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Abstract

This investigation was carried out with the aim of verifying whether transmittance detection modes on soaked paper, which is a simple and attractive determination approach for microfluidic paper-based analytical devices, can be improved by using deep eutectic solvents (DESs) as suitable media for minimizing reflection and refraction phenomena affecting these measurements. With this purpose, we tested two DESs such as ethaline and glyceline by checking that paper soaked with both two DESs displayed a quite higher transparency than that soaked with water (the absorbance decreased of about 25%). This result is particularly important in that DESs offer the appreciable advantage of being characterized by a negligible vapor pressure, unlike water or the majority of organic media, thus allowing long-term detections or analysis of very small samples to be conducted avoiding any problem caused by the solvent evaporation. As a proof of concept, we have then compared the detection of the patent blue V dye (E131) in ethaline solutions with that of the same dye dissolved in water. These determinations were performed on paper discs defined by a circular hydrophobic barrier which were installed into a plastic holder, which was constructed on purpose by the 3D technology to fit the cell housing of a Varian Cary 50 bio benchtop spectrophotometer adopted in our spectrophotometric measurements. The results found on paper discs soaked with ethaline were totally satisfactory in that they were characterized by a good repeatability and allowed a calibration plot to be constructed in a quite wide concentration range which allowed quite low concentrations to be detected (in the µM range) and was characterized by a good enough correlation coefficient. On the contrary, the results found on paper discs soaked with water were totally unsatisfactory since they were strongly affected by both the solvent evaporation and a more marked ripple present in the recorded spectra.

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... Such a choice was made to facilitate the analysis of materials such as paper, whose common characteristic is its internal inhomogeneity that introduces scattering and noise [74,75]. The propagation of light through such inhomogeneous medium differs significantly from the propagation of light in a homogeneous material, since the light scatters off points in its path, thus making colorimetric measurements quite vulnerable if appropriate precautions are not taken [53,76,77]. Finally, the developed instrument was used to quantify the dye content in some commercial products and the nitrite concentration in aqueous solutions, prepared on purpose in our laboratories, comparing in all cases the results obtained with those found with a benchtop instrument. ...
... Therefore, PADs were prepared as described previously for this type of deposition [76]. Briefly, a series of paper discs, each defined by a circular hydrophobic barrier, was printed onto a filter paper foil from Labor (Cordenons, PN, IT) by using the fused deposition modeling (FDM) technology. ...
... A Labor paper foil was fixed on the glass bed of the 3D printer with paper-tapes, paying attention to maintain the paper completely flat. PCL on paper was printed using a procedure similar to that reported in literature [49,76] by printing directly over paper (0.2 mm layer height) in order to complete printing with a single layer. Printing options were set to avoid the nozzle to pass over already printed parts and the filament flow was set to 120 % in order to increase sealing. ...
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Surface tension is a key physiochemical property for the application of deep eutectic solvents (DESs) in the field of interface and colloid. However, the surface tension of DESs has not been systematically studied. Here, a comprehensive investigation on the surface tension of 50 typical DESs was carried out. The effect of hydrogen-bonding donors (HBDs) and hydrogen-bonding acceptors (HBAs) on the surface tension was investigated. Furthermore, the surface tension of mixed systems of DESs with other solvents, water, water+salt (take KCl as a representative), ethanol, acetone, isopropanol, and ethyl acetate (EtAc) was studied. It was found that both HBDs and HBAs had a significant influence on the surface tension of DESs. The presence of crystal water in the salt component of DESs would decrease the surface tension of DESs. Besides, the surface tension of DESs increased significantly when the water mole fraction was higher than 0.9, which was well consistent with the tendency of IR-spectra. However, the surface tension of DESs decreased continuously with the increase of the mol ratio of other investigated solvents.
Article
A simple, instrument-free, paper-based analytical device with dual-emission carbon dots (CDs) (blue CDs and red CDs) was developed for the semi-quantitative, visual and sensitive speciation analysis of lead ions in real sample with a sensitive de-tection limit of 2.89 nM. When the paper strip is immersed into the sample solution, the blue fluorescence was quenched by Pb2+ in solution, while the red fluorescence serves as background reference without color change, and significant color evolu-tions from blue to red were observed under the ultraviolet lamp, resulting into a semi-quantitative visual detection. Further-more, a smartphone was used in visual detection of lead ions by identifying the RGB value of the fluorescent probe solution and corresponding paper strip. The application of smartphones and fluorescent paper strip has greatly shortened the detec-tion time and reduced the cost of detection, providing a new strategy for the on-site and semi-quantitative detection of heavy metal ions in water sample.
Article
The search for green solvents that can replace harsh organic solvents and relatively toxic ionic liquids (ILs) has led to the discovery of deep eutectic solvents (DES). DES are now rapidly emerging in numerous applications owing to their green character, biodegradability, tuneability, low cost and simple preparation, compared to other solvents. The possibility that natural DES might play a role as an alternative media to water in living organisms pushed the researchers to investigate their use as solvents for the poorly water soluble macromolecules. However, the addition of water in most of their applications must be controlled to maintain DES' supramolecular structure and properties. This review presents the impact of water on DES, used as solvents for the biological macromolecules mainly phospholipids, proteins, nucleic acids and polysaccharides. The effect of water on the DES' supramolecular network and its physico-chemical properties is discussed and the applications of DES as solvents for the biological macromolecules, in the absence and presence of water, are highlighted.
Article
The deep eutectic solvent ethaline, containing choline chloride as H-bond acceptor and ethylene glycol as H-bond donor and one of its mixture with water are studied in this work. Ethaline is anhydrous, with a 1:2 mol ratio. Hydrated ethaline, choline chloride:ethylene glycol:water, was studied in a 1:1.98:0.95 mol ratio. Several volumetric, acoustic, optical, thermal, surface, and transport properties were measured and calculated. The working temperature ranges from 278.15 to 338.15 K at pressure = 0.1 MPa. The effects of temperature, water inclusion, and the nature of the donor compound are evaluated. With regard to temperature, the system's behaviour is as expected: a linear relation for the thermodynamic properties and agreement with the Vogel-Fulcher-Tammann equation for the transport properties. The water molecules hardly modify the ethaline structure. The choline chloride – ethylene glycol interactions are weaker than those for choline chloride - glycerol.
Article
In this work, a rapid and sensitive paper-based analytical device (PAD) method was developed for screening detection of total tetracyclines (TCs) in environment water. TCs form firstly a narrow stacking band on a paper channel by field amplification stacking, and then the band was visualized by fluorescent imaging which was induced by an ultraviolet light-emitting diode (UV LED). The image was acquired by a smartphone camera for quantitative analysis. Under optimal conditions, the sensitivity of this portable PAD system was 250 times enhanced within 2 min by online electrokinetic stacking and linear response was demonstrated in the range of 5–80 ng mL⁻¹(R² = 0.997) with detection limit of 4.5 ng mL⁻¹. The applicability was demonstrated by detection of total TCs in environmental water with recovery ranging from 87 to 112% (RSD = 4.1–16.3%).
Article
In this paper, two Natural Deep Eutectic Solvents, glyceline (Gly) and glyceline-water (GlyW), containing choline chloride as acceptor H-bond compound and glycerol as donor H-bond group are studied. For glyceline the mole relation is 1 (choline chloride): 2 (glycerol) and for glyceline-water the mole relation is 1 (choline chloride): 1.99 (glycerol): 1.02 water. The ternary NADES has been synthetized and characterized chemically by NMR techniques for this work. Several thermophysical properties in a wide range of temperature (278.15–338.15) K and at atmospheric pressure (0.1 MPa) have been measured for both compounds: density, ρ speed of sound, u, refractive index, nD, surface tension,σ isobaric molar heat capacity, Cp,m, kinematic viscosity, ν and electric conductivity,κ. Furthermore, some related properties have been also calculated: isobaric expansibility, αp, isentropic compressibility, κS, molar refraction, Rm, entropy and enthalpy of surface formationper unit surface area (ΔSs and ΔHs), and dynamic viscosity, η and viscous flow and electrical conductivity activation energies. The results have been discussed in terms of the effect of temperature and the inclusion of water. We conclude that the compound containing water into the structure has a higher molar volume and a higher fluidity. The binary NADES (Gly) is a more structured liquid than ternary one (GlyW).
Article
Hydrogen cyanide is a highly toxic compound employed for applications such as electroplating, production of organic solvents, fish stunning, and even as a chemical weapon. In this work, we describe a new microfluidic paper-based assay for selective cyanide determination, based on the reaction of the cyanide anion with palladium dimethylglyoximate (DMG) followed by colorimetric reaction of DMG with nickel. Quantification was performed by measuring the absorbance of light passing through the paper, employing an LED emitting at 525 nm and a log ratio amplifier circuit emulating Lambert-Beer's law. This offers an alternative to the smartphone-based methodologies for signal treatment usually employed in colorimetric μPAD-based methods The technique enabled linear calibration within the range 100–500 ppb of HCN, as well as a detection limit of 10 ppb for HCN in gaseous samples. The sampling time used for this concentration range was 5 min. The method was also tested for the quantification of cyanide in aqueous samples by adding H3PO4 to the sample, followed by exposure of the paper sensor to the gaseous HCN generated. A detection limit of 1 μM was achieved, which makes the method also suitable for detection of cyanide in liquid samples.
Article
A colorimetric point-of-care paper-based analytical device (PAD) is developed for detecting adulterated beverages using whiskey falsified with caramel color as a model. Combining principal component analysis and calibration curves facilitated identification of adulteration in samples seized by the Brazilian Federal Police, at only B$0.02 per sample.
Article
Paper-based devices are a leading alternative among the main analytical tools for point-of-care testing, due to their portability, low-cost, and ease-of-use. Colorimetric readouts are the most common method of detection in these microfluidic devices, enabling qualitative, semi-quantitative and fully quantitative analysis of multiple analytes. There are manifold ways to obtain a colorimetric output in such devices, including nanoparticles, dyes, redox and pH indicators, and each has unique drawbacks and benefits. There are also multiple variables that impact the analysis of colorimetric reactions in microfluidic paper-based systems, including color homogeneity, image capture methods, and the data handling itself. Here, we present a critical review of recent developments and challenges of colorimetric detection on microfluidic paper-based analytical devices (µPADs), and present thoughts and insights towards future perspectives in the area to improve the use of colorimetric readouts in conjunction with µPADs.
Article
Deep eutectic solvents (DESs) are ionic liquids analogs that have been the subject of a growing interest in the scientific community. Governed by their favorable chemical and physical properties, they were utilized in a wide variety of fields. DESs possessing both desirable and undesirable properties for a specific application are not uncommon. As such, investigation into the variation of their properties upon mixing, in order to understand and improve their properties for a specific application, seems promising. In this study, the measurement of the physical and selected excess thermodynamic properties of Ethaline upon addition of Glyceline was carried out. The deviation of excess molar volume as a function of Glyceline molar fraction was observed to be alternating between negative and positive. This implies that the predominant interactions is due to either the difference in the sizes and shapes of the constituent molecules or to the effect dispersion forces. The highest deviations of the excess molar volume were observed at 30 and 90 mol% Glyceline. Density, viscosity, pH, RI and conductivity of the pure and DES mixtures were measured at different Glyceline molar fractions within the temperature range of 20 to 80 °C. © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.
Article
Paper is increasingly recognized as a user-friendly and ubiquitous substrate for construction of microfluidic devices. Microfluidic paper-based analytical devices (μPADs) provide an alternative technology for development of affordable, portable, disposable and low-cost diagnostic tools for improving point of care testing (POCT) and disease screening in the developing world, especially in those countries with no- or low-infrastructure and limited trained medical and health professionals. We in this review present fabrication techniques for microfluidic devices and their respective applications for biological detection as reported to date. These include: (i) fabrication techniques: examples of devices fabricated by using two-dimensional (2D) and three-dimensional (3D) methods; (ii) detection application: biochemical, immunological and molecular detection by incorporating efficient detection methods such as, colorimetric detection, electrochemical detection, fluorescence detection, chemiluminescence (CL) detection, electrochemiluninescence (ECL) detection, photoelectrochemi (PEC) detection and so on. In addition, main advantages, disadvantages and future trends for the devices are also discussed in this review.
Article
We propose here simple electrochemical cells assembled with electrodes pencil drawn on paper for conducting one-spot tests enabling olive oil to be easily distinguished from other vegetable oils. They consist of small circular pads of hydrophilic paper defined by hydrophobic barriers, these last printed by using custom-designed rubber stamps, where working, reference and counter electrodes are drawn by pencil leads. These cells were first wetted with a small volume of aqueous electrolyte, avoiding coating of the upper surface of electrodes. A controlled volume of edible oil samples was then applied on top of the moist cell. The results found proved that these devices can be adopted as effective platforms suitable for the detection of electroactive compounds present in edible oils. In fact, they allow voltammetric profiles to be recorded not only for the oxidation of water soluble species (ortho-diphenols, as well as some mono-phenols and polyphenols) present in olive oils, but also for electroactive hydrophobic components (e.g. α-tocopherol) present in sunflower oils which were chosen as model of seed oils. The whole of collected findings pointed out that simple one-spot tests performed by these devices enable olive oils to be easily distinguished from other edible oils on the basis of their clearly different voltammetric profiles. A satisfactory inter-device reproducibility (±13%) was estimated by applying strictly similar extra virgin olive oil samples onto seven different cells carefully prepared by the same procedure. An operating mechanism able to account for the detection of also electroactive hydrophobic compounds present in oils is proposed. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
Article
Deep eutectic solvents (DES) are new emerging alternatives to conventional ionic liquids that may find a number of interesting applications in industrial and chemical processes. In this study, the densities, ρ, and refractive indices, nD, of the DESs (choline chloride + ethylene glycol) and (choline chloride + glycerol) and their aqueous mixtures were investigated at atmospheric pressure over the temperature range 298.15–333.15 K and across a complete composition range. The excess molar volumes, VE, and refractive index deviations, ΔnD, were also calculated from experimental results. The calculated excess molar volumes were negative at all temperatures over the entire range of composition considered, suggesting the presence of strong interactions between water and the DES in the mixtures. The refractive index deviations, on the other hand, were found positive in the entire concentration range. The calculated properties were fitted to a Redlich–Kister type equation to correlate them to the temperature and composition. The correlations used satisfactorily represent the densities and refractive indices of the pure DESs and their aqueous binary mixtures as functions of temperature and composition as indicated by the low overall average absolute deviations obtained in the calculations.
Article
Deep eutectic solvents are cheap and biodegradable alternatives to conventional ionic liquids and volatile organic solvents. In this work, we present new measurements on the densities of the deep eutectic solvent choline chloride:glycerol (GLY) and its aqueous mixtures in the temperature range (298.15–323.15) K and pressures up to 50 MPa. The density was measured using a vibrating-tube density meter and the experimental uncertainty was estimated to be ±0.1%. Density data were used to derive other properties such as isothermal compressibility, isobaric expansivity, and excess molar volume. The excess molar volumes of the mixtures of GLY (1) + H2O (2) were investigated and an empirical equation was used to represent their dependence on temperature, pressure, and composition. The density data at elevated pressures were correlated with the temperature, pressure, and composition by a Tait-type equation.
Article
Deep Eutectic Solvents (DESs) are a novel class of solvents with potential industrial applications in separation processes, chemical reactions, metal recovery and metal finishing processes such as electrodeposition and electropolishing. Macroscopic physical properties such as viscosity, conductivity, eutectic composition and surface tension are already available for several DESs, but the microscopic transport properties for this class of compounds are not well understood and the literature lacks experimental data that could give a better insight into the understanding of such properties. This paper presents the first pulsed field gradient nuclear magnetic resonance (PFG-NMR) study of DESs. Several choline chloride based DESs were chosen as experimental samples, each of them with a different associated hydrogen bond donor. The molecular equilibrium self-diffusion coefficient of both the choline cation and hydrogen bond donor was probed using a standard stimulated echo PFG-NMR pulse sequence. It is shown that the increasing temperature leads to a weaker interaction between the choline cation and the correspondent hydrogen bond donor. The self-diffusion coefficients of the samples obey an Arrhenius law temperature-dependence, with values of self-diffusivity in the range of [10(-10)-10(-13) m(2) s(-1)]. In addition, the results also highlight that the molecular structure of the hydrogen bond donor can greatly affect the mobility of the whole system. While for ethaline, glyceline and reline the choline cation diffuses slower than the associated hydrogen bond donor, reflecting the trend of molecular size and molecular weight, the opposite behaviour is observed for maline, in which the hydrogen bond donor, i.e. malonic acid, diffuses slower than the choline cation, with self-diffusion coefficients values of the order of 10(-13) m(2) s(-1) at room temperature, which are remarkably low values for a liquid. This is believed to be due to the formation of extensive dimer chains between malonic acid molecules, which restricts the mobility of the whole system at low temperature (<30 °C), with malonic acid and choline chloride having almost identical diffusivity values. Diffusion and viscosity data were combined together to gain insights into the diffusion mechanism, which was found to be the same as for ionic liquids with discrete anions.
Article
Microfluidic paper-based analytical devices (microPADs) are a new class of point-of-care diagnostic devices that are inexpensive, easy to use, and designed specifically for use in developing countries. (To listen to a podcast about this feature, please go to the Analytical Chemistry multimedia page at pubs.acs.org/page/ancham/audio/index.html.).
Article
This article describes a point-of-care (POC) system--comprising a microfluidic, paper-based analytical device (micro-PAD) and a hand-held optical colorimeter--for quantifying the concentration of analytes in biological fluids. The micro-PAD runs colorimetric assays, and consists of paper that has been (i) patterned to expose isolated regions of hydrophilic zones and (ii) wet with an index-matching fluid (e.g., vegetable oil) that is applied using a disposable, plastic sleeve encasement. Measuring transmittance through paper represents a new method of quantitative detection that expands the potential functionality of micro-PADs. This prototype transmittance colorimeter is inexpensive, rugged, and fully self-contained, and thus potentially attractive for use in resource-limited environments and developing countries.
Article
(Chemical Equation Presented) By the book: A method for patterning paper with photoresist to create well-defined, millimeter-sized channels comprising hydrophilic paper bounded by hydrophobic polymer is described. This type of patterned paper is a prototype of a class of low-cost, portable, and technically simple platforms for running multiplexed bioassays with microliter volumes of a single biological sample.
Novel approaches for colorimetric measurements in analytical chemistry
  • Fernandes
G.M. Fernandes, W.R. Silva, D.N. Barreto, R.S. Lamarca, P.C.F. Lima Gomes, J. Flávio da S Petruci, A.D. Batista, Novel approaches for colorimetric measurements in analytical chemistry, Anal. Chim. Acta 1135 (2020) 187-203, https://doi.org/10.1016/j.aca.2020.07.030.
Eutectics: formation, properties and applications
  • Yu