Research reported in this publication was supported by a University of Houston New Faculty Grant, a seed grant from the Texas Center for Superconductivity, and the American Chemical Society Petroleum Research Fund (52537-DNI).

1. Preparation of Colloid-polymer Mixtures
Note: This protocol uses poly(methyl methacrylate) (PMMA) particles, sterically stabilized using poly (12-hydroxystearic acid) and labeled with a fluorescent dye (such as Nile Red, rhodamine B, or fluorescein), that were synthesized following a standard recipe52.
<ol>
	<li>Prepare a 3:1 w/w mixture of cyclohexyl bromide&#160;(CXB) and decahydronaphthalene (DHN) as a stock solvent. This mixture nearly matches the density and index of refraction of the particles. Add an organic salt, tetrabutylammonium chloride (TBAC)46, to the solvent at a concentration of 1.5 mM to partially screen the charges on the particles.</li>
	<li>To precisely determine the density of the particles, prepare a suspension at approximate particle volume fraction &#934; = 0.10 in the CXB:DHN solvent. Centrifuge the suspension at 800 x g for 75 min and add CXB or DHN dropwise to improve the buoyancy matching. In these experiments, the density of the PMMA particles was measured to be &#961; = 1.223 g/ml.</li>
	<li>Prepare a concentrated stock suspension of PMMA particles (here, &#934; = 0.40) in the CXB:DHN solvent mixture.</li>
	<li>Prepare a concentrated solution of linear polystyrene (PS) in the CXB:DHN solvent mixture. Here, a solution of PS of molecular weight Mw &#8776; 3,000,000 (radius of gyration rg = 15 nm) is prepared at concentration cp &#8776; 50 mg/ml.</li>
	<li>Mix appropriate weights of the particle, polymer, and solvent stock mixtures to formulate suspensions at the desired concentrations of particles and polymers. 
	Note: Here, suspensions of monodispersed particles are prepared at constant colloid volume fraction &#934; = 0.15 and variable polymer concentration in the free volume53 cp = 0&#8211;25 mg/ml, and bidispersed suspensions containing two sizes of colloidal particles, with each size bearing a distinct fluorescent label, are prepared at fixed total colloid volume fraction &#934; = 0.15, volume fraction ratio of small particles r = 0.50, and polymer concentration in the free volume of 5 or 25 mg/ml.</li>
	<li>After each suspension is prepared, add CXB or DHN dropwise and centrifuge the samples at 800 x g for at least 75 min to confirm that the particles and clusters within the suspension remain buoyancy matched.</li>
	<li>Equilibrate all samples for at least 24 hr prior to imaging experiments.</li>
</ol>
2. Quiescent Sample Experiments: Phase Behavior
<ol>
	<li>To determine the bulk phase behavior, fabricate rectangular chambers from glass coverslips (Figure 1a). For the colloid-polymer mixtures in this study, chambers of thickness h = 1 mm (set by the thickness of a microscope slide) give bulk behavior.</li>
	<li>To access multiple confinements in a single microscopy experiment, fabricate thin wedge-shaped chambers, using a single coverslip as a spacer on one wedge (Figure 1b). The opening angle of the chamber is &#60;0.5&#176;, so that in a single field of view the walls are very nearly parallel. A representative chamber allows access to confinement thicknesses of h = 6 to &#62;100 &#181;m.</li>
	<li>Build chambers on a coverslip base for imaging on an inverted microscope and seal with UV-curable epoxy, which does not dissolve in the CXB-DHN solvent mixture.</li>
	<li>Image samples using a confocal microscope. This protocol demonstrates imaging with a line-scanning confocal attached to an inverted microscope equipped with a 100X oil immersion lens of numerical aperture NA = 1.40.</li>
	<li>Excite the dyes using a laser source. Here wavelengths &#955; = 491 or 561 nm are used to excite the fluorescein and rhodamine/Nile Red dyes, respectively.</li>
	<li>In the point-scanning system, generate an image by rapidly scanning the focal point across the sample (in the x-y plane) using the confocal software. A two-dimensional image of 512 pixels x 512 pixels, covering approximately 50 &#956;m x 50 &#956;m, can be acquired in 1/32 sec. Improve the image quality by averaging multiple images or increasing the acquisition time.</li>
	<li>Locate the bottom of the chamber (z = 0), for example by focusing on particles adhered to its bottom. In this setup, the height (z) increases with increasing focus into the chamber.</li>
	<li>As an example, characterize the effect of confinement on the dynamics of the particles by acquiring a 2-D time series of images (in the x-y plane) at the midplane of the chamber. In a typical experiment, 500 images of dimension 512 pixels x 512 pixels are acquired at a frame rate of 1 frame/sec (time spacing &#8710;t = 1 sec).</li>
	<li>As a second example, characterize the 3-D structure of particles by acquiring a three-dimensional series of images (x,y,z). In a typical experiment, two-dimensional images (512 pixels x 512 pixels) are acquired at multiple z positions within the chamber, with a constant spacing of &#8710;z = 0.2 &#181;m between consecutive images set by a piezo. A volume stack covering a thickness of h = 30 &#181;m thus contains 151 images.</li>
	<li>Locate and track particles over time in 2-D or 3-D using particle-tracking software written in IDL23,54-56, MATLAB57,58, LabView59, or Python60. These algorithms typically allow the centers of the particles to be resolved within 40&#8211;50 nm. Successful particle tracking requires that the particles move less than the interparticle spacing between consecutive frames.</li>
	<li>From the particle positions, calculate structural and dynamic metrics. Three convenient metrics shown here are the 3-D pair correlation function g(r)61, the 2-D mean-squared displacement (MSD)58,62, and the 2-D self part of the van Hove correlation function Gs(x,t)58. The latter two metrics can be also calculated in 3-D.</li>
</ol>
3. Flowing Experiments: Flow Properties
<ol>
	<li>Fabricate a simple flow cell using a glass microcapillary with square cross-section (100 &#956;m x 100 &#956;m) that is affixed to Teflon tubing. Use glass coverslips to support the capillary and provide mechanical rigidity, as shown in the schematic in Figure 7.</li>
	<li>Load the colloid-polymer mixture into a glass syringe. Attach the syringe to a syringe pump or a pneumatic fluid dispensing system.</li>
	<li>Mount the flow cell setup onto the inverted microscope. Keep the syringe, flow cell, and outlet at the same height to minimize the effect of gravity on the flow profile.</li>
	<li>Control the flow rate of the suspension through the flow cell by the volumetric flow rate (for the syringe pump) or the applied pressure (for the pressure box). The average velocity of the suspension in the microchannel also depends upon the suspension formulation. Typical values of the maximum velocity in the square microchannel measured here are 200&#8211;2,000 &#956;m/sec.</li>
	<li>During flow, acquire a 2-D confocal time series at fast frame rates. Here, 500 images of dimension 512 pixels x 512 pixels are acquired at 32 frames/sec (time spacing &#916;t = 1/32 sec) at different heights above the bottom of the microchannel (z = 0 &#181;m) ranging from z = 5&#8211;50 &#181;m. Each image covers roughly half of the lateral dimension (y) of the microchannel, as shown in the inset to Figure 7. If the particles appear elliptical, increase the frame rate of acquisition.</li>
	<li>As in quiescent experiments, locate the particles in 2-D using standard algorithms for locating and tracking particles in IDL or MATLAB. For slow flows, in which particles move less than the average interparticle distance between frames, use tracking algorithms to obtain the trajectories.</li>
	<li>Use image correlation to calculate the velocity profiles for fast flows.
	<ol>
		<li>Subdivide the image into horizontal images of constant height (y) along the direction of flow (x). For two sequential images I1(x,y) and I2(x,y) shift the latter image by a factor &#916;x and then calculate the cross-covariance between I1(x,y) and I2(x+&#916;x,y).</li>
		<li>Identify the peak position of the histogram of &#916;x values that maximize the cross-covariance between each pair of images to obtain the mean advection velocity at each lateral position y. If this distribution is not strongly peaked, acquire images at a faster frame rate.</li>
	</ol>
	</li>
</ol>

The authors have nothing to disclose.

Colloidal suspensions are widely studied as models for confined phase behavior, because micron-sized colloidal particles exhibit significantly slower dynamics than atoms and molecules and thus can be readily imaged and tracked over time10. For these fundamental studies, understanding the effect of interparticle attractions on confined phase behavior offers the opportunity to explore phenomena such as capillary condensation and evaporation21,22,67. In addition, confined attractive suspensions appear ...

This paper demonstrates (a) confocal imaging of quiescent and flowing confined colloid-polymer mixtures in two and three dimensions and (b) particle-tracking and correlation analyses of the resultant images to obtain quantitative information on the phase behavior and flow properties.
Colloidal suspensions with attractive interparticle interactions appear ubiquitously in technological applications as materials for directed assembly1-3, drug delivery4, improved hydrocarbon recovery5-7, and energy storage8. A common feature of these applications is that the particles must be flowed through fine geometries, such as nozzles, print heads, microchannels, or porous media, and/or be shaped into thin films or rods. Techniques used to probe the structure of micron-sized colloids in confined geometries, including electron microscopy17,18, x-ray microscopy19, and laser-diffraction microscopy20, can be used to measure the structure and dynamics of particles on the microscale. These techniques, however, do not allow access to the trajectories of individual particles, from which structural and dynamic metrics can be computed for direct comparison to numerical simulations21,22.
Confocal microscopy is a variant of fluorescence microscopy that enables imaging of thin sections of a fluorescent sample. For colloidal science10, this technique is particularly useful for imaging deep within dense suspensions or in three dimensions. Particle-tracking algorithms23 applied to two- or three-dimensional time series of confocal micrographs yield the trajectories of all visible particles. As a result, the combination of confocal microscopy and particle-tracking has been applied to study the phase behavior, structure, and dynamics of colloidal suspensions, including ordered crystals24-27 and disordered glasses28-31 and gels32-35.
Other image analysis algorithms can be applied to measure particle dynamics from time series of confocal micrographs. For example, diffusive particle dynamics can be studied by analyzing the fluctuations in intensity over time using confocal differential dynamic microscopy36. When the particle displacements are larger than the interparticle spacing, image correlation37 based on particle image&#160;velocimetry38-40 can be applied to measure velocity profiles of the particles. The combination of tracking and correlation algorithms has allowed colloidal dynamics to be measured in systems undergoing slow and fast flow11-16,41-45.
We use colloid-polymer mixtures as models for attractive colloidal suspensions9. In these mixtures, the range and strength of the attractive interparticle potential are controlled via the ratio of the polymer radius of gyration to the particle radius&#160;and the concentration of the polymer and the electrostatic repulsion is controlled via the addition of a monovalent&#160;organic salt46. Because the interparticle interactions can be carefully tuned, the solidification of these mixtures has been extensively studied with confocal microscopy 34,47-51.
Here we demonstrate confocal imaging and image analysis37 of quiescent and flowing colloid-polymer mixtures, in which the colloid volume fraction is held fixed at &#934; = 0.15, that probe the effect of confinement on the phase behavior and flow properties of these mixtures. These techniques are widely applicable to particulate systems that are refractive index-matched and in which the particles and/or solvent can be labeled with a fluorescent dye.

<table border="0" cellpadding="0" cellspacing="0" style="width:752px;" width="751">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Name of Material/ Equipment</td>
			<td style="width:103px;">Company</td>
			<td style="width:119px;">Catalog Number</td>
			<td style="width:315px;">Comments/Description</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Cyclohexyl bromide</td>
			<td style="width:103px;">Sigma Aldrich</td>
			<td style="width:119px;">135194</td>
			<td style="width:315px;">CAS Number&#160; 108-85-0, Molecular wt. =163.06, Used in stock solvent</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Decahydronapthalene</td>
			<td style="width:103px;">Sigma Aldrich</td>
			<td style="width:119px;">D251</td>
			<td style="width:315px;">CAS Number 91-17-8, Molecular wt. = 138.25, Used in stock solvent</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Nile Red</td>
			<td style="width:103px;">Sigma Aldrich</td>
			<td style="width:119px;">72485</td>
			<td style="width:315px;">Fluorescent dye</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Fluorescein 5(6)-isothiocyanate</td>
			<td style="width:103px;">Sigma Aldrich</td>
			<td style="width:119px;">F3651</td>
			<td style="width:315px;">Fluorescent dye</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Rhodamine B</td>
			<td style="width:103px;">Sigma Aldrich</td>
			<td style="width:119px;">83689</td>
			<td style="width:315px;">Fluorescent dye</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Dynamic Light Scattering&#160;</td>
			<td style="width:103px;">Brookhaven Instruments</td>
			<td style="width:119px;">BI-APD</td>
			<td style="width:315px;">DLS equipment used for particle size measurement</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Polystyrene&#160;</td>
			<td style="width:103px;">Varian/Agilent</td>
			<td style="width:119px;">PL20138-23</td>
			<td style="width:315px;">Polystyrene (polymer) for inducing depletion attraction</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">tetrabutyl(ammonium chloride) (TBAC)</td>
			<td style="width:103px;">Sigma Aldrich</td>
			<td style="width:119px;">86870</td>
			<td style="width:315px;">monovalent salt</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Cover slips</td>
			<td style="width:103px;">Fisher Scientific</td>
			<td style="width:119px;">12-518-210&#160;</td>
			<td style="width:315px;">48&#10761;65 mm</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Cover slips</td>
			<td style="width:103px;">Fisher Scientific</td>
			<td style="width:119px;">12-540B</td>
			<td style="width:315px;">22&#10761;22 mm</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">UV Adhesive</td>
			<td style="width:103px;">Norland Adhesive</td>
			<td style="width:119px;">NOA 68T</td>
			<td style="width:315px;">Part Number 68T01 (UV cured adhesive)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">VT Eye</td>
			<td style="width:103px;">Visitech</td>
			<td style="width:119px;">VT Eye</td>
			<td style="width:315px;">confocal scanner</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">VT Infinity</td>
			<td style="width:103px;">Visitech</td>
			<td style="width:119px;">VT Infinity</td>
			<td style="width:315px;">confocal scanner</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Microscope&#160;</td>
			<td style="width:103px;">Leica</td>
			<td style="width:119px;">DMI3000B</td>
			<td style="width:315px;">Inverted Microscope</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Centrifuge</td>
			<td style="width:103px;">Thermo Scientific&#160;</td>
			<td style="width:119px;">Sorvall ST 16</td>
			<td style="width:315px;">1-5000 rpm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Glass slides</td>
			<td style="width:103px;">VWR</td>
			<td style="width:119px;">48382-171</td>
			<td style="width:315px;">25&#10761;75 mm, 1.0 mm thick</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">microcapillary</td>
			<td style="width:103px;">Vitrocom</td>
			<td style="width:119px;">8510-100</td>
			<td style="width:315px;">0.1&#10761;0.1 mm square cross section, 100 mm length</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Teflon tubing</td>
			<td style="width:103px;">smallparts</td>
			<td style="width:119px;">SLTT 26-72</td>
			<td style="width:315px;">Zeus PTFE Sublite Wall Tubing 26 AWG .016&#34; ID x .0030&#34; Wall</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Epoxy</td>
			<td style="width:103px;">Devcon</td>
			<td style="width:119px;">DA051</td>
			<td style="width:315px;">5 minute epoxy</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Syringe</td>
			<td style="width:103px;">Micromate/Cadence</td>
			<td style="width:119px;">5004</td>
			<td style="width:315px;">glass syringe with metal luer lock tip</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Syringe tips&#160;</td>
			<td style="width:103px;">Nordson</td>
			<td align="right">7018462</td>
			<td style="width:315px;">32 GA precision tips&#160;</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Syringe pump&#160;</td>
			<td style="width:103px;">New Era Pump system Inc.&#160;</td>
			<td style="width:119px;">NE1002X</td>
			<td style="width:315px;">Programmable microfluidic pump (syringepump.com)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Weigh balance</td>
			<td style="width:103px;">Mettler Toledo</td>
			<td style="width:119px;">AB204-S</td>
			<td style="width:315px;">0.0001-220 g</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">PMMA particles</td>
			<td style="width:103px;">synthesized</td>
			<td style="width:119px;"></td>
			<td style="width:315px;">poly(methylmethacrylate) colloidal particles</td>
		</tr>
	</tbody>
</table>

confocal imaging of confined quiescent and flowing colloid-polymer mixtures

The behavior of confined colloidal suspensions with attractive interparticle interactions is critical to the rational design of materials for directed assembly1-3, drug delivery4, improved hydrocarbon recovery5-7, and flowable electrodes for energy storage8. Suspensions containing fluorescent colloids and non-adsorbing polymers are appealing model systems, as the ratio of the polymer radius of gyration to the particle radius&#160;and concentration of polymer control the range and strength of the interparticle attraction, respectively. By tuning the polymer properties and the volume fraction of the colloids, colloid fluids, fluids of clusters, gels, crystals, and glasses can be obtained9.&#160;Confocal microscopy, a variant of fluorescence microscopy, allows an optically transparent and fluorescent sample to be imaged with high spatial and temporal resolution in three dimensions. In this technique, a small pinhole or slit blocks the emitted fluorescent light from regions of the sample that are outside the focal volume of the microscope optical system. As a result, only a thin section of the sample in the focal plane is imaged. This technique is particularly well suited to probe the structure and dynamics in dense colloidal suspensions at the single-particle scale: the particles are large enough to be resolved using visible light and diffuse slowly enough to be captured at typical scan speeds of commercial confocal systems10. Improvements in scan speeds and analysis algorithms have also enabled quantitative confocal imaging of flowing suspensions11-16,37.&#160;In this paper, we demonstrate confocal microscopy experiments to probe the confined phase behavior and flow properties of colloid-polymer mixtures. We first prepare colloid-polymer mixtures that are density- and refractive-index matched. Next, we report a standard protocol for imaging quiescent dense colloid-polymer mixtures under varying confinement in thin wedge-shaped cells. Finally, we demonstrate a protocol for imaging colloid-polymer mixtures during microchannel flow.

To demonstrate confocal imaging and particle-tracking, we investigated the effect of confinement on the phase behavior of colloid-polymer mixtures63-65. For these experiments the colloid diameter was 2a = 0.865 &#956;m. The colloid volume fraction was fixed at &#934; = 0.15 and the concentration of polymer cp was varied from 0 to 23.6 mg/ml. Representative confocal images are shown in Figure 263, left column. From the particle positions obtained using tr...

Watch this Scientific Journal Video about Confocal Imaging of Confined Quiescent and Flowing Colloid-polymer Mixtures at JoVE.com

Confocal Imaging of Confined Quiescent and Flowing Colloid-polymer Mixtures

Confocal microscopy is used to image quiescent and flowing colloid-polymer mixtures, which are studied as model systems for attractive suspensions. Image analysis algorithms are used to calculate structural and dynamic metrics for the colloidal particles that measure changes due to geometric confinement.

The behavior of confined colloidal suspensions with attractive interparticle interactions is critical to the rational design of materials for directed ...

confocal-imaging-confined-quiescent-flowing-colloid-polymer

Research

JoVE Journal

Chemistry

12.1K Aufrufe.  University of Houston.  Die konfokale Mikroskopie ist mit Bild und fließende Ruhe Kolloid-Polymer-Mischungen, die als Modellsysteme für attraktive Suspensionen untersucht werden. Bildanalysealgorithmen werden verwendet, um strukturelle und dynamische Messgrößen für die kolloidalen Partikel, die aufgrund von geometrischen Änderungen Haft Messung berechnen. 

Serie: Confocal Imaging of Confined Quiescent and Flowing Colloid-polymer Mixtures

Synthesis of Immunotargeted Magneto-plasmonic Nanoclusters

Magnetic and plasmonic properties combined in a single nanoparticle provide a synergy that is advantageous in a number of biomedical applications including contrast enhancement in novel magnetomotive imaging modalities, simultaneous capture&#160;and detection of circulating tumor cells (CTCs),&#160;and multimodal molecular imaging combined with photothermal therapy of cancer cells. These applications have stimulated significant interest in development of protocols for synthesis of magneto-plasmonic nanoparticles with optical absorbance in the near-infrared (NIR) region and a strong magnetic moment. Here, we present a novel protocol for synthesis of such hybrid nanoparticles that is based on an oil-in-water microemulsion method. The unique feature of the protocol described herein is synthesis of magneto-plasmonic nanoparticles of various sizes from primary blocks which also have magneto-plasmonic characteristics. This approach yields nanoparticles with a high density of magnetic and plasmonic functionalities which are uniformly distributed throughout the nanoparticle volume. The hybrid nanoparticles can be easily functionalized by attaching antibodies through the Fc moiety leaving the Fab portion that is responsible for antigen binding available for targeting.

Here, we describe a protocol for synthesis of magneto-plasmonic nanoparticles with a strong magnetic moment and a strong near-infrared (NIR) absorbance. The protocol also includes antibody conjugation to the nanoparticles through the Fc moiety for various biomedical applications which require molecular specific targeting.

Magnetic and plasmonic properties combined in a single nanoparticle provide a synergy that is advantageous in a number of biomedical applications ...

Preparation and In Vitro Characterization of Dendrimer-based Contrast Agents for Magnetic Resonance Imaging

Paramagnetic complexes of gadolinium(III) with acyclic or macrocyclic chelates are the most commonly used contrast agents (CAs) for magnetic resonance imaging (MRI). Their purpose is to enhance the relaxation rate of water protons in tissue, thus increasing the MR image contrast and the specificity of the MRI measurements. Current clinically approved contrast agents are low molecular weight molecules that are rapidly cleared from the body. The use of dendrimers as carriers of paramagnetic chelators can play an important role in the future development of more efficient MRI contrast agents. Specifically, the increase in local concentration of the paramagnetic species results in a higher signal contrast. Furthermore, this CA provides a longer tissue retention time due to its high molecular weight and size. Here, we demonstrate a convenient procedure for the preparation of macromolecular MRI contrast agents based on poly(amidoamine) (PAMAM) dendrimers with monomacrocyclic DOTA-type chelators (DOTA &#8211; 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate). The chelating unit was appended by exploiting the reactivity of the isothiocyanate (NCS) group towards the amine surface groups of the PAMAM dendrimer to form thiourea bridges. Dendrimeric products were purified and analyzed by means of nuclear magnetic resonance spectroscopy, mass spectrometry, and elemental analysis. Finally, high resolution MR images were recorded and the signal contrasts obtained from the prepared dendrimeric and the commercially available monomeric agents were compared.

Preparation and In Vitro Characterization of Dendrimer-based Contrast Agents for Magnetic Resonance Imaging

This protocol describes the preparation and characterization of a dendrimeric magnetic resonance imaging (MRI) contrast agent that carries cyclen-based macrocyclic chelates coordinating paramagnetic gadolinium ions. In a series of MRI experiments in vitro, this agent produced an amplified MRI signal when compared to the commercially available monomeric analogue.

Paramagnetic complexes of gadolinium(III) with acyclic or macrocyclic chelates are the most commonly used contrast agents (CAs) for magnetic resonance ...

Direct Imaging of Laser-driven Ultrafast Molecular Rotation

We present a method for visualizing laser-induced, ultrafast molecular rotational wave packet dynamics. We have developed a new 2-dimensional Coulomb explosion imaging setup in which a hitherto-impractical camera angle is realized. In our imaging technique, diatomic molecules are irradiated with a circularly polarized strong laser pulse. The ejected atomic ions are accelerated perpendicularly to the laser propagation. The ions lying in the laser polarization plane are selected through the use of a mechanical slit and imaged with a high-throughput, 2-dimensional detector installed parallel to the polarization plane. Because a circularly polarized (isotropic) Coulomb exploding pulse is used, the observed angular distribution of the ejected ions directly corresponds to the squared rotational wave function at the time of the pulse irradiation. To create a real-time movie of molecular rotation, the present imaging technique is combined with a femtosecond pump-probe optical setup in which the pump pulses create unidirectionally rotating molecular ensembles. Due to the high image throughput of our detection system, the pump-probe experimental condition can be easily optimized by monitoring a real-time snapshot. As a result, the quality of the observed movie is sufficiently high for visualizing the detailed wave nature of motion. We also note that the present technique can be implemented in existing standard ion imaging setups, offering a new camera angle or viewpoint for the molecular systems without the need for extensive modification.

We present a protocol for creating a real-time movie of a molecular rotational wave packet using a high-resolution Coulomb explosion imaging setup.

We present a method for visualizing laser-induced, ultrafast molecular rotational wave packet dynamics. We have developed a new 2-dimensional Coulomb ...

Measurements of Long-range Electronic Correlations During Femtosecond Diffraction Experiments Performed on Nanocrystals of Buckminsterfullerene

The precise details of the interaction of intense X-ray pulses with matter are a topic of intense interest to researchers attempting to interpret the results of femtosecond X-ray free electron laser (XFEL) experiments. An increasing number of experimental observations have shown that although nuclear motion can be negligible, given a short enough incident pulse duration, electronic motion cannot be ignored. The current and widely accepted models assume that although electrons undergo dynamics driven by interaction with the pulse, their motion could largely be considered &#39;random&#39;. This would then allow the supposedly incoherent contribution from the electronic motion to be treated as a continuous background signal and thus ignored. The original aim of our experiment was to precisely measure the change in intensity of individual Bragg peaks, due to X-ray induced electronic damage in a model system, crystalline C60. Contrary to this expectation, we observed that at the highest X-ray intensities, the electron dynamics in C60 were in fact highly correlated, and over sufficiently long distances that the positions of the Bragg reflections are significantly altered. This paper describes in detail the methods and protocols used for these experiments, which were conducted both at the Linac Coherent Light Source (LCLS) and the Australian Synchrotron (AS) as well as the crystallographic approaches used to analyse the data.

We describe an experiment designed to probe the electronic damage induced in nanocrystals of Buckminsterfullerene (C60) by intense, femtosecond pulses of X-rays. The experiment found that, surprisingly, rather than being stochastic, the X-ray induced electron dynamics in C60 are highly correlated, extending over hundreds of unit cells within the crystals1.

The precise details of the interaction of intense X-ray pulses with matter are a topic of intense interest to researchers attempting to interpret the ...

Separation of Aldehydes and Reactive Ketones from Mixtures Using a Bisulfite Extraction Protocol

The purification of organic compounds is an essential component of routine synthetic operations. The ability to remove contaminants into an aqueous layer by generating a charged structure provides an opportunity to use extraction as a simple purification technique. By combining the use of a miscible organic solvent with saturated sodium bisulfite, aldehydes and reactive ketones can be successfully transformed into charged bisulfite adducts that can then be separated from other organic components of a mixture by the introduction of an immiscible organic layer. Here, we describe a simple protocol for the removal of aldehydes, including sterically-hindered neopentyl aldehydes and some ketones, from chemical mixtures. Ketones can be separated if they are sterically unhindered cyclic or methyl ketones. For aliphatic aldehydes and ketones, dimethylformamide is used as the miscible solvent to improve removal rates. The bisulfite addition reaction can be reversed by basification of the aqueous layer, allowing for the re-isolation of the reactive carbonyl component of a mixture.

Here, we present a protocol to remove aldehydes and reactive ketones from mixtures by a liquid-liquid extraction protocol directly with saturated sodium bisulfite in a miscible solvent. This combined protocol is rapid and facile to perform. The aldehyde or ketone can be re-isolated by the basification of the aqueous layer.

The purification of organic compounds is an essential component of routine synthetic operations. The ability to remove contaminants into an aqueous layer ...

Regioselective O-Glycosylation of Nucleosides via the Temporary 2',3'-Diol Protection by a Boronic Ester for the Synthesis of Disaccharide Nucleosides

Disaccharide nucleosides, which consist of disaccharide and nucleobase moieties, have been known as a valuable group of natural products having multifarious bioactivities. Although chemical O-glycosylation is a commonly beneficial strategy to synthesize disaccharide nucleosides, the preparation of substrates such as glycosyl donors and acceptors requires&#160;tedious protecting&#160;group manipulations and a purification at each synthetic step. Meanwhile, several research groups have reported that boronic and borinic esters serve as a protecting or activating group of carbohydrate derivatives to achieve the regio- and/or stereoselective acylation, alkylation, silylation, and glycosylation. In this article, we demonstrate the procedure for the regioselective O-glycosylation of unprotected ribonucleosides utilizing boronic acid. The esterification of 2&#39;,3&#39;-diol of ribonucleosides with boronic acid makes the temporary protection of diol, and, following O-glycosylation with a glycosyl donor in the presence of p-toluenesulfenyl chloride and silver triflate, permits the regioselective reaction of the 5&#39;-hydroxyl group to afford the disaccharide nucleosides. This method could be applied to various nucleosides, such as guanosine, adenosine, cytidine, uridine, 5-metyluridine, and 5-fluorouridine. This article and the accompanying video represent&#160;useful (visual) information for the O-glycosylation of unprotected nucleosides and their analogs for the synthesis of not only disaccharide nucleosides, but also a variety of biologically relevant derivatives.

Regioselective O-Glycosylation of Nucleosides via the Temporary 2&#039;,3&#039;-Diol Protection by a Boronic Ester for the Synthesis of Disaccharide Nucleosides

Here, we present protocols for the synthesis of disaccharide nucleosides by the regioselective O-glycosylation of ribonucleosides via a temporary protection of their 2&#39;,3&#39;-diol moieties utilizing a cyclic boronic ester. This method applies to several unprotected nucleosides such as adenosine, guanosine, cytidine, uridine, 5-methyluridine, and 5-fluorouridine to give corresponding disaccharide nucleosides.

Disaccharide nucleosides, which consist of disaccharide and nucleobase moieties, have been known as a valuable group of natural products having ...

Automation of a Positron-emission Tomography (PET) Radiotracer Synthesis Protocol for Clinical Production

The development of new positron-emission tomography (PET) tracers is enabling researchers and clinicians to image an increasingly wide array of biological targets and processes. However, the increasing number of different tracers creates challenges for their production at radiopharmacies. While historically it has been practical to dedicate a custom-configured radiosynthesizer and hot cell for the repeated production of each individual tracer, it is becoming necessary to change this workflow. Recent commercial radiosynthesizers based on disposable cassettes/kits for each tracer simplify the production of multiple tracers with one set of equipment by eliminating the need for custom tracer-specific modifications. Furthermore, some of these radiosynthesizers enable the operator to develop and optimize their own synthesis protocols in addition to purchasing commercially-available kits. In this protocol, we describe the general procedure for how the manual synthesis of a new PET tracer can be automated on one of these radiosynthesizers and validated for the production of clinical-grade tracers. As an example, we use the ELIXYS radiosynthesizer, a flexible cassette-based radiochemistry tool that can support both PET tracer development efforts, as well as routine clinical probe manufacturing on the same system, to produce [18F]Clofarabine ([18F]CFA), a PET tracer to measure in vivo deoxycytidine kinase (dCK) enzyme activity. Translating a manual synthesis involves breaking down the synthetic protocol into basic radiochemistry processes that are then translated into intuitive chemistry &#34;unit operations&#34; supported by the synthesizer software. These operations can then rapidly be converted into an automated synthesis program by assembling them using the drag-and-drop interface. After basic testing, the synthesis and purification procedure may require optimization to achieve the desired yield and purity. Once the desired performance is achieved, a validation of the synthesis is carried out to determine its suitability for the production of the radiotracer for clinical use.

Automation of a Positron-emission Tomography PET Radiotracer Synthesis Protocol for Clinical Production

Positron-emission tomography (PET) imaging sites that are involved in multiple early clinical research trials need robust and versatile radiotracer manufacturing capabilities. Using the radiotracer [18F]Clofarabine as an example, we illustrate how to automate the synthesis of a radiotracer using a flexible, cassette-based radiosynthesizer and validate the synthesis for clinical use.

The development of new positron-emission tomography (PET) tracers is enabling researchers and clinicians to image an increasingly wide array of biological ...

Imaging Corrosion at the Metal-Paint Interface Using Time-of-Flight Secondary Ion Mass Spectrometry

Corrosion developed at the paint and aluminum (Al) metal-paint interface of an aluminum alloy is analyzed using time-of-flight secondary ion mass spectrometry (ToF-SIMS), illustrating that SIMS is a suitable technique to study the chemical distribution at a metal-paint interface. The painted Al alloy coupons are immersed in a salt solution or exposed to air only. SIMS provides chemical mapping and 2D molecular imaging of the interface, allowing direct visualization of the morphology of the corrosion products formed at the metal-paint interface and mapping of the chemical after corrosion occurs. The experimental procedure of this method is presented to provide technical details to facilitate similar research and highlight pitfalls that may be encountered during such experiments.

Time-of-flight secondary ion mass spectrometry is applied to demonstrate the chemical mapping and corrosion morphology at the metal-paint interface of an aluminum alloy after being exposed to a salt solution compared with a specimen exposed to air.

Corrosion developed at the paint and aluminum (Al) metal-paint interface of an aluminum alloy is analyzed using time-of-flight secondary ion mass ...

Technical Aspect of the Automated Synthesis and Real-Time Kinetic Evaluation of [11C]SNAP-7941

Positron emission tomography (PET) is an essential molecular imaging technique providing insights into pathways and using specific targeted radioligands for in vivo investigations. Within this protocol, a robust and reliable remote-controlled radiosynthesis of [11C]SNAP-7941, an antagonist to the melanin-concentrating hormone receptor 1, is described. The radiosynthesis starts with cyclotron produced [11C]CO2 that is subsequently further reacted via a gas-phase transition to [11C]CH3OTf. Then, this reactive intermediate is introduced to the precursor solution and forms the respective radiotracer. Chemical as well as the radiochemical purity are determined by means of RP-HPLC, routinely implemented in the radiopharmaceutical quality control process. Additionally, the molar activity is calculated as it is a necessity for the following real-time kinetic investigations. Furthermore, [11C]SNAP-7941 is applied to MDCKII-WT and MDCKII-hMDR1 cells for evaluating the impact of P-glycoprotein (P-gp) expression on cell accumulation. For this reason, the P-gp expressing cell line (MDCKII-hMDR1) is either used without or with blocking prior to experiments by means of the P-gp substrate (&#177;)-verapamil and the results are compared to the ones observed for the wildtype cells. The overall experimental approach demonstrates the importance of a precise time-management that is essential for every preclinical and clinical study using PET tracers radiolabelled with short-lived nuclides, such as carbon-11 (half-life: 20 min).

Technical Aspect of the Automated Synthesis and Real-Time Kinetic Evaluation of [11C]SNAP-7941

Here, we represent a protocol for the fully automated radiolabelling of [11C]SNAP-7941 and the analysis of the real-time kinetics of this PET-tracer on P-gp expressing and non-expressing cells.

Positron emission tomography (PET) is an essential molecular imaging technique providing insights into pathways and using specific targeted radioligands ...

Resolving Water, Proteins, and Lipids from In Vivo Confocal Raman Spectra of Stratum Corneum through a Chemometric Approach

Development of this in vivo confocal Raman spectroscopic method enables the direct measurement of water, proteins, and lipids with depth resolution in human subjects. This information is very important for skin-related diseases and characterizing skin care product performance. This protocol illustrates a method for confocal Raman spectra collection and the subsequent analysis of the spectral dataset leveraging chemometrics. The goal of this method is to establish a standard protocol for data collection and provide general guidance for data analysis. Preprocessing (e.g., removal of outlier spectra) is a critical step when processing large datasets from clinical studies. As an example, we provide guidance based on prior knowledge of a dataset to identify the types of outliers and develop specific strategies to remove them. A principal component analysis is performed, and the loading spectra are compared with spectra from reference materials to select the number of components used in the final multivariate curve resolution (MCR) analysis. This approach is successful for extracting meaningful information from a large spectral dataset.

Here, we present a protocol for collection of confocal Raman spectra from human subjects in clinical studies combined with chemometric approaches for spectral outlier removal and the subsequent extraction of key features.

Development of this in vivo confocal Raman spectroscopic method enables the direct measurement of water, proteins, and lipids with depth resolution in ...