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.

High magnetization FeCo nanoparticles for magnetorheological fluids with enhanced response.

We present results concerning the fabrication of a new magnetorheological fluid with FeCo magnetic nanoparticles (NPs) as magnetic fillers. These NPs have been fabricated by using the chemical reduction technique and show a pure crystalline phase with size ranging among 30-50 nm and high magnetization, 212 ± 2 A m2 kg-1. They agglomerate due to the strong magnetic dipolar interaction among them. These FeCo nanoparticles were used to synthesize a magnetorheological fluid by using oleic acid as surfactant, mineral oil as carrier liquid and Aerosil 300 as additive to control the viscosity of the fluid. The synthesized fluid showed a strong magnetorheological response with increasing shear stress values as the magnetic field intensity increases. Thus, we have measured a superior performance up to 616.7 kA m-1, with a yield stress value of 2729 Pa, and good reversibility after demagnetization process. This value competes with the best ones reported in the most recent literature. We have compared the obtained results with our previous reported ones by using high magnetization Fe NPs fabricated by the electrical explosion of wire method (Fe-EEW).

Separation under thermogravitational effects in binary mixtures.

In the present work, by using a parallelepipedic thermogravitational microcolumn, the temperature gradient influence on the stability of the flow has been examined, emphasizing mixtures with positive Soret coefficients. Experiments were conducted for DCMIX2 Toluene/Methanol and DCMIX3 Water/Ethanol binary subsystems because of their broad range of positive Soret values for high concentrations of methanol and ethanol, respectively. Two different mixtures have been studied here in order to confirm the thermogravitational stability of the mixtures. Experiments were compared with numerical simulations carried out using the open-source software platform OpenFOAM.

Thermodiffusion in multicomponent n-alkane mixtures.

Compositional grading within a mixture has a strong impact on the evaluation of the pre-exploitation distribution of hydrocarbons in underground layers and sediments. Thermodiffusion, which leads to a partial diffusive separation of species in a mixture due to the geothermal gradient, is thought to play an important role in determining the distribution of species in a reservoir. However, despite recent progress, thermodiffusion is still difficult to measure and model in multicomponent mixtures. In this work, we report on experimental investigations of the thermodiffusion of multicomponent n-alkane mixtures at pressure above 30 MPa. The experiments have been conducted in space onboard the Shi Jian 10 spacecraft so as to isolate the studied phenomena from convection. For the two exploitable cells, containing a ternary liquid mixture and a condensate gas, measurements have shown that the lightest and heaviest species had a tendency to migrate, relatively to the rest of the species, to the hot and cold region, respectively. These trends have been confirmed by molecular dynamics simulations. The measured condensate gas data have been used to quantify the influence of thermodiffusion on the initial fluid distribution of an idealised one dimension reservoir. The results obtained indicate that thermodiffusion tends to noticeably counteract the influence of gravitational segregation on the vertical distribution of species, which could result in an unstable fluid column. This confirms that, in oil and gas reservoirs, the availability of thermodiffusion data for multicomponent mixtures is crucial for a correct evaluation of the initial state fluid distribution.

Thermodiffusion, molecular diffusion and Soret coefficients of aromatic+n-alkane binary mixtures.

In the present work, we have measured the thermodiffusion coefficient of 51 binary liquid mixtures at 25 oC. These mixtures correspond to the series of the aromatics toluene and 1-methylnaphthalene with n-alkanes nCi (i = 6, 8, 10, 12, and 14) at different mass fractions in the whole range. For that, we have used the thermogravitational technique. It is shown that the thermodiffusion coefficient is a linear function of the mass fraction in all the mixtures. Extrapolating the lines, we obtain the thermodiffusion coefficient in dilute solutions of n-alkanes for both toluene and 1-methylnaphthalene. These limiting values show a linear dependence with the inverse of the product of the molecular weights. In addition, we have measured the molecular diffusion coefficient of all the mixtures at 0.5 of mass fraction and at 25 oC, by the sliding symmetric tubes technique. It is observed that the product of this coefficient with the viscosity at the same concentrations takes a constant value for each of the series considered. Finally, we have also determined the Soret coefficient of the equimass mixtures by the combination of the measurements of thermodiffusion and molecular diffusion coefficients.

Soret coefficients of the ternary mixture 1,2,3,4-tetrahydronaphthalene + isobutylbenzene + n-dodecane.

In this work, the transport coefficients of the ternary mixtures of the diffusion coefficient measurements in ternary mixtures 1 project were determined. The analyzed ternary mixtures are formed by 1,2,3,4-tetrahydronaphthalene, isobutylbenzene, and dodecane (nC12) at different compositions. In all cases, the analysis was carried out at 25 °C. The thermodiffusion coefficients were measured by a new thermogravitational column, and the molecular diffusion coefficients were determined by the sliding symmetric tubes technique. Finally, the Soret coefficients were ascertained from the measurements of the thermodiffusion and molecular diffusion coefficients. In addition, two new quantitative correlations which enable the prediction of the thermodiffusion and Soret coefficients of a ternary mixture are presented. The comparison between the experimental and the predicted data shows a good agreement. The presented results help to complete the lack of experimental data in ternary mixtures. In addition, this work improves the fundamental understanding of multicomponent mixtures.

Contribution to the benchmark for ternary mixtures: Determination of Soret coefficients by the thermogravitational and the sliding symmetric tubes techniques.

This work is part of an international project for the research on the transport properties in ternary mixtures. Six different teams have analysed the same mixture by independent techniques in order to compare the results and validate the techniques. This work is the contribution of the team of Mondragon Unibertsitatea for ground conditions measurements. This team has measured the thermodiffusion coefficients by the thermogravitational techniques and the molecular diffusion coefficients by the Sliding Symmetric Tubes technique. The Soret coefficients have been determined by the combination of the thermodiffusion and molecular diffusion coefficients. The mixture chosen for the study is the one formed by 1,2,3,4-tetrahydronaphtalene, isobutylbenzene and n-dodecane at mass fraction of 80% of THN, 10% of IBB and 10% of n C12, and at 25°C. The good agreement between the results of the different teams shows the validity of the techniques used in this work.

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.

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.

Development of a thermogravitational microcolumn with an interferometric contactless detection system.

We present a new type of thermogravitational (TG) column, a so-called TG microcolumn with transparent windows and a very small sample volume of less than 50 µL. The TG microcolumn has a planar geometry with a thickness of 0.523 ± 0.004 mm, a height of 30 mm, and a width of 3 mm. The concentration difference between two points at different heights is measured with an interferometer using active phase control. From the concentration difference we can determine the thermal diffusion coefficient, D(T), using the refractive index variation with concentration, which has to be determined independently. We studied the three binary mixtures of dodecane, isobutylbenzene, and 1,2,3,4-tetrahydronaphthalene with a concentration of 50 wt % at a temperature of 298 K. The thermal diffusion coefficients agree within a few percent with the proposed benchmark values. In addition we investigated also the binary mixture toluene/n-hexane and compare the results with literature values. For the investigated mixtures the typical measurement times were between 30 min and 2 h with an applied temperature difference of ΔT = 6 K.

Determination of molecular diffusion coefficient in n-alkane binary mixtures: empirical correlations.

In this work we have measured the molecular diffusion coefficient of the n-alkane binary series nC(i)-nC(6), nC(i)-nC(10), and nC(i)-nC(12) at 298 K and 1 atm and a mass fraction of 0.5 by using the so-called sliding symmetric tubes technique. The results show that the diffusion coefficient at this concentration is proportional to the inverse viscosity of the mixture. In addition, we have also measured the diffusion coefficient of the systems nC(12)-nC(6), nC(12)-nC(7), and nC(12)-nC(8) as a function of concentration. From the data obtained, it is shown that the diffusion coefficient of the n-alkane binary mixtures at any concentration can be calculated from the molecular weight of the components and the dynamic viscosity of the corresponding mixture at 50% mass fraction.

Measurement of thermodiffusion coefficient in n-alkane binary mixtures: composition dependence.

In this work, we have measured the thermodiffusion coefficient of different n-alkane binary mixtures at several concentrations using the thermogravitational technique. In particular, we have studied the n-dodecane/n-heptane system as a function of composition and other systems covering a large range of mass differences and concentration at 25 degrees C and 1 atm. The results show that for any concentration the thermodiffusion coefficient of n-alkane mixtures is proportional to the mass difference between the components and to the ratio of the thermal expansion coefficient and viscosity of the mixture. The obtained equation allows us to determine the infinite dilution values of the thermodiffusion coefficient. We compare these values with recent experimental results in dilute polymer solutions and analyze the Brenner theory of thermodiffusion. Finally, it is shown that the thermodiffusion coefficient depends linearly with the mass fraction, and it can be calculated from the viscosity and thermal expansion of the pure components.

Thermodiffusion coefficients of binary and ternary hydrocarbon mixtures.

In this study, we have measured the thermodiffusion coefficients of six hydrocarbon liquid ternary mixtures at 25 degrees C using the thermogravitational technique. Mixtures of 1,2,3,4-tetrahydronaphthalene-isobutylbenzene-n-dodecane at four different concentrations and 1,2,3,4-tetrahydronaphthalene-isobutylbenzene-n-decane at two concentrations have been considered. We have used a plane-thermogravitational column with a small gap dimension to improve the accuracy of the recently reported data. The obtained results have been confirmed by measurements in a cylindrical column. We have also measured the thermodiffusion coefficients of 13 binary mixtures between the different components of ternaries in order to analyze the validity of the additive rule proposed in the literature to determine thermodiffusion coefficients of ternary mixtures from binary thermodiffusion data. A new correlation based on column separation, which reproduces the data within the experimental error, is proposed.

An improved theoretical model for thermal diffusion coefficient in liquid hydrocarbon mixtures: Comparison between experimental and numerical results.

Thermal diffusion or Soret effect is a phenomenon of mass transport in fluid mixtures driven by temperature gradients. In this paper, we have studied thermal diffusion coefficients for different binary n-alkane mixtures (equal mass fraction) through both theoretical and experimental methods. The theoretical model is based on the irreversible thermodynamics. Particularly, the nonequilibrium thermodynamic property tau is examined and remodeled with a consideration of vapor-liquid equilibrium in binary mixtures. The experimental method is based on the thermogravitational technique. The new model provides a good agreement with the experimental data from this study and in the literature.

Thermal diffusion and molecular diffusion values for some alkane mixtures: a comparison between thermogravitational column and thermal diffusion forced rayleigh scattering.

In the present work we studied the thermal diffusion behavior of n-decane in various alkanes by thermogravitational column (TC) technique and the thermal diffusion forced Rayleigh scattering (TDFRS) method. The investigated lighter alkanes compared to n-decane are n-pentane, n-hexane, n-heptane, n-octane, and the heavier ones are n-tetradecane, n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane, and n-eicosane. The binary mixture n-decane/ n-pentane we investigated at several different concentrations; all other mixtures were only investigated at a mass fraction of 50%. Even for the volatile n-pentane/ n-decane mixture the deviations between the thermal diffusion coefficients determined by the different methods agreed within the error bars. Typically the agreement between the two methods was in the order of 5%. In comparison to recently published TC and TDFRS data we found deviations in the order of 30% up to 40%. We analyze and discuss the possible reasons for the discrepancies for the present and the past publications.