The authors acknowledge many useful discussions with M. Caggioni and support from Proctor and Gamble in the form of an internship for NAB.

1. Preparation of One-Time Use Materials in Device
<ol>
	<li>Preparation of tube
	<ol>
		<li>Cut tubing into 15 cm segments. Tubing has 1.6 mm inner diameter and 3.2 mm outer diameter.</li>
		<li>Hang tube segments vertically using tape. Place paper towel underneath tubes to collect the excess fluoropolymer solution.</li>
		<li>Inject 100 &#181;l&#160;of fluoropolymer solution into top opening of each tube segment using syringe, such that it will come into contact with entire circumference on the inner-wall.</li>
		<li>Allow tube segments to hang in place for 1 hr&#160;to remove excess amount of fluoropolymer solution.</li>
		<li>Clean out any fluoropolymer solution from bottom side of tube that didn&#8217;t drip out. Remove tubing from hanging position and dispose of paper towels.</li>
		<li>Place tube segments into oven at 100 &#176;C for 1 hr&#160;to anneal the fluoropolymer coating layer.</li>
		<li>Remove tube segments from oven. Use tweezers, as tube segments will be hot.</li>
	</ol>
	</li>
	<li>Preparation of diluted magnetic bead solution
	<ol>
		<li>Calculate magnetic bead concentration needed to achieve the desired carry-over volume, as determined by the relationship between carry-over volume and MB mass shown in Figure 2. 
		Note: The original MB solution has 1 g of MBs in 50 ml&#160;of solution. Considering a test chamber volume of 20 &#181;l, dilute original MB solution with distilled water to a ratio of 6:4 (MB solution:water) to obtain a carry-over volume of ~0.4 &#181;l. Adjust dilution ratio when different carry-over volume is desired.</li>
		<li>Place a 20 ml&#160;sample vial onto a micro-balance. Zero the balance.</li>
		<li>Agitate the magnetic bead solution container, then withdraw 0.6 ml&#160;using a micro-pipette.</li>
		<li>Dispense pipetted solution into the sample vial on balance.</li>
		<li>Dispense 0.4 ml&#160;of distilled water into the sample vial.</li>
	</ol>
	</li>
	<li>Fluorescent dye liquid preparation
	<ol>
		<li>Dissolve 2 wt.% of dye into DI water by vortexing the solution for 1 min.</li>
	</ol>
	</li>
</ol>
2. Preparation of Experimental Setup for Fluorescence Experiments
<ol>
	<li>Preparation of tubing device.
	<ol>
		<li>Insert a female Luer-lock connector onto one end of the tubing.</li>
		<li>Place the tube into a Luer-lock syringe that has a 3 ml&#160;volume and 0.1 ml&#160;graduation.</li>
		<li>Place the syringe into the syringe pump and set the feed rate at 2 ml/hr.</li>
		<li>For accurate insertion of liquids into the tubing, use the syringe pump to withdraw the solution containing the magnetic beads and fluorescent dye.</li>
		<li>Insert 20 &#181;l&#160;of magnetic bead solution into tube using syringe pump withdrawal. This liquid segment is referred to as the test chamber (test chamber volume can vary depending on the experiment). Vortex the container with magnetic bead solution for 1 min&#160;and then agitate by hand during the withdrawal cycle to form uniform MB dispersions.</li>
		<li>After test chamber liquid insertion is concluded, withdraw 6 &#181;l&#160;of air into the tube. This volume of air will later form a valve in between the two liquid segments.</li>
		<li>After air gap insertion is completed, begin withdrawal 180 &#181;l&#160;of liquid with fluorescent dye. This liquid segment is referred to as the reservoir. Reservoir volume can vary depending on the experiment. Larger reservoir volume is beneficial to minimize the change of dye concentration.</li>
		<li>Place a second female Luer-lock connector onto the other end of the tube.</li>
		<li>Remove the tube device from the syringe.</li>
		<li>Place Luer-lock caps on both ends of the device.</li>
	</ol>
	</li>
	<li>Optics setup for fluorescence experiments
	<ol>
		<li>Turn on all components connected to the inverted microscope.</li>
		<li>Turn on the computer and open the microscope imaging software.</li>
	</ol>
	</li>
</ol>
3. Experimental Procedure for Fluorescence Experiments
<ol>
	<li>Take initial fluorescence intensity measurement of test chamber and reservoir using the inverted microscope. When analyzing the fluorescence of the sample, ensure that the focus is in the center position (in both x and y directions) of the liquid segment within the tube. Record measurements in data spreadsheet.</li>
	<li>Place device over top of cube magnet such that the magnetic beads all segregate to one area in the test chamber. Transfer the beads to the reservoir by moving the device over top of the magnet (~ 10 sec). The 1 inch neodymium cube magnet is grade N48 with a pull force of 45.6 kg.</li>
	<li>Once magnetic bead cluster is transferred through the air gap and into the reservoir, agitate the magnetic beads by placing the device over top of the magnet and rotating to release the liquid being trapped within the cluster. Continue agitation of the magnetic beads until homogenization of the reservoir has been completed (~ 30-45 sec).</li>
	<li>Place device over top of magnet such that the magnetic beads in the reservoir all segregate to one area. Transfer the magnetic bead cluster back to the test chamber.</li>
	<li>Once the cluster reaches the test chamber, agitate the magnetic beads by placing the device over top of the magnet and rotating to release the trapped fluorescent liquid within. Continue agitation of the magnetic beads until homogenization of the test chamber has been completed (~ 30-45 sec).</li>
	<li>Take fluorescence intensity measurements of both the test chamber and reservoir using the inverted microscope. Record measurements in data spreadsheet.</li>
	<li>Steps 3.2-3.6 are repeated until both liquid segments converge to similar fluorescence intensities (~ 100 cycles).</li>
</ol>
4. Numerical Analysis of Fluorescent Data
<ol>
	<li>With the fluorescent intensity data stored into a spreadsheet, perform numerical analysis using MATLAB.</li>
	<li>Derive equations to calculate a theoretical value of fluorescence intensity in both the reservoir and test chamber. Incorporate the following equations into a MATLAB script file: 
	where I is the fluorescence intensity (A.U.), V is volume (&#181;l), n is the number of transfers, R is the reservoir, T is the test chamber, and C is carry-over.</li>
	<li>Using MATLAB, generate plots and analyze to determine the carry-over volume for all experiments. Use this data to produce Figure 2.</li>
</ol>
5. Preparation of Experimental Setup for Surfactant Experiments
<ol>
	<li>Preparation of tubing device.
	<ol>
		<li>Insert a female Luer-lock onto one end of the tubing.</li>
		<li>Place the tube into a Luer-lock syringe.</li>
		<li>Place the syringe into the syringe pump and set the feed rate at 2 ml/hr.</li>
		<li>For accurate insertion of liquids into the tubing, use the syringe pump to withdraw the solution containing the magnetic beads and surfactant.</li>
		<li>Insert 20 &#181;l&#160;magnetic bead solution into tube using syringe pump withdrawal. This liquid segment is referred to as the test chamber (test chamber volume can vary depending on the experiment). Agitate the container with magnetic bead solution by hand during the withdrawal cycle to form uniform MB dispersions.</li>
		<li>After test chamber liquid insertion is concluded, withdraw 6 &#181;l&#160;of air into the tube. This volume of air will later be referred to as the air gap.</li>
		<li>After air gap insertion is completed, begin withdrawal 180 &#181;l&#160;of pure C12E5 surfactant. This will later be referred to as the reservoir.</li>
	</ol>
	</li>
	<li>Optics setup for surfactant experiments.
	<ol>
		<li>Move syringe pump with tubing device such that the test chamber with magnetic beads is in focus with the stereo microscope.</li>
		<li>Place a sheet of polarizer film on top of an LED light source. Slide the LED light source underneath the tube attached to the syringe pump.</li>
		<li>Attach another polarizer film to the lens of the stereo microscope using tape. Be sure that the two polarizer films have a 90 degree offset from each other.</li>
		<li>Mount a CCD (charge coupled device) camera to the stereo microscope. Connect the camera to the computer and open up the imaging software.</li>
	</ol>
	</li>
</ol>
6. Experimental Procedure for Surfactant Experiments
<ol>
	<li>Place the cube magnet next to the test chamber while the magnet is mounted onto a stand.</li>
	<li>Once the magnetic beads form a cluster, begin pumping liquids in the tube at the feed rate of 2 ml/hr such that the magnetic bead cluster is moved from the test chamber, across the air gap, and into the surfactant reservoir chamber.</li>
	<li>Once the magnetic bead cluster reaches the midpoint of the reservoir chamber, stop the pumping on the syringe pump.</li>
	<li>Move the cube magnet away from the tube, allowing for magnetic beads to separate and reduce the diffusion time of the liquid trapped in the magnetic bead cluster.</li>
	<li>Watch the computer screen to observe the H2O/C12E5 mixture cycle through different phases.</li>
	<li>Once the diffusion and phase change of the liquid is completed, place the magnet back to its former destination by the reservoir so the magnetic beads form into a cluster.</li>
	<li>Using the syringe pump, withdraw the liquids such that the magnetic bead cluster is transferred from the surfactant reservoir, across the air gap, and back into the H2O test chamber.</li>
	<li>Once the magnetic bead cluster reaches the midpoint of the test chamber, stop the pumping on the syringe pump.</li>
	<li>Move the cube magnet away from the tube. This will allow magnetic beads to separate and will help reduce the diffusion time of the liquid trapped in the magnetic bead cluster.</li>
	<li>Watch the computer screen to observe the H2O/C12E5 mixture cycle through different phases.</li>
	<li>Once the diffusion and phase change of the liquid is completed, place the magnet back to its former destination by the test chamber&#160;so the magnetic beads form into a cluster.</li>
	<li>Repeat steps 6.2-6.11 until the test chamber displays a phase change.</li>
</ol>

<ol>
	<li>Gijs, M. A., Lacharme, F., Lehmann, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+applications+of+magnetic+particles+for+biological+analysis+and+catalysis.">Microfluidic applications of magnetic particles for biological analysis and catalysis.</a> Chemical review. 110, 1518-1563 (2009).</li><li>Kozissnik, B., Dobson, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biomedical+applications+of+mesoscale+magnetic+particles.">Biomedical applications of mesoscale magnetic particles.</a> MRS Bulleti. 38, 927-932 (2013).</li><li>Ali-Cherif, A., Begolo, S., Descroix, S., Viovy, J. -. L., Malaquin, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Programmable+Magnetic+Tweezers+and+Droplet+Microfluidic+Device+for+High-Throughput+Nanoliter+Multi-Step+Assays.">Programmable Magnetic Tweezers and Droplet Microfluidic Device for High-Throughput Nanoliter Multi-Step Assays.</a> Angewandte Chemie International Editio. 51, 10765-10769 (2012).</li><li>Blumenschein, N. A., Han, D., Caggioni, M., Steckl, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Magnetic+Particles+as+Liquid+Carriers+in+the+Microfluidic+Lab-in-Tube+Approach+To+Detect+Phase+Change.">Magnetic Particles as Liquid Carriers in the Microfluidic Lab-in-Tube Approach To Detect Phase Change.</a> ACS Applied Materials, &amp; Interface. 6, 8066-8072 (2014).</li><li>Bordelon, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+a+low-resource+RNA+extraction+cassette+based+on+surface+tension+valves.">Development of a low-resource RNA extraction cassette based on surface tension valves.</a> ACS applied materials. 3, 2161-2168 (2011).</li><li>Adams, N. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design+criteria+for+developing+low-resource+magnetic+bead+assays+using+surface+tension+valves.">Design criteria for developing low-resource magnetic bead assays using surface tension valves.</a> Biomicrofluidic. 7, 014104 (2013).</li><li>Hishida, M., Tanaka, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transition+of+the+hydration+state+of+a+surfactant+accompanying+structural+transitions+of+self-assembled+aggregates.">Transition of the hydration state of a surfactant accompanying structural transitions of self-assembled aggregates.</a> Journal of Physics: Condensed Matte. 24, 284113 (2012).</li><li>Strey, R., Schomacker, R., Roux, D., Nallet, F., Olsson, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dilute+lamellar+and+L3+phases+in+the+binary+water-C12E5+system.">Dilute lamellar and L3 phases in the binary water-C12E5 system.</a> Journal of the Chemical Society, Faraday Transaction. 86, 2253-2261 (1990).</li><li>Chen, B. -. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dissolution+Rates+of+Pure+Nonionic+Surfactants.">Dissolution Rates of Pure Nonionic Surfactants.</a> Langmui. 16, 5276-5283 (2000).</li><li>Warren, P. B., Buchanan, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinetics+of+surfactant+dissolution.">Kinetics of surfactant dissolution.</a> Current Opinion in Colloid, &amp; Interface Scienc. 6, 287-293 (2001).</li><li>Laughlin, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The Aqueous Phase Behavior of Surfactant. , (1996).</li><li>Laughlin, R. G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phase+Studies+by+Diffusive+Interfacial+Transport+Using+Near-Infrared+Analysis+for+Water+(DIT-NIR).">Phase Studies by Diffusive Interfacial Transport Using Near-Infrared Analysis for Water (DIT-NIR).</a> The Journal of Physical Chemistry. 104, 7354-7362 (2000).</li><li>Lynch, M. L., Kochvar, K. A., Burns, J. L., Laughlin, R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aqueous-Phase+Behavior+and+Cubic+Phase-Containing+Emulsions+in+the+C12E2&#8722;Water+System.">Aqueous-Phase Behavior and Cubic Phase-Containing Emulsions in the C12E2&#8722;Water System.</a> Langmui. 16, 3537-3542 (2000).</li></ol>

The authors have no competing financial interests.

In most common techniques for phase diagram investigation, multiple samples with different compositions and ratios need to be prepared and have to reach thermodynamic equilibrium which causes a lengthy process and a significant amount of material. Some challenges can be resolved by DIT (diffusive interfacial transport) method using flat capillary and the infrared analysis method, but none of them can resolve all challenges with low cost investment.
The feasibility of using magnetic beads as li...

Magnetic beads (MBs) on the order of 1 micrometer in diameter have been used1,2 quite often in microfluidic-based applications, particularly for biomedical devices. In these devices, MBs have offered capabilities such as cell and nucleic acid separation, contrast agents, and drug delivery, to name a few. The combination of external (magnetic field) control and droplet-based microfluidics has enabled3 control of immunoassays using small volumes (&#60;100 nl). MBs have also shown promise when used for liquid handling4. This approach uses the MBs to transport biomolecules between liquid segments within a tube separated by an air valve. This method is not as powerful as other more complex lab-on-chip devices seen in the past, but it is much simpler and does offer the capability of handling microliter-sized volumes of liquid. A similar approach has recently been reported5 by Haselton&#8217;s group and applied to biomedical assays.
One of the most important aspect of this device is the liquid segment separation offered by the surface-tension-controlled air valve. Microliter volumes of liquid attached to MBs are transported through this air gap between liquid segments using an externally applied magnetic field. Microparticle MBs (from ~0.4-7 &#181;m in diameter with an average of 1.9 &#181;m) under the effect of the external magnetic field create a micro-porous cluster that traps liquid within. The strength of this liquid entrapment is sufficient to withstand the forces of surface tension when transporting the MBs from one reservoir to the next. Typically, this effect is undesirable, as most approaches only want transport of specific molecules (such as biomarkers) contained within the liquids6. However, as can be seen in our work, this effect can be utilized to become a positive aspect of the device.
We have utilized this &#8216;lab-in-tube&#8217; approach, shown schematically in Figure 1, for analyzing phase diagrams in binary materials systems. The surfactant C12E5 has been chosen as the main focus of characterization, as it is widely used in industrial applications such as pharmaceuticals, food products, cosmetics, etc. In particular, the H2O/C12E5 binary system was investigated because it provides a rich set of phases to explore. We have focused on one specific aspect of this chemical mixture, namely the transitions to liquid crystalline phases under certain concentrations7-9. This transition is readily observed in our device by incorporating polarizers in the optical microscopy studies in order to highlight phase boundaries.
Being able to map phase diagrams is a very important area of study in order to understand the kinetics involved with phase transition10. The ability to precisely determine the interaction of surfactants with solvents and other components is crucial due to their complexity and many distinct phases11. Many other techniques have previously been used to characterize phase change. The conventional approach involves making many samples, each consisting of different concentrations and allowing them to equilibrate, which requires lengthy processing times and high quantity of sample volumes. Then, samples are typically analyzed by optical methods such as diffusive interfacial transport (DIT), which offers high-resolution of such surfactant compositions12,13. Similar to the method we have utilized, the DIT method uses polarized light to image distinct phase boundaries.

<table><tbody><tr><td>AccuBead</td><td>Bioneer Inc.</td><td>TS-1010-1</td><td>Magnetic beads</td></tr><tr><td>C12E5 Surfactant</td><td>Sigma-Aldrich</td><td>76437</td><td></td></tr><tr><td>Thermo Scientific Nalgene 890</td><td>Fisher Scientific</td><td>14176178</td><td></td></tr><tr><td>Cube Magnet</td><td>Apex Magnets</td><td>M1CU</td><td></td></tr><tr><td>Polarizer Film</td><td>Edmund Optics</td><td>38-493</td><td></td></tr><tr><td>Teflon AF</td><td>Dupont</td><td>400s1-100-1</td><td>Fluoropolymer solution</td></tr><tr><td>Keyacid Red Dye</td><td>Keystone</td><td>601-001-49</td><td>Fluorescent dye</td></tr><tr><td>Luer-Lock</td><td>Cole-Parmer</td><td>T-45502-12</td><td>Female</td></tr><tr><td>Luer-Lock</td><td>Cole-Parmer</td><td>T-45502-56</td><td>Male</td></tr><tr><td>Syringe</td><td>Fisher Scientific</td><td>14-823-435</td><td>3 ml</td></tr><tr><td>Syringe Pump</td><td>Stoelting</td><td>53130</td><td></td></tr><tr><td>Stereo Microscope</td><td>Nikon</td><td>SMZ-2T</td><td></td></tr><tr><td>Inverted Microscope</td><td>Nikon</td><td>Eclipse Ti-U</td><td>The filter cube used had an excitation wavelength range from 540-580 nm and a dichroic mirror at 585 nm, allowing for photoemission ranging from 593-668 nm.</td></tr><tr><td>Balance</td><td>Denver Instruments&amp;nbsp;</td><td>PI-225D</td><td></td></tr><tr><td>Microscope-Mounted Camera</td><td>Motic</td><td>5000</td><td></td></tr></tbody></table>

phase diagram characterization using magnetic beads as liquid carriers

Magnetic beads with ~1.9 &#181;m average diameter were used to transport microliter volumes of liquids between contiguous liquid segments with a tube for the purpose of investigating phase change of those liquid segments. The magnetic beads were externally controlled using a magnet, allowing for the beads to bridge the air valve between the adjacent liquid segments. A hydrophobic coating was applied to the inner surface of the tube to enhance the separation between two liquid segments. The applied magnetic field formed an aggregate cluster of magnetic beads, capturing a certain liquid amount within the cluster that is referred to as carry-over volume. A fluorescent dye was added to one liquid segment, followed by a series of liquid transfers, which then changed the fluorescence intensity in the neighboring liquid segment. Based on the numerical analysis of the measured fluorescence intensity change, the carry-over volume per mass of magnetic beads has been found to be ~2 to 3 &#181;l/mg. This small amount of liquid allowed for the use of comparatively small liquid segments of a couple hundred microliters, enhancing the feasibility of the device for a lab-in-tube approach. This technique of applying small compositional variation in a liquid volume was applied to analyzing the binary phase diagram between water and the surfactant C12E5 (pentaethylene glycol monododecyl ether), leading to quicker analysis with smaller sample volumes than conventional methods.

Using the Lab-in-Tube approach for transporting &#181;l-volume amounts of liquid with magnetic beads along with MATLAB for numerical analysis, average liquid carry-over volumes, as a function of magnetic bead mass, were found (Figure 2). Higher mass of magnetic beads provides higher carry-over volume in the rate of 2-3 &#181;l/mg. The experimental setup (Figure 1) was used to observe phase change within the H2O/C12E5 binary system. Since the H2O/C12E5 system is well...

Watch this Scientific Journal Video about Phase Diagram Characterization Using Magnetic Beads as Liquid Carriers at JoVE.com

Phase Diagram Characterization Using Magnetic Beads as Liquid Carriers

Here, we present a protocol to investigate multi-component phase diagrams using externally controlled magnetic beads as liquid carriers in a lab-in-tube approach. This approach can aid in applications that seek to gather further information on phase change in complex liquid systems.

Magnetic beads with ~1.9 &#181;m average diameter were used to transport microliter volumes of liquids between contiguous liquid segments with a tube for ...

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Engineering

12.3K Views.  University of Cincinnati. Here, we present a protocol to investigate multi-component phase diagrams using externally controlled magnetic beads as liquid carriers in a lab-in-tube approach. This approach can aid in applications that seek to gather further information on phase change in complex liquid systems.

Video: Phase Diagram Characterization Using Magnetic Beads as Liquid Carriers

Sputter Growth and Characterization of Metamagnetic B2-ordered FeRh Epilayers

Chemically ordered alloys are useful in a variety of magnetic nanotechnologies. They are most conveniently prepared at an industrial scale using sputtering techniques. Here we describe a method for preparing epitaxial thin films of B2-ordered FeRh by sputter deposition onto single crystal MgO substrates. Deposition at a slow rate onto a heated substrate allows time for the adatoms to both settle into a lattice with a well-defined epitaxial relationship with the substrate and also to find their proper places in the Fe and Rh sublattices of the B2 structure. The structure is conveniently characterized with X-ray reflectometry and diffraction and can be visualised directly using transmission electron micrograph cross-sections. B2-ordered FeRh exhibits an unusual metamagnetic phase transition: the ground state is antiferromagnetic but the alloy transforms into a ferromagnet on heating with a typical transition temperature of about 380 K. This is accompanied by a 1% volume expansion of the unit cell: isotropic in bulk, but laterally clamped in an epilayer. The presence of the antiferromagnetic ground state and the associated first order phase transition is very sensitive to the correct equiatomic stoichiometry and proper B2 ordering, and so is a convenient means to demonstrate the quality of the layers that can be deposited with this approach. We also give some examples of the various techniques by which the change in phase can be detected.

A method to prepare epitaxial layers of ordered alloys by sputtering is described. The B2-ordered FeRh compound is used as an example, as it displays a metamagnetic transition that depends sensitively on the degree of chemical order and the exact composition of the alloy.

Chemically ordered alloys are useful in a variety of magnetic nanotechnologies. They are most conveniently prepared at an industrial scale using ...

Frequency Mixing Magnetic Detection Scanner for Imaging Magnetic Particles in Planar Samples

The setup of a planar Frequency Mixing Magnetic Detection (p-FMMD) scanner for performing Magnetic Particles Imaging (MPI) of flat samples is presented. It consists of two magnetic measurement heads on both sides of the sample mounted on the legs of a u-shaped support. The sample is locally exposed to a magnetic excitation field consisting of two distinct frequencies, a stronger component at about 77 kHz and a weaker field at 61 Hz. The nonlinear magnetization characteristics of superparamagnetic particles give rise to the generation of intermodulation products. A selected sum-frequency component of the high and low frequency magnetic field incident on the magnetically nonlinear particles is recorded by a demodulation electronics. In contrast to a conventional MPI scanner, p-FMMD does not require the application of a strong magnetic field to the whole sample because mixing of the two frequencies occurs locally. Thus, the lateral dimensions of the sample are just limited by the scanning range and the supports. However, the sample height determines the spatial resolution. In the current setup it is limited to 2 mm. As examples, we present two 20 mm &#215; 25 mm p-FMMD images acquired from samples with 1 &#181;m diameter maghemite particles in silanol matrix and with 50 nm magnetite particles in aminosilane matrix. The results show that the novel MPI scanner can be applied for analysis of thin biological samples and for medical diagnostic purposes.

A scanner for imaging magnetic particles in planar samples was developed using the planar frequency mixing magnetic detection technique. The magnetic intermodulation product response from the nonlinear nonhysteretic magnetization of the particles is recorded upon a two-frequency excitation. It can be used to take 2D images of thin biological samples.

The setup of a planar Frequency Mixing Magnetic Detection (p-FMMD) scanner for performing Magnetic Particles Imaging (MPI) of flat samples is presented. ...

Phase Behavior of Charged Vesicles Under Symmetric and Asymmetric Solution Conditions Monitored with Fluorescence Microscopy

Phase-separated giant unilamellar vesicles (GUVs) exhibiting coexisting liquid-ordered and liquid-disordered domains are a common biophysical tool to investigate the lipid raft hypothesis. Numerous studies, however, neglect the impact of physiological solution conditions. On that account, the current work presents the effect of high-salinity buffer and trans-membrane solution asymmetry on liquid-liquid phase separation in charged GUVs grown from dioleylphosphatidylglycerol, egg sphingomyelin, and cholesterol. The effects were studied under isothermal and varying temperature conditions.
We describe equipment and experimental strategies applicable for monitoring the stability of coexisting liquid domains in charged vesicles under symmetric and asymmetric high-salinity solution conditions. This includes an approach to prepare charged multicomponent GUVs in high-salinity buffer at high temperatures. The protocol entails the option to perform a partial exchange of the external solution by a simple dilution step while minimizing the vesicle dilution. An alternative approach is presented utilizing a microfluidic device that allows for a complete external solution exchange. The solution effects on phase separation were also studied under varying temperatures. To this end, we present the basic design and utility of an in-house built temperature control chamber. Furthermore, we reflect on the assessment of the GUV phase state, pitfalls associated with it and how to circumvent them.

Experiments on phase separated giant unilamellar vesicles (GUVs) frequently neglect physiological solution conditions. This work presents approaches to study the effect of high-salinity buffer on liquid-liquid phase separation in charged multicomponent GUVs as a function of trans-membrane solution asymmetry and temperature.

Phase-separated giant unilamellar vesicles (GUVs) exhibiting coexisting liquid-ordered and liquid-disordered domains are a common biophysical tool to ...

Chemistry

Fabrication Procedures and Birefringence Measurements for Designing Magnetically Responsive Lanthanide Ion Chelating Phospholipid Assemblies

Bicelles are tunable disk-like polymolecular assemblies formed from a large variety of lipid mixtures. Applications range from membrane protein structural studies by nuclear magnetic resonance (NMR) to nanotechnological developments including the formation of optically active and magnetically switchable gels. Such technologies require high control of the assembly size, magnetic response and thermal resistance. Mixtures of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and its lanthanide ion (Ln3+) chelating phospholipid conjugate, 1,2-dimyristoyl-sn-glycero-3-phospho-ethanolamine-diethylene triaminepentaacetate (DMPE-DTPA), assemble into highly magnetically responsive assemblies such as DMPC/DMPE-DTPA/Ln3+ (molar ratio 4:1:1) bicelles. Introduction of cholesterol (Chol-OH) and steroid derivatives in the bilayer results in another set of assemblies offering unique physico-chemical properties. For a given lipid composition, the magnetic alignability is proportional to the bicelle size. The complexation of Ln3+ results in unprecedented magnetic responses in terms of both magnitude and alignment direction. The thermo-reversible collapse of the disk-like structures into vesicles upon heating allows tailoring of the assemblies&#39; dimensions by extrusion through membrane filters with defined pore sizes. The magnetically alignable bicelles are regenerated by cooling to 5 &#176;C, resulting in assembly dimensions defined by the vesicle precursors. Herein, this fabrication procedure is explained and the magnetic alignability of the assemblies is quantified by birefringence measurements under a 5.5 T magnetic field. The birefringence signal, originating from the phospholipid bilayer, further enables monitoring of polymolecular changes occurring in the bilayer. This simple technique is complementary to NMR experiments that are commonly employed to characterize bicelles.

Fabrication procedures for highly magnetically responsive lanthanide ion chelating polymolecular assemblies are presented. The magnetic response is dictated by the assembly size, which is tailored by extrusion through nanopore membranes. The assemblies&#39; magnetic alignability and temperature-induced structural changes are monitored by birefringence measurements, a complimentary technique to nuclear magnetic resonance and small angle neutron scattering.

Bicelles are tunable disk-like polymolecular assemblies formed from a large variety of lipid mixtures. Applications range from membrane protein structural ...

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic glasses (MGs). Despite their amorphous nature, the identification of hyperfine interactions unveils faint structural modifications. For this purpose, we have employed two techniques that utilize nuclear resonance among nuclear levels of a stable 57Fe isotope, namely M&#246;ssbauer spectrometry and nuclear forward scattering (NFS) of synchrotron radiation. The effects of heat treatment upon (Fe2.85Co1)77Mo8Cu1B14 MG are discussed using the results of ex situ and in situ experiments, respectively. As both methods are sensitive to hyperfine interactions, information on structural arrangement as well as on magnetic microstructure is readily available. M&#246;ssbauer spectrometry performed ex situ describes how the structural arrangement and magnetic microstructure appears at room temperature after the annealing under certain conditions (temperature, time), and thus this technique inspects steady states. On the other hand, NFS data are recorded in situ during dynamically changing temperature and NFS examines transient states. The use of both techniques provides complementary information. In general, they can be applied to any suitable system in which it is important to know its steady state but also transient states.

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

Here, we present a protocol to describe ex situ and in situ investigations of structural transformations in metallic glasses. We employed nuclear-based analytical methods which inspect hyperfine interactions. We demonstrate the applicability of M&#246;ssbauer spectrometry and nuclear forward scattering of synchrotron radiation during temperature-driven experiments.

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic ...

Measuring Magnetically-Tuned Ferroelectric Polarization in Liquid Crystals

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due to their potential applications for future device technologies such as sensors and storage. However, conventional approaches, which usually utilize materials containing magnetic metal ions (or radicals), have a major problem: only a few materials have been found to show the coupling phenomena at room temperature. Recently, we proposed a new approach to achieve room-temperature magnetoelectrics. In contrast to conventional approaches, our alternative proposal focuses on a completely different material, a &#34;liquid crystal&#34;, free from magnetic metal ions. In such liquid crystals, a magnetic field can be utilized to control the orientational state of constituent molecules and the corresponding electric polarization through magnetic anisotropy of the molecules; it is an unprecedented mechanism of the magnetoelectric effect. In this context, this paper provides a protocol to measure ferroelectric properties induced by a magnetic field, that is, the direct magnetoelectric effect, in a liquid crystal. With the method detailed here, we successfully detected magnetically-tuned electric polarization in the chiral smectic C phase of a liquid crystal at room temperature. Taken together with the flexibility of constituent molecules, which directly affects the magnetoelectric responses, the introduced method will serve to allow liquid crystal cells to acquire more functions as room-temperature magnetoelectrics and associated optical materials.

In this report, we present a protocol to examine direct magnetoelectric effects, i.e., induction of ferroelectric polarization by applying magnetic fields, in liquid crystals. This protocol provides a unique approach, supported by the softness of liquid crystals, to achieve room-temperature magnetoelectrics.

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due ...

Stable Aqueous Suspensions of Manganese Ferrite Clusters with Tunable Nanoscale Dimension and Composition

Manganese ferrite clusters (MFCs) are spherical assemblies of tens to hundreds of primary nanocrystals whose magnetic properties are valuable in diverse applications. Here we describe how to form these materials in a hydrothermal process that permits the independent control of product cluster size (from 30 to 120 nm) and manganese content of the resulting material. Parameters such as the total amount of water added to the alcoholic reaction media and the ratio of manganese to iron precursor are important factors in achieving multiple types of MFC nanoscale products. A fast purification method uses magnetic separation to recover the materials making production of grams of magnetic nanomaterials quite efficient. We overcome the challenge of magnetic nanomaterial aggregation by applying highly charged sulfonate polymers to the surface of these nanomaterials yielding colloidally stable MFCs that remain non-aggregating even in highly saline environments. These non-aggregating, uniform, and tunable materials are excellent prospective materials for biomedical and environmental applications.

We report a one-pot hydrothermal synthesis of manganese ferrite clusters (MFCs) that offers independent control over material dimension and composition. Magnetic separation allows rapid purification while surface functionalization using sulfonated polymers ensures the materials are non-aggregating in biologically relevant medium. The resulting products are well positioned for biomedical applications.

Manganese ferrite clusters (MFCs) are spherical assemblies of tens to hundreds of primary nanocrystals whose magnetic properties are valuable in diverse ...

Magnetometric Characterization of Redox-Active MOFs Solid-State Electrochemistry

Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks

Electrochemical energy storage has been a widely discussed application of redox-active metal-organic frameworks (MOFs) in the past 5 years. Although MOFs show outstanding performance in terms of gravimetric or areal capacitance and cyclic stability, unfortunately their electrochemical mechanisms are not well understood in most cases. Traditional spectroscopic techniques, such as X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS), have only provided vague and qualitative information about valence changes of certain elements, and the mechanisms proposed based on such information are often highly disputable. In this article, we report a series of standardized methods, including the fabrication of solid-state electrochemical cells, electrochemistry measurements, the disassembly of cells, the collection of MOF electrochemical intermediates, and physical measurements of the intermediates under the protection of inert gases. By using these methods for quantitatively clarifying the electronic and spin state evolution within a single electrochemical step of redox-active MOFs, one can provide clear insight into the nature of electrochemical energy storage mechanisms not only for MOFs, but also for all other materials with strongly correlated electronic structures.

Author Spotlight: Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks  

Ex situ magnetic surveys can directly provide bulk and local information on a magnetic electrode to reveal its charge storage mechanism step by step. Herein, electron spin resonance (ESR) and magnetic susceptibility are demonstrated to monitor the evaluation of paramagnetic species and their concentration in a redox-active metal-organic framework (MOF).

Electrochemical energy storage has been a widely discussed application of redox-active metal-organic frameworks (MOFs) in the past 5 years. Although MOFs ...

Imaging the Motion of Fully Reconstituted Cdc45/Mcm2-7/GINS (CMG)

Hybrid Ensemble and Single-molecule Assay to Image the Motion of Fully Reconstituted CMG

Eukaryotes have one replicative helicase known as CMG, which centrally organizes and drives the replisome, and leads the way at the front of replication forks. Obtaining a deep mechanistic understanding of the dynamics of CMG is critical to elucidating how cells achieve the enormous task of efficiently and accurately replicating their entire genome once per cell cycle. Single-molecule techniques are uniquely suited to quantify the dynamics of CMG due to their unparalleled temporal and spatial resolution. Nevertheless, single-molecule studies of CMG motion have thus far relied on pre-formed CMG purified from cells as a complex, which precludes the study of the steps leading up to its activation. Here, we describe a hybrid ensemble and single-molecule assay that allowed imaging at the single-molecule level of the motion of fluorescently labeled CMG after fully reconstituting its assembly and activation from 36 different purified S. cerevisiae polypeptides. This assay relies on the double functionalization of the ends of a linear DNA substrate with two orthogonal attachment moieties, and can be adapted to study similarly complex DNA-processing mechanisms at the single-molecule level.

Author Spotlight: Investigating the Motion Dynamics of the Eukaryotic Replisome Components at the Single-Molecule Level

We report a hybrid ensemble and single-molecule assay to directly image and quantify the motion of fluorescently labeled, fully reconstituted Cdc45/Mcm2-7/GINS (CMG) helicase on linear DNA molecules held in place in an optical trap.

Eukaryotes have one replicative helicase known as CMG, which centrally organizes and drives the replisome, and leads the way at the front of replication ...

Biochemistry

Quantifying Mixing using Magnetic Resonance Imaging

Mixing is a unit operation that combines two or more components into a homogeneous mixture. This work involves mixing two viscous liquid streams using an in-line static mixer. The mixer is a split-and-recombine design that employs shear and extensional flow to increase the interfacial contact between the components. A prototype split-and-recombine (SAR) mixer was constructed by aligning a series of thin laser-cut Poly (methyl methacrylate) (PMMA) plates held in place in a PVC pipe. Mixing in this device is illustrated in the photograph in Fig. 1. Red dye was added to a portion of the test fluid and used as the minor component being mixed into the major (undyed) component. At the inlet of the mixer, the injected layer of tracer fluid is split into two layers as it flows through the mixing section. On each subsequent mixing section, the number of horizontal layers is duplicated. Ultimately, the single stream of dye is uniformly dispersed throughout the cross section of the device.
 Using a non-Newtonian test fluid of 0.2% Carbopol and a doped tracer fluid of similar composition, mixing in the unit is visualized using magnetic resonance imaging (MRI). MRI is a very powerful experimental probe of molecular chemical and physical environment as well as sample structure on the length scales from microns to centimeters. This sensitivity has resulted in broad application of these techniques to characterize physical, chemical and/or biological properties of materials ranging from humans to foods to porous media 1, 2. The equipment and conditions used here are suitable for imaging liquids containing substantial amounts of NMR mobile 1H such as ordinary water and organic liquids including oils. Traditionally MRI has utilized super conducting magnets which are not suitable for industrial environments and not portable within a laboratory (Fig. 2). Recent advances in magnet technology have permitted the construction of large volume industrially compatible magnets suitable for imaging process flows. Here, MRI provides spatially resolved component concentrations at different axial locations during the mixing process. This work documents real-time mixing of highly viscous fluids via distributive mixing with an application to personal care products.

Magnetic resonance imaging (MRI) provides a powerful tool to evaluate the effectiveness of process equipment during operation. We discuss the use of MRI to visualize mixing in a static mixer. The application is relevant to personal care products, but can be applied to a broad range of food, chemical, biomass and biological fluids.

Mixing is a unit operation that combines two or more components into a homogeneous mixture.  This work involves mixing two viscous liquid streams using an ...

Phase Diagram Characterization Using Magnetic Beads as Liquid Carriers

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