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...

<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 border="0" cellpadding="0" cellspacing="0">
	<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&#160;</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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12.1K vistas.  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.