Los autores agradecen el Departamento de Química y la Escuela de Graduados de la Universidad Estatal de Missouri por su apoyo a este proyecto. También reconocemos el Laboratorio de Microscopía Electrónica en el Laboratorio Nacional de Investigación del Cáncer de Frederick para el uso de su microscopio electrónico de transmisión y rejillas recubiertas de carbono.

1. Síntesis de fosfuro de indio / sulfuro de zinc (InP / ZnS) Quantum Dots <ol><li> Síntesis de fosfuro de indio (InP) Quantum Dot Núcleos <ol><li> Montar un fondo redondo de 100 ml, de 3 bocas, con un condensador de 12 pulgadas. Añadir 30 ml de oleilamina (OLA), cloruro de 0,398 g de indio (III) (incl 3), 0,245 g de cinc (II) cloruro (ZnCl2) y se agita durante la evacuación a temperatura ambiente usando un vacío durante 1 hora. La solución debería aparecer incoloro con un precipitado blanco. </li><li> El uso de una manta de calentamiento con un termopar y controlador de temperatura proporcional-integral-derivativo (PID), aumentar la temperatura de la solución a 120 ° C. Evacuar la solución bajo vacío durante 20 min para eliminar las impurezas de bajo punto de ebullición que pueden afectar el crecimiento del núcleo. Nota: Si bien es posible utilizar un baño de arena y termómetro, usando una manta de calentamiento y PID aumenta la uniformidad y reproducibilidad de los productos de reacción. </li><li> Bajo gas inerte (por ejemplo,, N 2), reflujo la solución y aumentar la temperatura a 220 ° C durante 15 min. La incl 3 y ZnCl 2 completamente disuelven, lo que resulta en una solución de color amarillo pálido. Deje que la temperatura se estabilice durante 10 min. </li><li> Purgar una jeringa desechable de 3 ml de plástico y 4 pulgadas, 22 aguja G con gas nitrógeno. El uso de la jeringa, entregar rápidamente 0,5 ml de tris (dimetilamino) fosfina (TDMAP) a la solución incl 3. La temperatura de la solución disminuye ligeramente y vuelve a 220 ° C. La solución cambia de transparente, amarillo claro a opaco, negro. </li><li> Después de 9,5 min, retirar el matraz de reacción de la camisa de calentamiento hasta que la temperatura disminuye por debajo de 200 ° C. Para proteger la integridad de los núcleos de InP, proceder directamente a la capa de ZnS en el paso 1.2.1. </li></ol></li><li> Síntesis del sulfuro de zinc (ZnS Conchas) Quantum Dot <ol><li> Colocar el matraz de reacción de la etapa 1.1.5 en una manta de calefacción y estabilizar el temperatura a 200 ° C. Agregar lentamente 3,58 g dodecanotiol (DDT) en el transcurso de 15 segundos a la solución que contiene los puntos cuánticos de InP. Deje que la solución reaccione durante 1 hora. Nota: grosor de la cáscara ZnS puede variarse aumentando o disminuyendo la cantidad de estearato de zinc añadido en la etapa 1.2.4. La alteración de la cantidad de ZnCl 2 o dodecanotiol en los pasos 1.1.1 y 1.2.1 puede afectar significativamente la calidad de los puntos cuánticos cambiando la cinética de reacción. <ol><li> Después, retire el matraz de reacción de la camisa de calentamiento y permita que la solución se enfríe a aproximadamente 60 ° C. </li></ol></li><li> Una vez que la solución de InP / ZnS alcanza ~ 60 ° C, añadir 10 ml de hexanos y transferir toda la solución de aproximadamente 45 ml a un tubo de centrífuga de polipropileno de 50 ml. Centrifugar la muestra (3.000 xg durante 10 min) para eliminar los precursores sólidos sin reaccionar. </li><li> transferir con cuidado el sobrenadante a una botella de centrífuga de polipropileno de 250 ml, añadir 200 ml de acetona, y se centrifuga la solución (3.000 xg durante 10 min) para precipitar los puntos cuánticos InP / ZnS. Este volumen también se puede dividir de manera uniforme en cuatro tubos de 50 ml por centrifugación si una centrífuga con rotor / los accesorios necesarios no está disponible. Decantar el sobrenadante y secar el pellet QD a fondo con gas nitrógeno para eliminar la acetona. </li><li> Resuspender los puntos cuánticos en 20 ml OLA utilizando ultrasonidos, transferir a un fondo redondo de 50 ml, de 3 bocas, que contiene 0,474 g de estearato de zinc, y revuelva. Evacuar la solución bajo vacío durante 20 min a TA. </li><li> Bajo gas nitrógeno, aumentar la temperatura a 180 ° C y permite que la reacción continúe durante 3 h. Si bien no hay cambios visuales notables en la solución de reacción que se producen durante esta reacción, la adición de estearato de zinc aumenta el grosor del cascarón ZnS, aumentando así QY mediante la mejora de pasivación de la superficie de los puntos cuánticos 12.. Una vez que la reacción se ha completado, retirar el matraz de la manta calefactora y permita que la solución se enfríe a aproximadamente 60 ° C. </li><li> Una vez que los soluti InP / ZnSen alcances ~ 60 ° C, añadir 20 ml de hexanos y transferir a un tubo de centrífuga de 50 ml de polipropileno. Centrifugar la muestra (3.000 xg durante 10 min) para eliminar el estearato de zinc sin reaccionar. </li><li> transferir con cuidado el sobrenadante a una botella de centrífuga de 250 ml de polipropileno, añadir 200 ml de acetona, y se centrifuga la solución (3.000 xg durante 10 min) para precipitar InP / ZnS puntos cuánticos. Con cuidado, se decanta el sobrenadante y se seca a fondo con gas nitrógeno para eliminar la acetona. </li><li> Disolver el precipitado InP / ZnS QD en 30 ml de hexano. Vortex y someter a ultrasonidos brevemente la solución para asegurar una dispersión completa. </li><li> Repita los pasos de purificación 1.2.6-1.2.8 dos veces más para asegurar la eliminación completa de ligandos orgánicos en exceso. Las interacciones entre el polímero anfifílico y el QD en el paso 1.2 pueden verse comprometidas en presencia de un exceso de ligandos. </li><li> Con cálculos detallados por Xie, et al. 16, determinar el tamaño y concentración de los puntos cuánticos InP / ZnS sintetizados usando espectroscopia UV-Vis. <br/&gt; Nota: La característica espectral importante para este análisis es el hombro del pico de absorción. El valor de longitud de onda y la absorbancia del máximo de este hombro se utiliza para calcular el tamaño y la concentración de los puntos cuánticos, respectivamente. Esta reacción típicamente produce aproximadamente 5 mol de los puntos cuánticos con un pico de emisión a 600 nm. Para sintetizar los puntos cuánticos de diferentes colores, la duración y / o la temperatura de la reacción se pueden modificar. Un tiempo de reacción más largo y / o una temperatura más alta de los resultados de la solución en un pico de emisión desplazada al rojo. Por ejemplo, el aumento de la temperatura de reacción a 240 ° C y mantener el tiempo de reacción de 10 min se traducirá en puntos cuánticos con un pico máximo de emisiones nm 680. Del mismo modo, la reducción de tiempo de reacción a 2 min y la duplicación de cloruro de zinc utilizado resultará en puntos cuánticos con un pico de emisión máxima nm 470. Estos puntos cuánticos InP / ZnS son estables durante al menos un mes a 4 ° C en la oscuridad bajo gas inerte. </li></ol></li></ol> 2. aguaSolubilización de InP / ZnS Quantum Dots El uso de un polímero anfífilo <ol><li> solubilización en agua <ol><li> Uso de los puntos cuánticos InP / ZnS desde el paso 1.2.10, diluir una parte de los puntos cuánticos con hexanos para obtener 1 ml de 1 M puntos cuánticos. <ol><li> En un tubo de centrífuga, transferir 0,25 ml de InP / ZnS puntos cuánticos en cada tubo. Añadir 1 ml de acetona o metanol para el tubo de centrífuga y se centrifuga (3.000 xg durante 10 min). Retirar con cuidado el sobrenadante y disolver cada precipitado en 1 ml de tetrahidrofurano (THF). </li><li> La transferencia de los puntos cuánticos InP / ZnS disueltos en THF en un matraz de 100 ml de fondo redondo y se diluye con 16 ml de THF. Para reducir el número de agregados en solución, los puntos cuánticos someter a ultrasonidos durante 5-10 minutos. </li></ol></li><li> Disolver 30 mg de poli (ácido maleico alt andhydride- -1-octadeceno), 3- (dimetilamino) -1-propilamina (PMAL-d) en 10 ml de agua de grado molecular. Baño de agua sonicación o agitación suave hasta que la solución es translúcido es suficiente para disolver completamente el polímero. losuso de vórtice o agitación vigorosa puede producir muchas burbujas, lo que dificulta la interacción del polímero con el QD. Añadir la solución de polímero 10 ml a los 100 ml matraz de fondo redondo que contiene InP / ZnS puntos cuánticos en THF. </li><li> Se evapora THF de la solución QD / polímero usando un evaporador rotatorio. Colocar el matraz en un baño de hielo mientras se evapora para facilitar la interacción entre el polímero y QD. Dependiendo de la fuerza del vacío, más THF se evapora después de 10 min y la solución aparece turbia. <ol><li> Una vez que la solución se evapora a 10 ml, quitar el matraz del evaporador rotativo y añadir 30 ml de agua de grado molecular. Devolver el matraz al evaporador rotatorio y continuar a evaporarse a 2 ml. Esta etapa de evaporación final puede tomar muchas horas; asegurar el baño de hielo se mantiene. </li></ol></li><li> Quitar los puntos cuánticos InP / ZnS solubles en agua del matraz de fondo redondo con una pipeta. Filtrar la solución QD utilizando una jeringa de plástico de 3 ml unido a un sy nylon 0,1 micrasringe filtrar en un tubo de centrífuga de 5 ml. </li><li> Coloque los puntos cuánticos en una unidad de diálisis de membrana de MWCO de 20.000 y se dializa frente a tampón borato 0,05 M pH 8,5 para eliminar el exceso de polímero. (Añadir lentamente tetraborato decahidrato sódico 0,05 M en ácido bórico 0,05 M, con agitación vigorosa, hasta que el pH es 8,5 para hacer esta solución tampón de borato.) El uso de un concentrador de vacío, concentrar los puntos cuánticos en tampón de borato a 1 ml. </li><li> Para el almacenamiento, purgar la solución con nitrógeno gaseoso antes del sellado con Parafilm. Los puntos cuánticos InP / ZnS solubles en agua son estables durante al menos 4 meses a 4 ° C en la oscuridad. </li></ol></li></ol>

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Los autores no tienen nada que revelar.

Este protocolo se detalla la síntesis de los puntos cuánticos InP / ZnS altamente fluorescentes que se pueden utilizar en muchos sistemas biológicos. Los productos sintetizados QD aquí exhiben un solo pico de emisión de fluorescencia centrada en 600 nm con una FWHM de 73 nm (Figura 1), que es comparable a otras síntesis anteriormente descritos 12. El tiempo de reacción y la temperatura de reacción son pasos muy importantes debido a su profundo efecto sobre la calidad de la síntesis d...

A correction was made to: <a href="http://www.jove.com/video/53684/synthesis-cd-free-inpzns-quantum-dots-suitable-for-biomedical" target="_blank">Synthesis of Cd-free InP/ZnS Quantum Dots Suitable for Biomedical Applications</a>. There was an error with an author's given name. The author's name was corrected to:
Katye M. Fichter
from:
Kathryn M. Fichter

A correction was made to: <a href="http://www.jove.com/video/53684/synthesis-cd-free-inpzns-quantum-dots-suitable-for-biomedical" target="_blank">Synthesis of Cd-free InP/ZnS Quantum Dots Suitable for Biomedical Applications</a>.

Erratum: Synthesis of Cd-free InP/ZnS Quantum Dots Suitable for Biomedical Applications

Los puntos cuánticos (QDs) son semiconductores nanocristales que exhiben propiedades fluorescentes cuando se irradian con luz 1. Debido a su pequeño tamaño (2-5 nm), que es similar a muchas biomoléculas más grandes, y la facilidad de biofuncionalización, los puntos cuánticos son una herramienta muy atractiva para aplicaciones biomédicas. Ellos han encontrado uso en el etiquetado biológica, una sola molécula de imágenes de células vivas, la administración de fármacos, de formación de imágenes in vivo, la detección de patógenos, y el seguimiento de la célula, entre muchos otros usos 2-8. Los puntos cuánticos basados ​​en Cd se han utilizado más comúnmente en aplicaciones biomédicas debido a su intensa fluorescencia y reducidos anchos de pico de emisión 9. Sin embargo, han surgido preocupaciones debido a la toxicidad potencial de los iones Cd2 + 10 que puede ser puesto en libertad debido a la degradación de la nanopartícula. Recientemente, puntos cuánticos basados ​​en InP se han explorado como una alternativa a los puntos cuánticos basados ​​en Cd porque mantienen muchas de las características de fluorescenciaCd de puntos cuánticos basados ​​y puede ser más biocompatible 11. Puntos cuánticos basados ​​en Cd se han encontrado para ser significativamente más tóxico que los puntos cuánticos basados ​​en InP en ensayos in vitro en concentraciones tan bajas como 10 pM, después de sólo 48 h 11. El color de los puntos cuánticos de emisión de fluorescencia es de tamaño ajustable-1. Es decir, como el tamaño de los aumentos de QD, la emisión de fluorescencia es desplazada al rojo. El tamaño y las dimensiones dispersidad de los productos QD puede ser modificado cambiando la temperatura, duración de la reacción, o las condiciones de concentración de precursor durante la reacción 12. Mientras que el pico de emisión de los puntos cuánticos InP es típicamente más amplio y menos intenso que los puntos cuánticos basados ​​en Cd, InP puntos cuánticos puede hacerse en una gran variedad de colores diseñados para evitar el solapamiento espectral, y son lo suficientemente intensa para la mayoría de aplicaciones biomédicas 12. La síntesis se detalla en este protocolo da los puntos cuánticos con un pico de emisión roja centrada a 600 nm. Varios pasos se toman after síntesis de los núcleos QD para mantener la integridad óptica de los puntos cuánticos y para hacerlos compatibles para aplicaciones biológicas. La superficie del núcleo QD debe ser protegido de defectos de la oxidación o de superficie que pueden causar enfriamiento rápido; Por lo tanto, una concha de ZnS se reviste sobre el núcleo para producir InP / ZnS (core / shell) qds 13. Este revestimiento se ha demostrado que protege la fotoluminiscencia del producto QD. La presencia de iones de zinc durante la síntesis de InP QD se ha demostrado que limitar defectos de la superficie, así como distribución de tamaño de disminución 12. Incluso con la presencia de Zn 2 + en el medio de reacción, la síntesis de InZnP son muy poco probable 12. Después del recubrimiento, los puntos cuánticos resultantes InP / ZnS se recubren en ligandos hidrófobos tales como óxido de trioctilfosfina (TOPO) o oleilamina 12,14. Un polímero anfifílico puede interactuar con ligandos hidrófobos en la superficie QD, así como las moléculas de agua a granel para impartir solubilidad en agua 15. polímeros anfifílicos con carbogrupos químicos xylate se pueden utilizar como &quot;asas químicas&quot; para funcionalizar adicionalmente los puntos cuánticos. Este protocolo se detalla la síntesis y funcionalización de InP / puntos cuánticos ZnS solubles en agua con la emisión de fluorescencia muy intensa y tamaño relativamente pequeño-dispersidad. Estos puntos cuánticos son potencialmente menos tóxicos que los puntos cuánticos CdSe / ZnS de uso común. En esto, la síntesis de InP / ZnS puntos cuánticos ofrece una alternativa práctica a los puntos cuánticos basados ​​en Cd para aplicaciones biomédicas.

<table><tbody><tr><td>Oleylamine</td><td>Acros</td><td>129540010</td><td></td></tr><tr><td>Zinc(II) chloride</td><td>Sigma</td><td>030-003-00-2</td><td></td></tr><tr><td>Indium(III) chloride</td><td>Chem-Impex</td><td>24560</td><td></td></tr><tr><td>Tris(dimethylamino)phosphine</td><td>Encompass</td><td>50-901-10500</td><td></td></tr><tr><td>1-dodecanethiol</td><td>Acros</td><td>117625000</td><td></td></tr><tr><td>Hexanes</td><td>Fisher Sci</td><td>H292-4</td><td></td></tr><tr><td>Acetone</td><td>TransChemical</td><td>UN 1090</td><td></td></tr><tr><td>Zinc Stearate</td><td>Aldrich Chem</td><td>307564-1KG</td><td></td></tr><tr><td>Tetrahydrofuran</td><td>Acros</td><td>34845-0010</td><td></td></tr><tr><td>Molecular Water</td><td>Fisher Sci</td><td>BP2470-1</td><td></td></tr><tr><td>Poly(maleic anhyrdride-&lt;em&gt;alt&lt;/em&gt;-1-tetradecene), 3-(dimethylamino)-1-propylamine derivative</td><td>Sigma</td><td>90771-1G</td><td></td></tr><tr><td>Boric acid</td><td>Fisher Sci</td><td>BP168-500</td><td></td></tr><tr><td>Sodium Tetraborate Decahydrate</td><td>Fisher Sci</td><td>BP175-500</td><td></td></tr><tr><td>Rhodamine B</td><td>Aldrich Chem</td><td>R95-3</td><td></td></tr><tr><td>Nitrogen gas</td><td>Airgas</td><td>UN1066</td><td></td></tr><tr><td>Trypan blue</td><td>Thermo Sci</td><td>SV30084.01</td><td></td></tr><tr><td>3 ml plastic Luer-lock syringe</td><td>BD</td><td>309657</td><td></td></tr><tr><td>Luer-lock Needle</td><td>Air-Tite</td><td>8300014471</td><td>4 inch, 22 gauge</td></tr><tr><td>50 ml polypropyene centrifuge tube</td><td>Falcon</td><td>352098</td><td></td></tr><tr><td>250 ml centrifuge bottle</td><td>Thermo Sci</td><td>05-562-23</td><td>Nalgene PPCO</td></tr><tr><td>5 ml centrifuge tubes</td><td>Argos-Tech</td><td>T2076</td><td></td></tr><tr><td>1.5 ml microcentrifuge tubes</td><td>Bio Plas</td><td>4150</td><td></td></tr><tr><td>0.1 &amp;mu;m Syringe filter</td><td>Whatman</td><td>6786-1301</td><td>Puradisc 13 mm nylon filter</td></tr><tr><td>Slide-A-Lyzer MINI Dialysis Unit</td><td>Thermo Sci</td><td>69590</td><td>20,000 MWCO</td></tr><tr><td>Rotary Evaporator</td><td>Heidolph</td><td></td><td></td></tr><tr><td>Centrifuge 5072</td><td>Eppendorf</td><td></td><td>Swinging Bucket with 50&amp;nbsp;ml tube adapters</td></tr><tr><td>Lambda 650 UV/VIS Spectrometer</td><td>Perkin Elmer</td><td></td><td>UV-Vis Spectrophotometer</td></tr><tr><td>LS 55 Fluorescence Spectrometer</td><td>Perkin Elmer</td><td></td><td>Fluorometer</td></tr><tr><td>Axio Observer.A1</td><td>Zeiss</td><td></td><td>epifluorescence microscope</td></tr><tr><td>AxioCam MRm</td><td>Zeiss</td><td></td><td>CCD Camera</td></tr><tr><td>Tecnai TF20 Microscope</td><td>FEI</td><td></td><td>Transmisison Electron Miscroscope</td></tr><tr><td>TEM Eagle CCD</td><td>FEI</td><td></td><td>TEM CCD Camera</td></tr><tr><td>NanoBrook Omni DLS</td><td>Brookhaven</td><td></td><td>Dynamic Light Scattering Instrument</td></tr></tbody></table>

synthesis of cd-free inp/zns quantum dots suitable for biomedical applications

Fluorescent nanocrystals, specifically quantum dots, have been a useful tool for many biomedical applications. For successful use in biological systems, quantum dots should be highly fluorescent and small/monodisperse in size. While commonly used cadmium-based quantum dots possess these qualities, they are potentially toxic due to the possible release of Cd2+ ions through nanoparticle degradation. Indium-based quantum dots, specifically InP/ZnS, have recently been explored as a viable alternative to cadmium-based quantum dots due to their relatively similar fluorescence characteristics and size. The synthesis presented here uses standard hot-injection techniques for effective nanoparticle growth; however, nanoparticle properties such as size, emission wavelength, and emission intensity can drastically change due to small changes in the reaction conditions. Therefore, reaction conditions such temperature, reaction duration, and precursor concentration should be maintained precisely to yield reproducible products. Because quantum dots are not inherently soluble in aqueous solutions, they must also undergo surface modification to impart solubility in water. In this protocol, an amphiphilic polymer is used to interact with both hydrophobic ligands on the quantum dot surface and bulk solvent water molecules. Here, a detailed protocol is provided for the synthesis of highly fluorescent InP/ZnS quantum dots that are suitable for use in biomedical applications.

Los núcleos no recubiertos InP no demuestran fluorescencia visible por el ojo sustancial. Sin embargo, InP / ZnS (core / shell) puntos cuánticos fluorescentes brillantes parecen a simple vista bajo irradiación UV. La fluorescencia de InP / ZnS los puntos cuánticos se ha caracterizado mediante espectroscopía de fluorescencia. El espectro de fluorescencia de los puntos cuánticos en hexanos (Figura 1) se excita a 533 nm muestra un pico principal centrado a 600 nm con ...

Watch this Scientific Journal Video about Synthesis of Cd-free InP/ZnS Quantum Dots Suitable for Biomedical Applications at JoVE.com

Synthesis of Cd-free InP/ZnS Quantum Dots Suitable for Biomedical Applications

In this protocol, the synthesis of Cd-free InP/ZnS quantum dots (QDs) is detailed. InP-based QDs are gaining popularity due to the toxicity of Cd2+ ions that may be released through nanoparticle degradation. After synthesis, QDs are solubilized in water using an amphiphilic polymer for use in biomedical applications.

Síntesis de Cd-libre EAD / ZnS puntos cuánticos Adecuado para aplicaciones biomédicas

Fluorescent nanocrystals, specifically quantum dots, have been a useful tool for many biomedical applications. For successful use in biological systems, ...

synthesis-cd-free-inpzns-quantum-dots-suitable-for-biomedical

Research

JoVE Journal

Chemistry

13.6K vistas.  Missouri State University. In this protocol, the synthesis of Cd-free InP/ZnS quantum dots (QDs) is detailed. InP-based QDs are gaining popularity due to the toxicity of Cd2+ ions that may be released through nanoparticle degradation. After synthesis, QDs are solubilized in water using an amphiphilic polymer for use in biomedical applications.

Video: Synthesis of Cd-free InP/ZnS Quantum Dots Suitable for Biomedical Applications

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

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

Solubilization and Bio-conjugation of Quantum Dots and Bacterial Toxicity Assays by Growth Curve and Plate Count

Quantum dots (QDs) are fluorescent semiconductor nanoparticles with size-dependent emission spectra that can be excited by a broad choice of wavelengths. QDs have attracted a lot of interest for imaging, diagnostics, and therapy due to their bright, stable fluorescence1,2 3,4,5. QDs can be conjugated to a variety of bio-active molecules for binding to bacteria and mammalian cells6.
QDs are also being widely investigated as cytotoxic agents for targeted killing of bacteria. The emergence of multiply-resistant bacterial strains is rapidly becoming a public health crisis, particularly in the case of Gram negative pathogens 7. Because of the well-known antimicrobial effect of certain nanomaterials, especially Ag, there are hundreds of studies examining the toxicity of nanoparticles to bacteria 8. Bacterial studies have been performed with other types of semiconductor nanoparticles as well, especially TiO2 9,10-11, but also ZnO12 and others including CuO 13. Some comparisons of bacterial strains have been performed in these studies, usually comparing a Gram negative strain with a Gram positive. With all of these particles, mechanisms of toxicity are attributed to oxidation: either the photogeneration of reactive oxygen species (ROS) by the particles or the direct release of metal ions that can cause oxidative toxicity. Even with these materials, results of different studies vary greatly. In some studies the Gram positive test strain is reportedly more sensitive than the Gram negative 10; in others it is the opposite 14. These studies have been well reviewed 15.
In all nanoparticle studies, particle composition, size, surface chemistry, sample aging/breakdown, and wavelength, power, and duration of light exposure can all dramatically affect the results. In addition, synthesis byproducts and solvents must be considered16 17. High-throughput screening techniques are needed to be able to develop effective new nanomedicine agents.
CdTe QDs have anti-microbial effects alone18 or in combination with antibiotics. In a previous study, we showed that coupling of antibiotics to CdTe can increase toxicity to bacteria but decrease toxicity to mammalian cells, due to decreased production of reactive oxygen species from the conjugates19. Although it is unlikely that cadmium-containing compounds will be approved for use in humans, such preparations could be used for disinfection of surfaces or sterilization of water.
In this protocol, we give a straightforward approach to solubilizing CdTe QDs with mercaptopropionic acid (MPA). The QDs are ready to use within an hour. We then demonstrate coupling to an antimicrobial agent.
The second part of the protocol demonstrates a 96-well bacterial inhibition assay using the conjugated and unconjugated QDs. The optical density is read over many hours, permitting the effects of QD addition and light exposure to be evaluated immediately as well as after a recovery period. We also illustrate a colony count for quantifying bacterial survival.

Nanoparticles such as semiconductor quantum dots (QDs) can be used to create photoactivatable agents for anti-microbial or anti-cancer applications. This technique shows how to water-solubilize cadmium telluride (CdTe) QDs, conjugate them to an antibiotic, and perform a bacterial inhibition assay based upon growth curves and plate count.

Solubilización y Bio-Corrector ortográfico y de los puntos cuánticos y Ensayos de toxicidad bacteriana por curva de crecimiento y Recuento

Quantum dots (QDs) are fluorescent semiconductor nanoparticles with size-dependent emission spectra that can be excited by a broad choice of wavelengths. ...

Bioingeniería

Synthesis of Ligand-free CdS Nanoparticles within a Sulfur Copolymer Matrix

Aliphatic ligands are typically used during the synthesis of nanoparticles to help mediate their growth in addition to operating as high-temperature solvents. These coordinating ligands help solubilize and stabilize the nanoparticles while in solution, and can influence the resulting size and reactivity of the nanoparticles during their formation. Despite the ubiquity of using ligands during synthesis, the presence of aliphatic ligands on the nanoparticle surface can result in a number of problems during the end use of the nanoparticles, necessitating further ligand stripping or ligand exchange procedures. We have developed a way to synthesize cadmium sulfide (CdS) nanoparticles using a unique sulfur copolymer. This sulfur copolymer is primarily composed of elemental sulfur, which is a cheap and abundant material. The sulfur copolymer has the advantages of operating both as a high temperature solvent and as a sulfur source, which can react with a cadmium precursor during nanoparticle synthesis, resulting in the generation of ligand free CdS. During the reaction, only some of the copolymer is consumed to produce CdS, while the rest remains in the polymeric state, thereby producing a nanocomposite material. Once the reaction is finished, the copolymer stabilizes the nanoparticles within a solid polymeric matrix. The copolymer can then be removed before the nanoparticles are used, which produces nanoparticles that do not have organic coordinating ligands. This nascent synthesis technique presents a method to produce metal-sulfide nanoparticles for a wide variety of applications where the presence of organic ligands is not desired.

Herein we present a method to synthesize ligand-free cadmium sulfide (CdS) nanoparticles based on a unique sulfur copolymer. The sulfur copolymer operates as a high temperature solvent and a sulfur source during the nanoparticle synthesis and stabilizes the nanoparticles after the reaction.

Síntesis del ligando libre de CdS nanopartículas dentro de una matriz de copolímero de azufre

Aliphatic ligands are typically used during the synthesis of nanoparticles to help mediate their growth in addition to operating as high-temperature ...

Advanced Compositional Analysis of Nanoparticle-polymer Composites Using Direct Fluorescence Imaging

The fabrication of polymer-nanoparticle composites is extremely important in the development of many functional materials. Identifying the precise composition of these materials is essential, especially in the design of surface catalysts, where the surface concentration of the active component determines the activity of the material. Antimicrobial materials which utilize nanoparticles are a particular focus of this technology. Recently swell encapsulation has emerged as a technique for inserting antimicrobial nanoparticles into a host polymer matrix. Swell encapsulation provides the advantage of localizing the incorporation to the external surfaces of materials, which act as the active sites of these materials. However, quantification of this nanoparticle uptake is challenging. Previous studies explore the link between antimicrobial activity and surface concentration of the active component, but this is not directly visualized. Here we show a reliable method to monitor the incorporation of nanoparticles into a polymer host matrix via swell encapsulation. We show that the surface concentration of CdSe/ZnS nanoparticles can be accurately visualized through cross-sectional fluorescence imaging. Using this method, we can quantify the uptake of nanoparticles via swell encapsulation and measure the surface concentration of encapsulated particles, which is key in optimizing the activity of functional materials.

Here we present a reliable method to monitor the incorporation of nanoparticles into a polymer host matrix via swell encapsulation. We show that the surface concentration of cadmium selenide quantum dots can be accurately visualized through cross-sectional fluorescence imaging.

Análisis de la composición avanzada de compuestos de nanopartículas poliméricas Uso de la imagen de fluorescencia directa

The fabrication of polymer-nanoparticle composites is extremely important in the development of many functional materials. Identifying the precise ...

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

Here, we describe a protocol that allows for shape-anisotropic cadmium chalcogenide nanocrystals (NCs), such as nanorods (NRs) and tetrapods (TPs), to be covalently and site-specifically linked via their end facets, resulting in polymer-like linear or branched chains. The linking procedure begins with a cation-exchange process in which the end facets of the cadmium chalcogenide NCs are first converted to silver chalcogenide. This is followed by the selective removal of ligands at their surface. This results in cadmium chalcogenide NCs with highly reactive silver chalcogenide end facets that spontaneously fuse upon contact with each other, thereby establishing an interparticle facet-to-facet attachment. Through the judicious choice of precursor concentrations, an extensive network of linked NCs can be produced. Structural characterization of the linked NCs is carried out via low- and high-resolution transmission electron microscopy (TEM), as well as energy-dispersive X-ray spectroscopy, which confirm the presence of silver chalcogenide domains between chains of cadmium chalcogenide NCs.

A protocol detailing how shape-anisotropic colloidal cadmium chalcogenide nanocrystals can be covalently linked via their end facets is presented here.

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 ...

Enhanced Electron Injection and Exciton Confinement for Pure Blue Quantum-Dot Light-Emitting Diodes by Introducing Partially Oxidized Aluminum Cathode

Stable and efficient red (R), green (G), and blue (B) light sources based on solution-processed quantum dots (QDs) play important roles in next-generation displays and solid-state lighting technologies. The brightness and efficiency of blue QDs-based light-emitting diodes (LEDs) remain inferior to their red and green counterparts, due to the inherently unfavorable energy levels of different colors of light. To solve these problems, a device structure should be designed to balance the injection holes and electrons into the emissive QD layer. Herein, through a simple autoxidation strategy, pure blue QD-LEDs which are highly bright and efficient are demonstrated, with a structure of ITO/PEDOT:PSS/Poly-TPD/QDs/Al:Al2O3. The autoxidized Al:Al2O3 cathode can effectively balance the injected charges and enhance radiative recombination without introducing an additional electron transport layer (ETL). As a result, high color-saturated blue QD-LEDs are achieved with a maximum luminance over 13,000 cd m-2, and a maximum current efficiency of 1.15 cd A-1. The easily controlled autoxidation procedure paves the way for achieving high-performance blue QD-LEDs.

A protocol is presented for fabricating high-performance, pure blue ZnCdS/ZnS-based quantum dots light-emitting diodes by employing an autoxidized aluminum cathode.

Inyección electrónica mejorada y el confinamiento de excitón de punto cuántico de puro azul diodos emisores de luz mediante la introducción de cátodo de aluminio parcialmente oxidadas

Stable and efficient red (R), green (G), and blue (B) light sources based on solution-processed quantum dots (QDs) play important roles in next-generation ...

Production and Targeting of Monovalent Quantum Dots

The multivalent nature of commercial quantum dots (QDs) and the difficulties associated with producing monovalent dots have limited their applications in biology, where clustering and the spatial organization of biomolecules is often the object of study. We describe here a protocol to produce monovalent quantum dots (mQDs) that can be accomplished in most biological research laboratories via a simple mixing of CdSe/ZnS core/shell QDs with phosphorothioate DNA (ptDNA) of defined length. After a single ptDNA strand has wrapped the QD, additional strands are excluded from the surface. Production of mQDs in this manner can be accomplished at small and large scale, with commercial reagents, and in minimal steps. These mQDs can be specifically directed to biological targets by hybridization to a complementary single stranded targeting DNA. We demonstrate the use of these mQDs as imaging probes by labeling SNAP-tagged Notch receptors on live mammalian cells, targeted by mQDs bearing a benzylguanine moiety.

We provide detailed instructions for the preparation of monovalent targeted quantum dots (mQDs) from phosphorothioate DNA of defined length. DNA wrapping occurs in high yield, and therefore, products do not require purification. We demonstrate the use of the SNAP tag to target mQDs to cell-surface receptors for live-cell imaging applications.

Producción y focalización de monovalente Quantum Dots

The multivalent nature of commercial quantum dots (QDs) and the difficulties associated with producing monovalent dots have limited their applications in ...

Inkjet Printing All Inorganic Halide Perovskite Inks for Photovoltaic Applications

A method for synthesizing photoactive inorganic&#160;perovskite quantum dot inks and an inkjet printer deposition method, using the synthesized inks, are demonstrated. The ink synthesis is based on a simple wet chemical reaction and the inkjet printing protocol is a facile step by step method. The inkjet printed thin films have been characterized by X-ray diffraction, optical absorption spectroscopy, photoluminescent spectroscopy, and electronic transport measurements. X-ray diffraction of the printed quantum dot films indicates a crystal structure consistent with an orthorhombic room temperature phase with (001) orientation. In conjunction with other characterization methods, the X-ray diffraction&#160;measurements show high quality films can be obtained through the inkjet printing method.

A protocol for synthesizing inorganic-lead-halide hybrid perovskite quantum dot inks for inkjet printing and the protocol for preparing and printing the quantum dot inks in an inkjet printer with post characterization techniques are presented.

Inyección de tinta impresión todos halogenuros inorgánicos perovskita tintas para aplicaciones fotovoltaicas

A method for synthesizing photoactive inorganic&#160;perovskite quantum dot inks and an inkjet printer deposition method, using the synthesized inks, are ...

Synthesis of In37P20(O2CR)51 Clusters and Their Conversion to InP Quantum Dots

This text presents a method for the synthesis of In37P20(O2C14H27)51 clusters and their conversion to indium phosphide quantum dots. The In37P20(O2CR)51 clusters have been observed as intermediates in the synthesis of InP quantum dots from molecular precursors (In(O2CR)3, HO2CR, and P(SiMe3)3) and may be isolated as a pure reagent for subsequent study and use as a single-source precursor. These clusters readily convert to crystalline and relatively monodisperse samples of quasi-spherical InP quantum dots when subjected to thermolysis conditions in the absence of additional precursors above 200 &#176;C. The optical properties, morphology, and structure of both the clusters and quantum dots are confirmed using UV-Vis spectroscopy, photoluminescence spectroscopy, transmission electron microscopy, and powder X-ray diffraction. The molecular symmetry of the clusters is additionally confirmed by solution-phase 31P NMR spectroscopy. This protocol demonstrates the preparation and isolation of atomically-precise InP clusters, and their reliable and scalable conversion to InP QDs.

Synthesis of In37P20O2CR51 Clusters and Their Conversion to InP Quantum Dots

A protocol for the synthesis of In37P20(O2C14H27)51 clusters and their conversion to indium phosphide quantum dots is presented.

Síntesis de37P20(O2CR)51 racimos y su conversión a puntos cuánticos INP

This text presents a method for the synthesis of In37P20(O2C14H27)51 clusters and their conversion to indium phosphide quantum dots. The In37P20(O2CR)51 ...