Questo lavoro è stato supportato da JCO A * STAR Investigatorship concedere (progetto n. 1437 00135), A * STAR Science & Engineering Consiglio settore pubblico finanziamenti per la ricerca (progetto n. 1421200076) e progetti di ricerca congiunta un JSP-NUS concedere (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>

Non abbiamo nulla da rivelare.

La tecnica di collegamento descritta in questo lavoro permette per cadmio forma-anisotropo calcogenuri nanoparticelle che possono subire scambio cationico con Ag+ da unire, faccetta sfaccettatura, in assembly come catene lineari o ramificate reti. Il mancato formano ben dispersi, vasti assemblee di nanoparticelle collegate faccetta--sfaccettatura è spesso a causa di due motivi: (i) la ODPA non è disperso bene nella soluzione contenente NR, che può essere affrontata di sonicating la miscela per il prescritto quantità di tempo dettagliata nel protocollo; o (ii) la concentrazione di Ag+ utilizzata è non ottimale. Quando la concentrazione di Ag+ utilizzata è troppo bassa, la maggior parte delle nanoparticelle calcogenuri cadmio non subiscono scambio cationico, conseguente poco o nessun collegamento (come descritto nei Risultati rappresentante). Quando la concentrazione di Ag+ utilizzata è troppo alta, più domini di Ag2S modulo su ogni particella, con conseguente grave aggregazione su collegamento.
Il nostro approccio per il collegamento di faccetta--sfaccettatura delle nanoparticelle inorganiche forma-anisotropo è attualmente limitata a nanoparticelle di metallo calcogenuri che possono subire scambio cationico con Ag+ o Cu+ (non illustrato in questo lavoro) sotto reazione delicata condizioni. Gli sforzi sono in corso per ampliare il repertorio di materiali inorganici che possono essere collegati direttamente tramite la nostra strategia sintetica. Precedentemente abbiamo dimostrato che la faccetta sfaccettatura legata nanoparticella assembly possono subire ulteriori processi di scambio cationico e può essere trasformato in altri materiali semiconduttori pur mantenendo la loro architettura collegato5. Questo modificato la procedura di collegamento, anche se più noioso, può ampliare significativamente la diversità dei nanomateriali di semiconduttore che possono essere portati insieme in assembly sfaccettatura-collegata.
Perché le assemblee delle nanoparticelle di semiconduttore collegati sono unite in join faccetta-sfaccettatura, sono accoppiati elettronicamente a vicenda. Questo può essere vantaggioso per le applicazioni come soluzione-elaborati optoelettronica, dove un problema principale è il trasporto di carica poveri attraverso isolanti ligandi che circondano le nanoparticelle di semiconduttori. Ulteriore lavoro è necessario per valutare l'efficacia delle assemblee di nanoparticelle di semiconduttore collegati come materiale attivo in dispositivi optoelettronici.

Il montaggio diretto di semiconduttore colloidali NCs offre una via sintetica per la fabbricazione di nanostrutture cui proprietà fisico-chimiche sono sia la somma collettiva di o radicalmente diversi da loro individuali NC particelle elementari1 , 2 , 3 , 4. tra i vari approcci all'Assemblea di nanoparticelle, il metodo di fissaggio orientato - in quale NCs essenzialmente sono fusi con l'altro - si distingue come uno che consente di accoppiamento elettronico interparticella. Tuttavia, attaccamento orientata convenzionale richiede in genere il delicato bilanciamento della particella dipolo, ligando e interazioni solvente che sono generalmente difficili da eseguire e rendere applicabile a sistemi diversi di NC.
Recentemente abbiamo sviluppato un metodo di bagnato-chimico di unirsi covalentemente cadmio forma-anisotropo calcogenuri NCs introducendo un intermedio reattivo inorganico attraverso un processo di nucleazione sito-selettivo. Le particelle sono successivamente collegate tramite la fusione spontanea dei reattivi inorganici intermedio dei domini5. Anche se la tecnica è ancora basata su un meccanismo orientato allegato, c'è molto meno bisogno di considerare deboli interazioni interparticella, consentendo in tal modo maggiore flessibilità e controllo. Il collegamento di cadmio forma-anisotropo calcogenuri NCs è effettuato convertendo prima loro sfaccettature di punta in argento calcogenuri tramite un processo di scambio cationico parziale (in soluzione); Questo è seguito dalla rimozione selettiva di ligandi passivazione della superficie. NCs quindi si uniscono tramite la fusione delle sfaccettature esposta calcogenuri d'argento, conseguente assemblee del cadmio calcogenuri NCs collegati-to-end.
In questo protocollo, dimostriamo che il collegamento tra tecnica può essere applicata ad una varietà di forma-anisotropo cadmio calcogenuri NCs (cioè, CdSe-seminato CD NRs e seminato CdSe CdSe NRs o TPs), rendimento lineare lunga NR catene o altamente ramificati TP reti. Questi risultati suggeriscono che la tecnica può essere estesa a una vasta gamma di forme di NC e metallo calcogenuri suscettibili di scambio cationico d'argento.

<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

Qui, descriviamo un protocollo che permette di cadmio forma-anisotropo calcogenuri nanocristalli (NCs), ad esempio nanorod (NRs) e tetrapodi (TPs), per essere covalentemente e site-specifically collegati tramite loro sfaccettature fine, conseguente simil-polimero lineare o ramificata catene. La procedura di collegamento inizia con un processo di scambio cationico in cui le sfaccettature di fine del cadmio calcogenuri NCs verrà convertito in calcogenuri d'argento. Questo è seguito dalla rimozione selettiva di ligandi alla loro superficie. In questo modo cadmio calcogenuri NCs con altamente reattivo calcogenuri d'argento fine sfaccettature che si fondono spontaneamente al contatto con l'altro, stabilendo così un allegato di faccetta--sfaccettatura interparticella. Attraverso la scelta giudiziosa delle concentrazioni di precursore, una vasta rete di NCs collegato può essere prodotto. Caratterizzazione strutturale del NCs collegate avviene tramite bassa e alta risoluzione microscopia elettronica a trasmissione (TEM), così come spettroscopia a raggi x energia-dispersiva, che confermano la presenza di domini di calcogenuri d'argento tra le catene di cadmio calcogenuri NCs.

Utilizzando CdSe-seminato CD NRs come sistema modello, come illustrato nella Figura 1(a), abbiamo dimostrato che possiamo utilizzare un parziale processo di scambio di Ag+ per trasformare in modo specifico le sfaccettature sulle punte NR Ag2S. Le sfaccettature di2S Ag sono ricoperti dalle DDA, che reagisce con ODPA tramite una reazione acido-base per formare un sale insolubile5. Questo fa sì che i ligandi DDA essere rimosso dalle sfaccettature2S Ag, causando loro di fondersi con l'altro al contatto e alla forma collegata catene NR, come mostrato in Figura 1(b). Per accertare se l'individuo NRs si fondono all'interno della catena o semplicemente sono tenute insieme da forze di Van der Waals, analisi HRTEM sulle regioni congiunte è stata effettuata. Come illustrato nella Figura 1(c), c'è un dominio distinto nel contatto epitassiale con due NRs. Un'analisi FFT dell'immagine HRTEM (inserto di Figura 1(c)) rivela l'esistenza di due costanti reticolari differenti che possono essere attribuite ad i facet (001) di Ag2S e CD. Inoltre, punto raggi x energia-dispersiva analisi di spettroscopia (EDX) sulla regione sollevatore prominente Mostra la presenza di Ag e l'assenza di Cd (Figura 1(d)), che conferma la nostra nozione di Ag2punta S CdSe-seminato CD NRs colmato tramite la fusione di Ag2 S domini. La resa e la natura statistica del processo di collegamento possono essere visualizzati tramite un istogramma (Figura 1(e)) che indica il numero di barre collegati all'interno di una catena NR.
Il meccanismo per il collegamento precedentemente è stato segnalato da Sabyasachi et al. 5 e non saranno descritti in dettaglio in questo lavoro. Si è osservato che, senza l'aggiunta di ODPA, nessun collegamento viene effettuato come si vede nella Figura 2(a), secondo la visione che l'aggiunta di ODPA provoca i nativi leganti di superficie della punta2S Ag a venire fuori. Questo può essere visto chiaramente in Figura 2(c), come mostra l'istogramma per la reazione di una parte cospicua del singolo, scollegato NRs. La presenza di dimeri potrebbe essere a causa di residui che ODPA rimasto dalla reazione di sintesi NR, permettendo una piccola quantità di collegamento per verificarsi. Oltre a ODPA, la concentrazione di AgNO3 inoltre è stata trovata per essere estremamente importante, come illustrato nella Figura 2(b), dove sono state ottenute solo brevi catene sotto le concentrazioni non ottimale di AgNO3. Dove la concentrazione di Ag+ usata era troppo bassa, l'istogramma mostra che la distribuzione è stata pesantemente verso lunghezze di catena. Infatti, le statistiche di collegamento per le catene illustrate nella Figura 2(b) caratteristica una percentuale sostanziale di dimeri, seguita da monomeri, come si vede nella Figura 2(d).
Oltre alla testa di serie CdSe CD NRs, indichiamo che l'Ag+-processo di collegamento mediato può essere esteso a testa di serie CdSe CdSe NRs e TPs, che sono mostrati in Figura 3(a) e (b), rispettivamente. Sotto le condizioni di reazione riassunte nella tabella 1, mostriamo che possiamo realizzare reti simili concatenate di CdSe-seminato CdSe NRs e TPs, come esemplificato nella Figura 3(c) e (d). Come nel caso di Ag2S-collegato CdSe-seminato CD NRs, le nanoparticelle di CdSe CdSe-teste di serie sono collegate tramite Ag2Se intermedi.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56009/56009fig1.jpg"> Figura 1. Caratterizzazione di collegato CdSe-seminato NRs CD. (a) a bassa risoluzione che mostra di immagine TEM come-sintetizzato CdSe-seminato CD NR. (b) a bassa risoluzione immagine TEM risultati Ag2S-collegato CdSe-seminato CdS NRs. (c) ad alta risoluzione (HRTEM) immagine TEM di un singolo giunto tra due NRs. Inset è un Fast Fourier Transform (FFT) dell'immagine HRTEM, mostrando due punti diversi della grata che sono attribuito a CD e Ag2S. (d) analisi EDX punto su un punto singolo collegamento, confermando la sua composizione come Ag2S. (e) istogramma mostra la distribuzione del numero di NRs per catena in un campione tipico collegato NR. <a href="//cloudflare-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/56009/56009fig1large.jpg" target="_blank">Clicca qui per visualizzare una versione più grande di questa figura.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56009/56009fig2.jpg"> Figura 2 . Risultati delle condizioni di reazione non ottimale. (a) immagine TEM di CdSe-seminato NRs CD con punte di2S Ag che ha subito la procedura di collegamento, con l'eccezione che nessun ODPA è stato utilizzato. (b) immagine TEM mostrando brevi catene di Ag2S-collegato NRs CD CdSe-seminato quando la concentrazione di Ag+ non è stata ottimizzata. (c) istogramma che mostra che la maggior parte delle specie presenti sono singolo NRs quando ODPA è assente. (d) istogramma che mostra che, quando la concentrazione di Ag+ non è ottimizzata, solo brevi catene sono presenti. <a href="//cloudflare-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/56009/56009fig2large.jpg" target="_blank">Clicca qui per visualizzare una versione più grande di questa figura.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56009/56009fig3.jpg"> Figura 3 . Estensione del processo di collegamento di nanostrutture CdSe CdSe-seminato. (a) a bassa risoluzione immagine TEM mostrando come sintetizzato CdSe-seminato CdSe NRs. (b) Low-resolution TEM immagine mostrando come sintetizzato CdSe-seminato CdSe TPs. (c) Low-resolution l'immagine mostrando la testa di serie CdSe CdSe NRs dopo il collegamento. (d) a bassa risoluzione immagine TEM mostrando la testa di serie CdSe CdSe TPs dopo il collegamento. <a href="//cloudflare-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/56009/56009fig3large.jpg" target="_blank">Clicca qui per visualizzare una versione più grande di questa figura.</a>
<table fo:keep-together.within-page="1"><tbody>
<tr>
<td>Nanoparticella</td>
			<td>Concentrazione della soluzione di NC (mM)</td>
			<td>Concentrazione della soluzione di Ag+ (mM)</td>
			<td>Mescolando tempo (ore)</td>
		</tr>
<tr>
<td>CdSe seminato CD NRs</td>
			<td>3</td>
			<td>1</td>
			<td>1</td>
		</tr>
<tr>
<td>CdSe seminato CdSe NRs</td>
			<td>5</td>
			<td>0,8</td>
			<td>1</td>
		</tr>
<tr>
<td>CdSe seminato CdSe TPs</td>
			<td>5</td>
			<td>0.6</td>
			<td>0,5</td>
		</tr>
</tbody></table>Tabella 1. Riepilogo delle concentrazioni approssimative della soluzione NC e l'Ag+ soluzione e del tempo richiesto agitazione.

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 protocollo di dettagliare come forma-anisotropo cadmio colloidale calcogenuri nanocristalli possono essere legata covalentemente tramite loro sfaccettature di fine sono presentato qui.

Faccetta--sfaccettatura che collega di cadmio colloidale forma-anisotropo Chalcogenide nanostrutture

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

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Chemistry

7.6K Views.  National University of Singapore. Un protocollo di dettagliare come forma-anisotropo cadmio colloidale calcogenuri nanocristalli possono essere legata covalentemente tramite loro sfaccettature di fine sono presentato qui.

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 Quantum Dots per singola molecola Imaging

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

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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.

Rivelare processi dinamici dei materiali in liquidi con liquido di trasmissione microscopia elettronica cellulare

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 ...

Chimica

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.

Sintesi e caratterizzazione di supramolecolari colloidi

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

Creating Sub-50 Nm Nanofluidic Junctions in PDMS Microfluidic Chip via Self-Assembly Process of Colloidal Particles

Polydimethylsiloxane (PDMS) is the prevailing building material to make microfluidic devices due to its ease of molding and bonding as well as its transparency. Due to the softness of the PDMS material, however, it is challenging to use PDMS for building nanochannels. The channels tend to collapse easily during plasma bonding. In this paper, we present an evaporation-driven self-assembly method of silica colloidal nanoparticles to create nanofluidic junctions with sub-50 nm pores between two microchannels. The pore size as well as the surface charge of the nanofluidic junction is tunable simply by changing the colloidal silica bead size and surface functionalization outside of the assembled microfluidic device in a vial before the self-assembly process. Using the self-assembly of nanoparticles with a bead size of 300 nm, 500 nm, and 900 nm, it was possible to fabricate a porous membrane with a pore size of ~45 nm, ~75 nm and ~135 nm, respectively. Under electrical potential, this nanoporous membrane initiated ion concentration polarization (ICP) acting as a cation-selective membrane to concentrate DNA by ~1,700 times within 15 min. This non-lithographic nanofabrication process opens up a new opportunity to build a tunable nanofluidic junction for the study of nanoscale transport processes of ions and molecules inside a PDMS microfluidic chip.

We propose a simple self-assembly technique of silica colloidal nanoparticles to create a nanofluidic junction between two microchannels in polydimethylsiloxane (PDMS). Using this technique, a nanoporous bead membrane with a pore size down to ~45 nm was built inside a microchannel and applied to electrokinetic preconcentration of DNA samples.

Creazione di Sub-50 Nm nanofluidic giunzioni in PDMS Microfluidic Chip tramite processo di auto-assemblaggio di particelle colloidale

Polydimethylsiloxane (PDMS) is the prevailing building material to make microfluidic devices due to its ease of molding and bonding as well as its ...

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.

Morfologie autoassemblanti Ottenuto da elicoidali policarbodiimide copolimeri e loro derivati ​​triazolici

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 elettronica in trasmissione di liquidi-cellula per l'inseguimento auto-assemblaggio delle nanoparticelle

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.

Fabbricazione di matrici Nanocup oro periodica mediante Litografia colloidale

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

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.

Array Ligand Nano-cluster in un doppio strato lipidico supportati

Currently there is considerable interest in creating ordered arrays of adhesive protein islands in a sea of passivated surface for cell biological ...

Bioingegneria

Fabrication of Zero Mode Waveguides for High Concentration Single Molecule Microscopy

In single molecule fluorescence enzymology, background fluorescence from labeled substrates in solution often limits fluorophore concentration to pico- to nanomolar ranges, several orders of magnitude less than many physiological ligand concentrations. Optical nanostructures called zero mode waveguides (ZMWs), which are 100&#8722;200 nm in diameter apertures fabricated in a thin conducting metal such as aluminum or gold, allow imaging of individual molecules at micromolar concentrations of fluorophores by confining visible light excitation to zeptoliter effective volumes. However, the need for expensive and specialized nanofabrication equipment has precluded the widespread use of ZMWs. Typically, nanostructures such as ZMWs are obtained by direct writing using electron beam lithography, which is sequential and slow. Here, colloidal, or nanosphere, lithography is used as an alternative strategy to create nanometer-scale masks for waveguide fabrication. This report describes the approach in detail, with practical considerations for each phase. The method allows thousands of aluminum or gold ZMWs to be made in parallel, with final waveguide diameters and depths of 100&#8722;200 nm. Only common lab equipment and a thermal evaporator for metal deposition are required. By making ZMWs more accessible to the biochemical community, this method can facilitate the study of molecular processes at cellular concentrations and rates.

Described here is a nanosphere lithography method for parallel fabrication of zero mode waveguides, which are arrays of nanoapertures in a metal-clad glass microscopy coverslip for single molecule imaging at nano- to micromolar concentrations of fluorophores. The method takes advantage of colloidal crystal self-assembly to create a waveguide template.

Fabbricazione di guide d'onda in modalità zero per microscopia ad alta concentrazione a singola molecola

In single molecule fluorescence enzymology, background fluorescence from labeled substrates in solution often limits fluorophore concentration to pico- to ...

Faccetta--sfaccettatura che collega di cadmio colloidale forma-anisotropo Chalcogenide nanostrutture

Riepilogo

Esplora Altri Video

Capitoli in questo video

Compact Quantum Dots per singola molecola Imaging

Rivelare processi dinamici dei materiali in liquidi con liquido di trasmissione microscopia elettronica cellulare

Seeded Synthesis of CdSe/CdS Rod and Tetrapod Nanocrystals

Sintesi e caratterizzazione di supramolecolari colloidi

Creazione di Sub-50 Nm nanofluidic giunzioni in PDMS Microfluidic Chip tramite processo di auto-assemblaggio di particelle colloidale

Morfologie autoassemblanti Ottenuto da elicoidali policarbodiimide copolimeri e loro derivati triazolici

Microscopia elettronica in trasmissione di liquidi-cellula per l'inseguimento auto-assemblaggio delle nanoparticelle

Fabbricazione di matrici Nanocup oro periodica mediante Litografia colloidale

Array Ligand Nano-cluster in un doppio strato lipidico supportati

Fabbricazione di guide d'onda in modalità zero per microscopia ad alta concentrazione a singola molecola

Faccetta--sfaccettatura che collega di cadmio colloidale forma-anisotropo Chalcogenide nanostrutture

Riepilogo

Esplora Altri Video

Capitoli in questo video

Compact Quantum Dots per singola molecola Imaging

Rivelare processi dinamici dei materiali in liquidi con liquido di trasmissione microscopia elettronica cellulare

Seeded Synthesis of CdSe/CdS Rod and Tetrapod Nanocrystals

Sintesi e caratterizzazione di supramolecolari colloidi

Creazione di Sub-50 Nm nanofluidic giunzioni in PDMS Microfluidic Chip tramite processo di auto-assemblaggio di particelle colloidale

Morfologie autoassemblanti Ottenuto da elicoidali policarbodiimide copolimeri e loro derivati ​​triazolici

Microscopia elettronica in trasmissione di liquidi-cellula per l'inseguimento auto-assemblaggio delle nanoparticelle

Fabbricazione di matrici Nanocup oro periodica mediante Litografia colloidale

Array Ligand Nano-cluster in un doppio strato lipidico supportati

Fabbricazione di guide d'onda in modalità zero per microscopia ad alta concentrazione a singola molecola

Morfologie autoassemblanti Ottenuto da elicoidali policarbodiimide copolimeri e loro derivati triazolici