A Smartwatch Integrated with a Paper-based Microfluidic Patch for Sweat Electrolytes Monitoring

Here, a smartwatch for sweat monitoring was presented for perspiration analysis. The smartwatch played the part of analyzing, computing, and displaying the real-time data with the feature of comfortable wearing and lightweight ergonomic design. Moreover, the paper-based microfluidic patch with a three-dimensional structure was proposed to realize the sweat collection and solve the issue of sweat accumulation. To further realizing the sweat monitoring, the potassium and sodium ion-selective electrodes were developed by the screen-printing technique. The experiment of on-body monitoring the K⁺ and Na⁺ in sweat had been carried out to further demonstrate the feasibility of the smartwatch.     

Concurrent determination and separation of inorganic cations and anions in microchip electrophoresis with precisely controlled high‐voltage

An improved method for the concurrent determination and separation of cations and anions by microchip electrophoresis with capacitively coupled contactless conductivity detection (ME‐C⁴D) is described. Two kinds of microchip structures were designed. The first microchip has a long bent separation channel. And for the defects of the first microchip, the second microchip with a Y‐type separation channel has been proposed. The background electrolyte (BGE) composed of 20 mm His/MES and 0.01 mm CTAB was optimized for inhibiting the electroosmotic flow (EOF). Due to the low electroosmotic flow, the cations and anions migrate in opposite directions and can be separated from each other. With the precisely controlled high‐voltage, cations and anions can be migrated in microchannels according to our requirements and sequentially detected by a C⁴D detector built in‐house. Samples containing K⁺, Na⁺, Li⁺, Cl⁻, F⁻ and PO₄³⁻ were analyzed simultaneously in a single run (within 140 s) by both methods. The reproducibility obtained by both methods remained below 5% for migration time and within 3.5–9.1% for peak areas. The proposed concurrent determination methods are inexpensive, simple, fast, ease of operation, high degree of integration.     

Measurement of Nitrogen Mustard Degradation Products by Poly(dimethylsiloxane) Microchip Electrophoresis with Contactless Conductivity Detection

A poly(dimethylsiloxane) (PDMS) microfluidic device with contactless conductivity detection for the determination of nitrogen mustard degradation products is reported. Three alkyl ethanolamines: N‐methyldiethanolamine (MDEA), N‐ethyldiethanolamine (EDEA), and triethanolamine (TEA), (degradation/ precursor products of HN‐1, HN‐2 and HN‐3 blister agents) were analyzed by microchip capillary electrophoresis (CE). The original PDMS channel was coated by poly(ethyleneimine) (PEI) to improve the separation of three ethanolamines. Experimental conditions for the separation and detection processes have been optimized to yield well defined separation and high sensitivity. The response times for the three ethanolamines were less than 5 min., the detection limits were 2.0–4.0 mg L^?1 and the relative standard derivations for the migration times and peak heights were 1.6–2.3% and 4.1–5.7%, respectively. The linearity of calibration for each of the compounds was as follows: MDEA, r²=0.970; EDEA, r²=0.994; TEA, r²=0.988. Applicability of this method for natural (lake and tap) water samples was also demonstrated. Compared to conventional analytical methods, this miniaturized system offers promise for on‐site monitoring of degradation products of the nitrogen mustard class of chemical warfare agents, with advantages of cost‐effective construction, simple operation, portability, and small required sample volumes.     

Development of a PDMS‐based microchip electrophoresis device for continuous online in vivo monitoring of microdialysis samples

A PDMS‐based microfluidic system for online coupling of microdialysis sampling to microchip electrophoresis with fluorescence detection for in vivo analysis of amino acid neurotransmitters using naphthalene‐2,3‐dicarboxaldehyde and sodium cyanide as the derivatization reagents is described. Fabricating chips from PDMS rather than glass was found to be simpler and more reproducible, especially for chips with complex designs. The microchip incorporated a 20‐cm serpentine channel in which sample plugs were introduced using a “simple” injection scheme; this made fluid handling and injection on‐chip easier for the online system compared with gated or valve‐based injection. The microchip was evaluated offline for the analysis of amino acid standards and rat brain microdialysis samples. Next, precolumn derivatization was incorporated into the chip and in vivo online microdialysis‐microchip electrophoresis studies were performed. The system was employed for the continuous monitoring of amino acid neurotransmitters in the extracellular fluid of the brain of an anesthetized rat. Fluorescein was dosed intravenously and monitored simultaneously online as a marker of in vivo blood–brain barrier permeability. The microdialysis‐microchip electrophoresis system described here will be employed in the future for simultaneous monitoring of changes in blood–brain barrier permeability and levels of amino acid neurotransmitters in the rat stroke model.     

A Disposable Planar Paper‐Based Potentiometric Ion‐Sensing Platform

Ion‐selective electrodes (ISEs) are widely used tools for fast and accurate ion sensing. Herein their design is simplified by embedding a potentiometric cell into paper, complete with an ISE, a reference electrode, and a paper‐based microfluidic sample zone that offer the full function of a conventional ISE setup. The disposable planar paper‐based ion‐sensing platform is suitable for low‐cost point‐of‐care and in‐field testing applications. The design is symmetrical and each interfacial potential within the cell is well defined and reproducible, so that the response of the device can be theoretically predicted. For a demonstration of clinical applications, paper‐based Cl^? and K⁺ sensors are fabricated with highly reproducible and linear responses towards different concentrations of analyte ions in aqueous and biological samples. The single‐use devices can be fabricated by a scalable method, do not need any pretreatment prior to use, and only require a sample volume of 20 μL.     

Determination of Point of Zero Charge of Tunisian Kaolinites by Potentiometric and Mass Titration Methods

This paper deals with determining points of zero charge of natural and Na⁺‐saturated mineral kaolinites using two methods: (1) acid‐base potentiometric titration was employed to obtain the adsorption of H⁺ and OH^? on amphoteric surfaces in solutions of varying ionic strengths in order to determinate graphically the point of zero net proton charge (PZNPC) defined equally as point of zero salt effect (PZSE); (2) mass titration curve at different electrolyte concentrations in order to estimate PZNPCs by interpolation and to compare with those determined by potentiometric titrations. The two methods involved points of zero charge approximately similar for the two kaolinites between 6.5‐7.8, comparable to those reported previously and were in the range expected for these clay minerals. The comparison of potentiometric surface titration curves obtained at 25 °C and those published in the literature reveals significant discrepancies both in the shape and in the pH of PZNPCs values.     

Non-enzyme electrochemical sensing fabrics and wearable applications based on bimetallic NiCo-MOFs

Portable sweat analysis devices for real-time monitoring of health-related biomarkers with great detection accuracy and high sensitivity are attracting public interest. Here, we report a flexible fabric sweat analysis devices bimetallic Metal Organic Frameworks (MOFs) for detection of glucose in sweat without any biological enzymes. The synergy between Ni²⁺ and Co²⁺ and the large surface area (424.41 m² g⁻¹) and high porosity (0.0542 cm³ g⁻¹) of NiCo-MOF make NiCo-MOF an interesting electrode modification material in the working electrode. Furthermore, the ultra-high porosity and huge surface area of the MOFs structure are required for electrocatalysts in alkaline media. On the basis of the above, we have developed a fabric-based analytical patch, which is sufficient for simultaneous real-time detection of glucose in sweat.     

Dual fluorescence/contactless conductivity detection for microfluidic chip

A new dual detection system for microchip is reported. Both fluorescence detector (FD) and contactless conductivity detector (CCD) were combined together and integrated on a microfluidic chip. They shared a common detection position and responded simultaneously. A blue light-emitting diode was used as excitation source and a small planar photodiode was used to collect the emitted fluorescence in fluorescence detection, which made the device more compact and portable. The coupling of the fluorescence and contactless conductivity modes at the same position of a single separation channel enhanced the detection characterization of sample and offered simultaneous detection information of both fluorescent and charged specimen. The detection conditions of the system were optimized. K⁺, Na⁺, fluorescein sodium, fluorescein isothiocyanate (FITC) and FITC-labeled amino acids were used to evaluate the performance of the dual detection system. The limits of detection (LOD) of FD for fluorescein Na⁺, FITC, FITC-labeled arginine (Arg), glycine (Gly) and phenylalanine (Phe) were 0.02 μmol L⁻¹, 0.05 μmol L⁻¹, 0.16 μmol L⁻¹, 0.15 μmol L⁻¹, 0.12 μmol L⁻¹ respectively, and the limits of detection (LOD) of CCD achieved 0.58 μmol L⁻¹ and 0.39 μmol L⁻¹ for K⁺ and Na⁺ respectively.     

A New Validated Potentiometric Method for Batch and Continuous Quality Control Monitoring of Oseltamivir Phosphate (Taminil) in Drug Formulations and Biological Fluids

A new validated potentiometric method is described for batch and continuous quality control monitoring of the drug oseltamivir phosphate (Taminil) (OST). The method involves the development of a potentiometric sensor responsive to the drug based on the use of the ion‐association complex of (OST⁺) cation with phosphomolybdate anion (PMA^?) as an electroactive material in a poly(vinyl chloride) matrix membrane plasticized with o‐nitrophenyloctyl ether (o‐NPOE). Optimization of the performance characteristics of the sensor is described. A membrane incorporating the OST‐PMA‐NPOE complex in a tubular flow through detector is used in a two channel flow injection set up for continuous monitoring of the drug at a frequency of ～30 samples h^?1. The sensor shows fast near‐Nernstian response for OST over the concentration range 5.2×10^?5–0.8×10^?2 M (21.34 µg mL^?1–3.23 mg mL^?1) with a detection limit of 9.1×10^?6 M (3.73 µg mL^?1) over the pH range 4.6–6.1. The sensor displays good selectivity for OST drug over some basic drugs, inorganic cations, excipients and diluents commonly used in the drug formulations. Validation of the assay method is tested by measuring the lower detection limit, range, linearity, bias, trueness, accuracy, precision, and between‐day‐variability, within day reproducibility, selectivity and ruggedness (robustness). The results reveal good potentiometric performance of the proposed sensor for determination of OST in pharmaceutical capsules and in biological fluid matrices as well as for testing the dissolution profile of the drug and drug homogeneity.     

Corrosion Behavior of Biocompatible Stainless Steels in Physiological Medium for Non‐invasive Diagnosis of Small Fiber Neuropathies Applications

A non‐invasive device based on measurements of electrochemical skin conductance can detect small fiber neuropathy, a sweat gland dysfunction implicated in several diseases. The measurement is related to sweat composition and notably to chloride concentration. To optimize the electrode material, in vitro experiments are performed in mimetic sweat solutions. This work reports on the resistance to pitting corrosion of biocompatible stainless steels (AISI 304L, AISI 430, AISI 430T, D2205) in sweat mimicking electrolyte at pH 7 with variable chloride concentration, to determine the most sensitive material to sweat composition. AISI 430 is promising due to its high sensitivity to chloride concentration variations.     

Development and optimization of an integrated PDMS based‐microdialysis microchip electrophoresis device with on‐chip derivatization for continuous monitoring of primary amines

An all‐PDMS on‐line microdialysis‐microchip electrophoresis with on‐chip derivatization and electrophoretic separation for near real‐time monitoring of primary amine‐containing analytes is described. Each part of the chip was optimized separately, and the effect of each of the components on temporal resolution, lag time, and separation efficiency of the device was determined. Aspartate and glutamate were employed as test analytes. Derivatization was accomplished with naphthalene‐2,3,‐dicarboxyaldehyde/cyanide (NDA/CN^?), and the separation was performed using a 15‐cm serpentine channel. The analytes were detected using LIF detection.     

Transparent Electronic Skin Device Based on Microstructured Silver Nanowire Electrode

Transparent, flexible electronic skin holds a wide range of applications in robotics, humanmachine interfaces, artificial intelligence, prosthetics, and health monitoring. Silver nanowire are mechanically flexible and robust, which exhibit great potential in transparent and electricconducting thin film. Herein, we report on a silver-nanowire spray-coating and electrodemicrostructure replicating strategy to construct a transparent, flexible, and sensitive electronic skin device. The electronic skin device shows highly sensitive piezo-capacitance response to pressure. It is found that micropatterning the surface of dielectric layer polyurethane elastomer by replicating from microstructures of natural-existing surfaces such as lotus leaf, silk, and frosted glass can greatly enhance the piezo-capacitance performance of the device. The microstructured pressure sensors based on silver nanowire exhibit good transparency, excellent flexibility, wide pressure detection range (0-150 kPa), and high sensitivity (1.28 kPa^-1).     

Wearable Multiparameter Platform Based on AlGaN/GaN High‐electron‐mobility Transistors for Real‐time Monitoring of pH and Potassium Ions in Sweat

Biosensors based on field‐effect transistor (FET) structures have attracted considerable attention because they offer rapid, inexpensive parallel sensing and ultrasensitive label‐free detection. However, long‐term repeatable detection cannot be performed, and Ag/AgCl reference electrode design is complicated, which has hindered FET biosensors from becoming truly wearable health‐monitoring platforms. In this paper, we propose a novel wearable detection platform based on AlGaN/GaN high‐electron‐mobility transistors (HEMTs). In this platform, a sweatband was used to continuously collect sweat, and a pH detecting unit and a potassium ion detecting unit were formed by modifying different sensitive films to realize the long‐term stable and repeatable detection of pH and potassium ions. Experimental data show that the wearable detection platform based on AlGaN/GaN HEMTs has good sensitivity (pH 3–7 sensitivity is 45.72 μA/pH; pH 7.4–9 sensitivity is 51.073 μA/pH; and K⁺ sensitivity is 4.94 μA/lgα_K⁺), stability (28 days) and repeatability (the relative standard deviation (RSD) of pH 3–7 sensitivity is 2.6 %, the RSD of pH 7.4–9 sensitivity is 2.1 %, and the RSD of K⁺ sensitivity is 7.3 %). Our newly proposed wearable platform has excellent potential for predictive analytics and personalized medical treatment.     

An Asymmetric Supercapacitor–Diode (CAPode) for Unidirectional Energy Storage

A new asymmetric capacitor concept is proposed providing high energy storage capacity for only one charging direction. Size‐selective microporous carbons (w<0.9 nm) with narrow pore size distribution are demonstrated to exclusively electrosorb small anions (BF₄^?) but size‐exclude larger cations (TBA⁺ or TPA⁺), while the counter electrode, an ordered mesoporous carbon (w>2 nm), gives access to both ions. This architecture exclusively charges in one direction with high rectification ratios (RR=12), representing a novel capacitive analogue of semiconductor‐based diodes (“CAPode”). By precise pore size control of microporous carbons (0.6 nm, 0.8 nm and 1.0 nm) combined with an ordered mesoporous counter electrode (CMK‐3, 4.8 nm) electrolyte cation sieving and unidirectional charging is demonstrated by analyzing the device charge‐discharge response and monitoring individual electrodes of the device via in situ NMR spectroscopy.     

Bio‐Inspired Photonic‐Crystal Microchip for Fluorescent Ultratrace Detection

Ultratrace detection attracts great interest because it is still a challenge to the early diagnosis and drug testing. Enriching the targets from highly diluted solutions to the sensitive area is a promising method. Inspired by the fog‐collecting structure on Stenocara beetle’s back, a photonic‐crystal (PC) microchip with hydrophilic–hydrophobic micropattern was fabricated by inkjet printing. This device was used to realize high‐sensitive ultratrace detection of fluorescence analytes and fluorophore‐based assays. Coupled with the fluorescence enhancement effect of a PC, detection down to 10^?16 mol L^?1 was achieved. This design can be combined with biophotonic devices for the detection of drugs, diseases, and pollutions of the ecosystem.     

A microchip sensor for calcium determination

A newly designed glass-PDMS microchip-based sensor for use in the determination of Ca²⁺ ions has been developed, utilizing reflectance measurements from arsenazo III (1,8-dihydroxynaphthalene-3,6-disulfonic acid-2,7-bis[(azo-2)-phenyl arsenic acid]) immobilized on the surface of polymer beads. The beads, produced from cross-linked poly(p-chloromethylstyrene) (PCMS), were covalently modified with polyethylenimine (PEI) to which the Arsenazo III could be adsorbed. The maximum amount of Arsenazo III which could be immobilized onto the PEI-attached PCMS beads was found to be 373.71 mg g⁻¹ polymer at pH 1. Once fabricated, the beads were utilized at the detection point of the microfluidic sensor device with a fiber optic assembly for reflectance measurements. Samples were mobilized past the detection point in the sensor where they interact with the immobilized dye. The sensor could be regenerated and re-used by rinsing with HCl solution. The pH, voltage, linear range, and the effect of interfering ions were evaluated for Ca²⁺ determination using this microchip sensor. At the optimum potential, 0.8 kV, and pH 9.0, the linear range of the microchip sensor was 3.57 × 10⁻⁵ – 5.71 × 10⁻⁴ M Ca²⁺, with a limit of detection (LOD) of 2.68 × 10⁻⁵ M. The microchip biosensor was then applied for clinical analysis of calcium ions in serum with good results. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Microliter Volume Determination of Cosmetic Mercury with a Partially Crosslinked Poly(4‐vinylpyridine) Modified Screen‐Printed Three‐Electrode Portable Assembly

We successfully demonstrated microliter (μL) volume determination of Mercury (Hg) using an in‐built screen‐printed three electrodes containing partially crosslinked poly(4‐vinlylpyridine) (designated as pcPVP) modified carbon‐working, carbon‐counter, and Ag⁺‐quasireference electrodes (SPE/pcPVP) in a pH 4 acetate buffer solution with 2 M KCl by using the square wave anodic stripping voltammetric (SWASV) technique. Instrumental and solution phase conditions were systematically optimized. Experiments were carried out by simply placing a 500 μL‐droplet of Hg containing real sample mixed with the base electrolyte on the SPE/pcPVP surface. The SPE/Ag⁺ quasi‐reference system shifted the Hg‐SWASV detection potential ca. 250 mV positive, but the quantitative current values were appreciably similar to that of a standard Ag/AgCl reference electrode. Under optimal condition, the calibration graph is linear in the window of 100–1000 ppb of the Hg droplet system with a detection limit of 69.5 ppb (S/N=3). Finally real sample assays were demonstrated for prohibited cosmetic Hg containing skin‐lightening agents in parallel with ICP‐OES measurements.     

Rapid pre-concentration of Escherichia coli in a microfluidic paper-based device using ion concentration polarization

We report a microfluidic paper based analytical device implementing ion concentration polarization (ICP) for rapid pre-concentration of Escherichia coli in water. The fabricated device consists of a paper channel with a Nafion^® membrane and in-built micro wire electrodes to supply electric voltage to induce the ICP effect. E. coli cells were stained with SYTO 9 and fluorescence was used as a sensing method. The device achieved high concentration factor up to 2 × 10⁵ within minutes. The effect of total ion concentration, on ICP and fluorescence intensity was studied. The reported device and method are suitable and effective for detection of E. coli during ballast water quality monitoring, coastal water quality monitoring where high salinity water is present.     

Microfluidic chip capillary electrophoresis coupled with electrochemiluminescence for enantioseparation of racemic drugs using central composite design optimization

Optimization based on central composite design (CCD) for enantioseparation of anisodamine (AN), atenolol (AT), and metoprolol (ME) in human urine was developed using a microfluidic chip‐CE device. Coupling the flexible and wide working range of microfluidic chip‐CE device to CCD for chiral separation of AN, AT, and ME in human urine, a total of 15 experiments is needed for the optimization procedure as compared to 75 experiments using the normal one variable at a time optimization. The optimum conditions obtained are found to be more robust as shown by the curvature effects of the interaction factors. The developed microfluidic chip‐CE‐ECL system with adjustable dilution ratios has been validated by satisfactory recoveries (89.5–99% for six enanotiomers) in urine sample analysis. The working range (0.3–600 μM), repeatability (3.1–4.9% RSD for peak height and 4.0–5.2% RSD for peak area), and detection limit (0.3–0.6 μM) of the method developed are found to meet the requirements for bedside monitoring of AN, AT, and ME in patients under critical conditions. In summary, the hyphenation of CCD with the microfluidic chip‐CE device is shown to offer a rapid means for optimizing the working conditions on simultaneous separation of three racemic drugs using the microfluidic chip‐CE device developed.     

A novel microchip based on indium tin oxide coated glass for contactless conductivity detection

A microfluidic chip manufactured from glass substrate and indium tin oxide (ITO) coated glass use for contactless conductivity detection was developed. The detecting electrodes were fabricated by screen-printing and chemical etching methods using an ITO-coated glass wafer. Then, the glass substrate containing separation channels was bonded with the bare side of the processed ITO-coated glass, thus producing an electrophoresis chip integrated with contactless conductivity detector. The prepared microchip displayed considerable stability and reproducibility. Sensitive response was obtained at optimal conditions (including the gap between electrodes, excitation frequency, and excitation voltage). The feasibility of this microfluidic device was examined by detection of inorganic ions, and further demonstrated by the quantification of aminopyrine and caffeine in a compound pharmaceutical. The two ingredients can be completely separated within 1 min. The detection limits were 8 μg mL⁻¹ and 3 μg mL⁻¹, respectively; with the correlation coefficient of 0.996-0.998 in the linear range from 10 μg mL⁻¹ to 800 μg mL⁻¹. The results have showed that the present method is sensitive, reliable and fast.