s at −400 mV (with respect to the open circuit potential). A 10-fold decrease from the initial potassium concentration in the thin-layer solution was detected through either a potentiometric potassium-selective sensor or an optode confronted to the actuator system. This work is significant, because it provides empirical evidence for interconnected charge transfer processes in CNT–membrane systems (actuators) that result in controlled ion uptake from the solution, which is monitored by a sensor. One potential application of this concept is the removal of ionic interferences in a sample by means of the actuator to enhance precision of analytical assessments of a charged or neutral target in the sample with the sensor.
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| 31. |
- Xu, Kequan
(author)
-
Electrochemical detection of trace metals: from traditional techniques to new ultrathin membrane electrodes
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- Accurate detection of trace metals in environmental waters is an analytical challenge that is still open for the time being. The current state of the field reveals the predominance of the so-called hanging mercury drop electrode (HMDE) for multi-metal detection by means of anodic stripping voltammetry (ASV) readout. Being aware of the high toxicity of mercury and the high risk of a serious environmental footprint when water measurements are performed with the HMDE, in the past years, the electrochemistry field has rapidly moved towards the provision of tangible alternatives. Yet, none of the proposed methodologies has reached appropriate maturation and/or analytical features to substitute the use of the HMDE in the detection of trace metal ions in water.The investigations presented in this thesis are framed within the direction of new analytical strategies for the detection of trace metals in water, with special focus on the silver ion (Ag+). Voltammetric ion-selective electrodes (ISEs) with a working mechanism conceived on the basis of interconnected charge-transfer (CT) and ion-transfer (IT) processes are selected for such purpose due to their unique characteristics towards decentralized measurements.The first chapter of the thesis aims to provide a general background about electrochemistry measurements of ions, providing special attention to all-solid-state voltammetric ISEs based on ultrathin membranes that provide the CT–IT mechanism. Fundaments about ASV and the use of the HMDE for trace metal detection are also revised. Of particular interest is the case of Ag+ determination, which is not fully addressed with the HMDE. Accordingly, the state-of-the-art of electrochemical analysis of trace Ag+ has been established (Paper I).The second chapter shows the experimental details and the third chapter presents and discusses all the results obtained in this thesis.The first section is about a new analytical strategy for nanomolar detection of Ag+ in waters by coupling a silver-selective electrode (AgSE) based on a CT–IT mechanism with IT stripping voltammetry readout (Paper II). Specifically, the IT occurs via providing the CT process in electrodes that are modified with a redox-active conductive polymer and an ultrathin silver-selective membrane placed on top. Thus, the CT–IT tandem in voltammetric ISEs is unprecedently demonstrated for the detection of Ag+ in different water samples.The second section is based on the improvement of the limit of detection of the developed AgSE to detect sub-nanomolar concentration of Ag+ even in the presence of high interference levels, e.g., sodium ion (Paper III). Through the reduction of the total ion-exchange capacity of the ultrathin membrane, it is possible to increase the effectiveness towards the intake of Ag+ versus sodium ions (Na+) when IT stripping voltammetry is applied. The resulting ISE displayed a limit of detection of 0.05 nM, with a linear range of response up to 10 nM and is successfully applied for the analysis of Ag+ in several water samples, including seawater.The third section presents the investigation of the HMDE for multi-metal detection at trace levels in soil waters while establishing the fundaments, features and controversies of the technique (Paper IV). The entire replacement of the HMDE will only occur when multi-metal trace detection is provided by a sole electrode or an electrode array able to provide similar analytical characteristics, which are collected in this thesis, while avoiding the use of mercury or any other pollutant in the electrode manufacturing.The fourth section inquiries the possibility of using voltammetric ISE based on interconnected CT–IT processes for other trace metals, in particular lead and copper ions (Pb2+ and Cu2+) (Paper V). Despite more work being necessary in that direction, preliminary insights have revealed the potential of the CT–IT technique developed in this thesis towards multi-metal detection either with the incorporation in the membrane of multiple ionophores with different selectivity profiles for each metal or with a multi-sensor array. Accordingly, the research work presented in this thesis has a strong potential towards future investigations in this direction.
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| 32. |
- Xu, Kequan, et al.
(author)
-
Electrochemical detection of trace silver
- 2021
-
In: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 374
-
Journal article (peer-reviewed)abstract
- Increasing utilization of silver and silver nanoparticles (AgNPs) in daily processes and products has led to a significant growth in scientific interest in methods for monitoring silver. In particular, the amount of silver ions (Ag +) released to the environment is known to have a detrimental effect on aquatic ecology, and thus some control actions have been implemented in recent years; for example, the manufacturing industry is now required to control and certify the quantity of AgNPs present in products. Electrochemical sensors are well suited to the task of silver monitoring due to several beneficial properties, including low costs, fast measurements, and facile adaptation to miniaturized, portable instrumentation. The predominant method for electrochemical silver determination involves potentiometric ion selective electrodes (ISEs) and voltammetric measurements. Reviewing the literature of the last ten years reveals significant improvements in the analytical performance of electrochemical sensors, mainly related to the development of new protocols, selective receptors, and electrode materials. Remarkably, ISEs with limits of detection (LOD) in the nanomolar range have been reported, employing careful control of ion fluxes across the membrane interfaces. What's more, sub-nanomolar LODs are attainable by stripping voltammetry using either ligand-based deposition strategies or thin layer membranes coupled to conducting polymers. Selectivity has also been optimized through the membrane composition of ISEs, with special focus on Ag+ ionophores. Furthermore, novel voltammetric methods allow for discrimination between Ag+ and AgNPs. However, there is still a dearth of studies applying such electrochemical sensors to on-site water analysis, and hence, further research is needed in order to translate these laboratory scale achievements to real-world contexts. Overall, this review describes the state-of-the-art in electrochemical silver detection, and provides a comprehensive description of those aspects contributing to the further development and improvement of analytical performance.
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| 33. |
- Xu, Kequan, et al.
(author)
-
Ultrathin ion-selective membranes for trace detection of lead, copper and silver ions
- 2022
-
In: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 427
-
Journal article (peer-reviewed)abstract
- Voltammetric ion-selective electrodes (ISEs) based on poly(3-octylthiophene) (POT) in connection with ultra-thin membranes formulated with different selective receptors (i.e., ionophores) are proposed for detection of lead, copper and silver ions (Pb2+, Cu2+ and Ag+). The working mechanism of the POT-membrane electrode is based on interconnected charge transfer processes on both sides of the membrane, with the overall process depending on the electron transfer in the POT lattice ultimately linked to the ion transfer at the membrane–sample interface. This latter is demonstrated to be controlled by (i) the membrane composition and (ii) the accumulation/stripping electrochemical protocol, allowing the detection of traces of Ag+, Pb2+ and Cu2+. In the case of the Pb2+-selective electrode, the voltammogram displays several peaks that are hypothesized to correspond to different ion–ionophore stoichiometries. Following the signal related to the principal stoichiometry (1:1), a Pb2+ concentration as low as 0.1 nM is measurable. In contrast, the Cu2+- and Ag+-selective electrodes show only one peak for the corresponding ion analyte, which can be also detected at nanomolar concentrations. The results obtained with the three electrodes support their further usage for multi-ion detection in water samples through either a multi-ionophore-based electrode or multiple-electrode device. In any case, the membrane composition, in terms of the ionophore/exchanger molar ratio, is key to achieving a successful analytical application. Upcoming efforts may be directed at the replacement of traditional trace metal ion detection with the hanging mercury drop electrode to develop a more sustainable electrochemical approach without diminishing the analytical performance.
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| 34. |
- Xuan, Xing, et al.
(author)
-
A Wearable Biosensor for Sweat Lactate as a Proxy for Sport Performance Monitoring
- 2022
-
In: Analysis & Sensing. - : Wiley-VCH Verlagsgesellschaft. - 2629-2742. ; 3:4
-
Journal article (peer-reviewed)abstract
- 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.
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| 35. |
- Xuan, Xing, et al.
(author)
-
A Wearable Biosensor for Sweat Lactate as a Proxy for Sport Performance Monitoring
- 2023
-
In: Analysis & Sensing. - : Wiley. - 2629-2742. ; 3:4
-
Journal article (other academic/artistic)abstract
- 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.
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| 36. |
- Xuan, Xing, et al.
(author)
-
Fully Integrated Wearable Device for Continuous Sweat Lactate Monitoring in Sports.
- 2023
-
In: ACS Sensors. - : American Chemical Society (ACS). - 2379-3694. ; 8:6, s. 2401-2409
-
Journal article (peer-reviewed)abstract
- 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.
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| 37. |
- Xuan, Xing, et al.
(author)
-
Lactate Biosensing for Reliable On-Body Sweat Analysis
- 2021
-
In: ACS Sensors. - : American Chemical Society (ACS). - 2379-3694. ; 6:7, s. 2763-2771
-
Journal article (peer-reviewed)abstract
- 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.
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