Este trabajo fue apoyado por JCO A * STAR Investigatorship conceder (proyecto Nº 1437 00135), A * STAR ciencia e Ingeniería Consejo Sector público financiación de la investigación (proyecto no. 1421200076) y un proyectos de investigación conjuntos de JSP-NUS conceden (WBS R143-000-611-133).

<ol>
	<li>Figuerola, 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=End-to-End+Assembly+of+Shape-Controlled+Nanocrystals+via+a+Nanowelding+Approach+Mediated+by+Gold+Domains.">End-to-End Assembly of Shape-Controlled Nanocrystals via a Nanowelding Approach Mediated by Gold Domains.</a> Adv. Mat. 21, 550-554 (2009).</li><li>Tang, Z., Kotov, N. A., Giersig, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spontaneous+Organization+of+Single+CdTe+Nanoparticles+into+Luminescent+Nanowires.">Spontaneous Organization of Single CdTe Nanoparticles into Luminescent Nanowires.</a> Science. 297, 237-240 (2002).</li><li>Kim, D., Kim, W. D., Kang, M. S., Kim, S. -. H., Lee, D. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-Organization+of+Nanorods+into+Ultra-Long+Range+Two-Dimensional+Monolayer+End-to-End+Network.">Self-Organization of Nanorods into Ultra-Long Range Two-Dimensional Monolayer End-to-End Network.</a> Nano Lett. 15, 714-720 (2015).</li><li>Schliehe, 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=Ultrathin+PbS+Sheets+by+Two-Dimensional+Oriented+Attachment.">Ultrathin PbS Sheets by Two-Dimensional Oriented Attachment.</a> Science. 329, 550-553 (2010).</li><li>Chakrabortty, 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=Facet+to+facet+Linking+of+Shape+Anisotropic+Inorganic+Nanocrystals+with+Site+Specific+and+Stoichiometric+Control.">Facet to facet Linking of Shape Anisotropic Inorganic Nanocrystals with Site Specific and Stoichiometric Control.</a> Nano Lett. 16, 6431-6436 (2016).</li><li>Leatherdale, C. A., Woo, W. K., Mikulec, F. V., Bawendi, M. 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+Absorption+Cross+Section+of+CdSe+Nanocrystal+Quantum+Dots.">On the Absorption Cross Section of CdSe Nanocrystal Quantum Dots.</a> J Phys Chem B. 106, 7619-7622 (2002).</li><li>Dabbousi, B. O., 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=(CdSe)ZnS+Core-Shell+Quantum+Dots:+Synthesis+and+Characterization+of+a+Size+Series+of+Highly+Luminescent+Nanocrystallites.">(CdSe)ZnS Core-Shell Quantum Dots: Synthesis and Characterization of a Size Series of Highly Luminescent Nanocrystallites.</a> J Phys Chem B. 101, 9463-9475 (1997).</li><li>Carbone, L., 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=Synthesis+and+Micrometer-Scale+Assembly+of+Coilloidal+CdSe/CdS+Nanorods+Prepared+by+Seeded+Grwoth+Approach.">Synthesis and Micrometer-Scale Assembly of Coilloidal CdSe/CdS Nanorods Prepared by Seeded Grwoth Approach.</a> Nano Lett. 7, 2942-2950 (2007).</li><li>Shaviv, 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=Absorption+properties+of+Metal-Semiconductor+Hybrid+Nanoparticles.">Absorption properties of Metal-Semiconductor Hybrid Nanoparticles.</a> ACS Nano. 5, 4712-4719 (2011).</li><li>Lim, 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=Controlled+Synthesis+of+CdSe+Tetrapods+with+High+Morphological+Uniformity+by+the+Persistent+Kinetic+Growth+and+the+Halide-Mediated+Phase+Transformation.">Controlled Synthesis of CdSe Tetrapods with High Morphological Uniformity by the Persistent Kinetic Growth and the Halide-Mediated Phase Transformation.</a> Chem Mat. 25, 1443-1449 (2013).</li></ol>

No tenemos nada que revelar.

La vinculación técnica descrita en este trabajo permite cadmio forma anisotrópica calcógeno nanopartículas que pueden experimentar intercambio catiónico con Ag+ que se ensamblarán, faceta a faceta, en montajes como cadenas lineales o ramificadas redes. Fracaso para formar asambleas bien dispersos, extensa de nanopartículas enlazadas faceta a faceta suele ser debido a dos razones: () la ODPA no se dispersan bien en la solución que contiene NR, que puede ser abordada por sonicando la mezcla para la prescripción cantidad de tiempo que se detallan en el protocolo; o (ii) la concentración de Ag+ utilizada es no óptima. Cuando la concentración de Ag+ utilizada es demasiado baja, la mayoría de las nanopartículas de chalcogenide cadmio no sometidos a intercambio catiónico, dando como resultado poca o ninguna vinculación (como se describe en los Resultados de representante). Cuando la concentración de Ag+ utilizada es demasiado alta, varios dominios de forma de2S Ag en cada partícula, resultando en agregación severa sobre vinculación.
Nuestro enfoque hacia la faceta a faceta vinculación de forma anisotrópica nanopartículas inorgánicas actualmente está limitada a las nanopartículas de metal chalcogenide que pueden someterse a intercambio catiónico con Ag+ o Cu+ (no se muestra en este trabajo) bajo suaves de la reacción condiciones. Se está intentando ampliar el repertorio de materiales inorgánicos que puede vincularse directamente a través de nuestra estrategia sintética. Previamente demostramos que la faceta a faceta vinculada nanopartículas asambleas pueden someterse a otros procesos de intercambio catiónico y pueden ser transformados en otros materiales del semiconductor conservando su arquitectura vinculados5. Esto modifica procedimiento de vinculación, aunque más tedioso, puede ampliar significativamente la diversidad de los nanomateriales semiconductores que se reunió en asambleas faceta vinculada.
Porque las Asambleas de las nanopartículas de semiconductores vinculados están a faceta a faceta, electrónicamente están acoplados uno al otro. Esto puede ser ventajoso para aplicaciones como solución procesada optoelectrónica, donde un problema importante es el transporte de carga pobre a través de ligandos que rodean las nanopartículas de semiconductores de aislamiento. Se necesitará más trabajo para evaluar la eficacia de asambleas de nanopartículas de semiconductores vinculados como el material activo en dispositivos optoelectrónicos.

La Asamblea dirigida del semiconductor coloidal NCs ofrece un camino sintético para la fabricación de nanoestructuras cuyas propiedades fisicoquímicas sean la suma colectiva de o radicalmente diferentes de sus individuales de bloques NC1 , 2 , 3 , 4. entre los diversos enfoques para ensamblaje de nanopartículas, el método de accesorio orientada - en que NCs son esencialmente fusionados entre sí - está parado hacia fuera como uno que permite el acoplamiento electrónico entre partículas. Sin embargo, convencional accesorio orientado típicamente requiere el delicado equilibrio de la partícula dipolo, ligando y las interacciones solvente-basó que son generalmente difíciles de ejecutar y hacer aplicable a diferentes sistemas de NC.
Recientemente hemos desarrollado un método de química húmeda de unirse covalentemente a cadmio forma anisotrópica calcógeno NCs introduciendo un intermedio reactivo inorgánico a través de un proceso de nucleación sitio selectivo. Posteriormente, las partículas están unidas por la fusión espontánea de los reactivos inorgánicos dominios intermedios5. Aunque la técnica aún se basa en un mecanismo orientado a conexión, hay mucho menos necesidad de considerar las interacciones entre partículas débiles, permitiendo más flexibilidad y control. La vinculación de cadmio forma anisotrópica calcógeno NCs se lleva a cabo primera convirtiendo sus facetas de punta a calcógeno plata mediante un proceso de intercambio catiónico parcial (en solución); Esto es seguido por la remoción selectiva de ligandos apaciguando la superficie. El NCs luego vienen juntos a través de la fusión de las facetas de chalcogenide plata expuestos, resultando en asambleas de cadmio calcógeno NCs ligadas end-to-end.
En este protocolo, se demuestra que la vinculación técnica puede aplicarse a una variedad de cadmio forma anisotrópica calcógeno NCs (es decir, semillas de CdSe CdS NRs y sembrado de CdSe CdSe NRs o TPs), que rinde lineares largas cadenas NR o TP muy ramificado redes. Estos resultados sugieren que la técnica puede extenderse a una amplia variedad de formas de NC y chalcogenides metálicos susceptibles de intercambio de catión plata.

<table><tbody><tr><td>Cadmium oxide (CdO), 99.5%</td><td>Sigma Aldrich</td><td></td><td>Highly toxic</td></tr><tr><td>Tri-n-octylphosphine oxide (TOPO), 90 % and 99%</td><td>Sigma Aldrich</td><td></td><td>Technical and analytical grade</td></tr><tr><td>Cadmium acetylacetonate (Cd(acac)&lt;sub&gt;2&lt;/sub&gt;), 99.9%</td><td>Sigma Aldrich</td><td></td><td>Highly toxic</td></tr><tr><td>Hexadecanediol (HDDO), 90%</td><td>Sigma Aldrich</td><td></td><td>Technical grade</td></tr><tr><td>1-octadecene (ODE), 90%</td><td>Sigma Aldrich</td><td></td><td>Technical grade</td></tr><tr><td>Dodecylamine (DDA), 98%</td><td>Sigma Aldrich</td><td></td><td>Toxic</td></tr><tr><td>Cadmium nitrate tetrahydrate ((CdNO&lt;sub&gt;3&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;.4H&lt;sub&gt;2&lt;/sub&gt;O), 98%</td><td>Sigma Aldrich</td><td></td><td>Highly toxic</td></tr><tr><td>Myristic acid (MA), 99%</td><td>Sigma Aldrich</td><td></td><td>Analytical grade</td></tr><tr><td>Octyl phosphonic acid (OPA), 97%</td><td>Sigma Aldrich</td><td></td><td>Analytical grade</td></tr><tr><td>Oleylamine (Oly), 70%</td><td>Sigma Aldrich</td><td></td><td>Technical grade</td></tr><tr><td>Hexadecyltrimethylammonium bromide (CTAB), 95%</td><td>Sigma Aldrich</td><td></td><td>Toxic</td></tr><tr><td>Selenium pellets (Se, 5 mm), 99.99%</td><td>Sigma Aldrich</td><td></td><td>Analytical grade</td></tr><tr><td>Hexadecylamine (HDA), 90%</td><td>Alfa Aesar</td><td></td><td>Technical grade, toxic</td></tr><tr><td>n-tetradecylphosphonic acid (TDPA), 98%&amp;nbsp;</td><td>Alfa Aesar</td><td></td><td>Analytical grade</td></tr><tr><td>Silver nitrate (AgNO&lt;sub&gt;3&lt;/sub&gt;), 99.9%</td><td>Alfa Aesar</td><td></td><td>Analytical grade</td></tr><tr><td>Oleic acid (OA), 90%</td><td>Alfa Aesar</td><td></td><td>Technical grade</td></tr><tr><td>Tri-n-octylphosphine (TOP), 97%</td><td>Strem</td><td></td><td>Analytical grade, toxic, air sensitive</td></tr><tr><td>n-hexylphosphonic acid (HPA), 97%</td><td>Strem</td><td></td><td>Analytical grade</td></tr><tr><td>n-octadecylphosphonic acid (ODPA), 97%</td><td>Strem</td><td></td><td>Analytical grade</td></tr><tr><td>Tellurium powder (Te), 99.9%</td><td>Strem</td><td></td><td>Air sensitive</td></tr><tr><td>Tri-n-butylphosphine (TBP), 99%</td><td>Strem</td><td></td><td>Analytical grade, highly toxic, air sensitive</td></tr><tr><td>Diisooctylphosphonic acid (DIPA), 90%</td><td>Fluka</td><td></td><td>Technical grade, toxic</td></tr></tbody></table>

facet-to-facet linking of shape-anisotropic colloidal cadmium chalcogenide nanostructures

Aquí, describimos un protocolo que permite de forma anisotrópica cadmio calcógeno nanocristales (NCs), como nanobarras (NRs) y tetrápodos (TPs), covalente y site-specifically vinculados a través de sus aspectos finales, dando como resultado polímeros como lineal o ramificado cadenas. El procedimiento de enlace comienza con un proceso de intercambio catiónico en la que las facetas de la final del calcógeno cadmio NCs se convierten primero a calcógeno plata. Esto es seguido por la eliminación selectiva de los ligandos en la superficie. Esto resulta en cadmio calcógeno NCs con calcógeno plata altamente reactivo extremo facetas que espontáneamente al con con mutuamente, estableciendo un apego de faceta a faceta entre partículas. A través de la juiciosa elección de las concentraciones de precursores, se puede producir una extensa red de NCs vinculados. Caracterización estructural de las NCs vinculados se lleva a cabo a través de baja y alta resolución microscopia electrónica de transmisión (TEM), así como energía-dispersivo espectroscopia de rayos x, que confirman la presencia de dominios de chalcogenide plata entre cadenas de cadmio calcógeno NCs.

Usando semillas de CdSe CdS NRs como modelo, como se ilustra en la figura 1(a), hemos demostrado que podemos utilizar un proceso de intercambio de Ag+ parcial específicamente transformar las facetas en los consejos NR para Ag2S. Las facetas de2S Ag son capsuladas por DDA, que reacciona con ODPA mediante una reacción ácido-base para formar una sal insoluble5. Esto hace que los ligandos de PDD deben retirarse de las facetas de2S Ag, haciendo que se fusionan entre sí al contacto y a la forma ligada a cadenas de NR, como se muestra en la figura 1(b). Para determinar si el individuo NRs se fusionan dentro de la cadena o simplemente se mantienen unidas por fuerzas de Van der Waals, se realizó análisis HRTEM en las regiones comunes. Como se ilustra en la figura 1(c), existe un dominio distinto en el contacto epitaxial con dos NRs. Un análisis FFT de la imagen HRTEM (recuadro de la figura 1(c)) revela la existencia de dos constantes diferentes enrejado que se puede atribuir a las facetas (001) de Ag2S y CdS. Además, punto de radiografía Energía-dispersivo Análisis de espectroscopía (EDX) en la región de acoplamiento prominente muestran la presencia de Ag y la ausencia de Cd (figura 1(d)), lo que corrobora nuestra noción de Ag2punta S semillas de CdSe CdS NRs puente vía la fusión de la Ag2 Dominios de S. El rendimiento y la naturaleza estadística del proceso de enlace se pueden visualizar mediante un histograma (figura 1(e)) que muestra el número de barras vinculados dentro de una cadena NR.
El mecanismo de vinculación fue divulgado previamente por Sabyasachi et al. 5 y no se describirá en detalle en este trabajo. Se observa que, sin la adición de ODPA, ninguna vinculación ocurre como se ve en la figura 2(a), según la opinión de que la adición de ODPA causa los ligandos superficie maternas de la punta de2S Ag para despegarse. Esto puede verse claramente en la figura 2(c), como muestra en el histograma para la reacción de una gran proporción de solo, disociados NRs. La presencia de dímeros podría deberse a residual que ODPA sobrante de la reacción de síntesis NR, lo que permite una pequeña cantidad de enlazar para ocurrir. Aparte de ODPA, la concentración de AgNO3 también fue encontrada para ser extremadamente importante, como se ilustra en la figura 2(b), donde sólo las cadenas cortas se obtuvieron con concentraciones no óptimas de AgNO3. Donde la concentración de Ag+ utilizada era demasiado baja, el histograma muestra que la distribución fue cargada pesadamente hacia longitudes más cortas de la cadena. De hecho, las estadísticas de enlaces para las cadenas que se muestra en la figura 2(b) característica de una proporción importante de dímeros, seguido de monómeros, como se ve en la figura 2(d).
Además de semillas de CdSe CdS NRs, demostramos que el Ag+-proceso vinculación mediada puede ampliarse a semillas de CdSe CdSe NRs y TPs, que se muestran en la figura 3(a) y (b), respectivamente. En las condiciones de reacción resumidas en la tabla 1, mostramos que podemos lograr redes encadenadas similares de semillas CdSe CdSe NRs y TPs, como se ejemplifica en la figura 3(c) y (d). Como en el caso de Ag2vinculado S semillas de CdSe CdS NRs, las nano-partículas CdSe CdSe semillas están vinculados mediante Ag2Se intermedios.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56009/56009fig1.jpg"> Figura 1. Caracterización de ligado semillas CdSe CdS NRs. (a) de baja resolución que muestra imagen TEM como había sintetizado con semillas de CdSe CdS NR. (b) baja resolución TEM imagen Ag2vinculado S semillas de CdSe CdS NRs. (c) alta resolución TEM (HRTEM) imagen de un solo conjunto entre dos NRs. recuadro es un Fast Fourier transforma (FFT) de la imagen HRTEM, mostrando dos puntos diferentes del enrejado que son atribuido a CD y Ag2S. (d) análisis EDX de punto en un punto de enlace único, confirmando su composición Ag2S. (e) histograma muestra la distribución de la cantidad de NRs por cadena en una típica muestra NR vinculada. <a href="//cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56009/56009fig1large.jpg" target="_blank">Haga clic aquí para ver una versión más grande de esta figura.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56009/56009fig2.jpg"> Figura 2 . Resultados de condiciones no óptimas de reacción. (a) imagen de TEM de semillas CdSe CdS NRs con puntas de2S de Ag que experimentaron el procedimiento enlace, con la excepción que no ODPA fue utilizado. (b) TEM imagen cadenas cortas de Ag2vinculado S semillas de CdSe CdS NRs cuando no se ha optimizado la concentración de Ag+ . (c) histograma muestra que la mayoría de las especies presentes son solo NRs cuando ODPA está ausente. (d) histograma mostrando que cuando la concentración de Ag+ no está optimizada, las cadenas sólo cortas están presentes. <a href="//cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56009/56009fig2large.jpg" target="_blank">Haga clic aquí para ver una versión más grande de esta figura.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56009/56009fig3.jpg"> Figura 3 . Extensión del proceso enlace a semillas de CdSe CdSe nanoestructuras. (a) baja resolución TEM imagen sintetizada como semillas de CdSe CdSe NRs. (b) Low-resolution TEM imagen sintetizada como semilla de CdSe CdSe TPs. (c) Low-resolution TEM imagen semillas CdSe CdSe NRs después enlazan a. (d) baja resolución TEM imagen el TPs de CdSe CdSe semillas después de la vinculación. <a href="//cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56009/56009fig3large.jpg" target="_blank">Haga clic aquí para ver una versión más grande de esta figura.</a>
<table fo:keep-together.within-page="1"><tbody>
<tr>
<td>Nanopartículas</td>
			<td>Concentración de solución NC (mM)</td>
			<td>Concentración de solución de Ag+ (mM)</td>
			<td>Revolvimiento de tiempo (horas)</td>
		</tr>
<tr>
<td>Sembrado de CdSe CdS NRs</td>
			<td>3</td>
			<td>1</td>
			<td>1</td>
		</tr>
<tr>
<td>CdSe sembrado CdSe NRs</td>
			<td>5</td>
			<td>0,8</td>
			<td>1</td>
		</tr>
<tr>
<td>CdSe semillas TPs CdSe</td>
			<td>5</td>
			<td>0.6</td>
			<td>0.5</td>
		</tr>
</tbody></table>Tabla 1. Resumen de la concentración aproximada de la solución de NC y el Ag+ solución y el tiempo de batido necesario.

Watch this Scientific Journal Video about Facet-to-facet Linking of Shape-anisotropic Colloidal Cadmium Chalcogenide Nanostructures at JoVE.com

Facet-to-facet Linking of Shape-anisotropic Colloidal Cadmium Chalcogenide Nanostructures

Un protocolo que detalla cómo forma anisotrópica cadmio coloidal calcógeno nanocristales pueden ser covalente a través de sus facetas de extremo se presenta aquí.

Faceta a faceta vincular de forma anisotrópica cadmio coloidal calcógeno nanoestructuras

Here, we describe a protocol that allows for shape-anisotropic cadmium chalcogenide nanocrystals (NCs), such as nanorods (NRs) and tetrapods (TPs), to be ...

facet-to-facet-linking-shape-anisotropic-colloidal-cadmium

Nanyang Technological University

Research

JoVE Journal

Chemistry

7.6K vistas.  National University of Singapore. Un protocolo que detalla cómo forma anisotrópica cadmio coloidal calcógeno nanocristales pueden ser covalente a través de sus facetas de extremo se presenta aquí.

Video: Facet-to-facet Linking of Shape-anisotropic Colloidal Cadmium Chalcogenide Nanostructures

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 Puntos Cuánticos for Imaging sola molécula

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

Investigación

Ingeniería

Revealing Dynamic Processes of Materials in Liquids Using Liquid Cell Transmission Electron Microscopy

The recent development for in situ transmission electron microscopy, which allows imaging through liquids with high spatial resolution, has attracted significant interests across the research fields of materials science, physics, chemistry and biology. The key enabling technology is a liquid cell. We fabricate liquid cells with thin viewing windows through a sequential microfabrication process, including silicon nitride membrane deposition, photolithographic patterning, wafer etching, cell bonding, etc. A liquid cell with the dimensions of a regular TEM grid can fit in any standard TEM sample holder. About 100 nanoliters reaction solution is loaded into the reservoirs and about 30 picoliters liquid is drawn into the viewing windows by capillary force. Subsequently, the cell is sealed and loaded into a microscope for in situ imaging. Inside the TEM, the electron beam goes through the thin liquid layer sandwiched between two silicon nitride membranes. Dynamic processes of nanoparticles in liquids, such as nucleation and growth of nanocrystals, diffusion and assembly of nanoparticles, etc., have been imaged in real time with sub-nanometer resolution. We have also applied this method to other research areas, e.g., imaging proteins in water. Liquid cell TEM is poised to play a major role in revealing dynamic processes of materials in their working environments. It may also bring high impact in the study of biological processes in their native environment.

We have developed a self-contained liquid cell, which allows imaging through liquids using a transmission electron microscope. Dynamic processes of nanoparticles in liquids can be revealed in real time with sub-nanometer resolution.

Revelando los procesos dinámicos de los materiales en líquidos con líquido de transmisión celular Microscopía Electrónica

The recent development for in situ transmission electron microscopy, which allows imaging through liquids with high spatial resolution, has attracted ...

Seeded Synthesis of CdSe/CdS Rod and Tetrapod Nanocrystals

We demonstrate a method for the synthesis of multicomponent nanostructures consisting of CdS and CdSe with rod and tetrapod morphologies. A seeded synthesis strategy is used in which spherical seeds of CdSe are prepared first using a hot-injection technique. By controlling the crystal structure of the seed to be either wurtzite or zinc-blende, the subsequent hot-injection growth of CdS off of the seed results in either a rod-shaped or tetrapod-shaped nanocrystal, respectively. The phase and morphology of the synthesized nanocrystals are confirmed using X-ray diffraction and transmission electron microscopy, demonstrating that the nanocrystals are phase-pure and have a consistent morphology. The extinction coefficient and quantum yield of the synthesized nanocrystals are calculated using UV-Vis absorption spectroscopy and photoluminescence spectroscopy. The rods and tetrapods exhibit extinction coefficients and quantum yields that are higher than that of the bare seeds. This synthesis demonstrates the precise arrangement of materials that can be achieved at the nanoscale by using a seeded synthetic approach.

A protocol for the seeded synthesis of rod-shaped and tetrapod-shaped multicomponent nanostructures consisting of CdS and CdSe is presented.

We demonstrate a method for the synthesis of multicomponent nanostructures consisting of CdS and CdSe with rod and tetrapod morphologies. A seeded ...

Química

Synthesis and Characterization of Supramolecular Colloids

Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical properties for applications in photonics, drug delivery and coating technology. Here we present a new family of colloidal building blocks, coined supramolecular colloids, whose self-assembly is controlled through surface-functionalization with a benzene-1,3,5-tricarboxamide (BTA) derived supramolecular moiety. Such BTAs interact via directional, strong, yet reversible hydrogen-bonds with other identical BTAs. Herein, a protocol is presented that describes how to couple these BTAs to colloids and how to quantify the number of coupling sites, which determines the multivalency of the supramolecular colloids. Light scattering measurements show that the refractive index of the colloids is almost matched with that of the solvent, which strongly reduces the van der Waals forces between the colloids. Before photo-activation, the colloids remain well dispersed, as the BTAs are equipped with a photo-labile group that blocks the formation of hydrogen-bonds. Controlled deprotection with UV-light activates the short-range hydrogen-bonds between the BTAs, which triggers the colloidal self-assembly. The evolution from the dispersed state to the clustered state is monitored by confocal microscopy. These results are further quantified by image analysis with simple routines using ImageJ and Matlab. This merger of supramolecular chemistry and colloidal science offers a direct route towards light- and thermo-responsive colloidal assembly encoded in the surface-grafted monolayer.

A protocol for the synthesis and characterization of colloids coated with supramolecular moieties is described. These supramolecular colloids undergo self-assembly upon the activation of the hydrogen-bonds between the surface-anchored molecules by UV-light.

Síntesis y caracterización de supramoleculares Coloides

Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical ...

Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives

A facile method for the preparation of polycarbodiimide-based secondary structures (e.g., nano-rings, &#34;craters,&#34; fibers, looped fibers, fibrous networks, ribbons, worm-like aggregates, toroidal structures, and spherical particles) is described. These aggregates are morphologically influenced by extensive hydrophobic side chain-side chain interactions of the singular polycarbodiimide strands, as inferred by atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques. Polycarbodiimide-g-polystyrene copolymers (PS-PCDs) were prepared by a combination of synthetic methods, including coordination-insertion polymerization, copper(I)-catalyzed azide alkyne cycloaddition (CuAAC) &#34;click&#34; chemistry, and atom transfer radical polymerization (ATRP). PS-PCDs were found to form specific toroidal architectures at low concentrations in CHCl3. To determine the influence of a more polar solvent medium (i.e., THF and THF/EtOH) on polymer aggregation behavior, a number of representative PS-PCD composites have been tested to show discrete concentration-dependent spherical particles. These fundamental studies are of practical interest to the development of experimental procedures for desirable architectures by directed self-assembly in thin film. These architectures may be exploited as drug carriers, whereas other morphological findings represent certain interest in the area of novel functional materials.

Here, we present a protocol to prepare and visualize secondary structures (e.g., fibers, toroidal architectures, and nano-spheres) derived from helical polycarbodiimides. The morphology characterized by both atomic force microscopy (AFM) and scanning electron microscopy (SEM) was shown to depend on molecular structure, concentration, and the solvent of choice.

Morfologías auto-montaje Obtenido a partir helicoidales policarbodiimida copolímeros y sus derivados de triazol

A facile method for the preparation of polycarbodiimide-based secondary structures (e.g., nano-rings, &#34;craters,&#34; fibers, looped fibers, fibrous ...

Liquid-cell Transmission Electron Microscopy for Tracking Self-assembly of Nanoparticles

Drying a nanoparticle dispersion is a versatile way to create self-assembled structures of nanoparticles, but the mechanism of this process is not fully understood. We have traced the trajectories of individual nanoparticles using liquid-cell transmission electron microscopy (TEM) to investigate the mechanism of the assembly process. Herein, we present the protocols used for liquid-cell TEM studies of the self-assembly mechanism. First, we introduce the detailed synthetic protocols used to produce uniformly sized platinum and lead selenide nanoparticles. Next, we present the microfabrication processes used to produce liquid cells with silicon nitride or silicon windows and then describe the loading and imaging procedures of the liquid-cell TEM technique. Several notes are included to provide helpful tips for the entire process, including how to manage the fragile cell windows. The individual motions of nanoparticles tracked by liquid-cell TEM revealed that changes in the solvent boundaries caused by evaporation affected the self-assembly process of nanoparticles. The solvent boundaries drove nanoparticles to primarily form amorphous aggregates, followed by flattening of the aggregates to produce a 2-dimensional (2D) self-assembled structure. These behaviors are also observed for different nanoparticle types and different liquid-cell compositions.

Here we introduce experimental protocols for the real-time observation of a self-assembly process using liquid-cell transmission electron microscopy.

Microscopia electrónica de transmisión de líquido de la célula para el rastreo de autoensamblaje de las nanopartículas

Drying a nanoparticle dispersion is a versatile way to create self-assembled structures of nanoparticles, but the mechanism of this process is not fully ...

Fabrication of Periodic Gold Nanocup Arrays Using Colloidal Lithography

Within recent years, the field of plasmonics has exploded as researchers have demonstrated exciting applications related to chemical and optical sensing in combination with new nanofabrication techniques. A plasmon is a quantum of charge density oscillation that lends nanoscale metals such as gold and silver unique optical properties. In particular, gold and silver nanoparticles exhibit localized surface plasmon resonances-collective charge density oscillations on the surface of the nanoparticle-in the visible spectrum. Here, we focus on the fabrication of periodic arrays of anisotropic plasmonic nanostructures. These half-shell (or nanocup) structures can exhibit additional unique light-bending and polarization-dependent optical properties that simple isotropic nanostructures cannot. Researchers are interested in the fabrication of periodic arrays of nanocups for a wide variety of applications such as low-cost optical devices, surface-enhanced Raman scattering, and tamper indication. We present a scalable technique based on colloidal lithography in which it is possible to easily fabricate large periodic arrays of nanocups using spin-coating and self-assembled commercially available polymeric nanospheres. Electron microscopy and optical spectroscopy from the visible to near-infrared (near-IR) was performed to confirm successful nanocup fabrication. We conclude with a demonstration of the transfer of nanocups to a flexible, conformal adhesive film.

We demonstrate the fabrication of periodic gold nanocup arrays using colloidal lithographic techniques and discuss the importance of nanoplasmonic films.

Fabricación de matrices Nanocup oro periódicas usando litografía coloidal

Within recent years, the field of plasmonics has exploded as researchers have demonstrated exciting applications related to chemical and optical sensing ...

Microscopic Visualization of Porous Nanographenes Synthesized through a Combination of Solution and On-Surface Chemistry

On-surface synthesis has recently been regarded as a promising approach for the generation of new molecular structures. It has been particularly successful in the synthesis of graphene nanoribbons, nanographenes and intrinsically reactive and instable, yet attractive species. It is based on the combination of solution chemistry aimed at preparation of appropriate molecular precursors for further ultra-high vacuum surface assisted transformations. This approach also owes its success to an incredible development of characterization techniques, such as scanning tunneling/atomic force microscopy and related methods, which allow detailed, local characterization at atomic scale. While the surface-assisted synthesis can provide molecular nanostructures with outstanding precision, down to single atoms, it suffers from basing on metallic surfaces and often limited yield. Therefore, the extension of the approach away from metals and the struggle to increase productivity seem to be significant challenges toward wider applications. Herein, we demonstrate the on-surface synthesis approach for generation of non-planar nanographenes, which are synthesized through a combination of solution chemistry and sequential surface-assisted processes, together with the detailed characterization by scanning probe microscopy methods.

<meta charset="utf8"></head><body>Visualización microscópica de nanografenos porosos sintetizados a través de una combinación de química en solución y en superficie

A combination of solution and surface assisted synthesis opens new directions in the atomically precise synthesis of nanostructures. Scanning tunneling microscopy (STM) supplemented by non-contact atomic force microscopy (nc-AFM) enables detailed characterization of newly designed and generated carbon-based nano-objects.

Visualización microscópica de nanografenos porosos sintetizados a través de una combinación de química en solución y en superficie

On-surface synthesis has recently been regarded as a promising approach for the generation of new molecular structures. It has been particularly ...

Ligand Nano-cluster Arrays in a Supported Lipid Bilayer

Currently there is considerable interest in creating ordered arrays of adhesive protein islands in a sea of passivated surface for cell biological studies. In the past years, it has become increasingly clear that living cells respond, not only to the biochemical nature of the molecules presented to them but also to the way these molecules are presented. Creating protein micro-patterns is therefore now standard in many biology laboratories; nano-patterns are also more accessible. However, in the context of cell-cell interactions, there is a need to pattern not only proteins but also lipid bilayers. Such dual proteo-lipidic patterning has so far not been easily accessible. We offer a facile technique to create protein nano-dots supported on glass and propose a method to backfill the inter-dot space with a supported lipid bilayer (SLB). From photo-bleaching of tracer fluorescent lipids included in the SLB, we demonstrate that the bilayer exhibits considerable in-plane fluidity. Functionalizing the protein dots with fluorescent groups allows us to image them and to show that they are ordered in a regular hexagonal lattice. The typical dot size is about 800 nm and the spacing demonstrated here is 2 microns. These substrates are expected to serve as useful platforms for cell adhesion, migration and mechano-sensing studies.

We present a protocol to functionalize glass with nanometric protein patches surrounded by a fluid lipid bilayer. These substrates are compatible with advanced optical microscopy and are expected to serve as platform for cell adhesion and migration studies.

Faceta a faceta vincular de forma anisotrópica cadmio coloidal calcógeno nanoestructuras

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