Name: synthesis of ligand-free cds nanoparticles within a sulfur copolymer matrix
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The authors would like to acknowledge the State of Washington for supporting this research through the University of Washington Clean Energy Institute Exploratory Fellowship Program, and National Science Foundation (NSF) Sustainable Energy Pathway (SEP) Award CHE-1230615.

注意:镉的前体是剧毒，必须非常小心处理。佩戴合适的防护设备，采用适当的工程控制，并咨询有关材料安全数据表（MSDS）。此外，纳米颗粒的生成可能存在额外的危害。本文所描述的反应是用标准真空气体歧管进行的，以便在惰性气氛中进行的实验。所有的化学品均商购并且原样使用。这个协议是基于一个先前开发的合成方法，这是我们最近别处所述。5 1.硫共聚物合成<ol><li> 熔火之元素硫的制备 <ol><li>地方元素硫（4克，124.8毫摩尔，S 8，99.5％）与一个附加冷凝器和温度探头50毫升三颈烧瓶中。用真空和氮气数次执行泵和吹扫循环。 </li><li>氮气下热至150℃，搅拌，这将导致硫成为黄色液体。 </li></ol></li><li> 硫共聚物的制备 <ol><li>一旦所有的硫的溶解到液体，立即注入α甲基苯乙烯（330微升，2.5毫摩尔，99％）到溶液中。 </li><li>热溶液至185℃，以500rpm搅拌10分钟。作为共聚物的形式，该解决方案将从黄色变色到橙色，终于产生深红色。 </li><li>除去从热溶液中，并冷却到室温。当其冷却时，共聚物会慢慢结晶，以形成一种橙色橡胶状固体。在此阶段，该共聚物可以在室温下保存用于随后的合成，或者可以立即使用。 </li></ol></li></ol> 2.硫化镉纳米粒子合成<ol><li>乙酰丙酮镉（Cd的（ACAC），900毫克，2.9毫摩尔99.9％）来自前面步骤添加到三颈烧瓶中，以使粉末放置均匀地涂在固体硫共聚物（4.0克，116毫摩尔）的顶部。 </li><li>上用氮气和真空几次烧瓶执行泵和吹扫循环。 </li><li>加热在氮气下将溶液至200℃，同时搅拌。硫共聚物会熔化并与镉前体混合，并在纳米颗粒成核和生长过程将开始。 </li><li>允许纳米颗粒中生长30分钟。 注:改变反应时间会影响纳米粒子的生长，所以有可能调整纳米颗粒的最终尺寸5所述的30分钟的反应时间将与7-10纳米的尺寸范围为5 </li><li>除去从热溶液中，并允许冷却到室温。 </li><li>一旦冷却，取出从烧瓶中并储存在室温下的固体纳米复合材料。 </li></ol> 3.除去硫共聚物和隔离纳米粒子<ol><li> 硫磺共聚物的去除 </s仲&gt; <ol><li>放置所述纳米复合材料（200毫克）在20毫升玻璃小瓶中，并添加氯仿（20毫升）中。 </li><li>在放置1小时超声波发生器和超声小瓶，打破了纳米复合材料，并暂停该解决方案中的纳米粒子。 </li><li>分离溶液进入两台30毫升离心管中，另外20毫升氯仿添加到每个。 </li><li>离心在8,736×g离心15分钟将溶液（相对离心力）。 </li><li>从离心管中倒出硫共聚物，确保不打扰解决纳米粒子。 </li></ol></li><li> 所述纳米粒子的隔离 <ol><li>加入氯仿至每个离心管（30ml）中，并超声处理15分钟，再分散安定纳米颗粒。 </li><li>重复部分3.1.4，3.1.5和3.2.1三次以上描述，以确保所有的硫共聚物的已被删除的步骤。一旦所有的硫共聚物被移除，滗析溶液将没有罗手指有一个橙色。 </li><li>加入氯仿（2ml）中于每个离心管中收集的最终纳米颗粒。 </li><li>结合所收集的纳米颗粒在一个20ml玻璃瓶（4 ml溶液总）和放置玻璃小瓶在真空下除去所有氯仿和干燥的纳米颗粒。在这个阶段，将所得的纳米粒子的质量可以被确定并以确定使用的起始原料和产物的摩尔比，反应的产率相比，前体的起始物质。 </li></ol></li></ol> 4.表征纳米CdS <ol><li> 透射电子显微镜 <ol><li>稀释在氯仿分离的纳米颗粒（20毫克）（20毫升）和ultrasonicate 1小时。 </li><li>稀释15分钟的氯仿该溶液（5滴/ 5毫升）和超声处理。 </li><li>放下最后的解决方案与上一个400多孔碳支持膜超薄碳薄膜基材目铜透射电子显微镜（TEM）栅格。 </li><li>放置TEM网格在玻璃小瓶中并在真空下保持过夜，以从样品中除去任何残留的溶剂。 </li><li>一旦干燥完成后，使用200千伏的加速电压，为3的光点尺寸和一个附加的能量色散X射线光谱（EDS）的检测器获得的TEM图像。 </li></ol></li><li> X射线衍射 <ol><li>稀释在氯仿中分离纳米颗粒（10毫克/毫升）。 </li><li>清洁镀钼的钠钙玻璃基片（1 平方厘米）通过超声处理在洗涤剂，去离子水，丙酮和异丙醇中，每个10分钟。最后，清洁的空气等离子清洗基板的下降铸造前10分钟。 </li><li>从跌落4.2.1 7μl递增投的解决方案在底材上的4.2.2。 </li><li>一旦电影已经干涸，获得X射线衍射（XRD）数据。在扫描速度收集使用7000个数据点的数据每秒1数据点用铜的KαX射线源和1.54059埃的入射波长。 </li></ol></li><li> 光谱解决方案 <ol><li>分散在氯仿中，声处理分离的纳米颗粒（0.1毫克/毫升）30分钟，发生的样品在密封的石英杯中。 </li><li>驱散从第2.6节所述纳米复合材料和从部分1.2.3中的甲酰胺的硫共聚物（1毫克/毫升），搅拌在700rpm，并加热至70℃，以促进该材料的悬浮液中。 </li><li>获得的光致发光（PL）和吸收光谱对所有三个样品。进行使用分光计光学吸收测量与横跨紫外线，可见光和近红外范围（UV-VIS-NIR）延伸的三检测器。使用荧光分光光度计以330nm的激发波长进行PL测量。 注:表征使用部分讨论了纳米技术的具体协议4.1.5，4.2.4，一ND 4.3.2变化很大，取决于所使用的特定设备的性质，所以我们在座的只是一般的特性参数。有兴趣的读者是针对几个综述文章使用这些分析技术的CdS纳米粒子有关的详细信息17 - 19 </li></ol></li></ol>

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The authors disclose no competing financial interests.

We have developed a method to synthesize CdS nanoparticles within a sulfur copolymer matrix. This sulfur copolymer is composed of elemental sulfur and methylstyrene.5 An important feature of this method is that the copolymer can be used as both a high-temperature solvent and a sulfur source that reacts with a cadmium precursor to produce CdS nanoparticles in solution.5 The critical step in the procedure is the synthesis of the sulfur copolymer with a suitable ratio of methylstyrene and sulfur. The use of methylstyrene and in the appropriate concentration is important to form the copolymer that can be stored as a powder at room temperature, and then be heated to produce a liquid to allow the nanoparticle synthesis to occur. During the synthesis, only some of the sulfur reacts with the cadmium precursor, while the remainder stays within the sulfur copolymer.5 Once the reaction solution is cooled and solidified, this procedure produces CdS nanoparticles suspended within a sulfur copolymer matrix.5 The copolymer can subsequently be removed, producing nanoparticles that do not have conventional organic ligands.5 A limitation of our method however, is that once the copolymer is removed, the nanoparticles are prone to aggregation, which can be prevented when conventional organic ligands are present. This makes it difficult to control the self-assembly of our nanoparticles during film formation. The nanoparticle size can be tuned by varying the reaction time, although another limitation is that this method produces nanoparticles with a higher level of polydispersity in size than conventional techniques,5,18 which broadens the absorption and emission spectra of our nanoparticles.
This nascent synthesis method can be useful in a range of fields where the presence of conventional aliphatic ligands diminishes the charge transfer or surface reaction properties of the nanoparticles. Furthermore, this synthesis method is relatively simple in comparison to other methods that require multistep ligand exchange or ligand stripping procedures to remove conventional aliphatic ligands.1-4 For example, one set of nanoparticles could be functionalized with a range of ligands to produce nanoparticles with a spectrum of different properties.9 In addition, this method could be used to produce nanoparticle based devices where the presence of organic ligands would otherwise introduce unwanted carbon impurities.10,12

虽然证明对合成是有用的，常规的脂族配位体存在许多用于纳米颗粒的光子和电化学装置的实施挑战。脂肪族配体高度绝缘，疏水性，并构成显著障碍电化学表面反应。1因此，一些研究已经开发了配体交换和配体剥离与功能部分或剥去配体取代这些脂肪族配体的协议，露出了光秃秃的纳米粒子表面1 - 3这些反应，但是，提出几个问题的内在。它们显著添加到合成过程的复杂性，不总是进行完全，并能恶化的纳米颗粒，使用这些技术时，器件制造过程中，可反过来强加显著问题的表面上。4 我们已经开发了硫共聚物，其可以用作硫化镉纳米粒子的合成过程中既高温溶剂和硫源。5该共聚物是基于由。Chung等人 ，使用元素硫和1,3-二异丙烯基苯（DIB）开发的网络共聚物。6在我们的情况下，甲基单体实现的，而不是DIB。的甲基单体限制交联反应，否则将产生一个高的分子量网络共聚物。5,6-只有一个乙烯基官能团的对甲基苯乙烯单体的存在促进形成低聚自由基一旦加热，这使得硫共聚物具体操作为并联纳米颗粒合成过程中的液体溶剂和硫源5，硫聚合物通过元素硫加热至150℃，这将导致在S 8环转变到线性结构液体硫双基形式产生。接下来，甲基注入我<html> n要在甲基分子与硫原子1:50摩尔比液体硫。5所述的甲基双键与硫链反应产生的共聚物，如在图1中。5硫共聚物，然后冷却和镉前体加入。然后将该混合物再加热到200℃，在此期间，硫共聚物熔化，并在纳米颗粒成核和生长过程发起的溶液内5 A 20:是用来硫镉前体的摩尔比为1:1，所以，只有某些硫在反应过程中消耗掉。5该共聚物由一旦反应已终止的固体聚合物基质中悬浮它们稳定纳米颗粒。5的共聚物可以在合成之后被去除，导致生产不具有的CdS纳米粒子的有机配位配体，如在图2 5所示内容】"&gt;在这项工作中提出的合成方法是比较简单的，在文献中提出的其它方法的比较。1 - 3,7在传统连接的纳米颗粒已被证明存在问题，或不希望的，适用于不同范围的应用这种技术可以打开大门更高吞吐量测试，其中一个批次纳米粒子可用于检查后续functionalizations的完整频谱，而不需要复杂且耗时的配位体剥离或交换过程。2,4,8,9这些未连接的纳米颗粒也提供机会通过消除碳源，以减少印刷纳米器件通常观察到的碳缺陷的数量。10 - 16本详细的协议旨在帮助他人实施这种新方法，并帮助推动各种会发现场的积极使用它具有特殊的意义。

<table><tbody><tr><td>Sulfur (S&lt;sub&gt;8&lt;/sub&gt;), 99.5%</td><td>Sigma Aldrich</td><td>84683</td><td></td></tr><tr><td>&amp;alpha;-methylstyrene, 99%</td><td>Sigma Aldrich</td><td>M80903</td><td></td></tr><tr><td>Cadmium acetylacetonate (Cd(acac)), 99.9%</td><td>Sigma Aldrich</td><td>517585</td><td>Highly Toxic</td></tr><tr><td>Chloroform (CHCl&lt;sub&gt;3&lt;/sub&gt;), 99.5%</td><td>Sigma Aldrich</td><td>C2432</td><td></td></tr><tr><td>Hotplate / magnetic stirrer</td><td>IKA RCT&amp;nbsp;</td><td>3810001</td><td></td></tr><tr><td>Temperature controller with probe and heating mantle</td><td>Oakton Temp 9000</td><td>WD-89800</td><td></td></tr><tr><td>Centrifuge</td><td>Beckman Coulter Allegra X-22</td><td>392186</td><td></td></tr><tr><td>Centrifuge Tubes</td><td>Thermo Scientific</td><td>3114</td><td>Teflon for resistance to chlorinated solvents</td></tr><tr><td>TEM with attached EDS detector</td><td>FEI Tecnai G2 F-20 with EDAX detector</td><td></td><td></td></tr><tr><td>TEM Sample Grid</td><td>Ted Pella</td><td>1824</td><td>Ultrathin carbon film substrate with holey carbon support films on a 400 mesh copper grid</td></tr><tr><td>XRD</td><td>Bruker F-8 Focus Diffractometer</td><td></td><td></td></tr><tr><td>Molybdenum coated soda lime glass substrates</td><td></td><td></td><td>750 nm thick sputtered molybdenum layer</td></tr><tr><td>Quartz Fluorescence Cuvettes</td><td>Sigma Aldrich</td><td>Z803073</td><td>10 mm by 10 mm, 4 polished sides with screw top</td></tr><tr><td>UV-Vis-NIR</td><td>Perkin Elmer Lambda 1050 Spectrometer</td><td></td><td>With 3D WB Detector Module</td></tr><tr><td>PL</td><td>Horiba FL3-21tau Fluorescence Spectrophotometer</td><td></td><td></td></tr></tbody></table>

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.

在图3a的TEM图像显示了已硫共聚物内成核之前的硫共聚物已被完全除去小的CdS纳米粒子（3-4纳米）。在图3a中的图像通过取纳米颗粒溶液的等分试样后，立即将溶液达到200℃获得的。 图3b示出已在溶液中生长30分钟的硫共聚物已经完全以前大纳米颗粒（7-10纳米）除去。 图3c示出图3b中的突出显示区域的更高放大率的图像。在图3c一种纳米颗粒具有测得为3.3埃的特别清楚原子面间隔。 3.3埃的原子面间隔是具有闪锌矿硫化镉或纤锌矿的CdS的（002）面间距的（111）面间距是一致的。 图3D示出，一旦硫共聚物完全除去并溶解在氯仿中，纳米颗粒会聚集在一起。在图3d给出的EDS数据证实硫 ​​化镉的化学计量（接近1:1），并确认该硫共聚物已被有效去除。 在先前的出版物中，我们使用傅立叶变换红外光谱（FTIR）和质子核磁共振谱（1 H NMR）表明，一旦硫共聚物是完全除去，这些纳米颗粒不具有传统的有机配体。5一项研究通过纳格等。人发现，金属硫化物纳米颗粒可以与阴离子硫物质被有效地连接。7，我们断定，纳米颗粒使用这种方法也同样构成的纳米颗粒表面上的硫物种进行。在图3d给出的EDS数据表明有轻微的化学计量过量的硫，这是按照与硫物种对nanopar存在察员的表面。 为降铸纳米颗粒薄膜的X射线衍射图案示于图4，并与纤锌矿的形成相一致，还可能闪锌矿结构的CdS。设在26.6度的峰对应于3.3埃的原子面间隔，它与闪锌矿硫化镉或纤锌矿的CdS的（002）面间距的（111）面间距一致，证实了在TEM看到的平面间距图3c的图像。 使用UV-Vis光谱， 如图5中的硫共聚物和纳米复合材料进行了分析。由于每个分散体的浓度相等时，数据表明，该纳米复合材料显示出在比较的显著增强吸光度仅硫共聚物。在图6示出呈现的光致发光的数据，该纳米复合材料表现出峰，它是从散装蓝移硫化镉带隙（510纳米，2.4电子伏特），而硫共聚物峰是比较小的。 分离的纳米颗粒也使用紫外-可见-近红外和PL光谱一旦硫共聚物除去检验。 图7示出了既在UV-VIS-NIR和PL数据。在图6中，纳米颗粒具有在硫化镉的体材料带隙和小吸收边缘是在450-550纳米范围内的相应的宽吸收光谱为中心的广泛的PL峰。一旦硫聚合物被除去，所述纳米颗粒表面不再钝化并包含由于悬空键的存在表面缺陷。这导致新的表面介导的能量状态的存在是随后相比于在图5和6的纳米复合材料呈现的光谱拓宽和红移的PL及吸收光谱18,20 - 22另外，在显示出量子限制效应，这也拓宽了光谱的纳米颗粒群体的纳米颗粒的结果的多分散性。23因此，与我们以前的工作相结合，这个数据支持权利要求，这些纳米颗粒不具有传统的缺陷钝化一旦有机配体硫共聚物被除去。5此外，该数据表明，硫共聚物之前的去除钝化的CdS纳米粒子的表面上的缺陷。 <img alt="图1" src="/files/ftp_upload/54047/54047fig1.jpg" /> 图硫共聚物的合成1和结构，元素硫被加热产生线性结构的液态硫双基，其与甲基产生硫共聚物反应。 <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/54047/54047fig1large.jpg" target="_blank">请点击此处查看大图</a>这一数字。 <img alt="图2" src="/files/ftp_upload/54047/54047fig2.jpg" /> 图2.纳米粒子生长和隔离。硫化镉纳米粒子核和硫共聚物内生长。一旦反应完成，硫共聚物被删除，产生无配体硫化镉纳米粒子。 <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/54047/54047fig2large.jpg" target="_blank">请点击此处查看该图的放大版本。</a> <img alt="图3" src="/files/ftp_upload/54047/54047fig3.jpg" /> 图3孤立的CdS纳米粒子的TEM图像。 一个 ）3-4纳米的CdS纳米粒子开始共聚物内生长。B）7-10一旦终止反应纳米颗粒。小号共聚物仍然存在在这个阶段。 三 ）突出放大图像在B，D区）的去除量S共聚物后TEM照片。插图显示EDS数据。 <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/54047/54047fig3large.jpg" target="_blank">请点击此处查看该图的放大版本。</a> <img alt="图4" src="/files/ftp_upload/54047/54047fig4.jpg" /> 图4.硫化镉纳米颗粒薄膜的XRD图。XRD图形与纤锌矿或闪锌矿的CdS的形成是一致的。钼峰由于基板。 <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/54047/54047fig4large.jpg" target="_blank">请点击此处查看该图的放大版本。</a> <img alt="图5" src="/files/ftp_upload/54047/54047fig5.jpg" /> 图硫共聚物纳米复合材料5吸收光谱，纳米复合材料表现出signif相比于单独的硫共聚物icantly增强吸收峰。这两种材料具有相同浓度而分散。 <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/54047/54047fig5large.jpg" target="_blank">请点击此处查看该图的放大版本。</a> <img alt="图6" src="/files/ftp_upload/54047/54047fig6.jpg" /> 图6.光致发光光谱硫共聚物和纳米复合材料。纳米复合材料表现出的峰值是蓝移从CD的大部分带隙（510纳米，2.4伏特），而硫共聚物呈现相对较少的光致发光。 <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/54047/54047fig6large.jpg" target="_blank">请点击这里查看更大的版本这个数字。</a> <img alt="图7" src="/files/ftp_upload/54047/54047fig7.jpg" /> Figu7.重无配体的CdS纳米粒子的吸收和光致发光光谱。该PL数据显示，在510 nm处的宽峰。紫外-可见-近红外数据显示，在450-550纳米范围内的弱吸收肩膀较宽的吸收曲线。 <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/54047/54047fig7large.jpg" target="_blank">请点击此处查看该图的放大版本。</a>

Watch this Scientific Journal Video about Synthesis of Ligand-free CdS Nanoparticles within a Sulfur Copolymer Matrix at JoVE.com

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

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.

a硫磺共聚物基质内的免费配体硫化镉纳米粒子的合成

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

synthesis-ligand-free-cds-nanoparticles-within-sulfur-copolymer

Nanyang Technological University

Research

JoVE Journal

Chemistry

9.4K 次观看.  University of Washington. 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.

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

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.

紧凑型量子点的单分子成像

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

科研

工程学

Harvesting Solar Energy by Means of Charge-Separating Nanocrystals and Their Solids

Conjoining different semiconductor materials in a single nano-composite provides synthetic means for the development of novel optoelectronic materials offering a superior control over the spatial distribution of charge carriers across material interfaces. As this study demonstrates, a combination of donor-acceptor nanocrystal (NC) domains in a single nanoparticle can lead to the realization of efficient photocatalytic1-5 materials, while a layered assembly of donor- and acceptor-like nanocrystals films gives rise to photovoltaic materials.
Initially the paper focuses on the synthesis of composite inorganic nanocrystals, comprising linearly stacked ZnSe, CdS, and Pt domains, which jointly promote photoinduced charge separation. These structures are used in aqueous solutions for the photocatalysis of water under solar radiation, resulting in the production of H2 gas. To enhance the photoinduced separation of charges, a nanorod morphology with a linear gradient originating from an intrinsic electric field is used5. The inter-domain energetics are then optimized to drive photogenerated electrons toward the Pt catalytic site while expelling the holes to the surface of ZnSe domains for sacrificial regeneration (via methanol). Here we show that the only efficient way to produce hydrogen is to use electron-donating ligands to passivate the surface states by tuning the energy level alignment at the semiconductor-ligand interface. Stable and efficient reduction of water is allowed by these ligands due to the fact that they fill vacancies in the valence band of the semiconductor domain, preventing energetic holes from degrading it. Specifically, we show that the energy of the hole is transferred to the ligand moiety, leaving the semiconductor domain functional. This enables us to return the entire nanocrystal-ligand system to a functional state, when the ligands are degraded, by simply adding fresh ligands to the system4.
To promote a photovoltaic charge separation, we use a composite two-layer solid of PbS and TiO2 films. In this configuration, photoinduced electrons are injected into TiO2 and are subsequently picked up by an FTO electrode, while holes are channeled to a Au electrode via PbS layer6. To develop the latter we introduce a Semiconductor Matrix Encapsulated Nanocrystal Arrays (SMENA) strategy, which allows bonding PbS NCs into the surrounding matrix of CdS semiconductor. As a result, fabricated solids exhibit excellent thermal stability, attributed to the heteroepitaxial structure of nanocrystal-matrix interfaces, and show compelling light-harvesting performance in prototype solar cells7.

A general strategy for the development of charge-separating semiconductor nanocrystal composites deployable for solar energy production is presented. We show that assembly of donor-acceptor nanocrystal domains in a single nanoparticle geometry gives rise to a photocatalytic function, while bulk-heterojunctions of donor-acceptor nanocrystal films can be used for photovoltaic energy conversion.

通过电荷分离纳米晶及其固体收获太阳能

Conjoining different semiconductor materials in a single nano-composite provides synthetic means for the development of novel optoelectronic materials ...

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.

硒化镉/硫化镉棒和纳米四脚合成种子

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

化学

Synthesis, Characterization, and Functionalization of Hybrid Au/CdS and Au/ZnS Core/Shell Nanoparticles

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large extinction coefficients which can be tuned across the visible spectrum. Research into the plasmonic enhancement of optical transitions has become popular, due to the possibility of altering and in some cases improving photo-absorption or emission properties of nearby chromophores such as molecular dyes or quantum dots. The electric field of the plasmon can couple with the excitation dipole of a chromophore, perturbing the electronic states involved in the transition and leading to increased absorption and emission rates. These enhancements can also be negated at close distances by energy transfer mechanism, making the spatial arrangement of the two species critical. Ultimately, enhancement of light harvesting efficiency in plasmonic solar cells could lead to thinner and, therefore, lower cost devices. The development of hybrid core/shell particles could offer a solution to this issue. The addition of a dielectric spacer between a gold nanoparticles and a chromophore is the proposed method to control the exciton plasmon coupling strength and thereby balance losses with the plasmonic gains. A detailed procedure for the coating of gold nanoparticles with CdS and ZnS semiconductor shells is presented. The nanoparticles show high uniformity with size control in both the core gold particles and shell species allowing for a more accurate investigation into the plasmonic enhancement of external chromophores.

The synthesis of uniform gold nanoparticles coated with semiconductor shells of CdS or ZnS is performed. The semiconductor coating is conducted by first depositing a silver sulfide shell and exchanging the silver cations for zinc or cadmium cations.

合成，表征和混合金/硫化镉和Au / ZnS核/壳纳米颗粒功能化

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large ...

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.

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.

镉免费的InP /硫化锌量子点的合成适合生物医学应用

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

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.

纳米粒子 - 聚合物复合材料使用直接荧光成像的先进成分分析

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.

形状-各向异性胶体镉硫纳米结构的 Facet-to-facet 连接

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

Synthesis of a Thiol Building Block for the Crystallization of a Semiconducting Gyroidal Metal-sulfur Framework

We present a method for preparing thioester molecules as the masked form of the thiol linkers and their utilization for accessing a semiconducting and porous metal-dithiolene network in the highly ordered single crystalline state. Unlike the highly reactive free-standing thiols, which tend to decompose and complicate the crystallization of metal-thiolate open frameworks, the thioester reacts in situ to provide the thiol species, serving to mitigate the reaction between the mercaptan units and the metal centers, and to improve crystallization consequently. Specifically, the thioester was synthesized in a one-pot procedure: an aromatic bromide (hexabromotriphenylene) reacted with excess sodium thiomethoxide under vigorous conditions to first form the thioether intermediate product. The thioether was then demethylated by the excess thiomethoxide to provide the thiolate anion that was acylated to form the thioester product. The thioester was conveniently purified by standard column chromatography, and then used directly in the framework synthesis, wherein NaOH and ethylenediamine serve to revert in situ the thioester to the thiol linker for assembling the single-crystalline Pb(II)-dithiolene network. Compared with other methods for thiol synthesis (e.g., by cleaving alkyl thioether using sodium metal and liquid ammonia), the thioester synthesis here uses simple conditions and economical reagents. Moreover, the thioester product is stable and can be conveniently handled and stored. More importantly, in contrast to the generic difficulty in accessing crystalline metal-thiolate open frameworks, we demonstrate that using the thioester for in situ formation of the thiol linker greatly improves the crystallinity of the solid-state product. We intend to encourage broader research efforts on the technologically important metal-sulfur frameworks by disclosing the synthetic protocol for the thioester as well as the crystalline framework solid.

Here, we present a one-pot, transition-metal-free synthesis of thiols and thioesters from aromatic halides and sodium thiomethoxide, followed by the preparation of single crystals of a metal-dithiolene network using thiol species generated in situ from the more stable and tractable thioester.

半导体回转金属硫框架结晶的硫醇构建块的合成

We present a method for preparing thioester molecules as the masked form of the thiol linkers and their utilization for accessing a semiconducting and ...

Ligand-Mediated Nucleation and Growth of Palladium Metal Nanoparticles

The size, size distribution and stability of colloidal nanoparticles are greatly affected by the presence of capping ligands. Despite the key contribution of capping ligands during the synthesis reaction, their role in regulating the nucleation and growth rates of colloidal nanoparticles is not well understood. In this work, we demonstrate a mechanistic investigation of the role of trioctylphosphine (TOP) in Pd nanoparticles in different solvents (toluene and pyridine) using in situ SAXS and ligand-based kinetic modeling. Our results under different synthetic conditions reveal the overlap of nucleation and growth of Pd nanoparticles during the reaction, which contradicts the LaMer-type nucleation and growth model. The model accounts for the kinetics of Pd-TOP binding for both, the precursor and the particle surface, which is essential to capture the size evolution as well as the concentration of particles in situ. In addition, we illustrate the predictive power of our ligand-based model through designing the synthetic conditions to obtain nanoparticles with desired sizes. The proposed methodology can be applied to other synthesis systems and therefore serves as an effective strategy for predictive synthesis of colloidal nanoparticles.

The main goal of this work is to elucidate the role of capping agents in regulating the size of palladium nanoparticles by combining in situ small angle x-ray scattering (SAXS) and ligand-based kinetic modeling.

配体介导成核与钯金属纳米粒子的生长

The size, size distribution and stability of colloidal nanoparticles are greatly affected by the presence of capping ligands. Despite the key contribution ...

The Effect of Ultraviolet Radiation on the Chemical Bath Deposition of Bis(thiourea) Cadmium Chloride Crystals and the Subsequent CdS Obtention

In this work, the effects on the preparation of bis(thiourea) cadmium chloride crystals when illuminated with ultraviolet (UV) light at a wavelength of 367 nm using the chemical bath deposition technique are studied comparatively. Two experiments are performed to make a comparison: one without UV light and the other with the aid of UV light. Both experiments are performed under equal conditions, at a temperature of 343 K and with a pH of 3.2. The precursors used are cadmium chloride (CdCl2) and thiourea [CS(NH2)2], which are dissolved in 50 mL of deionized water with an acidic pH. In this experiment, the interaction of electromagnetic radiation is sought at the moment the chemical reaction is carried out. The results demonstrate the existence of an interaction between the crystals and the UV light; the UV light assistance causes crystal growths in an acicular shape. Also, the final product obtained is cadmium sulfide and shows no evident difference when synthesized with or without the use of UV light.

The Effect of Ultraviolet Radiation on the Chemical Bath Deposition of Bisthiourea Cadmium Chloride Crystals and the Subsequent CdS Obtention

This article presents a protocol for the synthesis of bis(thiourea) cadmium chloride crystals by chemical bath deposition. Two experiments are described: one aided by ultraviolet light compared to one without ultraviolet light.

紫外辐射对双 (硫脲) 氯化镉晶体化学镀液沉积的影响及随后的 CdS 获得

In this work, the effects on the preparation of bis(thiourea) cadmium chloride crystals when illuminated with ultraviolet (UV) light at a wavelength of ...