Design and 3D printing of an electrochemical sensor for Listeria monocytogenes detection based on loop mediated isothermal amplification

The aim of this work is the design and 3D printing of a new electrochemical sensor for the detection of Listeria monocytogenes based on loop mediated isothermal amplification (LAMP). The food related diseases involve a serious health issue all over the world. Listeria monocytogenes is one of the major problems of contaminated food, this pathogen causes a disease called listeriosis with a high rate of hospitalization and mortality. Having a fast, sensitive and specific detection method for food quality control is a must in the food industry to avoid the presence of this pathogen in the food chain (raw materials, facilities and products). A point-of-care biosensor based in LAMP and electrochemical detection is one of the best options to detect the bacteria on site and in a very short period of time. With the numerical analysis of different geometries and flow rates during sample injection in order to avoid bubbles, an optimized design of the microfluidic biosensor chamber was selected for 3D-printing and experimental analysis. For the electrochemical detection, a novel custom gold concentric-3-electrode consisting in a working electrode, reference electrode and a counter electrode was designed and placed in the bottom of the chamber. The LAMP reaction was optimized specifically for a primers set with a limit of detection of 1.25 pg of genomic DNA per reaction and 100% specific for detecting all 12 Listeria monocytogenes serotypes and no other Listeria species or food-related bacteria. The methylene blue redox-active molecule was tested as the electrochemical transducer and shown to be compatible with the LAMP reaction and very clearly distinguished negative from positive food samples when the reaction is measured at the end-point inside the biosensor

Transport properties of the binary mixtures of the three organic liquids toluene, methanol, and cyclohexane

We report on the measurements of diffusion (D), thermodiffusion (DT), and Soret (ST) coefficients in binary pairs of the ternary system toluene-methanol-cyclohexane using different instrumental techniques: microgravity measurements (SODI/DCMIX2) on the International Space Station, thermogravitational column in combination with sliding symmetric tubes, optical beam deflection, optical digital interferometry, and counter flow cell. The binary systems have large regions where the mixtures are either not miscible or the Soret coefficient is negative. All the coefficients have been measured over a wide composition range with the exception of a miscibility gap. Results from different instruments and literature data are in favorable agreement over a broad composition range. Additionally, we have carefully measured the physical properties and the optical contrast factors (dn/dc) p, T and (dn/dT)p,c. The latter ones were also calculated using the Looyenga equation. The measurements in methanol-cyclohexane mixture revealed a decay of the diffusion coefficient when approaching the miscibility gap. We have interpreted this in the spirit of the pseudospinodal concept

Thermodiffusion Coefficients of Water/Ethanol Mixtures for Low Water Mass Fractions

The difficulty of measuring the thermodiffusion coefficients by optical properties of water-ethanol binary mixtures of approximately 20 wt % of water has been highlighted by several authors in recent years. This is because the concentration derivative of the refractive index (∂ n/∂ c) p,T is near zero at this concentration. For this reason, we measured the thermodiffusion coefficients by means of density analysis using the thermogravitational column technique from 5 wt % to 50 wt % at 25∘C. In addition, we measured the thermophysical properties such as density, dynamic viscosity, thermal expansion and mass expansion

Determination of the molecular diffusion coefficients in ternary mixtures by the sliding symmetric tubes technique

A new analytical methodology has been developed to determine the diagonal and cross-diagonal molecular diffusion coefficients in ternary mixtures by the Sliding Symmetric Tubes technique. The analytical solution is tested in binary mixtures obtaining good agreement with the results of the literature. Results are presented for the ternary mixture formed by tetralin, isobutylbenzene, and dodecane with an equal mass fraction for all the components (1–1–1) which is held at 25 °C. Diagonal and cross-diagonal coefficients are determined for the three possible orders of components, in order to compare the results with those available in the literature. A comparison with published results shows a good agreement for the eigenvalues of the diffusion matrix, and a reasonable agreement for the diagonal molecular diffusion coefficients

Physicochemical characterization of hydrophobic type III and type V deep eutectic solvents based on carboxylic acids

In the present work, novel type III and type V deep eutectic solvents (DESs) were prepared by mixing choline chloride (ChCl), tetrabutylammonium chloride (TBAC) or thymol as HBA, and different alkyl chain length carboxylic acids as HBD (acetic, oxalic, palmitic, stearic, oleic and linoleic acid) at various molar ratios. The hydrophobic DESs were characterized by infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1H NMR), concluding the formation of intermolecular interactions, as hydrogen bonds between the precursors. Thermogravimetric analysis (TGA) was used to obtain the thermal decomposition profiles of the prepared DESs, proving interactions between the precursors and decomposition temperatures with values, which are found in the ranges of the precursor constituents and higher than 170 °C. Other physicochemical properties, such as density, thermal expansion coefficient, dynamic viscosity, refractive index, surface tension, and thermal and ionic conductivities have been determined. Furthermore, the ability of these DESs as UV filter extractants from aqueous samples using a dispersive liquid–liquid microextraction (DLLME) previous to liquid chromatographic analysis was demonstrated. Therefore, these type III and type V DESs could be applied to the extraction of pollutants from environmental water samples

Thermodiffusion in Ternary Mixtures of Water/Ethanol/Triethylene Glycol: First Report on the DCMIX3-Experiments Performed on the International Space Station

We report on thermodiffusion experiments conducted on the International Space Station ISS during fall 2016. These experiments are part of the DCMIX (Diffusion and thermodiffusion Coefficients Measurements in ternary Mixtures) project, which aims at establishing a reliable data base of non-isothermal transport coefficients for selected ternary liquid mixtures. The third campaign, DCMIX3, focuses on aqueous systems with water/ethanol/triethylene glycol as an example, where sign changes of the Soret coefficient have already been reported for certain binary subsystems. Investigations have been carried out with the SODI (Selectable Optical Diagnostics Instrument) instrument, a Mach-Zehnder interferometer set up inside the Microgravity Science Glovebox in the Destiny Module of the ISS. Concentration changes within the liquids have been monitored in response to an external temperature gradient using phase-stepping interferometry. The complete data set has been made available in spring 2017. Due to additionally available measurement time, it was possible to collect a complete data set at 30∘C and an almost complete data set at 25∘C, which significantly exceeds the originally envisaged measurements at a single temperature only. All samples could be measured successfully. The SODI instrument and the DCMIX experiments have proven reliable and robust, allowing to extract meaningful data even in case of unforeseen laser instabilities. First assessments of the data quality have revealed six out of 31 runs with some problems in image contrast and/or phase step stability that will require more sophisticated algorithms. This publication documents all relevant parameters of the conducted experiments and also events that might have an influence on the final results. The compiled information is intended to serve as a starting point for all following data evaluations

Optimizing Polymer Lab-on-Chip Platforms for Ultrasonic Manipulation: Influence of the Substrate

The choice of substrate material in a chip that combines ultrasound with microfluidics for handling biological and synthetic microparticles can have a profound effect on the performance of the device. This is due to the high surface-to-volume ratio that exists within such small structures and acquires particular relevance in polymer-based resonators with 3D standing waves. This paper presents three chips developed to perform particle flow-through separation by ultrasound based on a polymeric SU-8 layer containing channelization over three different substrates: Polymethyl methacrylate (PMMA); Pyrex; and a cracked PMMA composite-like structure. Through direct observations of polystyrene microbeads inside the channel, the three checked chips exhibit their potential as disposable continuous concentration devices with different spatial pressure patterns at frequencies of resonance close to 1 Mhz. Chips with Pyrex and cracked PMMA substrates show restrictions on the number of pressure nodes established in the channel associated with the inhibition of 3D modes in the solid structure. The glass-substrate chip presents some advantages associated with lower energy requirements to collect particles. According to the results, the use of polymer-based chips with rigid substrates can be advantageous for applications that require short treatment times (clinical tests handling human samples) and low-cost fabrication

The Soret coefficients of the ternary system water/ethanol/triethylene glycol and its corresponding binary mixtures

Thermodiffusion in ternary mixtures is considered prototypic for the Soret effect of truly multicomponent systems. We discuss ground-based measurements of the Soret coefficient along the binary borders of the Gibbs triangle of the highly polar and hydrogen bonding ternary DCMIX3-system water/ethanol/triethylene glycol. All three Soret coefficients decay with increasing concentration, irrespective of the choice of the independent component, and show a characteristic sign change as a function of temperature and/or composition. With the exception of triethylene glycol/ethanol at high temperatures, the minority component always migrates toward the cold side. All three binaries exhibit temperature-independent fixed points of the Soret coefficient. The decay of the Soret coefficient with concentration can be related to negative excess volumes of mixing. The sign changes of the Soret coefficients of the binaries allow to draw far-reaching conclusions about the signs of the Soret coefficients of the corresponding ternary mixtures. In particular, we show that at least one ternary composition must exist, where all three Soret coefficients vanish simultaneously and no steady-state separation is observable

Sorption isotherm, glass transition, and diffusion coefficient of polyacrylamide/water solutions

The sorption isotherm, the glass transition, and the mutual diffusion coefficient of polyacrylamide/water solutions are obtained experimentally. All of these parameters are measured in the concentrated regime by gravimetric experiments. The mutual diffusion coefficient is also measured at high solvent concentrations by the sliding symmetric tubes technique. Three different polyacrylamide batches differing in their molar mass have been characterized. The results are expressed in terms of simple empirical correlations, suitable for use in process modelization or numerical simulations

Mass effect on the soret coefficient in n-alkane mixtures

We have determined the Soret coefficient of different equimolar and non equimolar n-alkane mixtures from measurements of the molecular diffusion and thermal diffusion coefficients. It is shown that equimolar mixtures behave as isotopic-like mixtures in which only the mass effect contributes to the Soret effect. In non equimolar mixtures, a small linear dependence with the molar fraction is observed. Finally, we have obtained a new correlation, which allows the determination of the Soret coefficient of n-alkane mixtures using the data of viscosity, the thermal expansion coefficient of the pure components, and the density of the equimolar mixture