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Organic electrochemical transistors (OECTs) have attracted great interest in the last few years as biochemical sensors due to their outstanding analytical performance, versatility, stability, and e...

Systematic errors in the calix [4] pyrrole-based potentiometric detection of creatinine have been observed in heavy smokers. This work further characterizes the interactions between the nicotinium cation and the cavitand as well as the resulting interference produced during the potentiometric detection. It is found that the nicotinium cation binds the electronic rich aromatic cavity defined by the pyrrole rings of the receptor's cone conformation with an estimated binding constant higher than 10

The use of a Pt electrode coated with a layer of Nafion has been described in previous works as an attractive way to perform the potentiometric detection of hydrogen peroxide. Despite of the attractive features of this approach, the nature of the non-Nernstian response of this system was not properly addressed. In this work, using a mixed potential model, the open circuit potential of the Pt electrode is shown to be under kinetic control of the oxygen reduction reaction (ORR). It is proposed that hydrogen peroxide acts as an oxygenated species that blocks free sites on the Pt surface, interfering with the ORR. Therefore, the effect of the polyelectrolyte coating can be understood in terms of the modulation of the factors that affects the kinetics of the ORR, such as an increase of the H+ concentration, minimization of the effect of the spectator species, etc. Because of the complexity and the lack of models that accurately describe systems with practical applications, this work is not intended to provide a mechanistic but rather a phenomenological view on problem. A general framework to understand the factors that affect the potentiometric response is provided. Experimental evidence showing that the use of polyelectrolyte coatings are a powerful way to control the mixed potential open new ways for the development of robust and simple potentiometric sensors.

Creatinine is a metabolite present in urine, and its concentration is used to diagnose and monitor kidney performance. For that reason, the development of new sensors to analyze this metabolite and obtain accurate results in a short period of time is necessary. An optical disposable sensor for monitoring creatinine levels in urine is described. The system, based on a new aryl-substituted calix[4]pyrrole synthetic receptor, has an unusual coextraction scheme. Due to the low pKa values of creatininium (pKa 4.8), a careful selection of a lipophilic pH indicator that works in acid medium is required. The sensor components were optimized, and the new sensor displays a good response time to creatinine (approximately 3 min) over a wide dynamic range (from 1 × 10−5 to 1 × 10−2 M). Moreover, the optical selectivity coefficients obtained for creatinine over common cations present in urine meet the requirements for real sample measurements. With a good sensor-to-sensor reproducibility (RSD, 5.1−6.9% in the middle of the range), this method provides a simple, quick, cost-effective, and selective alternative to the conventional methodology based on Jaffé’s reaction, FQM-118, MINECO (CTQ2016-78754-C2-1-R), Spanish Ministry of Economy and Competitiveness and European Regional Development Fund (ERDF) CTQ2016-77128-R, MINECO (CTQ2017-84319-P), Severo Ochoa Excellence Accreditation 2014-2018 SEV-2013-0319, FEDER funds (Project CTQ2017- 84319-P), CERCA Programme/Generalitat de Catalunya and AGAUR (2017 SGR 1123)

The growing demand for tools to generate chemical information in decentralized settings is creating a vast range of opportunities for potentiometric sensors, since their combination of robustness, simplicity of operation and cost can hardly be rivalled by any other technique. In previous works, we have shown that the mixed potential of a Pt electrode can be controlled with analytical purposes using a coating of Nafion, thus providing a way to develop a potentiometric biosensor for glucose. Unfortunately, the linear range of this device did not match the relevant clinical range for glucose in blood. This work presents a novel strategy to control the mixed potential that allows the development of a potentiometric biosensor for the direct detection of glucose in whole, undiluted blood without any sample pretreatment. By changing the ionomer, the analytical response can be tuned, shifting the linear range while keeping the sensitivity. Aquivion, a polyelectrolyte from the same family as Nafion, is used to stabilize the mixed potential of a platinized paper-based electrode, to entrap the enzyme and to reduce the interference from negatively charged species. Factors affecting the generation of the signal and the principle of detection are discussed. Optimization of the biosensor composition was achieved with particular focus on the characterization of the linear range and sensitivity. The accurate measurement of blood sugar levels in a single drop of whole blood with excellent recovery is presented.

A sensor for monitoring total ion activity is described, and its performance as a wearable device for monitoring the total ion levels of sweat is evaluated. The sensor works by tracking changes in the Donnan potential generated across a Nafion® membrane. This cation-exchange polymer was cast on a paper coated with carbon-ink, making the platform elegantly simple. Analytical parameters during calibration in aqueous solution include a sensitivity of 56.3±1.0 mV/dec.a(Na+) and a standard deviation between standard electrode potentials of 5.3 mV (N=5) for first time use. By integrating a paper based pseudo reference electrode, a miniature disposable electrochemical cell (the “IonSens” device) was created and demonstrated as a wearable sensor. Potentiometric measurements estimating the total ion activities were validated against conductivity measurements. Recoveries of eleven raw sweat samples were determined to be 95.2±6.6% (n=3). The perspiration conductivity profile of an athlete during exercise was monitored in real-time and visualized on a mobile phone application connected via Bluetooth®. The excellent reproducibility of the electrode without any conditioning is noteworthy and lends itself to applications including – but not limited to – the monitoring of total ion activity in sweat.

A novel paper-based potentiometric sensor with an enhanced response for the detection of glucose in biological fluids is presented. The electrode consists on platinum sputtered on a filter paper and a Nafion membrane to immobilize the enzyme glucose oxidase. The response obtained is proportional to the logarithm of the concentration of glucose, with a sensitivity of -119 +/- 8 mV.decade(-1), a linear range that spans from 10(-4)M to 10(-2.5) M and a limit of detection of 10(-4.5) M of glucose. It is shown that Nafion increases the sensitivity of the technique while minimizing interferences. Validation with human serum samples shows an excellent agreement when compared to standard methods. This approach can become an interesting alternative for the development of simple and affordable devices for point of care and home-based diagnostics.

The optimization, analytical characterization and validation of a novel ion-selective electrode for the highly sensitive and selective determination of creatinine in urine is presented. A newly synthesized calix[4]pyrrole-based molecule is used as an ionophore for the enhanced recognition of creatininium cations. The calculation of the complex formation constants in the polymeric membrane with creatininium, potassium and sodium confirms the strong selective interactions between the ionophore and the target. The optimization of the potentiometric sensor presented here yields an outstanding analytical performance, with a linear range that spans from 1µM to 10mM and limit of detection of 10-6.2M. The calculation of the selectivity coefficients against most commonly found interferences also show significant improvements when compared to other sensors already reported. The performance of this novel sensor is tested by measuring creatinine in real urine samples (N=50) and comparing the values against the standard colorimetric approach (Jaffe's reaction). The results show that this sensor allows the fast and accurate determination of creatinine in real samples with minimal sample manipulation.

Background It is vital for frontline emergency physicians to immediately recognize the signs and symptoms of measles to initiate appropriate therapy and prevent spread to the health care team and other patients. Objective This review serves as a clinically practical updated reference for when the differential diagnosis includes measles. Discussion Measles is a highly contagious illness that classically presents with a rash, fever, cough, coryza, and conjunctivitis. Cases in the United States since 2000 have been attributed mainly to travelers who are infected abroad and then spread the illness to small, susceptible populations within the United States. Complications from measles are relatively common and can be associated with significant morbidity and mortality. Clinical suspicion should be confirmed with laboratory testing, which is most commonly a serum immunoglobulin M. The management of measles is mainly supportive. Patients that require more aggressive management include those who are pregnant, immunocompromised, or unvaccinated. Treatment may consist of the measles vaccine, intravenous immunoglobulin, vitamin A, and even ribavirin. Additionally, special precautions are required by hospital workers to help prevent the spread of the virus, which include N-95 masks and patient isolation in an airborne infection isolation room. Conclusion Emergency physicians must be readily able to identify, contain patients with suspected measles, and determine who will need further medical management for this potentially life-threatening illness. As this public health crisis evolves, novel ways of screening for and reporting cases of measles is needed.

The fabrication and performance of a wearable paper‐based chemiresistor for monitoring perspiration dynamics (sweat rate and sweat loss) are detailed. A novel approach is introduced to measure the amount of aqueous solution in the order of microliters delivered to the sensor by monitoring a linear change in resistance along a conducting paper. The wearable sensor is based on a single‐walled carbon nanotubes and surfactant (sodium dodecylbenzenesulfonate) nanocomposite integrated within cellulose fibers of a conventional filter paper. The analytical performance and the sensing mechanism are presented. Monitoring sweat loss in the human body while exercising is demonstrated using the integration of a wireless reader and a user‐friendly interface. By addressing the barriers of cost, simplicity, and the truly in situ demanding measurements, this unique wearable sensor is expected to serve in the future in many different applications involving the on‐body detection of biofluids, such as a monitoring tool of dehydration levels for athletes as well as a tool for enhancing the sport performance by providing an accurate recovery of the hydration status in daily exercises.

Printed electrodes on a recyclable low-cost coated paper were used as a platform for constructing potentiometric ion sensors consisting of an ion-selective electrode (ISE) and a reference electrode (RE). The reference and working electrodes were printed by using a stable suspension of gold nanoparticles (AuNP) as the ink. Sintering turned the printed electrodes conductive. A poly(3,4-ethylenedioxythiophene) (PEDOT) layer, with poly(styrene sulfonate) (PSS) ions as counterions was deposited on the gold electrodes by electropolymerization, drop-casting or ink-jet printing. The reference electrode was prepared by further coating the PEDOT(PSS) layer with a poly(vinyl chloride) (PVC) membrane containing a lipophilic salt, tetrabutylammonium tetrabutylborate (TBA-TBB), thus resulting in a solid-contact reference electrode (SCRE). The working electrode was modified by coating the PEDOT(PSS) layer with a K+-selective membrane, to obtain a solid-contact K+-ISE. The electrochemical characteristics of the resulting electrode systems were studied by amperometric, potentiometric and electrochemical impedance spectroscopic (EIS) measurements. The potentiometric response toward K+ ions was additionally studied. The surface structure of the PEDOT(PSS) layers deposited by the different methods was studied with atomic force microscopic (AFM) measurements. It was shown that a well-functioning planar electrode platform with good electrochemical characteristics could be prepared by ink-jet printing in a repeatable manner. The planar electrode platform presented here offers a user-friendly and ecological alternative to perform chemical analysis from small sample volumes.

Despite predictions of their widespread application in healthcare and environmental monitoring, electrochemical sensors are yet to be distributed at scale, instead remaining largely confined to RD labs. This contrasts sharply with the situation for physical sensors, which are now ubiquitous and seamlessly embedded in the mature ecosystem provided by electronics and connectivity protocols. Although chemical sensors could be integrated into the same ecosystem, there are fundamental issues with these sensors in the three key areas of analytical performance, usability, and affordability. Nevertheless, advances are being made in each of these fields, leading to hope that the deployment of automated and user-friendly low-cost electrochemical sensors is on the horizon. Here, we present a brief survey of key challenges and advances in the development of distributed electrochemical sensors for liquid samples, geared towards applications in healthcare and wellbeing, environmental monitoring, and homeland security. As will be seen, in many cases the analytical performance of the sensor is acceptable; it is usability that is the major barrier to commercial viability at this moment. Were this to be overcome, the issue of affordability could be addressed. Graphical Abstract ᅟ.

Objective. To determine the frequency and distribution of ABO and Rh (D) antigens and, additionally, investigate gene diversity and the structure of Mexican populations.Materials and Methods. Blood groups were tested in 271,164 subjects from 2014 to 2016. The ABO blood group was determined by agglutination using the antibodies anti-A, Anti-B, and Anti-D for the Rh factor, respectively.Results. The overall distribution of ABO and Rh (D) groups in the population studied was as follows: O: 61.82%; A: 27.44%; B: 8.93%; and AB: 1.81%. For the Rh group, 95.58% of people were Rh (D), and 4.42% were Rh (d). Different distributions of blood groups across regions were found; additionally, genetic analysis revealed that theIOandIDallele showed an increasing trend from the north to the center, while theIAandIdallele tended to increase from the center to the north. Also, we found more gene diversity in bothlociin the north compared with the center, suggesting population structure in Mexico.Conclusion. This work could help health institutions to identify where they can obtain blood products necessary for medical interventions. Moreover, this piece of information contributes to the knowledge of the genetic structure of the Mexican populations which could have significant implications in different fields of biomedicine.

A new biosensor for monitoring glucose levels in beverages is presented. The measurements are performed using potentiometric detection. Working electrodes are made using platinised paper as support and a biocompatible polymeric membrane made of a mixture of polyvinyl alcohol and chitosan containing glucose oxidase as the recognition layer. The system is based on the detection of the hydrogen peroxide generated by an enzymatic reaction performed in a highly sensitive, selective and simple way. The biosensors display suitable analytical performance (sensitivity −119.6 ± 6.4 mV/dec in the 0.03–1.0 mM range with a limit of detection of 0.02 mM). Determination of glucose in commercial orange juices is presented. These results were validated against conventional standard methods, showing good accuracy and fast analytical response. The methodology presented herein does not require complex samples treatment, offering an alternative to conventional methods, particularly for determinations performed with minimal expertise and without a laboratory infrastructure.

A novel low-cost, compact and sensitive paper-based platform for the accurate monitoring of glucose in biological fluids is presented. Paper-based working and reference electrodes are combined to build a whole potentiometric cell, which also fits a sampling module for simple and fast determination of glucose in a single drop of blood. The working electrode is built using a platinized filter paper coated with a Nafion membrane that entraps the enzyme glucose oxidase; the reference electrode is made by casting a polyvinylbutyral-based membrane onto a conductive paper. The system works by detecting the hydrogen peroxide generated as a result of the enzymatic reaction. Selectivity is achieved due to the permselective behaviour of Nafion, while a significant enhancement of the sensitivity is reached by exploiting the Donnan-coupled formal potential. Under optimum conditions, a sensitivity of -95.9 +/- 4.8 mV per decade in the 0.3-3 mM range is obtained. Validation of the measurements has been performed against standard methods in human serum and blood. Final integration with a wireless reader allows for truly in situ measurements with a less than 2 minute procedure including a two-point calibration, washing and measurement. This low-cost analytical device opens up new prospects for rapid diagnostic results in nonlaboratory settings.

The potentiometric response to hydrogen peroxide of a platinum electrode coated with a layer of Nafion is presented. The results show that the Nafion membrane acts as an effective permselective barrier, thus significantly reducing the response to some redox active species, such as ascorbate. Even more interesting, these coated electrodes show a significantly enhanced sensitivity to hydrogen peroxide (H2O2) when the measurements are performed in solutions of high ionic strength. The influence of pH, ionic strength and supporting electrolyte on this enhancement are presented. Under optimized conditions these coated electrodes show a linear dependence with the logarithm of the concentration of H2O2, with sensitivities of -125.1 +/- 5.9mVdecade(-1) (several times higher than the bare electrodes) and a linear range that spans from 10(-5) M to 10(-3) M of H2O2. Preliminary studies suggest that the coupling between the redox potential on the Pt electrode and the Donnan potential of the membrane plays a role on this enhancement. Considering this improved sensitivity, selectivity, stability and linear ranges, this system shows promise as a future platform to build enzyme-based potentiometric biosensors.

A novel paper-based potentiometric sensor with an enhanced response for the detection of glucose in biological fluids is presented. The electrode consists on platinum sputtered on a filter paper and a Nafion membrane to immobilize the enzyme glucose oxidase. The response obtained is proportional to the logarithm of the concentration of glucose, with a sensitivity of ¿119±8 mV·decade¿1, a linear range that spans from 10¿4M to 10¿2.5 M and a limit of detection of 10¿4.5 M of glucose. It is shown that Nafion increases the sensitivity of the technique while minimizing interferences. Validation with human serum samples shows an excellent agreement when compared to standard methods. This approach can become an interesting alternative for the development of simple and affordable devices for point of care and home-based diagnostics.

Hydroponics is a water, energy, space, and cost efficient system for growing plants in constrained spaces or land exhausted areas. Precise control of hydroponic nutrients is essential for growing healthy plants and producing high yields. In this article we report for the first time on a new computer-operated analytical platform which can be readily used for the determination of essential nutrients in hydroponic growing systems. The liquid-handling system uses inexpensive components (i.e., peristaltic pump and solenoid valves), which are discretely computer-operated to automatically condition, calibrate and clean a multi-probe of solid-contact ion-selective electrodes (ISEs). These ISEs, which are based on carbon nanotubes, offer high portability, robustness and easy maintenance and storage. With this new computer-operated analytical platform we performed automatic measurements of K(+), Ca(2+), NO3(-) and Cl(-) during tomato plants growth in order to assure optimal nutritional uptake and tomato production.

The Communication describes a textile-based wearable multi-ion potentiometric sensor array. The printed flexible sensors operate favorably under extreme mechanical strains (that reflect daily activity) while offering attractive real-time non-invasive monitoring of electrolytes such as sodium and potassium.

The use of commercial carbon fibres (CCF) to build wearable potentiometric sensors for the real-time monitoring of sodium levels in sweat during exercise is presented. CCF are an attractive substrate for building wearable electrochemical sensors because of their good electrical conductivity, chemical inertness, flexibility and mechanical resilience. In the first part of this work, the analytical performance of these novel potentiometric ion-selective electrodes made with CCFs is presented. Then, through the incorporation of a solid-contact reference electrode, the development of a complete miniaturized potentiometric cell with a Nernstian response (59.2 +/- 0.6mV/log [Na+], N=4) is obtained. Finally, the cell is integrated into a wearable patch and attached onto the skin of an athlete. The analytical characterization of the wearable patch shows a near-Nernstian response (55.9 +/- 0.8mV/log [Na+], N=3) for sodium levels from 10(-3)M to 10(-1)M in artificial sweat, well within the physiological range of interest. The device shows low noise levels and very good stability (-0.4 +/- 0.3mVh(-1)). To improve the usability of the sensor in real scenarios, a calibration-free approach is also explored. This platform opens new and attractive avenues for the generation of meaningful personalized physiological information that could be applied - among many other fields - in sports, nutrition and healthcare.

Filiació URV: SI A versatile method for the preparation of efficient and reusable nanocatalysts involving the painting of a commercial filter paper with a Pd@CNT (CNT=carbon nanotubes) ink was herein explored. The resulting paper-based material provided excellent results in the semihydrogenation of alkynes and alkynols and could be recycled at least five times without loss of activity or selectivity

Balloon-embedded stretchable sensors, undergoing a simultaneous equal-multiaxial stretching along global bending motion, have been characterized and tested towards environmental and security monitoring missions. Stress-enduring inks are printed on the curvilinear surface of conventional rubber balloons and their resilience to extreme mechanical deformations, associated with repeated inflation and deflation cycles, is investigated. Unlike early studies of mechanical deformed electrochemical devices-performed with linear stretching or bending-the present balloon-embedded sensors undergo simultaneous multidimensional strains without any alteration of its electrochemical properties. Careful attention is given to the elastomeric, electrical, and electrochemical properties of the new expandable composite inks for addressing the extreme demands of the inflated spherical dynamic balloon substrate. The influence of the balloon inflation and corresponding multiaxial mechanical stress upon the electrochemical behavior is modeled analytically. The electrochemical detection of relevant military and homemade explosives in liquid and vapor phases is used to demonstrate the functionality and potential of the new balloon sensor system to diverse environmental and defense missions. Negligible changes in the response to explosive compounds are observed following multiple repeated inflation and deflation cycles, involving over 400% increase of the balloon area.

A new approach to develop ultra low-cost, robust, rugged, and disposable potentiometric sensors is presented. A suspension of carbon nanotubes in a water-surfactant mixture (carbon nanotubes ink) is applied on conventional filter papers to turn them into conductive papers, which are then used as a substrate to build ion-selective electrodes. The electrodes are made by drop casting a membrane on a small circular area of the conductive paper. In this way, the carbon nanotubes act as both electric conductors and ion-to-electron transducers of the potentiometric signal. Electrodes for sensing K+, NH4(+), and pH were built and tested using this approach, and the results were compared with classical solid-state ion selective electrodes using carbon nanotubes as transducers and glassy carbon as a substrate. In all cases, the analytical performance (sensitivity, linear ranges, limits of detection, selectivity, etc.) of these disposable paper electrodes was similar to that obtained for the more conventional type of ion-selective-electrodes. This opens new avenues for very low-cost platforms for generation of chemical information.

The flowing afterglow-atmospheric pressure glow discharge (APGD) ionization source described in part 1 of this study (in this issue) is applied to the direct analysis of condensed-phase samples. When either liquids or solids are exposed to the ionizing beam of the APGD, strong signals for the molecular ions of substances present on their surfaces can be detected without compromising the integrity of the solid sample structure or sample substrate. As was observed for gas-phase compounds in part 1 of this study, both polar and nonpolar substances can be ionized and detected by mass spectrometry. The parent molecular ion (or its protonated counterpart) is usually the main spectral feature, with little or no fragmentation in evidence. Preliminary quantitative results show that this approach offers very good sensitivity (detection limits in the picogram regime are reported for several test compounds in part 1 of this study) and linear response to the analyte concentration. Examples of the application of this strategy to the analysis of real-world samples, such as the direct analysis of pharmaceutical compounds or foods is provided. The ability of this source to perform spatially resolved analysis is also demonstrated. Preliminary studies of the mechanisms of the reactions involved are described.

Glow discharge sources have shown impressive analytical performance, cost effectiveness, and versatility but have traditionally been ill-suited for the analysis of liquids or solutions. However, in recent years, glow discharges operated at atmospheric pressure have shown progress in this direction. In particular, glow discharges have been operated with the solution to be analyzed acting as one of the electrodes (most typically, and most successfully, the cathode). These sources exhibit many of the traditional advantages of glow discharges (such as low power requirements) and possess the additional benefit of not requiring vacuum equipment. In the present study, a modified design is introduced and its analytical performance is evaluated. The modification from the most similar source is primarily a reduction in discharge volume (nearly 5-fold, to 2 mm(3)) and a corresponding increase in power density. With the new design, detection limits for a range of metals are greatly improved, with most now in the single and sub-part per billion range.

Novel membrane-free chemically modified polystyrene microspheres for the optical detection of sulphate in aqueous media are introduced. The working principle of this sensor is based on the surface mass-extraction equilibrium of the target species. This allows overcoming the strong hydration energy penalty, a typical problem for the detection of divalent anions. This optical sensor exhibits both enhanced sensitivity and selectivity, which allows the accurate detection of sulphate in biological samples. To illustrate these features the determination of sulphate in urine is presented.

An electrothermal vaporization (ETV) system useful for the analysis of solutions and slurries has been coupled with a sector-field inductively coupled plasma mass spectrometer (ICP–MS) equipped with an array detector. The ability of this instrument to record the transient signals produced for a number of analytes in ETV–ICP–MS is demonstrated. Detection limits for Mn, Fe, Co, Ni, Cu, Zn and Ga are in the range of 4–60 pg μL − 1 for aqueous solutions and in the low μg g − 1 range for the analysis of 10 mg mL − 1 slurries of Al 2 O 3 powders. The dynamic ranges measured for Fe, Cu and Ga spanned 3–5 orders of magnitude when the detector was operated in the low-gain mode and appear to be limited by the ETV system. Trace amounts of Fe, Cu and Ga could be directly determined in Al 2 O 3 powders at the 2–270 μg g − 1 level without the use of thermochemical reagents. The results well agree with literature values for Fe and Cu, whereas deviations of 50% at the 90 μg g − 1 level for Ga were found.

The use of nanostructured materials has promoted a new impulse in the chemical sensors area. Electrochemical sensors have taken advantage of the new properties associated with the nanometer-sized objects, and these properties have greatly influenced the performance and operational parameters of the sensing devices. This article provides an overview of the advantages and limitations of different nanomaterials used for the development of the potentiometric sensors. Different dimensional structures, from nanoparticles to graphene, have been used as elements in the recognition layer or the transducers of field-effect transistors and potentiometric electrodes. Moreover, the introduction of nanomaterials has enabled the development of new miniaturized sensors that display good performance, rapid responses, and reduced cost and are easy to use. These sensors can be used in situ or incorporated in garments and other everyday life objects. That is, the era of wearable chemical sensors has started.

The chemical reaction between Cu(II) and 1,5-diphenylcarbazide (DPC) is revised from an analytical perspective. It is shown that instead of a Cu–DPC complex, an oxygen mediated DPC oxidation to diphenylcarbazone (DPCO) is the main reaction involved where Cu(II) acts as catalyst. Therefore, the signal observed corresponds to the oxidation product DPCO. Under certain specific conditions a chelate complex between Cu(II) and DPCO can also be observed. Kinetic parameters of these reactions are calculated. These results set the basis for the development of analytical methodologies for the determination of Cu(II) at ultra-trace levels. Since the study of interferences revealed Mg(II) as the most serious, an optimised flow injection system which allows the in-lineelimination of Mg(II) is presented. The limit of detection (k = 3) calculated for 10 blank replicates is 0.05 μg L−1 (injection volume 20 μL), the analytical sensitivity equals 48 μg−1 L and the sample throughput is 120 h−1. Obtained results for Cu(II) determination in natural waters as well as the validation of the analytical methodology will be given and discussed.

Current and emerging capabilities of plasma-source mass spectrometry (PS-MS) as it is employed for elemental speciation analysis are reviewed. Fundamental concepts and their advantageous aspects, experimental conditions, and analytical performance are described and illustrated by recent examples from the literature. Novel instrumentation, techniques, and strategies for inductively-coupled plasma mass spectrometry (ICP-MS), microwave-induced plasma (MIP) mass spectrometry, glow-discharge (GD) mass spectrometry, and electrospray ionization (ESI), among others, are described. The use of ionization sources that provide tunable ionization, others that can be modulated between different sets of operating conditions, and others used in parallel is also examined.

The flow injection (FI) analytical determination of Se(IV) with 2,3-diaminonaphthalene (DAN) was assayed employing enhanced fluorometric detection. The different variables affecting the reaction rate between Se(IV) and DAN were studied in batch mode, and the best conditions for the 4,5-benzopiazselenol (Se–DAN complex) formation were found. On this basis, two different FI manifolds able to give optimal sensitivity were designed. Once established the optimal flow conditions for the product formation, a submicellar medium of sodium dodecylsulphate with the addition of beta-cyclodextrin was tested to perform enhanced fluorometric detection. A limit of detection of 0.3 ug l-1 of Se(IV), a linear dynamic range ranging between 1 and 500 ug l-1 of Se(IV) and a sampling throughput of 40 samples h-1 were obtained. A full discussion on each stage of the optimisation procedure and the validation of the propose methodology is provided. Fil: Pedro, Juana. Universidad Nacional del Litoral. Facultad de Ingeniería Química; Argentina Fil: Andrade, Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Magni, Diana. Universidad Nacional del Litoral. Facultad de Ingeniería Química; Argentina Fil: Tudino, Mabel Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Bonivardi, Adrian Lionel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina

A spectroscopic device for monitoring the temperature of aqueous solutions is presented. It uses a 950 nm light emission diode as light source and two photodiodes as detectors. Temperature is monitored following the thermally induced absorbance changes of the water-OH second overtone (approximately 960 nm). A linear response between the light absorbed by an aqueous solution and its temperature is found in the range from 15 to 95 degrees C. A prediction error of 0.1 degrees C and a precision of 0.07 degrees C in temperature measurement can be achieved. Up to 0.1 M of electrolyte concentration can be present in the solution without significantly affecting the temperature measurement. Different strategies, such as remote (noninvasive) or in situ (using a fiber-optic probe) temperature measurement, are shown, and their relative advantages are discussed.

A mathematical model for fitting the experimental ICM (integrated conductimetric method) curves developed by the authors in a previous work, is presented for the first time in this study. The proposed model fits the experimental curves with great precision and allows to predict physical dispersion for single-line flow injection system. The correlation of the model’s parameters with typical reactionless FIA peak parameters is also assessed. The IDQ coefficient—a novel dispersion estimator previously reported by the authors—can also be predicted when operational FIA variables are changed. Experimental and modelled profiles are compared as a function of the system’s variables, showing an excellent agreement.

A novel methodology for the determination of iron at the ppb level by spectrophotometric flow injection analysis is described. The method is based on the control of the flow dissolution of the colorimetric reagent 1,10-phenanthroline. This is achieved by means of the minimization of the area of contact between the carrier and the solid reagent, thus allowing the use of the fairly soluble organic compound without affecting the reactor lifetime. The reagent is melted inside an acrylic column (3.0 x 0.5 cm id) in such a way that a hollow space is left in the center after cooling. This new design improves some aspects of the performance of the classical solid-phase reactors as no problems related to the increase in the backpressure of the system are evidenced. Furthermore, the total reagent loading of the column is increased as no inert support is needed. A comparison between the performance of this novel methodology and that of the conventional packed reactor was performed and several advantages were observed: the use of higher flow rates, an increase in the reactor lifetime and a decrease in reagent consumption. A mathematical model to fit the concentration profiles of the dissolved reagent as a function of the residence time of the sample within the column is presented. The application of this strategy to the determination of Fe(II) improves the figures of merit in comparison to those obtained with a single-line homogeneous system: the limit of detection is 2 microg Fe L(-1) (3s) and the sensitivity is similar to that of the batch procedure. Results obtained for the determination of iron in natural waters are also presented.

A novel approach to monitor Li levels in blood in decentralized (out of the lab) settings is presented. The approach uses a potentiometric cell fully made with filter paper as a support. Electrodes were built using carbon nanotubes ink to create a conductive path and a suitable polymeric membrane. Solid-state ion-selective electrodes for Li and a reference electrode were built and optimized. The results obtained on real samples of serum and whole blood are comparable with those obtained by conventional standard approaches. This platform shows an outstanding performance for the direct, fast and low-cost monitoring of Li levels in blood.

A new wearable electrochemical sensor for monitoring the pH of wounds is introduced. The device is based on the judicious incorporation of a screen-printed pH potentiometric sensor into bandages. The fabrication of this sensor, which uses an electropolymerized polyani- line (PANi) conducting polymer for pH sensing, combines the screen-printing fabrication methodology with all- solid-state potentiometry for implementation of both the reference and the working electrodes. The pH bandage sensor displays a Nernstian response over a physiological- ly relevant pH range (5.5-8), with a noteworthy selectivi- ty in the presence of physiological levels of most common ions. The bandage-embedded sensor can track pH fluctu- ations with no apparent carry-over effect. The sensor dis- plays good resiliency against mechanical stress, along with superior repeatability and reproducibility. The in vitro performance of the device was successfully evaluated using buffer solutions emulating the composition of a wound. The novel pH-sensitive bandages facilitate new avenues towards the realization of telemedicine.

The development of a solid-contact potentiometric sensor based on conducting rubbers using a carbon nanotubes ink is described here. Commercial rubbers are turned into conductive ones by a simple and versatile method, i.e. painting an aqueous dispersion of single-walled carbon nanotubes on the polymer surface. On this substrate, both the working ion-selective electrode and the reference electrode are built in order to form an integrated potentiometric cell. As a proof-of-principle, selective potassium electrodes are fully characterized giving comparable performances to conventional electrodes (sensitivity, selectivity, stability, linear range, limit of detection and reproducibility). As an application of the rubber-based electrodes, a bracelet was constructed to measure potassium levels in artificial sweat. Since rubbers are ubiquitous in our quotidian life, this approach offers great promise for the generation of chemical information through daily objects.

The insights provided by integrated detection (conductimetric) as a novel approach to follow physical dispersion in continuous-flow manifolds are presented. This approach replaces the conventional instantaneous detection and permits to follow the dispersion phenomena, including details of the radial component as the sample plug travels the manifold. Integrated detection permits to look at the radial dispersion in a detailed manner inaccessible to instantaneous detection. The effect of different experimental parameters affecting mass distribution was studied (e.g., flow rate, tube length and diameter, injected sample volume, and reactor type) and their effects on integrated response curves are discussed. A single channel manifold employing aqueous nitric acid as the conducting carrier, and water injected as sample plug, and playing the role of an insulator, provided the physicochemical model for the reported studies.

A new solid-state reference electrode using a polymeric membrane of polyvinyl butyral (PVB), Ag/AgCl and NaCl to be used in decentralized chemical measurements is presented. The electrode is made by drop-casting the membrane cocktail onto a glassy carbon (GC) substrate. A stable potential (less than 1 mV dec(-1)) over a wide range of concentrations for the several chemical species tested is obtained. No significant influence to changes in redox potential, light and pH are observed. The response of this novel electrode shows good correlation when compared with a conventional double-junction reference electrode. Also good long-term stability (90±33 μV/h) and a lifetime of approximately 4 months are obtained. Aspects related to the working mechanisms are discussed. Atomic Force Microscopy (AFM) studies reveal the presence of nanopores and channels on the surface, and electrochemical impedance spectroscopy (EIS) of optimized electrodes show low bulk resistances, usually in the kΩ range, suggesting that a nanoporous polymeric structure is formed in the interface with the solution. Future applications of this electrode as a disposable device for decentralized measurements are discussed. Examples of the utilization on wearable substrates (tattoos, fabrics, etc) are provided.

This article describes the fabrication, characterization and application of an epidermal temporary-transfer tattoo-based potentiometric sensor, coupled with a miniaturized wearable wireless transceiver, for real-time monitoring of sodium in the human perspiration. Sodium excreted during perspiration is an excellent marker for electrolyte imbalance and provides valuable information regarding an individual's physical and mental wellbeing. The realization of the new skin-worn non-invasive tattoo-like sensing device has been realized by amalgamating several state-of-the-art thick film, laser printing, solid-state potentiometry, fluidics and wireless technologies. The resulting tattoo-based potentiometric sodium sensor displays a rapid near-Nernstian response with negligible carryover effects, and good resiliency against various mechanical deformations experienced by the human epidermis. On-body testing of the tattoo sensor coupled to a wireless transceiver during exercise activity demonstrated its ability to continuously monitor sweat sodium dynamics. The real-time sweat sodium concentration was transmitted wirelessly via a body-worn transceiver from the sodium tattoo sensor to a notebook while the subjects perspired on a stationary cycle. The favorable analytical performance along with the wearable nature of the wireless transceiver makes the new epidermal potentiometric sensing system attractive for continuous monitoring the sodium dynamics in human perspiration during diverse activities relevant to the healthcare, fitness, military, healthcare and skin-care domains.

10.1016/j.bios.2013.06.007 A new paper-based chemiresistor composed of a network of single-wall carbon nanotubes (SWCNTs) and anti-human immunoglobulin G (anti-HIgG) is reported herein. SWCNTs act as outstanding transducers because they provide high sensitivity in terms of resistance changes due to immunoreaction. As a result, the resistance-based biosensor reaches concentration detection as low as picomolar. The resulting paper-based biosensor is sensitive, selective and employs low-cost substrate and simple manufacturing stages. Since chemiresistors require low-power equipment and are able to detect low concentrations with inexpensive materials, the present approach may pave the way for the development of resistive biosensors at very low-cost with high performances.

A simple and generalized approach to build electrochemical sensors for wearable devices is presented. Commercial cotton yarns are first turned into electrical conductors through a simple dyeing process using a carbon nanotube ink. These conductive yarns are then partially coated with a suitable polymeric membrane to build ion-selective electrodes. Potentiometric measurements using these yarn-potentiometric sensors are demonstrated. Examples of yarns that can sense pH, K+ and NH4+ are presented. In all cases, these sensing yarns show limits of detection and linear ranges that are similar to those obtained with lab-made solid-state ion-selective electrodes. Through the immobilization of these sensors in a band-aid, it is shown that this approach could be easily implemented in a wearable device. Factors affecting the performance of the sensors and future potential applications are discussed.

A novel chemical ionization source for organic mass spectrometry is introduced. This new source uses a glow discharge in the flowing afterglow mode for the generation of excited species and ions. The direct-current gas discharge is operated in helium at atmospheric pressure; typical operating voltages and currents are around 500 V and 25 mA, respectively. The species generated by this atmospheric pressure glow discharge are mixed with ambient air to generate reagent ions (mostly ionized water clusters and NO+), which are then used for the ionization of gaseous organic compounds. A wide variety of substances, both polar and nonpolar, can be ionized. The resulting mass spectra generally show the parent molecular ion (M+ or MH+) with little or no fragmentation. Proton transfer from ionized water clusters has been identified as the main ionization pathway. However, the presence of radical molecular ions (M+) for some compounds indicates that other ionization mechanisms are also involved. The analytical capabilities of this source were evaluated with a time-of-flight mass spectrometer, and preliminary characterization shows very good stability, linearity, and sensitivity. Limits of detection in the single to tens of femtomole range are reported for selected compounds.

In mass spectrometry, several advantages can be derived when multiple mass-to-charge values are detected simultaneously and continuously. One such advantage is an improved duty cycle, which leads to superior limits of detection, better precision, shorter analysis times, and reduced sample sizes. A second advantage is the ability to reduce correlated noise by taking the ratio of two or more simultaneously collected signals, enabling greatly enhanced isotope ratio data. A final advantage is the elimination of spectral skew, leading to more accurate transient signal analysis. Here, these advantages are demonstrated by means of a novel Faraday-strip array detector coupled to a Mattauch−Herzog mass spectrograph. The same system is used to monitor elemental fractionation phenomena in laser ablation inductively coupled plasma mass spectrometry.

A miniaturized version of an atmospheric-pressure glow discharge using a solution as the cathode was recently evaluated for elemental analysis of continuously sampled aqueous solutions. Although continuous sampling is useful, transient analysis is required for certain applications, including chromatographic or similar separations, small-volume sampling, high-throughput sampling, and on-line preconcentration. The miniaturized solution-cathode glow discharge seems particularly well suited to transient analysis by virtue of its low dead volume and high sensitivity. Two benefits of transient analysis were exploited here: high throughput and small sample volume. Sampling 25-microL volumes at 1000 samples/h, the discharge achieved detection limits ranging from 5 pg (0.2 ppb) for Li to 6 ng (270 ppb) for Hg.