A Deep Eutectic Solvent-based Amperometric Sensor for the Detection of Low Oxygen Contents in Gaseous Atmospheres

Physicochemical Properties of Choline Chloride/Acetic Acid as a Deep Eutectic Solvent and Its Binary Solutions with DMSO at 298.15 to 353.15 K

Deep eutectic solvents (DESs) are considered to play an important role in green chemistry and other technological fields as an alternative to organic solvents. The present study reports measurements of density (ρ), speed of sound (u), dynamic viscosity (η), and electrical conductivity (κ) and investigates physicochemical properties of choline chloride/acetic acid (ChCl/AcA DES) and its binary mixtures with dimethyl sulfoxide (DMSO) over the entire composition and temperature (298.15-353.15 K) range. The density data are well fitted by a second-degree polynomial equation in T. DES/DMSO mixtures exhibit negative excess molar volume and isentropic compressibility deviation with a minimum in respective curves at x1 ≈ 0.15 (x1 is the mole fraction of DES in the mixture), which became deeper with increasing temperature. The ChCl/AcA DES and DMSO curves for excess partial molar volume cross each other at x1 ≈ 0.15, showing that the packing effect is dominant over specific interactions. A similar behavior is observed for excess molar viscosity, showing the minima at x1 ≈ 0.62, and substantiates volumetric results. The temperature dependence of viscosity and conductivity is well described by the Vogel-Fulcher-Tammann (VFT) equation.

Evolution of microscopic heterogeneity and dynamics in choline chloride-based deep eutectic solvents

Deep eutectic solvents (DESs) are an emerging class of non-aqueous solvents that are potentially scalable, easy to prepare and functionalize for many applications ranging from biomass processing to energy storage technologies. Predictive understanding of the fundamental correlations between local structure and macroscopic properties is needed to exploit the large design space and tunability of DESs for specific applications. Here, we employ a range of computational and experimental techniques that span length-scales from molecular to macroscopic and timescales from picoseconds to seconds to study the evolution of structure and dynamics in model DESs, namely Glyceline and Ethaline, starting from the parent compounds. We show that systematic addition of choline chloride leads to microscopic heterogeneities that alter the primary structural relaxation in glycerol and ethylene glycol and result in new dynamic modes that are strongly correlated to the macroscopic properties of the DES formed.

Tailoring the macroscopic properties of deep eutectic solvents requires knowing how these depend on the local structure and microscopic dynamics. The authors, with computational and experimental tools spanning a wide range of space- and timescales, shed light into the relationship between micro and macroscopic properties in glyceline and ethaline.

Paper-based aptamer-antibody biosensor for gluten detection in a deep eutectic solvent (DES)

Paper has been widely employed as cheap material for the development of a great number of sensors such as pregnancy tests, strips to measure blood sugar, and COVID-19 rapid tests. The need for new low-cost analytical devices is growing, and consequently the use of these platforms will be extended to different assays, both for the final consumer and within laboratories. This work describes a paper-based electrochemical sensing platform that uses a paper disc conveniently modified with recognition molecules and a screen-printed carbon electrode (SPCE) to achieve the detection of gluten in a deep eutectic solvent (DES). This is the first method coupling a paper biosensor based on aptamers and antibodies with the DES ethaline. Ethaline proved to be an excellent extraction medium allowing the determination of very low gluten concentrations. The biosensor is appropriate for the determination of gluten with a limit of detection (LOD) of 0.2 mg L⁻¹ of sample; it can detect gluten extracted in DES with a dynamic range between 0.2 and 20 mg L⁻¹ and an intra-assay coefficient of 10.69%. This approach can be of great interest for highly gluten-sensitive people, who suffer from ingestion of gluten quantities well below the legal limit, which is 20 parts per million in foods labeled gluten-free and for which highly sensitive devices are essential.

Modified Screen Printed Electrode Suitable for Electrochemical Measurements in Gas Phase

We describe a convenient assembly for screen printed carbon electrodes (SPCE) suitable for analyses in gaseous samples which are of course lacking in supporting electrolytes. It consists of a circular crown of filter paper, soaked in a RTIL or a DES, placed upon a disposable screen printed carbon cell, so as to contact the outer edge of the carbon disk working electrode, as well as peripheral counter and reference electrodes. The electrical contact between the paper crown soaked in RTIL or DES and SPCE electrodes is assured by a gasket, and all components are installed in a polylactic acid holder. As a result of this configuration, a sensitive, fast-responding, membrane-free gas sensor is achieved where the real working electrode surface is the boundary zone of the carbon working disk contacted by the paper crown soaked in the polyelectrolyte. This assembly provides a portable and disposable electrochemical platform, assembled by the easy immobilization onto a porous and inexpensive supporting material such as paper of RTILs or DESs which are characterized by profitable electrical conductivity and negligible vapor pressure. The electroanalytical performance of this device was evaluated by voltammetric and flow injection analyses of oxygen which was chosen as prototype of electroactive gaseous analytes. The results obtained pointed out that this assembly is very profitable for the analysis of gaseous atmospheres, especially when used as detector for FIA in gaseous streams.