Explore the vast range of titles available.

This paper describes an inexpensive, handheld device that couples the most common forms of electrochemical analysis directly to “the cloud” using any mobile phone, for use in resource-limited settings. The device is designed to operate with a wide range of electrode formats, performs on-board mixing of samples by vibration, and transmits data over voice using audio—an approach that guarantees broad compatibility with any available mobile phone (from low-end phones to smartphones) or cellular network (second, third, and fourth generation). The electrochemical methods that we demonstrate enable quantitative, broadly applicable, and inexpensive sensing with flexibility based on a wide variety of important electroanalytical techniques (chronoamperometry, cyclic voltammetry, differential pulse voltammetry, square wave voltammetry, and potentiometry), each with different uses. Four applications demonstrate the analytical performance of the device: these involve the detection of (i) glucose in the blood for personal health, (ii) trace heavy metals (lead, cadmium, and zinc) in water for in-field environmental monitoring, (iii) sodium in urine for clinical analysis, and (iv) a malarial antigen (Plasmodium falciparum histidine-rich protein 2) for clinical research. The combination of these electrochemical capabilities in an affordable, handheld format that is compatible with any mobile phone or network worldwide guarantees that sophisticated diagnostic testing can be performed by users with a broad spectrum of needs, resources, and levels of technical expertise.

In this work, we present a potentiometric pH sensor on textile substrate for wearable applications. The sensitive (thick film graphite composite) and reference electrodes (Ag/AgCl) are printed on cellulose-polyester blend cloth. An excellent adhesion between printed electrodes allow the textile-based sensor to be washed with a reliable pH response. The developed textile-based pH sensor works on the basis of electrochemical reaction, as observed through the potentiometric, cyclic voltammetry (100 mV/s) and electrochemical impedance spectroscopic (10 mHz to 1 MHz) analysis. The electrochemical double layer formation and the ionic exchanges of the sensitive electrode-pH solution interaction are observed through the electrochemical impedance spectroscopic analysis. Potentiometric analysis reveals that the fabricated textile-based sensor exhibits a sensitivity (slope factor) of 4 mV/pH with a response time of 5 s in the pH range 6–9. The presented sensor shows stable response with a potential of 47 ± 2 mV for long time (2000 s) even after it was washed in tap water. These results indicate that the sensor can be used for wearable applications.

A new biocomposite cross-linked glutaraldehyde-chitosan/MgO/Fe3O4 (CTS-GL/MgO/Fe3O4) adsorbent with magneto-responsiveness was prepared and applied for the removal of reactive blue 19 (RB-19), a synthetic textile dye. The prepared CTS-GL/MgO/Fe3O4 was structurally characterized using spectroscopic (XRD, FTIR, SEM–EDX), and its physicochemical properties were evaluated using potentiometry and pHpzc analyses. The influence of various adsorption parameters (A: CTS-GL/MgO/Fe3O4 dosage; B: initial solution pH; C: process temperature; and D: contact time) on the removal efficiency of RB-19 was statistically optimized using Box-Behnken design (BBD). The analysis of variance (ANOVA) indicates the presence of five significant statistical interactions between the adsorption parameters, as follows: AB, AC, AD, BC, and BD. The equilibrium dye uptake by the Freundlich isotherm model indicates heterogeneous adsorption, while the kinetics of adsorption was well-described by the pseudo-second-order model. The maximum adsorption capacity of CTS-GL/MgO/Fe3O4 towards RB-19 was 193.2 mg/g at 45 °C. This work highlights the development of a recoverable magnetic biocomposite adsorbent with favourable adsorption capacity towards a model textile dye with good separation ability by using an external magnetic field. Moreover, separation of the magnetic adsorbents from the treated solution is easy and convenient apply to continuous flow systems, which is highly preferred for industrial applications.

We report the mode of interaction of copper(II) ions with tyrosine (Tyr, L) in binary and ternary systems with Ado, AMP, ADP, and ATP (L’) as second ligands in an aqueous solution. The composition and overall stability constants of the complexes formed were determined using the potentiometric method. The coordination sites were identified through spectroscopic (VIS, EPR, IR) methods, as well as DFT and computational–molecular modeling. In the binary Cu(II)/Tyr system, the main reaction centers of the ligand molecule involved in the interactions with copper(II) ions are nitrogen (-NH[sub.2] group), as well as oxygen atoms (-COO[sup.−] group), as confirmed, for example, by comparing the mode of coordination in the CuH[sub.2](Tyr)[sub.2] species and the [CuH[sub.2](Tyr)[sub.2](H[sub.2]O)] × 1.5H[sub.2]O solid complex obtained. In the ternary Cu(II)/L/L’ systems, MLHxL’ and mixed MLL’ protonated complexes are formed. Only in the ATP system were no MLL’(OH)[sub.x] hydroxocomplexes found. An increase in the number of phosphate groups in ADP and ATP molecules has no effect on their participation in the coordination in ternary species, and these ligands interact just like in binary species (i.e., in ADP, both α- and β-phosphate groups, and in ATP, only the γ-phosphate group). It was observed that the introduction of a second ligand into the Cu(II)/Tyr system did not change, over the entire pH range studied, the tyrosine coordination mode.

Functionalized nanocomposites based on various type of graphene nanomaterials including graphene, graphene oxides (GOs), and doped graphene (oxides) are widely used as materials for various sensors that can display high sensitivity, selectivity and stability. This review with 347 references summarizes advances in the preparation and functionalization of graphene nanocomposites for the application of electrochemical sensors and biosensors. Following a general introduction into the field, the article is divided into subsections on (a) the synthesis and functionalization of nanocomposites (made from graphene, various kinds of GOs, heteroatom-doped GOs), (b) on methods for functionalization of composites (with other carbon nanomaterials, metal nanoparticles, metal oxide and metal sulfide nanoparticles), (c) on functionalization with inorganic materials including polyoxometalates, hexacyanoferrates, minerals), (d) on functionalization with organic materials such as amino acids, surfactants, organic dyes, ionic liquids, macrocycles (including cyclodextrins, crown ethers and calixarenes), and (e) on functionalization with organometallics and with various other organic compounds, (f) on functionalizations with polymers such as conventional polymers, polyelectrolytes, conducting polymers, molecularly imprinted polymers, (g) on functionalization with biomolecules including proteins and nucleic acids. Other subsections cover flexible graphene and GO based nanocomposites and 3D composites. Application of graphene and GO nanocomposites are then covered in a in large section that comprises electrochemical sensors and biosensors (based on voltammetry, amperometry, potentiometry, impedimetry, electrochemiluminescence, photoelectrochemistry, field effect transistors, electrochemical immunosensors) with specific subsections on gas sensors, enzymatic biosensors and gene sensors. A concluding section covers current challenges and perspectives of graphene and GO based (bio)sensing. Graphical abstract Illustration of electroanalytical applications of graphene functionalized with various materials, including carbon nanotube (CNT), fullerene (C 60 ), nanodiamond (ND), nanoparticle (NP), polyoxometalate (POM), metal hexacyanoferrate (MHCF), metalphthalocyanine (MPc), cyclodextrin (CD), poly(sodium 4-styrenesulfonate) (PSS), chitosan (CHIT), DNA and enzyme.

Development of oxidative and reductive flavors in wine can be influenced by the concentration and form of Cu within the wine. Electrochemical techniques have been devised to quantitate electrochemically active Cu (labile) in wine, as opposed to inactive Cu (non-labile). However, the electrochemical methods to measure labile Cu may be biased by the wine matrix, require lengthy calibration processes and/or unduly perturb the wine matrix during measurement. In this study, medium exchange stripping potentiometry was utilized with a thin mercury film on a screen-printed carbon electrode to provide a quantitation method that could largely overcome these limitations. The best average recoveries for 0.040 mg/L of labile Cu of 101 ± 15% (n = 12) were observed using composite calibration graphs prepared in oxidized wines and on multiple electrodes and using Pb as an internal standard. Composite calibration curves performed on different electrodes to the sample analysis were as effective in quantifying labile Cu as calibration curves performed on the same electrode as the sample. The results allow selection of a quantitation procedure that will suit the required speed and accuracy of labile Cu determination.

Multi-analyte sensing using exclusively laser-induced graphene (LIG)-based planar electrode systems was developed for sweat analysis. LIG provides 3D structures of graphene, can be manufactured easier than any other carbon electrode also on large scale, and in form of electrodes: hence, it is predestinated for affordable, wearable point-of-care sensors. Here, it is demonstrated that LIG facilitates all three electrochemical sensing strategies (voltammetry, potentiometry, impedance) in a multi-analyte system for sweat analysis. A potentiometric potassium-ion-selective electrode in combination with an electrodeposited Ag/AgCl reference electrode (RE) enabled the detection of potassium ions in the entire physiologically relevant range (1 to 500 mM) with a fast response time, unaffected by the presence of main interfering ions and sweat-collecting materials. A kidney-shaped interdigitated LIG electrode enabled the determination of the overall electrolyte concentration by electrochemical impedance spectroscopy at a fixed frequency. Enzyme-based strategies with amperometric detection share a common RE and were realized with Prussian blue as electron mediator and biocompatible chitosan for enzyme immobilization and protection of the electrode. Using glucose and lactate oxidases, lower limits of detection of 13.7 ± 0.5 μM for glucose and 28 ± 3 μM for lactate were obtained, respectively. The sensor showed a good performance at different pH, with sweat-collecting tissues, on a model skin system and furthermore in synthetic sweat as well as in artificial tear fluid. Response time for each analytical cycle totals 75 s, and hence allows a quasi-continuous and simultaneous monitoring of all analytes. This multi-analyte all-LIG system is therefore a practical, versatile, and most simple strategy for point-of-care applications and has the potential to outcompete standard screen-printed electrodes.

Flows containing suspended colloidal particles and dissolved solutes are found in a multitude of natural and man-made systems including hydraulic fractures, water filtration systems and microfluidic devices, e.g. those designed for biological or medical applications. In these types of systems, unexpected particle dynamics such as rapid particle transport and focusing has been observed in the presence of local solute gradients due to the cooperating or competing effects of fluid advection and particle diffusiophoresis, the latter driven by local chemical gradients. We develop analytical expressions for the fluid, solute and particle dynamics in long, narrow channels due to the combined influence of pressure-driven channel flow with diffusiophoretic and diffusioosmotic effects. The results confirm a rapid particle focusing effect that can be controlled by manipulating the particle, solute and flow properties, as well as the channel’s geometry and surface chemistry. Thus, we propose a new approach for performing microfluidic zeta potentiometry, as well as techniques for sorting, concentrating and/or capturing particles based on their sizes or zeta potentials. Finally, we demonstrate that diffusioosmotic effects can be used to pump fluid against a pressure gradient.

Detection of erythromycin (ERY) residues in commercial milk samples is crucial for the safety assessment. Herein, a printed circuit board was patterned as a feasible miniaturized potentiometric sensor for ERY determination in dairy samples. The proposed chip design fits to a 3.5-mm female audio plug to facilitate the potential measurements of working electrode versus reference one in this all-solid-state system. The sensor utilizes molecular imprinted polymer (MIP) for the selective recognition of the studied drug in such challenging matrix. The electrode stability is achieved through the addition of poly (3,4-ethylenedioxythiophene) nano-dispersion on its surface. The proposed device detects down to 6.6 × 10 −8 M ERY with a slope of 51 mV/decade in the 1 × 10 −7 –1 × 10 −3 M range. The results display high accuracy (99.9% ± 2.6) with satisfactory relative standard deviation for repeatability (1.6%) and reproducibility (5.0%). The effect of common antibiotic classes, namely, amphenicols, beta-lactams, fluoroquinolones, sulfonamides, and tetracyclines, can be neglected as evidenced by their calculated binding capacities towards the proposed MIP. The calculated selectivity coefficients also show a good electrode performance in the presence of naturally present inorganic ions allowing its application to different milk samples. Graphical abstract

A core-shell structured magnetic covalent organic frameworks of the type Fe 3 O 4 @COFs was prepared by using the Fe 3 O 4 nanoparticles as magnetic core, and 4,4”-diamino-p-terphenyl and 1,3,5-tris(p-formylphenyl)benzene as two building blocks. The Fe 3 O 4 @COFs were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive spectrum, Fourier transform infrared spectroscopy, zeta potentiometric analysis, X-ray diffraction, vibrating sample magnetometry, thermogravimetric analysis and the nitrogen adsorption-desorption isotherms. The Fe 3 O 4 @COFs have core-shell structure with average diameter of 200 ± 2.4 nm, a high specific surface area (124 m 2 ·g -1 ), uniform pore size distribution (3.1 nm), good magnetic responsivity (36.8 emu·g -1 ), good thermal and chemical stability. They were applied as the sorbents for magnetic solid phase extraction (MSPE) for fluoroquinolones (FQs) ciprofloxacin, enrofloxacin, lomefloxacin, gatifloxacin, levofloxacin and pefloxacin. The effects of sorbent dosage, extraction time, p H value, ionic strength, desorption solvent and desorption time were investigated. By combining MSPE with HPLC-DAD analysis, a rapid and sensitive method was developed for the enrichment and determination of these FQs. The method had good linearity in the range of 2.5-1500 ng·g -1 FQ concentration range and low limits of detection (0.25-0.5 ng·g -1 ). The method was successfully applied to the extraction and determination of FQs in (spiked) pork, milk and human plasma samples. Recoveries ranged from 78.7-103.5% (with RSD<6.2%). Graphical abstract Schematic representation of the magnetic covalent organic frameworks which prepared by using the Fe 3 O 4 nanoparticles as magnetic core, 4,4”-diamino-p-terphenyl and 1,3,5-tris(p-formylphenyl)benzene as two building blocks. The Fe 3 O 4 @COFs were applied as adsorbents for magnetic solid phase extraction of six fluoroquinolones (FQs) and HPLC-DAD was applied to analysis the extraction efficiencies.