Ran Tao bedankt sich für die Finanzierung durch das National Institute of Standards and Technology des US-Handelsministeriums im Rahmen des Zuschusses 70NANB15H112. Die Finanzierung von Aaron M. Forster erfolgte durch Zuwendungen des Kongresses an das National Institute of Standards and Technology.

<ol>
	<li>Macosko, C. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Rheology: principles, measurements, and applications. , (1994).</li><li>Larson, 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=.">.</a> The Structure and Rheology of Complex Fluids. , (1999).</li><li>Vermant, J., Moldenaers, P., Mewis, J., Ellis, M., Garritano, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Orthogonal+superposition+measurements+using+a+rheometer+equipped+with+a+force+rebalanced+transducer.">Orthogonal superposition measurements using a rheometer equipped with a force rebalanced transducer.</a> Review of Scientific Instruments. 68 (11), 4090-4096 (1997).</li><li>Ferry, J. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Viscoelastic Properties of Polymers. , (1980).</li><li>Yamamoto, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rate-dependent+relaxation+spectra+and+their+determination.">Rate-dependent relaxation spectra and their determination.</a> Transactions of the Society of Rheology. 15 (2), 331-344 (1971).</li><li>Simmons, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+servo-controlled+rheometer+for+measurement+of+the+dynamic+modulus+of+viscoelastic+liquids.">A servo-controlled rheometer for measurement of the dynamic modulus of viscoelastic liquids.</a> Journal of Scientific Instruments. 43 (12), 887-892 (1966).</li><li>Tanner, R. I., Williams, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+orthogonal+superposition+of+simple+shearing+and+small-strain+oscillatory+motions.">On the orthogonal superposition of simple shearing and small-strain oscillatory motions.</a> Rheologica Acta. 10 (4), 528-538 (1971).</li><li>Schoukens, G., Mewis, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nonlinear+rheological+behaviour+and+shear-dependent+structure+in+colloidal+dispersions.">Nonlinear rheological behaviour and shear-dependent structure in colloidal dispersions.</a> Journal of Rheology. 22 (4), 381-394 (1978).</li><li>Zeegers, J., 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+sensitive+dynamic+viscometer+for+measuring+the+complex+shear+modulus+in+a+steady+shear+flow+using+the+method+of+orthogonal+superposition.">A sensitive dynamic viscometer for measuring the complex shear modulus in a steady shear flow using the method of orthogonal superposition.</a> Rheologica Acta. 34 (6), 606-621 (1995).</li><li>Mewis, J., Schoukens, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanical+spectroscopy+of+colloidal+dispersions.">Mechanical spectroscopy of colloidal dispersions.</a> Faraday Discussions of the Chemical Society. 65, 58-64 (1978).</li><li>Lin, N. Y. C., Ness, C., Cates, M. E., Sun, J., Cohen, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tunable+shear+thickening+in+suspensions.">Tunable shear thickening in suspensions.</a> Proceedings of the National Academy of Sciences. 113 (39), 10774-10778 (2016).</li><li>Gracia-Fern&#225;ndez, 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+application+of+electro+and+orthogonal+superposition+rheology+on+a+starch/silicone+oil+suspension.">Simultaneous application of electro and orthogonal superposition rheology on a starch/silicone oil suspension.</a> Journal of Rheology. 60 (1), 121-127 (2015).</li><li>Sung, S. H., Kim, S., Hendricks, J., Clasen, C., Ahn, K. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Orthogonal+superposition+rheometry+of+colloidal+gels:+time-shear+rate+superposition.">Orthogonal superposition rheometry of colloidal gels: time-shear rate superposition.</a> Soft Matter. 14 (42), 8651-8659 (2018).</li><li>Colombo, 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=Superposition+rheology+and+anisotropy+in+rheological+properties+of+sheared+colloidal+gels.">Superposition rheology and anisotropy in rheological properties of sheared colloidal gels.</a> Journal of Rheology. 61 (5), 1035-1048 (2017).</li><li>Jacob, A. R., Poulos, A. S., Kim, S., Vermant, J., Petekidis, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Convective+Cage+Release+in+Model+Colloidal+Glasses.">Convective Cage Release in Model Colloidal Glasses.</a> Physical Review Letters. 115 (21), 218301 (2015).</li><li>Jacob, A. R., Poulos, A. S., Semenov, A. N., Vermant, J., Petekidis, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flow+dynamics+of+concentrated+starlike+micelles:+A+superposition+rheometry+investigation+into+relaxation+mechanisms.">Flow dynamics of concentrated starlike micelles: A superposition rheometry investigation into relaxation mechanisms.</a> Journal of Rheology. 63 (4), 641-653 (2019).</li><li>Moghimi, E., Vermant, J., Petekidis, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Orthogonal+superposition+rheometry+of+model+colloidal+glasses+with+short-ranged+attractions.">Orthogonal superposition rheometry of model colloidal glasses with short-ranged attractions.</a> Journal of Rheology. 63 (4), 533-546 (2019).</li><li>Tao, R., Forster, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=End+effect+correction+for+orthogonal+small+strain+oscillatory+shear+in+a+rotational+shear+rheometer.">End effect correction for orthogonal small strain oscillatory shear in a rotational shear rheometer.</a> Rheologica Acta. 59 (2), 95-108 (2020).</li><li>Schrag, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Deviation+of+velocity+gradient+profiles+from+the+"gap+loading"+and+"surface+loading"+limits+in+dynamic+simple+shear+experiments.">Deviation of velocity gradient profiles from the "gap loading" and "surface loading" limits in dynamic simple shear experiments.</a> Transactions of the Society of Rheology. 21 (3), 399-413 (1977).</li><li>Ewoldt, R. H., Johnston, M. T., Caretta, L. M., Spagnolie, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Complex Fluids in Biological Systems. Biological and Medical Physics, Biomedical Engineering. , 207-241 (2015).</li></ol>

Die vollständige Beschreibung der in diesem Dokument verwendeten Verfahren erfordert die Identifizierung bestimmter kommerzieller Produkte und ihrer Lieferanten. Die Aufnahme solcher Informationen sollte in keiner Weise als Hinweis darauf ausgelegt werden, dass diese Produkte oder Lieferanten von NIST empfohlen oder von NIST empfohlen werden oder dass sie notwendigerweise die besten Materialien, Instrumente, Software oder Lieferanten für die beschriebenen Zwecke sind.

In diesem Protokoll stellen wir ein detailliertes experimentelles Verfahren zur Durchführung von Viskositätskalibrierungsmessungen mit newtonschen Flüssigkeiten für eine kommerzielle orthogonale Überlagerungsrheologie mit einer doppelwandigen konzentrischen Zylindergeometrie vor. Die Kalibrierfaktoren, d. h. der primäre Endeffektfaktor C L und der orthogonale Endeffektfaktor CLo, werden unabhängig voneinander durch die Durchführung von Sweep-Tests mit kons...

Das Verständnis der rheologischen Eigenschaften komplexer Fluide ist für viele Branchen für die Entwicklung und Herstellung zuverlässiger und reproduzierbarer Produkte unerlässlich1. Zu diesen "komplexen Flüssigkeiten" gehören Suspensionen, polymere Flüssigkeiten und Schäume, die in unserem Alltag weit verbreitet sind, zum Beispiel in Körperpflegeprodukten, Lebensmitteln, Kosmetika und Haushaltsprodukten. Die rheologischen oder Fließeigenschaften (z. B. Viskosität) sind Schlüsselgrößen, die für die Festlegung von Leistungsmetriken für die Endverwendung und die Verarbeitbarkeit von Interesse sind, aber die Fließeigenschaften sind mit den Mikrostrukturen verbunden, die in komplexen Flüssigkeiten vorhanden sind. Ein herausragendes Merkmal komplexer Flüssigkeiten, das sie von einfachen Flüssigkeiten unterscheidet, ist, dass sie unterschiedliche Mikrostrukturen besitzen, die sich über mehrere Längenskalen erstrecken2. Diese Mikrostrukturen können leicht durch unterschiedliche Strömungsverhältnisse beeinflusst werden, was wiederum zu Veränderungen ihrer makroskopischen Eigenschaften führt. Die Entschlüsselung dieser Struktur-Eigenschafts-Schleife durch nichtlineares viskoelastisches Verhalten komplexer Fluide als Reaktion auf Strömung und Verformung bleibt eine herausfordernde Aufgabe für experimentelle Rheologen.
Die Rheologie der orthogonalen Überlagerung (OSP)3 ist eine robuste Technik, um diese Messherausforderung zu bewältigen. Bei dieser Technik wird eine oszillierende Scherströmung mit kleiner Amplitude orthogonal mit einer unidirektionalen primären stationären Scherströmung überlagert, was die gleichzeitige Messung eines viskoelastischen Relaxationsspektrums unter der auferlegten primären Scherströmung ermöglicht. Um genauer zu sein, kann die kleine oszillatorische Scherstörung mit Hilfe von Theorien in linearer Viskoelastizität4 analysiert werden, während die nichtlineare Strömungsbedingung durch die primäre stationäre Scherströmung erreicht wird. Da die beiden Strömungsfelder orthogonal und somit nicht gekoppelt sind, können die Störungsspektren direkt mit der Variation der Mikrostruktur unter der primären nichtlinearen Strömung5 in Beziehung gesetzt werden. Diese fortschrittliche Messtechnik bietet die Möglichkeit, Struktur-Eigenschafts-Verarbeitungsbeziehungen in komplexen Fluiden aufzuklären, um deren Formulierung, Verarbeitung und Anwendung zu optimieren.
Die Einführung der modernen OSP-Rheologie war nicht das Ergebnis einer plötzlichen Erleuchtung; Vielmehr basiert es auf jahrzehntelanger Entwicklung von kundenspezifischen Geräten. Der erste maßgefertigte OSP-Apparat stammt aus dem Jahr 1966 von Simmons6, und danach wurden viele Anstrengungen unternommen 7,8,9,10. Diese frühen kundenspezifischen Geräte leiden unter vielen Nachteilen, wie z. B. Ausrichtungsproblemen, dem Pumpeffekt (aufgrund der axialen Bewegung des Bobs zur orthogonalen Oszillation) und Einschränkungen der Instrumentenempfindlichkeit. Im Jahr 1997 modifizierten Vermant et al.3 den Force Rebalance Transducer (FRT) an einem kommerziellen separaten Motor-Wandler-Rheometer, der OSP-Messungen für Flüssigkeiten mit einem breiteren Viskositätsbereich als frühere Geräte ermöglichte. Diese Modifikation ermöglicht es dem Normalkraftaufnehmer, als spannungsgesteuertes Rheometer zu fungieren, das zusätzlich zur Messung der Axialkraft eine axiale Schwingung erzwingt. Vor kurzem wurden die für OSP-Messungen erforderlichen Geometrien nach der Methodik von Vermant für ein kommerzielles separates Motor-Wandler-Rheometer freigegeben.
Seit dem Aufkommen der kommerziellen OSP-Rheologie besteht ein wachsendes Interesse an der Anwendung dieser Technik für die Untersuchung verschiedener komplexer Flüssigkeiten. Beispiele hierfür sind kolloidale Suspensionen 11,12, kolloidale Gele13,14 und Gläser15,16,17. Während die Verfügbarkeit des kommerziellen Instruments die OSP-Forschung fördert, erfordert die komplizierte OSP-Geometrie ein tieferes Verständnis der Messung als andere rheologische Routinetechniken. Die OSP-Durchflusszelle basiert auf einer doppelwandigen konzentrischen Zylindergeometrie (oder Couette). Es verfügt über ein offenes oberes und offenes Bodendesign, damit Flüssigkeit zwischen den ringförmigen Lücken und dem Reservoir hin und her fließen kann. Trotz der Optimierung, die der Hersteller am Geometriedesign vorgenommen hat, erfährt das Fluid im OSP-Betrieb ein inhomogenes Strömungsfeld, geometrische Endeffekte und einen Restpumpenfluss, die alle zu erheblichen experimentellen Fehlern führen können. Unsere vorherige Arbeit18 berichtete über wichtige Endeffektkorrekturverfahren unter Verwendung von newtonschen Flüssigkeiten für diese Technik. Um korrekte Viskositätsergebnisse zu erhalten, sollten geeignete Endeffektfaktoren sowohl in primärer als auch in orthogonaler Richtung angewendet werden. In diesem Protokoll möchten wir eine detaillierte Kalibriermethodik für die rheologische OSP-Technik vorstellen und Empfehlungen für Best Practices zur Reduzierung von Messfehlern geben. Die in diesem Artikel beschriebenen Verfahren zum OSP-Geometrieaufbau, zur Probenbeladung und zu den OSP-Testeinstellungen sollten leicht für Messungen mit nicht-newtonschen Flüssigkeiten übernommen und übersetzt werden können. Wir empfehlen Anwendern, die hier beschriebenen Kalibrierungsverfahren zu verwenden, um die Endeffekt-Korrekturfaktoren für ihre Anwendungen vor OSP-Messungen an einer beliebigen Fluidklassifizierung (Newton oder Nicht-Newton) zu bestimmen. Wir stellen fest, dass die Kalibrierungsverfahren für Endfaktoren bisher nicht berichtet wurden. Das in diesem Artikel bereitgestellte Protokoll beschreibt auch eine Schritt-für-Schritt-Anleitung und Tipps zur Durchführung genauer rheologischer Messungen im Allgemeinen und die technischen Ressourcen zum Verständnis von "Rohdaten" im Vergleich zu "gemessenen" Daten, die von Rheometerbenutzern übersehen werden können.

<table>
	<tbody>
		<tr>
			<td>Advanced Peltier System</td>
			<td>TA Instruments</td>
			<td>402500.901</td>
			<td>Enviromental control device</td>
		</tr>
		<tr>
			<td>ARES-G2 Rheometer</td>
			<td>TA Instruments</td>
			<td>401000.501</td>
			<td>Rheometer</td>
		</tr>
		<tr>
			<td>Brookfield Silicone Fluid, 12500cP</td>
			<td>AMTEK Brookfield</td>
			<td>12500 cps</td>
			<td>Viscosity standard liquid</td>
		</tr>
		<tr>
			<td>OSP Slotted Bob, 33 mm</td>
			<td>TA Instruments</td>
			<td>402796.902</td>
			<td>Bob, upper geometry</td>
		</tr>
		<tr>
			<td>OSP Slotted Double Gap Cup, 34 mm</td>
			<td>TA Instruments</td>
			<td>402782.901</td>
			<td>Double wall cup, lower geometry</td>
		</tr>
		<tr>
			<td>Pipette (1 &#8211; 10 mL)</td>
			<td>Eppendorf</td>
			<td>3120000089</td>
			<td>To load test materials</td>
		</tr>
		<tr>
			<td>Pipette (100 &#8211; 1,000 &#181;L)</td>
			<td>Eppendorf</td>
			<td>3123000063</td>
			<td>To load test materials</td>
		</tr>
		<tr>
			<td>Pipette Tips (0.5 &#8211; 10 mL)</td>
			<td>Eppendorf</td>
			<td>022492098</td>
			<td>To load test materials</td>
		</tr>
		<tr>
			<td>Pipette Tips (50 &#8211; 1,000 &#181;L)</td>
			<td>Eppendorf</td>
			<td>022491555</td>
			<td>To load test materials</td>
		</tr>
		<tr>
			<td>Spatula</td>
			<td>VWR</td>
			<td>82027-532</td>
			<td>To load test materials</td>
		</tr>
		<tr>
			<td>TRIOS</td>
			<td>TA Instruments</td>
			<td>v4.3.1.39215</td>
			<td>Rheometer software</td>
		</tr>
	</tbody>
</table>

calibration procedures for orthogonal superposition rheology

Die Rheologie der orthogonalen Überlagerung (OSP) ist eine fortschrittliche rheologische Technik, bei der eine oszillierende Scherverformung mit kleiner Amplitude orthogonal zu einer primären Scherströmung überlagert wird. Diese Technik ermöglicht die Messung der Strukturdynamik komplexer Fluide unter nichtlinearen Strömungsbedingungen, was für das Verständnis und die Vorhersage des Verhaltens einer Vielzahl komplexer Fluide wichtig ist. Die rheologische OSP-Technik hat seit den 1960er Jahren eine lange Entwicklungsgeschichte, vor allem durch die speziell angefertigten Geräte, die die Leistungsfähigkeit dieser Technik hervorhoben. Die OSP-Technik ist jetzt kommerziell für die Rheologie-Community verfügbar. Angesichts des komplizierten Designs der OSP-Geometrie und des nicht idealen Strömungsfeldes sollten Benutzer das Ausmaß und die Quellen von Messfehlern verstehen. Diese Studie stellt Kalibrierverfahren mit newtonschen Flüssigkeiten vor, die Empfehlungen für Best Practices zur Reduzierung von Messfehlern enthalten. Insbesondere werden detaillierte Informationen über die Methode zur Bestimmung des Endeffektfaktors, das Probenfüllverfahren und die Identifizierung des geeigneten Messbereichs (z. B. Schergeschwindigkeit, Frequenz usw.) bereitgestellt.

Repräsentative Ergebnisse der Viskositätskalibrierungsmessungen an einem Silikonviskositätsstandard von 12,2 Pa s sind in Abbildung 5 und Abbildung 6 dargestellt. Beachten Sie, dass sowohl der primäre Endeffektfaktor als auch der orthogonale Endeffektfaktor für die Kalibrierungsläufe auf 1,00 eingestellt sind. Abbildung 5 zeigt die stationäre Scherviskosität und das Drehmoment als Funktion der Schergeschwindigkeit auf einer ...

Watch this Scientific Journal Video about Calibration Procedures for Orthogonal Superposition Rheology at JoVE.com

Calibration Procedures for Orthogonal Superposition Rheology

Wir präsentieren ein detailliertes Kalibrierungsprotokoll für eine kommerzielle orthogonale Überlagerungsrheologie-Technik unter Verwendung von newtonschen Flüssigkeiten, einschließlich Methoden zur Bestimmung des Endeffekt-Korrekturfaktors und Empfehlungen für Best Practices zur Reduzierung von experimentellen Fehlern.

Kalibrierverfahren für die orthogonale Überlagerungsrheologie

Orthogonal superposition (OSP) rheology is an advanced rheological technique that involves superimposing a small-amplitude oscillatory shear deformation ...

calibration-procedures-for-orthogonal-superposition-rheology

Research

JoVE Journal

Engineering

2.0K Aufrufe.  National Institute of Standards and Technology. Wir präsentieren ein detailliertes Kalibrierungsprotokoll für eine kommerzielle orthogonale Überlagerungsrheologie-Technik unter Verwendung von newtonschen Flüssigkeiten, einschließlich Methoden zur Bestimmung des Endeffekt-Korrekturfaktors und Empfehlungen für Best Practices zur Reduzierung von experimentellen Fehlern.

Serie: Calibration Procedures for Orthogonal Superposition Rheology

Compact Quantum Dots for Single-molecule Imaging

Single-molecule imaging is an important tool for understanding the mechanisms of biomolecular function and for visualizing the spatial and temporal heterogeneity of molecular behaviors that underlie cellular biology 1-4. To image an individual molecule of interest, it is typically conjugated to a fluorescent tag (dye, protein, bead, or quantum dot) and observed with epifluorescence or total internal reflection fluorescence (TIRF) microscopy. While dyes and fluorescent proteins have been the mainstay of fluorescence imaging for decades, their fluorescence is unstable under high photon fluxes necessary to observe individual molecules, yielding only a few seconds of observation before complete loss of signal. Latex beads and dye-labeled beads provide improved signal stability but at the expense of drastically larger hydrodynamic size, which can deleteriously alter the diffusion and behavior of the molecule under study.
Quantum dots (QDs) offer a balance between these two problematic regimes. These nanoparticles are composed of semiconductor materials and can be engineered with a hydrodynamically compact size with exceptional resistance to photodegradation 5. Thus in recent years QDs have been instrumental in enabling long-term observation of complex macromolecular behavior on the single molecule level. However these particles have still been found to exhibit impaired diffusion in crowded molecular environments such as the cellular cytoplasm and the neuronal synaptic cleft, where their sizes are still too large 4,6,7.
Recently we have engineered the cores and surface coatings of QDs for minimized hydrodynamic size, while balancing offsets to colloidal stability, photostability, brightness, and nonspecific binding that have hindered the utility of compact QDs in the past 8,9. The goal of this article is to demonstrate the synthesis, modification, and characterization of these optimized nanocrystals, composed of an alloyed HgxCd1-xSe core coated with an insulating CdyZn1-yS shell, further coated with a multidentate polymer ligand modified with short polyethylene glycol (PEG) chains (Figure 1). Compared with conventional CdSe nanocrystals, HgxCd1-xSe alloys offer greater quantum yields of fluorescence, fluorescence at red and near-infrared wavelengths for enhanced signal-to-noise in cells, and excitation at non-cytotoxic visible wavelengths. Multidentate polymer coatings bind to the nanocrystal surface in a closed and flat conformation to minimize hydrodynamic size, and PEG neutralizes the surface charge to minimize nonspecific binding to cells and biomolecules. The end result is a brightly fluorescent nanocrystal with emission between 550-800 nm and a total hydrodynamic size near 12 nm. This is in the same size range as many soluble globular proteins in cells, and substantially smaller than conventional PEGylated QDs (25-35 nm).

We describe the preparation of colloidal quantum dots with minimized hydrodynamic size for single-molecule fluorescence imaging. Compared to conventional quantum dots, these nanoparticles are similar in size to globular proteins and are optimized for single-molecule brightness, stability against photodegradation, and resistance to nonspecific binding to proteins and cells.

Compact Quantum Dots für Einzelmolekül-Imaging

Single-molecule imaging is an important tool for  understanding the mechanisms of biomolecular function and for visualizing the  spatial and temporal ...

Forschung

Ingenieurwesen

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.

Hyperpolarisiertem Xenon für NMR-und MRI-Anwendungen

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

Concurrent Quantitative Conductivity and Mechanical Properties Measurements of Organic Photovoltaic Materials using AFM

Organic photovoltaic (OPV) materials are inherently inhomogeneous at the nanometer scale. Nanoscale inhomogeneity of OPV materials affects performance of photovoltaic devices. Thus, understanding of spatial variations in composition as well as electrical properties of OPV materials is of paramount importance for moving PV technology forward.1,2 In this paper, we describe a protocol for quantitative measurements of electrical and mechanical properties of OPV materials with sub-100 nm resolution. Currently, materials properties measurements performed using commercially available AFM-based techniques (PeakForce, conductive AFM) generally provide only qualitative information. The values for resistance as well as Young's modulus measured using our method on the prototypical ITO/PEDOT:PSS/P3HT:PC61BM system correspond well with literature data. The P3HT:PC61BM blend separates onto PC61BM-rich and P3HT-rich domains. Mechanical properties of PC61BM-rich and P3HT-rich domains are different, which allows for domain attribution on the surface of the film. Importantly, combining mechanical and electrical data allows for correlation of the domain structure on the surface of the film with electrical properties variation measured through the thickness of the film.

Organic photovoltaic (OPV) materials are inherently inhomogeneous at the nanometer scale. Nanoscale inhomogeneity of OPV materials affects performance of photovoltaic devices. In this paper, we describe a protocol for quantitative measurements of electrical and mechanical properties of OPV materials with sub-100 nm resolution.

Concurrent Quantitative Leitfähigkeit und mechanische Eigenschaften Measurements of Organic Photovoltaic Materials mittels AFM

Organic photovoltaic  (OPV) materials are inherently inhomogeneous at the nanometer scale. Nanoscale  inhomogeneity of OPV materials affects performance ...

Detection and Recovery of Palladium, Gold and Cobalt Metals from the Urban Mine Using Novel Sensors/Adsorbents Designated with Nanoscale Wagon-wheel-shaped Pores

Developing low-cost, efficient processes for recovering and recycling palladium, gold and cobalt metals from urban mine remains a significant challenge in industrialized countries. Here, the development of optical mesosensors/adsorbents (MSAs) for efficient recognition and selective recovery of Pd(II), Au(III), and Co(II) from urban mine was achieved. A simple, general method for preparing MSAs based on using high-order mesoporous monolithic scaffolds was described. Hierarchical cubic Ia3d wagon-wheel-shaped MSAs were fabricated by anchoring chelating agents (colorants) into three-dimensional pores and micrometric particle surfaces of the mesoporous monolithic scaffolds. Findings show, for the first time, evidence of controlled optical recognition of Pd(II), Au(III), and Co(II) ions and a highly selective system for recovery of Pd(II) ions (up to ~95%) in ores and industrial wastes. Furthermore, the controlled assessment processes described herein involve evaluation of intrinsic properties (e.g., visual signal change, long-term stability, adsorption efficiency, extraordinary sensitivity, selectivity, and reusability); thus, expensive, sophisticated instruments are not required. Results show evidence that MSAs will attract worldwide attention as a promising technological means of recovering and recycling palladium, gold and cobalt metals.

Because of the importance and extensive use of palladium, gold and cobalt metals in high-technology equipment, their recovery and recycling constitute an important industrial challenge. The metal recovery system described herein is a simple, low-cost means for the effective detection, removal, and recovery of these metals from the urban mine.

Erkennung und Wiedergewinnung von Palladium, Gold und Kobalt-Metalle aus der Urban-Mine mit Hilfe neuartiger Sensoren / Adsorbentien mit nanoskaligen Wagon-Rad-förmigen Poren Ausgewiesene

Developing low-cost, efficient processes for recovering and recycling palladium, gold and cobalt metals from urban mine remains a significant challenge in ...

A Simple Dewar/Cryostat for Thermally Equilibrating Samples at Known Temperatures for Accurate Cryogenic Luminescence Measurements

The design and operation of a simple liquid nitrogen Dewar/cryostat apparatus based upon a small fused silica optical Dewar, a thermocouple assembly, and a CCD spectrograph are described. The experiments for which this Dewar/cryostat is designed require fast sample loading, fast sample freezing, fast alignment of the sample, accurate and stable sample temperatures, and small size and portability of the Dewar/cryostat cryogenic unit. When coupled with the fast data acquisition rates of the CCD spectrograph, this Dewar/cryostat is capable of supporting cryogenic luminescence spectroscopic measurements on luminescent samples at a series of known, stable temperatures in the 77-300 K range. A temperature-dependent study of the oxygen quenching of luminescence in a rhodium(III) transition metal complex is presented as an example of the type of investigation possible with this Dewar/cryostat. In the context of this apparatus, a stable temperature for cryogenic spectroscopy means a luminescent sample that is thermally equilibrated with either liquid nitrogen or gaseous nitrogen at a known measureable temperature that does not vary (&#916;T &#60; 0.1 K) during the short time scale (~1-10 sec) of the spectroscopic measurement by the CCD. The Dewar/cryostat works by taking advantage of the positive thermal gradient dT/dh that develops above liquid nitrogen level in the Dewar where h is the height of the sample above the liquid nitrogen level. The slow evaporation of the liquid nitrogen results in a slow increase in h over several hours and a consequent slow increase in the sample temperature T over this time period. A quickly acquired luminescence spectrum effectively catches the sample at a constant, thermally equilibrated temperature.

A simple liquid nitrogen Dewar/cryostat apparatus comprised of a small fused silica optical Dewar, a thermocouple, and a charge-coupled device (CCD) spectrograph are described. The experiments for which this Dewar/cryostat is designed require fast sample loading, freezing, and alignment, accurate and stable sample temperatures, and small size/portability.

Eine einfache Dewar / Kryostat für Thermisch Äquilibrieren Proben, die bei bekannten Temperaturen für eine genaue Cryogenic Lumineszenzmessungen

The design and operation of a simple liquid nitrogen Dewar/cryostat apparatus based upon a small fused silica optical Dewar, a thermocouple assembly, and ...

Dielectric RheoSANS &#8212; Simultaneous Interrogation of Impedance, Rheology and Small Angle Neutron Scattering of Complex Fluids

A procedure for the operation of a new dielectric RheoSANS instrument capable of simultaneous interrogation of the electrical, mechanical and microstructural properties of complex fluids is presented. The instrument consists of a Couette geometry contained within a modified forced convection oven mounted on a commercial rheometer. This instrument is available for use on the small angle neutron scattering (SANS) beamlines at the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR). The Couette geometry is machined to be transparent to neutrons and provides for measurement of the electrical properties and microstructural properties of a sample confined between titanium cylinders while the sample undergoes arbitrary deformation. Synchronization of these measurements is enabled through the use of a customizable program that monitors and controls the execution of predetermined experimental protocols. Described here is a protocol to perform a flow sweep experiment where the shear rate is logarithmically stepped from a maximum value to a minimum value holding at each step for a specified period of time while frequency dependent dielectric measurements are made. Representative results are shown from a sample consisting of a gel composed of carbon black aggregates dispersed in propylene carbonate. As the gel undergoes steady shear, the carbon black network is mechanically deformed, which causes an initial decrease in conductivity associated with the breaking of bonds comprising the carbon black network. However, at higher shear rates, the conductivity recovers associated with the onset of shear thickening. Overall, these results demonstrate the utility of the simultaneous measurement of the rheo-electro-microstructural properties of these suspensions using the dielectric RheoSANS geometry.

Here, we present a procedure for the measurement of simultaneous impedance, rheology and neutron scattering from soft matter materials under shear flow.

Dielectric RheoSANS - Gleichzeitige Interrogation von Impedanz, Rheologie und Kleinwinkelneutronenstreuung komplexer Fluide

A procedure for the operation of a new dielectric RheoSANS instrument capable of simultaneous interrogation of the electrical, mechanical and ...

Resonance Fluorescence of an InGaAs Quantum Dot in a Planar Cavity Using Orthogonal Excitation and Detection

The ability to perform simultaneous resonant excitation and fluorescence detection is important for quantum optical measurements of quantum dots (QDs). Resonant excitation without fluorescence detection &#8211; for example, a differential transmission measurement &#8211; can determine some properties of the emitting system, but does not allow applications or measurements based on the emitted photons. For example, the measurement of photon correlations, observation of the Mollow triplet, and realization of single photon sources all require collection of the fluorescence. Incoherent excitation with fluorescence detection &#8211; for example, above band-gap excitation &#8211; can be used to create single photon sources, but the disturbance of the environment due to the excitation reduces the indistinguishability of the photons. Single photon sources based on QDs will have to be resonantly excited to have high photon indistinguishability, and simultaneous collection of the photons will be necessary to make use of them. We demonstrate a method to resonantly excite a single QD embedded in a planar cavity by coupling the excitation beam into this cavity from the cleaved face of the sample while collecting the fluorescence along the sample&#39;s surface normal direction. By carefully matching the excitation beam to the waveguide mode of the cavity, the excitation light can couple into the cavity and interact with the QD. The scattered photons can couple to the Fabry-Perot mode of the cavity and escape in the surface normal direction. This method allows complete freedom in the detection polarization, but the excitation polarization is restricted by the propagation direction of the excitation beam. The fluorescence from the wetting layer provides a guide to align the collection path with respect to the excitation beam. The orthogonality of the excitation and detection modes enables resonant excitation of a single QD with negligible laser scattering background.

Resonant excitation of a single self-assembled quantum dot can be achieved using an excitation mode orthogonal to the fluorescence collection mode. We demonstrate a method using the waveguide and Fabry-Perot modes of a planar microcavity surrounding the quantum dots. The method allows complete freedom in the detection polarization.

Resonanz-Fluoreszenz ein InGaAs Quantum Dot in einem planaren Hohlraum mit orthogonalen Erregung und Erkennung

The ability to perform simultaneous resonant excitation and fluorescence detection is important for quantum optical measurements of quantum dots (QDs). ...

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.

Fertigung-Verfahren und Doppelbrechung Messungen für die Gestaltung von magnetisch reagieren Lanthanoid-Ionen chelatisierenden Phospholipid-Baugruppen

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

Atmospheric Pressure Fabrication of Large-Sized Single-Layer Rectangular SnSe Flakes

Tin selenide (SnSe) belongs to the family of layered metal chalcogenide materials with a buckled structure like phosphorene, and has shown potential for applications in two-dimensional nanoelectronics devices. Although many methods to synthesize SnSe nanocrystals have been developed, a simple way to fabricate large-sized single-layer SnSe flakes remains a great challenge. Herein, we show the experimental method to directly grow large-sized single-layer rectangular SnSe flakes on commonly used SiO2/Si insulating substrates using a straightforward two-step fabrication method in an atmospheric pressure quartz tube furnace system. The single-layer rectangular SnSe flakes with an average thickness of ~6.8 &#197; and lateral dimensions of about 30 &#181;m &#215; 50 &#181;m were fabricated by a combination of vapor transport deposition technique and nitrogen etching route. We characterized the morphology, microstructure, and electrical properties of the rectangular SnSe flakes and obtained excellent crystallinity and good electronic properties. This article about the two-step fabrication method can help researchers grow other similar two-dimensional, large-sized, single-layer materials using an atmospheric pressure system.

A protocol is presented demonstrating a two-step fabrication technique to grow large-sized single-layer rectangular shaped SnSe flakes on low-cost SiO2/Si dielectrics wafers in an atmospheric pressure quartz tube furnace system.

Atmosphärendruck-Herstellung von großformatigen Einzellagen-rechteckige SnSe Flocken

Tin selenide (SnSe) belongs to the family of layered metal chalcogenide materials with a buckled structure like phosphorene, and has shown potential for ...

Cutting Procedures, Tensile Testing, and Ageing of Flexible Unidirectional Composite Laminates

Many body armor designs incorporate unidirectional (UD) laminates. UD laminates are constructed of thin (&#60;0.05 mm) layers of high-performance yarns, where the yarns in each layer are oriented parallel to each other and held in place using binder resins and thin polymer films. The armor is constructed by stacking the unidirectional layers in different orientations. To date, only very preliminary work has been performed to characterize the ageing of the binder resins used in unidirectional laminates and the effects on their performance. For example, during the development of the conditioning protocol used in the National Institute of Justice Standard-0101.06, UD laminates showed visual signs of delamination and reductions in V50, which is the velocity at which half of the projectiles are expected to perforate the armor, after ageing. A better understanding of the material property changes in UD laminates is necessary to comprehend the long-term performance of armors constructed from these materials. There are no current standards recommended for mechanically interrogating unidirectional (UD) laminate materials. This study explores methods and best practices for accurately testing the mechanical properties of these materials and proposes a new test methodology for these materials. Best practices for ageing these materials are also described.

The goal of the study was to develop protocols to prepare consistent specimens for accurate mechanical testing of high-strength aramid or ultra-high-molar-mass polyethylene-based flexible unidirectional composite laminate materials and to describe protocols for performing artificial ageing on these materials.

Schneidverfahren, Zugprüfung und Alterung flexibler unidirektionaler Verbundlaminate

Many body armor designs incorporate unidirectional (UD) laminates. UD laminates are constructed of thin (&#60;0.05 mm) layers of high-performance yarns, ...