Magnetically Agitated Nanoparticle-Based Batch Reactors for Biocatalysis with Immobilized Aspartate Ammonia-Lyase

In this study, we investigated the influence of different modes of magnetic mixing on effective enzyme activity of aspartate ammonia-lyase from Pseudomonas fluorescens immobilized onto epoxy-functionalized magnetic nanoparticles by covalent binding (AAL-MNP). The effective specific enzyme activity of AAL-MNPs in traditional shake vial method was compared to the specific activity of the MNP-based biocatalyst in two devices designed for magnetic agitation. The first device agitated the AAL-MNPs by moving two permanent magnets at two opposite sides of a vial in x-axis direction (being perpendicular to the y-axis of the vial); the second device unsettled the MNP biocatalyst by rotating the two permanent magnets around the y-axis of the vial. In a traditional shake vial, the substrate and biocatalyst move in the same direction with the same pattern. In magnetic agitation modes, the MNPs responded differently to the external magnetic field of two permanent magnets. In the axial agitation mode, MNPs formed a moving cloud inside the vial, whereas in the rotating agitation mode, they formed a ring. Especially, the rotating agitation of the MNPs generated small fluid flow inside the vial enabling the mixing of the reaction mixture, leading to enhanced effective activity of AAL-MNPs compared to shake vial agitation.

Magnetic-buoyancy-induced mixing in AGB stars: a theoretical explanation of the non-universal relation of [Y/Mg] to age

Context. Abundance ratios involving Y or other slow-neutron capture elements are routinely used to infer stellar ages. Aims. We aim to explain the observed [Y/H] and [Y/Mg] abundance ratios of star clusters located in the inner disc with a new prescription for mixing in asymptotic giant branch (AGB) stars. Methods. In a Galactic chemical evolution model, we adopted a new set of AGB stellar yields in which magnetic mixing was included. We compared the results of the model with a sample of abundances and ages of open clusters located at different Galactocentric distances. Results. The magnetic mixing causes a less efficient production of Y at high metallicity. A non-negligible fraction of stars with super-solar metallicity is produced in the inner disc, and their Y abundances are affected by the reduced yields. The results of the new AGB model qualitatively reproduce the observed trends for both [Y/H] and [Y/Mg] versus age at different Galactocetric distances. Conclusions. Our results confirm from a theoretical point of view that the relation between [Y/Mg] and stellar age cannot be ‘universal’, that is, cannot be the same in every part of the Galaxy. It has a strong dependence on the star formation rate, on the s-process yields, and on their relation with metallicity, and it therefore varies throughout the Galactic disc.

A Novel Method for Antibiotic Detection in Milk Based on Competitive Magnetic Immunodetection

The misuse of antibiotics as well as incorrect dosage or insufficient time for detoxification can result in the presence of pharmacologically active molecules in fresh milk. Hence, in many countries, commercially available milk has to be tested with immunological, chromatographic or microbiological analytical methods to avoid consumption of antibiotic residues. Here a novel, sensitive and portable assay setup for the detection and quantification of penicillin and kanamycin in whole fat milk (WFM) based on competitive magnetic immunodetection (cMID) is described and assay accuracy determined. For this, penicillin G and kanamycin-conjugates were generated and coated onto a matrix of immunofiltration columns (IFC). Biotinylated penicillin G or kanamycin-specific antibodies were pre-incubated with antibiotics-containing samples and subsequently applied onto IFC to determine the concentration of antibiotics through the competition of antibody-binding to the antibiotic-conjugate molecules. Bound antibodies were labeled with streptavidin-coated magnetic particles and quantified using frequency magnetic mixing technology. Based on calibration measurements in WFM with detection limits of 1.33 ng·mL−1 for penicillin G and 1.0 ng·mL−1 for kanamycin, spiked WFM samples were analyzed, revealing highly accurate recovery rates and assay precision. Our results demonstrate the suitability of cMID-based competition assay for reliable and easy on-site testing of milk.

Micromixing Nanoparticles and Contaminated Water Under Different Velocities for Optimum Heavy Metal Ions Adsorption

Effective mixing between contaminated water and nanoparticles is of great importance in various purification applications of microfluidics, especially when heavy metals are involved. Electromagnetic and shear mixing is combined here to explore optimization mixing strategies. A contaminated water stream is confined between two fresh-water streams loaded with nanoparticles and their mixing is studied numerically. The magnetic mixing is superimposed here with a time-modulated gradient external magnetic field. Results show that as velocity ratio increases, mixing between the heavy metals and nanoparticles grows more efficient, mainly due to increased shear, however, magnetic field action is catalytic to homogenise the mixture as water streams move away from the inlets. The present findings may shorten the path to purifying water and reduce its shortage.

Microfluidic Magnetic Mixing at Low Reynolds Numbers and in Stagnant Fluids

Microfluidic mixing becomes a necessity when thorough sample homogenization is required in small volumes of fluid, such as in lab-on-a-chip devices. For example, efficient mixing is extraordinarily challenging in capillary-filling microfluidic devices and in microchambers with stagnant fluids. To address this issue, specifically designed geometrical features can enhance the effect of diffusion and provide efficient mixing by inducing chaotic fluid flow. This scheme is known as “passive” mixing. In addition, when rapid and global mixing is essential, “active” mixing can be applied by exploiting an external source. In particular, magnetic mixing (where a magnetic field acts to stimulate mixing) shows great potential for high mixing efficiency. This method generally involves magnetic beads and external (or integrated) magnets for the creation of chaotic motion in the device. However, there is still plenty of room for exploiting the potential of magnetic beads for mixing applications. Therefore, this review article focuses on the advantages of magnetic bead mixing along with recommendations on improving mixing in low Reynolds number flows (Re ≤ 1) and in stagnant fluids.

Non-Equilibrium Crystallization with Magnetic Stirring in Pt/Inconel 625 Micro-Joints Welded by Capacitor Charge

The presented work describes issue of magnetic mixing and segregation of metals during the formation of micro-joints using the capacitor welding method. The key aspect is the very short weld time, which is below 2 ms. The Pt/Inconel 625 micro-joints have been tested in the work. The 100-μm platinum wire was welded to Inconel 625 with the same thickness. During the welding process, the capacitor discharge characteristics were recorded with the oscilloscope. This allowed for a mathematical description of phenomena occurring during the creation of the micro-joint. Observations of the micro-structures from the scanning electron microscope in BSE mode confirmed the strong micro-segregation of the joint components. In addition, the effect of magnetic mixing of the joint components was observed. Weld geometry results obtained from the calculations showed good compliance with the real joint micro-structure observation data.