Name: use of a multi-compartment dynamic single enzyme phantom for studies of hyperpolarized magnetic resonance agents
Uploaded: 2016-04-15T14:00:00
Description: Watch this Scientific Journal Video about Use of a Multi-compartment Dynamic Single Enzyme Phantom for Studies of Hyperpolarized Magnetic Resonance Agents at JoVE.com

This work was supported in part by the Cancer Prevention and Research Institute of Texas (RP140021-P5), a Julia Jones Matthews Cancer Research Scholar CPRIT research training award (RP140106, CMW), and the National Institutes of Health (P30-CA016672).

NOTE: (Phantom Design) Two 3 ml chambers were machined out of Ultem and fitted with PEEK tubing (1.5875 mm OD and 0.762 mm ID) for injection and exhaust. The Chambers were placed in a 50 ml centrifuge tube filled with water (Figure 1). To avoid signal voids created by bubbles, the chambers and the lines were pre filled with deionized water (dH2O).
1. Solution Preparation
<ol>
	<li>Prepare 1 L buffer solution (81.3 mM Tris pH 7.6, 203.3 mM NaCl). Weigh out 11.38 g ...

<ol>
	<li>Merritt, M. E., 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=Hyperpolarized+13C+allows+a+direct+measure+of+flux+through+a+single+enzyme-catalyzed+step+by+NMR.">Hyperpolarized 13C allows a direct measure of flux through a single enzyme-catalyzed step by NMR.</a> Proceedings of the National Academy of Sciences of the United States of America 104. 104, 19773-19777 (2007).</li><li>Rodrigues, T. B., 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=Magnetic+resonance+imaging+of+tumor+glycolysis+using+hyperpolarized+13C-labeled+glucose.">Magnetic resonance imaging of tumor glycolysis using hyperpolarized 13C-labeled glucose.</a> Nature medicine. 20, 93-97 (2014).</li><li>Day, S. E., 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=Detecting+tumor+response+to+treatment+using+hyperpolarized+13C+magnetic+resonance+imaging+and+spectroscopy.">Detecting tumor response to treatment using hyperpolarized 13C magnetic resonance imaging and spectroscopy.</a> Nature medicine. 13, 1382-1387 (2007).</li><li>Keshari, K. R., 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=Hyperpolarized+13C+dehydroascorbate+as+an+endogenous+redox+sensor+for+in+vivo+metabolic+imaging.">Hyperpolarized 13C dehydroascorbate as an endogenous redox sensor for in vivo metabolic imaging.</a> Proceedings of the National Academy of Sciences of the United States of America. 108, 18606-18611 (2011).</li><li>Gallagher, F. A., 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=Magnetic+resonance+imaging+of+pH+in+vivo+using+hyperpolarized+13C-labelled+bicarbonate.">Magnetic resonance imaging of pH in vivo using hyperpolarized 13C-labelled bicarbonate.</a> Nature. 453, 940-943 (2008).</li><li>Larson, P. E., 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=Investigation+of+tumor+hyperpolarized+[1-13C]-pyruvate+dynamics+using+time-resolved+multiband+RF+excitation+echo-planar+MRSI.">Investigation of tumor hyperpolarized [1-13C]-pyruvate dynamics using time-resolved multiband RF excitation echo-planar MRSI.</a> Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 63, 582-591 (2010).</li><li>Cunningham, C. H., Dominguez Viqueira, W., Hurd, R. E., Chen, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Frequency+correction+method+for+improved+spatial+correlation+of+hyperpolarized+13C+metabolites+and+anatomy.">Frequency correction method for improved spatial correlation of hyperpolarized 13C metabolites and anatomy.</a> NMR in biomedicine. 27, 212-218 (2014).</li><li>Larson, P. E., 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=Fast+dynamic+3D+MR+spectroscopic+imaging+with+compressed+sensing+and+multiband+excitation+pulses+for+hyperpolarized+13C+studies.">Fast dynamic 3D MR spectroscopic imaging with compressed sensing and multiband excitation pulses for hyperpolarized 13C studies.</a> Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 65, 610-619 (2011).</li><li>Mayer, D., 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=Application+of+subsecond+spiral+chemical+shift+imaging+to+real-time+multislice+metabolic+imaging+of+the+rat+in+vivo+after+injection+of+hyperpolarized+13C1-pyruvate.">Application of subsecond spiral chemical shift imaging to real-time multislice metabolic imaging of the rat in vivo after injection of hyperpolarized 13C1-pyruvate.</a> Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 62, 557-564 (2009).</li><li>Walker, C. 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=A+Catalyzing+Phantom+for+Reproducible+Dynamic+Conversion+of+Hyperpolarized+[1-C-13]-Pyruvate.">A Catalyzing Phantom for Reproducible Dynamic Conversion of Hyperpolarized [1-C-13]-Pyruvate.</a> PloS one. 8, e71274 (2013).</li><li>Levin, Y. S., Mayer, D., Yen, Y. F., Hurd, R. E., Spielman, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optimization+of+fast+spiral+chemical+shift+imaging+using+least+squares+reconstruction:+application+for+hyperpolarized+(13)C+metabolic+imaging.">Optimization of fast spiral chemical shift imaging using least squares reconstruction: application for hyperpolarized (13)C metabolic imaging.</a> Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 58, 245-252 (2007).</li><li>von Morze, C., 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=Simultaneous+multiagent+hyperpolarized+(13)C+perfusion+imaging.">Simultaneous multiagent hyperpolarized (13)C perfusion imaging.</a> Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 72, 1599-1609 (2014).</li><li>Sogaard, L. V., Schilling, F., Janich, M. A., Menzel, M. I., Ardenkjaer-Larsen, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+measurement+of+apparent+diffusion+coefficients+of+hyperpolarized+(1)(3)C-labeled+metabolites.">In vivo measurement of apparent diffusion coefficients of hyperpolarized (1)(3)C-labeled metabolites.</a> NMR in biomedicine. 27, 561-569 (2014).</li><li>Patrick, P. S., 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=Detection+of+transgene+expression+using+hyperpolarized+13C+urea+and+diffusion-weighted+magnetic+resonance+spectroscopy.">Detection of transgene expression using hyperpolarized 13C urea and diffusion-weighted magnetic resonance spectroscopy.</a> Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 73, 1401-1406 (2015).</li></ol>

Real time imaging of hyperpolarized metabolites has many unique challenges for sequence design, validation, and quality control. The ability to resolve spatiotemporal and spectral heterogeneity offers substantial clinical potential but precludes QA and validation methods associated with conventional MRI. Complex imaging sequences or reconstruction algorithms can have subtle dependencies that render them difficult to characterize or validate outside of the imaging experiment. Biological heterogeneity and other practical c...

The clinical impact of hyperpolarized magnetic resonance imaging (MRI) of 13C-labeled compounds is critically dependent on its ability to measure chemical conversion rates through real time magnetic resonance spectroscopy and spectroscopic imaging1-5. During sequence development and verification, dynamic chemical conversion is generally achieved through in vivo or in vitro models6-9 that offer limited control and reproducibility. For robust testing and quality assurance, a more controlled system that preserves the chemical conversion endemic to this measurement would be preferred. We outline a method to achieve this conversion in a reproducible manner using a dynamic single enzyme phantom.
Most studies with hyperpolarized 13C agents focus on imaging hyperpolarized substrates in a functioning biological environment. This is the obvious choice if the goal is to study biological processes or determine potential for impact on clinical care. However, if characterization of some measurement system or data processing algorithm is desired, biological models have numerous drawbacks such as inherent spatial and temporal variability10. However, conventional static phantoms lack the chemical conversion that drives the primary clinical interest in MRI of hyperpolarized substrates, and cannot be used to characterize detection of conversion rates or other dynamic parameters11. Using a single enzyme system we can provide controllable and reproducible chemical conversion, enabling rigorous examination of dynamic imaging strategies.
This system is directed to investigators who are developing imaging strategies for hyperpolarized substrates and wish to characterize performance for comparison against alternate approaches. If static measurements are the desired endpoint then static 13C-labled metabolite phantoms will suffice11. On the other end if more complex biological characterization is critical to the method (delivery, cellular density, etc.) then actual biological models will be needed12-14. This system is ideal for assessment of imaging strategies that aim to provide a quantitative measure of apparent chemical conversion rates.

<table border="0" cellpadding="0" cellspacing="0" width="1045">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">BioSpect 7T</td>
			<td style="width:147px;">Bruker</td>
			<td style="width:195px;">BioSpec 70/30 USR</td>
			<td style="width:445px;">7 Tesla Pre-Clinical MRI Scanner</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">HyperSense</td>
			<td style="width:147px;">Oxford Instruments</td>
			<td style="width:195px;">Hypersense DNP Polarizer</td>
			<td>Dynamic Nuclear Polarizer for MRI agents</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">1-13C-Pyrvic Acid</td>
			<td style="width:147px;">Sigma Aldrich</td>
			<td style="width:195px;">677175</td>
			<td>Carbon 13 labled neat pyruvic acid</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Trityl Radical</td>
			<td style="width:147px;">GE Healthcare</td>
			<td style="width:195px;">OX063</td>
			<td>Free radical used in Dynamic Nuclear Polarization</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">NaOH</td>
			<td style="width:147px;">Sigma Aldrich</td>
			<td style="width:195px;">S8045</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">EDTA</td>
			<td style="width:147px;">Sigma Aldrich</td>
			<td style="width:195px;">E6758</td>
			<td style="width:445px;">Ethylenediaminetetraacetic acid</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">LDH</td>
			<td style="width:147px;">Worthingthon</td>
			<td style="width:195px;">LS002755</td>
			<td>Lactate Dehydrogenase from rabbit muscle</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">NADH</td>
			<td style="width:147px;">Sigma Aldrich</td>
			<td style="width:195px;">N4505</td>
			<td>&#946;-Nicotinamide adenine dinucleotide, reduced dipotassium salt</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Trizma</td>
			<td style="width:147px;">Sigma Aldrich</td>
			<td style="width:195px;">T7943</td>
			<td>Trizma&#174;&#160;Pre-set crystals</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">NaCl</td>
			<td style="width:147px;">Sigma Aldrich</td>
			<td style="width:195px;">S7653</td>
			<td></td>
		</tr>
	</tbody>
</table>

use of a multi-compartment dynamic single enzyme phantom for studies of hyperpolarized magnetic resonance agents

Imaging of hyperpolarized substrates by magnetic resonance shows great clinical promise for assessment of critical biochemical processes in real time. Due to fundamental constraints imposed by the hyperpolarized state, exotic imaging and reconstruction techniques are commonly used. A practical system for characterization of dynamic, multi-spectral imaging methods is critically needed. Such a system must reproducibly recapitulate the relevant chemical dynamics of normal and pathological tissues. The most widely utilized substrate to date is hyperpolarized [1-13C]-pyruvate for assessment of cancer metabolism. We describe an enzyme-based phantom system that mediates the conversion of pyruvate to lactate. The reaction is initiated by injection of the hyperpolarized agent into multiple chambers within the phantom, each of which contains varying concentrations of reagents that control the reaction rate. Multiple compartments are necessary to ensure that imaging sequences faithfully capture the spatial and metabolic heterogeneity of tissue. This system will aid the development and validation of advanced imaging strategies by providing chemical dynamics that are not available from conventional phantoms, as well as control and reproducibility that is not possible in vivo.

Slice-selective 2D images were acquired using a snapshot radEPSI sequence. Metabolite images were reconstructed using filtered back projection. The metabolite images were well aligned with proton images, as seen in Figure 2. In this system hyperpolarized lactate signal can only be generated from the enzymatic conversion of hyperpolarized pyruvate. In Figure 4, the bottom chamber, with higher LDH concentration, has a stronger lactate and weaker pyruvate si...

Watch this Scientific Journal Video about Use of a Multi-compartment Dynamic Single Enzyme Phantom for Studies of Hyperpolarized Magnetic Resonance Agents at JoVE.com

Use of a Multi-compartment Dynamic Single Enzyme Phantom for Studies of Hyperpolarized Magnetic Resonance Agents

A multi-compartment dynamic phantom is used to simulate some biology of interest for metabolic studies using hyperpolarized magnet resonance agents.

Imaging of hyperpolarized substrates by magnetic resonance shows great clinical promise for assessment of critical biochemical processes in real time. Due ...

The overall goal of this procedure is to measure the conversion of hyperpolarized pyruvate to lactate by magnetic resonance imaging or MRI in a controlled phantom environment. This method can help answer key questions in the hyperpolarized MRI field such as the ability of a system to detect chemical conversion of pyruvate by magnetic resonance. The main advantage of this technique is that chemical conversion of pyruvate proceeds similarly to metabolism in vivo but is more controllable and repeatable than in living systems.The implications of this technique extend towards diagnosis of cancer because the elevated conversion of pyruvate to lactate common in most cancers is simulated by the phantom environment. Though this method can provide insight into cancer it can also be applied to other metabolic imaging such as cardiac metabolism. Generally individuals new to this method may struggle because the time constraints inherent to hyperpolarized media are short.Visual demonstration of this method is critical as dissolution and ejection steps are difficult to learn because they have to happen rapidly and must be performed precisely. In a sample cup for a dynamic nuclear polarization or DNP system pipette 0.3 micro-liters of the gadoteridol solution and 13 milligrams of the pyruvic acid solution. Briefly stir this mixture in the sample cup with a pipette tip.Begin the sample insertion process by clicking the insert sample button on the DNP system console. On the sample wizard select normal sample and click next. Keeping the sample cup vertical gently place the insertion rod over the top of the sample cup.When prompted open the DNP system and insert the cup into the variable temperature insert using the insertion rod. Pull on the plunger at the end of the sample insertion rod to release the sample in the variable temperature insert. Remove the sample insertion rod from the system and click the next button on the DNP system console.Then initiate the polarization by clicking the polarise sample button on the DNP system console. In the RINMR software type HYPERSENSENMR to polarization monitoring software. Set build up configuration to one and press enter.Then click solid build up. After setting the location and name of the save file select the profile for carbon 13 in the drop down tab on the DNP system console. Click next.Check the box to enable sampling during the build up. Set sample time to 300 seconds and click finish up. Finally measure out 3.85 grams of the dissolution media either by volume with a five milliliter syringe or by weight using a scale.Place the phantom in the center of the magnet with easy access to the injection lines. Ensure that there is some container to catch the liquid that will vent out to the exhaust line. Prepare the high activity enzyme mixture by mixing 240 micro-liters of NADH solution 125 micro-liters of LDH solution and 335 micro-liters of buffer.Keep the solution in a three milliliter syringe that can be attached to the injection line. Then prepare the low activity enzyme mixture by mixing together 240 micro-liters of NADH solution 75 micro-liters of LDH solution and 385 micro-liters of buffer. Keep this mixture in a separate three milliliter syringe that can be attached to the injection line.To perform initial positioning load a new localizer scan. Wobble the proton coil by selecting Acq/Reco. Display and open the adjustment platform.On the adjustment panel select Wobble Adjust and click ppen. Set the sweep width to ten megahertz and click set up. After a moment the protons coils tuning and matching should appear in the acquisition window.Wobble the carbon coil by changing the coil element to 13C or element two and setting the sweep width to five megahertz. After a moment the carbons coils tuning and matching should appear in the acquisition window and if tuned properly, hit stop. To return to scan control press apply then back and finally press continue to begin the scan.It is critical that the scan in this step is fully set up before beginning dissolution. After dissolution has begun it should not be stopped and their will be little time to adjust sequence parameters before the hyperpolarized pyruvate is delivered. Load a new radio echo planar spectroscopic imaging scan.Set the slice thickness to 30 millimeters so as to cover the whole reaction chamber. Set the operation mode to carbon 13 by selecting the system tab and changing the operation mode to 13C transmit receive. Once the pyruvate has attained greater than 90%polarization the solutions and phantom are ready and the scan is configured.Click the run dissolution button on the DNP system console. When prompted move the dissolution stick into its operating position and inject the dissolution media. Close the DNP system and click the finished button on the DNP system console.It is important that injection of pyruvate and enzyme is done smoothly. This will ensure the enzyme mixture is properly mixed and delivered to the phantom chamber before the chemical conversion has completed. When the DNP system delivers the hyperpolarized pyruvate aspirate 500 micro-liters of the pyruvate solution into each of the high and low enzyme concentration solution syringes.Slowly inject each syringe into an injection line. Scanning can be initiated prior to injection or immediately after injection depending on the scan protocol used. After the dissolution is complete move the dissolution stick back to the resting position when prompted and then click finish.Representative results of a radio echo planar spectral imaging sequence are shown here. The pyruvate image shows the strong pyruvate signal in both chambers. The lactate image shows a weaker lactate signal but is still localized to the chambers.The signal ratio of hyperpolarized lactate and pyruvate can be used to estimate the enzyme activity in each chamber. The signal ratios in each chamber match the enzyme activity present. Once mastered, this technique can be done in one hour.While attempting this procedure it is important to remember to have the phantom mixture and imaging sequence ready before beginning the dissolution process. Following this procedure other hyperpolarized agents and enzymes can be used in order to answer additional questions like how well a sequence can image other chemical reactions. This technique paves the way for researchers in the field of hyperpolarized MRI to explore sequence performance using reproduceable phantoms.After watching this video you should have a good understanding of how to prepare an enzyme mixture to facilitate the conversion of hyperpolarized pyruvate to lactate and to polarize carbon 13 enriched pyruvate for imaging. Don't forget that working with strong magnetic fields can be extremely hazardous and precautions such as controlled access to the scan room should always be taken.

use-multi-compartment-dynamic-single-enzyme-phantom-for-studies

Research

JoVE Journal

Engineering

Hyperpolarized Xenon for NMR and MRI Applications

Nuclear magnetic resonance (NMR) spectroscopy and imaging (MRI) suffer from intrinsic low sensitivity because even strong external magnetic fields of ~10 T generate only a small detectable net-magnetization of the sample at room temperature 1. Hence, most NMR and MRI applications rely on the detection of molecules at relative high concentration (e.g., water for imaging of biological tissue) or require excessive acquisition times. This limits our ability to exploit the very useful molecular specificity of NMR signals for many biochemical and medical applications. However, novel approaches have emerged in the past few years: Manipulation of the detected spin species prior to detection inside the NMR/MRI magnet can dramatically increase the magnetization and therefore allows detection of molecules at much lower concentration 2.
Here, we present a method for polarization of a xenon gas mixture (2-5% Xe, 10% N2, He balance) in a compact setup with a ca. 16000-fold signal enhancement. Modern line-narrowed diode lasers allow efficient polarization 7 and immediate use of gas mixture even if the noble gas is not separated from the other components. The SEOP apparatus is explained and determination of the achieved spin polarization is demonstrated for performance control of the method.
The hyperpolarized gas can be used for void space imaging, including gas flow imaging or diffusion studies at the interfaces with other materials 8,9. Moreover, the Xe NMR signal is extremely sensitive to its molecular environment 6. This enables the option to use it as an NMR/MRI contrast agent when dissolved in aqueous solution with functionalized molecular hosts that temporarily trap the gas 10,11. Direct detection and high-sensitivity indirect detection of such constructs is demonstrated in both spectroscopic and imaging mode.

The production of hyperpolarized xenon by means of spin exchange optical pumping (SEOP) is described. This method yields a ~10000-fold enhancement of the nuclear spin polarization of Xe-129 and has applications in nuclear magnetic resonance spectroscopy and imaging. Examples of gas phase and solution state experiments are given.

Nuclear magnetic resonance (NMR) spectroscopy and imaging (MRI) suffer from intrinsic low sensitivity because even strong external magnetic fields of ~10 ...

Analysis of Contact Interfaces for Single GaN Nanowire Devices

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit a strong degradation after annealing due to the occurrence of void formation at the contact/SiO2 interface. This void formation can cause cracking and delamination of the metal film, which can increase the resistance or lead to a complete failure of the NW device. In order to address issues associated with void formation, a technique was developed that removes Ni/Au contact metal films from the substrates to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN NW devices. This procedure determines the degree of adhesion of the contact films to the substrate and NWs and allows for the characterization of the morphology and composition of the contact interface with the substrate and nanowires. This technique is also useful for assessing the amount of residual contamination that remains from the NW suspension and from photolithographic processes on the NW-SiO2 surface prior to metal deposition. The detailed steps of this procedure are presented for the removal of annealed Ni/Au contacts to Mg-doped GaN NWs on a SiO2 substrate.

A technique was developed that removes Ni/Au contact metal films from their substrate to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN nanowire devices.

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit  a strong degradation after annealing due to the  occurrence of void formation at the ...

Scalable Nanohelices for Predictive Studies and Enhanced 3D Visualization

Spring-like materials are ubiquitous in nature and of interest in nanotechnology for energy harvesting, hydrogen storage, and biological sensing applications.&#160; For predictive simulations, it has become increasingly important to be able to model the structure of nanohelices accurately.&#160; To study the effect of local structure on the properties of these complex geometries one must develop realistic models.&#160; To date, software packages are rather limited in creating atomistic helical models.&#160; This work focuses on producing atomistic models of silica glass (SiO2) nanoribbons and nanosprings for molecular dynamics (MD) simulations. Using an MD model of &#8220;bulk&#8221; silica glass, two computational procedures to precisely create the shape of nanoribbons and nanosprings are presented.&#160; The first method employs the AWK programming language and open-source software to effectively carve various shapes of silica nanoribbons from the initial bulk model, using desired dimensions and parametric equations to define a helix.&#160; With this method, accurate atomistic silica nanoribbons can be generated for a range of pitch values and dimensions.&#160; The second method involves a more robust code which allows flexibility in modeling nanohelical structures.&#160; This approach utilizes a C++ code particularly written to implement pre-screening methods as well as the mathematical equations for a helix, resulting in greater precision and efficiency when creating nanospring models.&#160; Using these codes, well-defined and scalable nanoribbons and nanosprings suited for atomistic simulations can be effectively created.&#160; An added value in both open-source codes is that they can be adapted to reproduce different helical structures, independent of material.&#160; In addition, a MATLAB graphical user interface (GUI) is used to enhance learning through visualization and interaction for a general user with the atomistic helical structures.&#160; One application of these methods is the recent study of nanohelices via MD simulations for mechanical energy harvesting purposes.

Accurate modeling of nanohelical structures is important for predictive simulation studies leading to novel nanotechnology applications.&#160; Currently, software packages and codes are limited in creating atomistic helical models.&#160; We present two procedures designed to create atomistic nanohelical models for simulations, and a graphical interface to enhance research through visualization.

Spring-like materials are ubiquitous in nature and of interest in nanotechnology for energy harvesting, hydrogen storage, and biological sensing ...

Preparation and Use of Photocatalytically Active Segmented Ag|ZnO and Coaxial TiO2-Ag Nanowires Made by Templated Electrodeposition

Photocatalytically active nanostructures require a large specific surface area with the presence of many catalytically active sites for the oxidation and reduction half reactions, and fast electron (hole) diffusion and charge separation. Nanowires present suitable architectures to meet these requirements. Axially segmented Ag|ZnO and radially segmented (coaxial) TiO2-Ag nanowires with a diameter of 200 nm and a length of 6-20 &#181;m were made by templated electrodeposition within the pores of polycarbonate track-etched (PCTE) or anodized aluminum oxide (AAO) membranes, respectively. In the photocatalytic experiments, the ZnO and TiO2 phases acted as photoanodes, and Ag as cathode. No external circuit is needed to connect both electrodes, which is a key advantage over conventional photo-electrochemical cells. For making segmented Ag|ZnO nanowires, the Ag salt electrolyte was replaced after formation of the Ag segment to form a ZnO segment attached to the Ag segment. For making coaxial TiO2-Ag nanowires, a TiO2 gel was first formed by the electrochemically induced sol-gel method. Drying and thermal annealing of the as-formed TiO2 gel resulted in the formation of crystalline TiO2 nanotubes. A subsequent Ag electrodeposition step inside the TiO2 nanotubes resulted in formation of coaxial TiO2-Ag nanowires. Due to the combination of an n-type semiconductor (ZnO or TiO2) and a metal (Ag) within the same nanowire, a Schottky barrier was created at the interface between the phases. To demonstrate the photocatalytic activity of these nanowires, the Ag|ZnO nanowires were used in a photocatalytic experiment in which H2 gas was detected upon UV illumination of the nanowires dispersed in a methanol/water mixture. After 17 min&#160;of illumination, approximately 0.2 vol% H2 gas was detected from a suspension of ~0.1 g of Ag|ZnO nanowires in a 50 ml 80 vol% aqueous methanol solution.

Preparation and Use of Photocatalytically Active Segmented Ag|ZnO and Coaxial TiO2-Ag Nanowires Made by Templated Electrodeposition

Procedures are outlined to prepare segmented and coaxial nanowires via templated electrodeposition in nanopores. As examples, segmented nanowires consisting of Ag and ZnO segments, and coaxial nanowires consisting of a TiO2 shell and a Ag core were made. The nanowires were used in photocatalytic hydrogen formation experiments.

Photocatalytically active nanostructures require a large specific surface area with the presence of many catalytically active sites for the oxidation and ...

High-Sensitivity Nuclear Magnetic Resonance at Giga-Pascal Pressures: A New Tool for Probing Electronic and Chemical Properties of Condensed Matter under Extreme Conditions

Nuclear Magnetic Resonance (NMR) is one of the most important techniques for the study of condensed matter systems, their chemical structure, and their electronic properties. The application of high pressure enables one to synthesize new materials, but the response of known materials to high pressure is a very useful tool for studying their electronic structure and developing theories. For example, high-pressure synthesis might be at the origin of life; and understanding the behavior of small molecules under extreme pressure will tell us more about fundamental processes in our universe. It is no wonder that there has always been great interest in having NMR available at high pressures. Unfortunately, the desired pressures are often well into the Giga-Pascal (GPa) range and require special anvil cell devices where only very small, secluded volumes are available. This has restricted the use of NMR almost entirely in the past, and only recently, a new approach to high-sensitivity GPa NMR, which has a resonating micro-coil inside the sample chamber, was put forward. This approach enables us to achieve high sensitivity with experiments that bring the power of NMR to Giga-Pascal pressure condensed matter research. First applications, the detection of a topological electronic transition in ordinary aluminum metal and the closing of the pseudo-gap in high-temperature superconductivity, show the power of such an approach. Meanwhile, the range of achievable pressures was increased tremendously with a new generation of anvil cells (up to 10.1 GPa), that fit standard-bore NMR magnets. This approach might become a new, important tool for the investigation of many condensed matter systems, in chemistry, geochemistry, and in physics, since we can now watch structural changes with the eyes of a very versatile probe.

Nuclear magnetic resonance is one of the most important spectroscopic tools. Here, the development of a new approach under high pressure, currently up to 10.1 GPa, is presented. This opens a new window into condensed matter physics and chemistry, where high-pressure research is of great importance.

Nuclear Magnetic Resonance (NMR) is one of the most important techniques for the study of condensed matter systems, their chemical structure, and their ...

A Method for Studying the Temperature Dependence of Dynamic Fracture and Fragmentation

The dynamic fracture of a body is a late-stage phenomenon typically studied under simplified conditions, in which a sample is deformed under uniform stress and strain rate. This can be produced by evenly loading the inner surface of a cylinder. Due to the axial symmetry, as the cylinder expands the wall is placed into a tensile hoop stress that is uniform around the circumference. While there are various techniques to generate this expansion such as explosives, electromagnetic drive, and existing gas gun techniques they are all limited in the fact that the sample cylinder must be at room temperature. We present a new method using a gas gun that facilitates experiments on cylinders from 150 K to 800 K with a consistent, repeatable loading. These highly diagnosed experiments are used to examine the effect of temperature on the fracture mechanisms responsible for failure, and their resulting influence on fragmentation statistics. The experimental geometry employs a steel ogive located inside the target cylinder, with the tip located about halfway in. A single stage light gas gun is then used to launch a polycarbonate projectile into the cylinder at 1,000 m/sec-1. The projectile impacts and flows around the rigid ogive, driving the sample cylinder from the inside. The use of a non-deforming ogive insert allows us to install temperature control hardware inside the rear of the cylinder. Liquid nitrogen (LN2) is used for cooling and a resistive high current load for heating. Multiple channels of upshifted photon Doppler velocimetry (PDV) track the expansion velocity along the cylinder enabling direct comparison to computer simulations, while High speed imaging is used to measure the strain to failure. The recovered cylinder fragments are also subject to optical and electron microscopy to ascertain the failure mechanism.

Fracture and fragmentation are late stage phenomena in dynamic loading scenarios and are typically studied using explosives. We present a technique for driving expansion using a gas gun which uniquely enables control of both loading rate and sample temperature.

The dynamic fracture of a body is a late-stage phenomenon typically studied under simplified conditions, in which a sample is deformed under uniform ...

A Cost-effective and Reliable Method to Predict Mechanical Stress in Single-use and Standard Pumps

Pumps are mainly used when transferring sterile culture broths in biopharmaceutical and biotechnological production processes. However, during the pumping process shear forces occur which can lead to qualitative and/or quantitative product loss. To calculate the mechanical stress with limited experimental expense, an oil-water emulsion system was used, whose suitability was demonstrated for drop size detections in bioreactors1. As drop breakup of the oil-water emulsion system is a function of mechanical stress, drop sizes need to be counted over the experimental time of shear stress investigations. In previous studies, the inline endoscopy has been shown to be an accurate and reliable measurement technique for drop size detections in liquid/liquid dispersions. The aim of this protocol is to show the suitability of the inline endoscopy technique for drop size measurements in pumping processes. In order to express the drop size, the Sauter mean diameter d32 was used as the representative diameter of drops in the oil-water emulsion. The results showed low variation in the Sauter mean diameters, which were quantified by standard deviations of below 15%, indicating the reliability of the measurement technique.

Shear stress investigations on an oil-water emulsion system result in drop breakup over the experimental time. To count drop sizes in pumping processes, the suitability of inline endoscopy was successfully demonstrated in this protocol.

Pumps are mainly used when transferring sterile culture broths in biopharmaceutical and biotechnological production processes. However, during the pumping ...

A Modular Microfluidic Technology for Systematic Studies of Colloidal Semiconductor Nanocrystals

Colloidal semiconductor nanocrystals, known as quantum dots (QDs), are a rapidly growing class of materials in commercial electronics, such as light emitting diodes (LEDs) and photovoltaics (PVs). Among this material group, inorganic/organic perovskites have demonstrated significant improvement and potential towards high-efficiency, low-cost PV fabrication due to their high charge carrier mobilities and lifetimes. Despite the opportunities for perovskite QDs in large-scale PV and LED applications, the lack of fundamental and comprehensive understanding of their growth pathways has inhibited their adaptation within continuous nanomanufacturing strategies. Traditional flask-based screening approaches are generally expensive, labor-intensive, and imprecise for effectively characterizing the broad parameter space and synthesis variety relevant to colloidal QD reactions. In this work, a fully autonomous microfluidic platform is developed to systematically study the large parameter space associated with the colloidal synthesis of nanocrystals in a continuous flow format. Through the application of a novel translating three-port flow cell and modular reactor extension units, the system may rapidly collect fluorescence and absorption spectra across reactor lengths ranging 3 - 196 cm. The adjustable reactor length not only decouples the residence time from the velocity-dependent mass transfer, it also substantially improves the sampling rates and chemical consumption due to the characterization of 40 unique spectra within a single equilibrated system. Sample rates may reach up to 30,000 unique spectra per day, and the conditions cover 4 orders of magnitude in residence times ranging 100 ms - 17 min. Further applications of this system would substantially improve the rate and precision of the material discovery and screening in future studies. Detailed within this report are the system materials and assembly protocols with a general description of the automated sampling software and offline data processing.

Detailed herein are the operation and assembly protocols of a modular microfluidic screening platform for the systematic characterization of colloidal semiconductor nanocrystal syntheses. Through fully adjustable system arrangements, highly efficient spectra collection may be carried out across 4 orders of magnitude reaction time scales within a mass transfer-controlled sampling space.

Colloidal semiconductor nanocrystals, known as quantum dots (QDs), are a rapidly growing class of materials in commercial electronics, such as light ...

Fabrication of Magnetic Nanostructures on Silicon Nitride Membranes for Magnetic Vortex Studies Using Transmission Microscopy Techniques

Electron and x-ray magnetic microscopies allow for high-resolution magnetic imaging down to tens of nanometers. However, the samples need to be prepared on transparent membranes which are very fragile and difficult to manipulate. We present processes for the fabrication of samples with magnetic micro- and nanostructures with spin configurations forming magnetic vortices suitable for Lorentz transmission electron microscopy and magnetic transmission x-ray microscopy studies. The samples are prepared on silicon nitride membranes and the fabrication consists of a spin coating, UV and electron-beam lithography, the chemical development of the resist, and the evaporation of the magnetic material followed by a lift-off process forming the final magnetic structures. The samples for the Lorentz transmission electron microscopy consist of magnetic nanodiscs prepared in a single lithography step. The samples for the magnetic x-ray transmission microscopy are used for time-resolved magnetization dynamic experiments, and magnetic nanodiscs are placed on a waveguide which is used for the generation of repeatable magnetic field pulses by passing an electric current through the waveguide. The waveguide is created in an extra lithography step.

A protocol for the fabrication of magnetic micro- and nanostructures with spin configurations forming magnetic vortices suitable for transmission electron microscopy (TEM) and magnetic transmission x-ray microscopy (MTXM) studies is presented.

Electron and x-ray magnetic microscopies allow for high-resolution magnetic imaging down to tens of nanometers. However, the samples need to be prepared ...

A 100 KW Class Applied-field Magnetoplasmadynamic Thruster

Applied-field magnetoplasmadynamic thrusters (AF-MPD thrusters) are hybrid accelerators in which electromagnetic and gas dynamic processes accelerate plasma to high speed; they have considerable potential for future space applications with the significant advantages of high specific impulse and thrust density. In this paper, we present a series of protocols for designing and manufacturing a 100 kW class of AF-MPD thruster with water-cooling structures, a 130 V maximum discharge voltage, a 800 A maximum discharge current, and a 0.25 T maximum strength of magnetic field. A hollow tantalum tungsten cathode acts as the only propellant inlet to inhibit the radial discharge, and it is positioned axially at the rear of the anode in order to relieve anode starvation. A cylindrical divergent copper anode is employed to decrease anode power deposition, where the length has been reduced to decrease the wall-plasma connecting area. Experiments utilized a vacuum system that can achieve a working vacuum of 0.01 Pa for a total propellant mass flow rate lower than 40 mg/s and a target thrust stand. The thruster tests were carried out to measure the effects of the working parameters such as propellant flow rates, the discharge current, and the strength of applied magnetic field on the performance and to allow appropriate analysis. The thruster could be operated continuously for significant periods of time with little erosion on the hollow cathode surface. The maximum power of the thruster is 100 kW, and the performance of this water-cooled configuration is comparable with that of thrusters reported in the literature.

The goal of this protocol is to introduce the design of a 100 kW class applied-field magnetoplasmadynamic thruster and relevant experimental methods.

Applied-field magnetoplasmadynamic thrusters (AF-MPD thrusters) are hybrid accelerators in which electromagnetic and gas dynamic processes accelerate ...