The authors thank Svilen Bobev for his help with the XRD spectra and K. Booksh for assistance with the sputter coater equipment.

1. Synthesis of Tree-like ZnO/CdSSe Nanostructures
<ol>
	<li>Pretreatment and gold coating of sapphire substrates 
	NOTE: The gold film acts as a catalyst in the growth of the ZnO nanowires.
	<ol>
		<li>Clean sapphire slides (a-plane, 10 &#215; 10 &#215; 1 mm) in 99.5% ethanol with 5 min of sonication to prepare the substrate for Au sputtering.</li>
		<li>Deposit a 10-nm (&#177; 2 nm)-thick film of gold onto the sapphire slides with a sputter coater and gold target.</li>
	</ol>
	</li>
	<li>Synthesis of ZnO nanowires 
	NOTE: The sonication step 1.2.2 results in a homogeneous ZnO and carbon (ZnO/C) mixture. After mixing, the mixture changes to a gray color. The compaction step 1.2.3 ensures that no air is present in the mixture and that the ZnO and carbon are in close contact. After CVD, a white film of ZnO nanowires should be deposited on the substrate, side facing down towards the boat.
	<ol>
		<li>Mix 1 g of ZnO nanopowder and activated carbon (mass fraction of 50:50) in 10 ml of 99.5% ethanol and stir well with a spatula.</li>
		<li>Sonicate the mixture in a water bath at 20 &#186;C for 30 min, and then dry it in an oven for ~5 hr at 80 &#186;C.</li>
		<li>Place the ZnO/C mixture in an alumina boat and compact it well with a spatula.</li>
		<li>Place the gold-coated sapphire slides on top of the alumina boat, with the gold-coated side facing down. Place the alumina boat in the center of the quartz tube in a horizontal tube furnace.</li>
		<li>Purge the quartz tube for 1 hr with Ar at a flow rate of 40 sccm at room temperature (RT). Increase the temperature from RT to 900 &#186;C at a rate of 80 &#186;C/min and keep the argon flow rate constant.</li>
		<li>Hold the temperature at 900 &#186;C for 2 hr. Open the quartz tube on both ends by removing the rubber stopper gas inlets and let air enter the tube to provide oxygen for the reaction.</li>
		<li>Keep the reaction temperature at 900 &#186;C for 3 hr with the rubber stoppers removed. Cool down to RT at a rate of 10 &#186;C/min.</li>
		<li>Take the boat and the slide out of the furnace.</li>
	</ol>
	</li>
	<li>Deposition of CdSSe branches on ZnO nanowires 
	NOTE: The alumina boat of CdS/Se was displayed in the center the quartz tube. The prepared ZnO nanowires were facing upward and were 10 cm downstream from the boat. After this second CVD, an orange/yellow film, which is the ZnO/CdSSe nanostructure, should be deposited on the slide.
	<ol>
		<li>Mix 0.5 g of CdS and CdSe (CdS/Se) powder well (mass fraction of 50:50) and place the mixture in an alumina boat. Compact the mixture well.</li>
		<li>Place the alumina boat of CdS/Se and the previously prepared ZnO nanowire sample in the quartz tube.</li>
		<li>Purge the tube with Ar at a flow rate of 40 sccm at RT for 1 hr. Increase the reaction temperature to 820 &#186;C at a rate of 80 &#186;C/min. Hold the temperature at 820 &#186;C for 30 min.</li>
		<li>Cool down to RT at a rate of 10 &#186;C/min. Take the boat and the slide out of the furnace.</li>
	</ol>
	</li>
	<li>Synthesis of control samples: ZnO and CdSSe nanowires
	<ol>
		<li>Synthesize ZnO nanowires as in section 1.2 under the same experimental conditions.</li>
		<li>Synthesize CdSSe nanowires as in section 1.3, under the same experimental conditions, with the same amount of CdS and CdSe composition, but with a clean, gold-coated sapphire slide as the substrate instead of the ZnO-deposited slide.</li>
	</ol>
	</li>
</ol>
2. Morphological and Crystallographic Characterization
<ol>
	<li>Mount the sample on the SEM stage with a clamp and place the sample in the vacuum chamber of the SEM instrument. Take SEM images on high-resolution mode with a working distance of 12.0 mm at a voltage of 3 kV and a magnification between 3,000X and 10,000X11,12.</li>
	<li>Take EDS data with the same sample using the X-ray detector at the same working distance of 12.0 mm. Set the instrument to analysis mode and adjust the voltage to 20 kV, resulting in a current of 20 to 40 &#181;A13.</li>
	<li>Collect XRD spectra on an X-ray powder diffractometer using filtered Cu K&#945; radiation (&#955;=1.5418 &#197;)11,12.</li>
</ol>
3. PL Emission Spectroscopy and Time-resolved PL Lifetime Measurements
NOTE: PL spectra and time-correlated single photon counting (TCSPC) measurements at RT were carried out using an amplified Ti:sapphire oscillator after second harmonic generation (SHG), producing a train of 50 fsec pulses centered at a 400-nm wavelength and with an output power of 1.76 mW14.
<ol>
	<li>Fix the sample into a sample holder that positions the sample face up to the laser and to the detector. Align the laser to focus on the sample. Measure the PL emission spectra of the samples from 500-nm to 900-nm wavelengths using a fiber spectrometer.</li>
	<li>Use a single-photon detector (avalanche photo diode or phototube) to measure time-resolved PL lifetimes with a color glass filter and a 500- or 650-nm interference bandpass filter.</li>
	<li>Insert ZnO, CdSSe, or ZnO/CdSSe slides into the sample holder. Measure the pure ZnO nanowires with the 500-nm bandpass filter and the CdSSe or ZnO/CdSSe samples with a 650-nm bandpass filter.</li>
	<li>Use a time-correlated single photon counter or a fast oscilloscope to measure the time-resolved fluorescence decay lifetimes.</li>
</ol>

<ol>
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Rep. 4, (2014).</li><li>Anta, J. A., Guill&#233;n, E., Tena-Zaera, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ZnO-Based+Dye-Sensitized+Solar+Cells.">ZnO-Based Dye-Sensitized Solar Cells.</a> J. Phys. Chem. C. 116 (21), 11413-11425 (2012).</li><li>Pelligra, C. I., Majewski, P. W., Osuji, C. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Large+area+vertical+alignment+of+ZnO+nanowires+in+semiconducting+polymer+thin+films+directed+by+magnetic+fields.">Large area vertical alignment of ZnO nanowires in semiconducting polymer thin films directed by magnetic fields.</a> Nanoscale. 5 (21), 10511-10517 (2013).</li><li>Reddy, N. 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Data and figures in this article are cited from the literature in nanotechnology by Li et al.17.

The vertical alignment of ZnO nanowires (stems) is based on epitaxial growth on the substrate. ZnO nanowires grow preferentially along the &#60;0001&#62; direction that matches with the periodicity of the a-plane of sapphire12. Therefore, the type and the quality of the substrate are very important. Different thicknesses of the gold coating on the substrate, from 5 nm to 20 nm, have been tested and showed no significant difference in the growth of ZnO nanowires. The length of the ZnO nanowires can be adjusted by changing the amount of the ZnO/C mixture that is used, the Ar flow rate, and the air exposure time. For synthesizing ZnO nanowires with a consistent length, an oxygen/argon mixture with a well-defined ratio or artificial air (oxygen/nitrogen mixture) is recommended as the carrier gas. So far, the longest ZnO nanowires that have been grown in our lab using this method were 30 &#181;m, and the shortest were 5 &#181;m.
During CdSSe deposition, the temperature at the substrate position is the key parameter that controls the composition of the ternary alloy. Inside the quartz tube, the temperature gradient from the center of the furnace towards the ends is controlled by the furnace settings, the tube length and diameter, and the flow rate of the carrier gas. The position of the substrate determines the growth temperature and consequently, the composition. Since we have strong indications that the growth of the CdSSe branches on the ZnO stem is epitaxial, as discussed below, it is important to find the position in the quartz tube with the correct temperature for the growth of a 50:50 S:Se mole ratio (around 720 &#186;C)14. For tuning the mole ratio of S and Se, several trials may be necessary to find the correct settings and position in the tube. The color of the resulting ZnO/CdSSe NTs is a first indicator of whether the proper ratio was achieved; it should be orange. A bright yellow color indicates a high sulfur content, while a dark red color indicates too much selenium in the CdSSe. The actual ratio can be measured by EDS or XRD.
The reason for the formation of CdSSe branches instead of a CdSSe/ZnO core-shell structure can be explained by the measurements of the crystal structure. The XRD shows a shoulder at 26.5&#176; that is identified as the (111) plane of the zincblende phase of CdSSe (Figure 3)16. The growth of the CdSSe branches is likely initiated by point defects on the (1010) surface of the hexagonal ZnO stem. The occurrence of the zincblende phase can be explained by the growth of cubic CdSSe on the (1010) surface of ZnO that differ in their lattice parameters by integer numbers and can give rise to epitaxial growth. As the branches grow longer, the crystal structure merges into the more stable hexagonal phase that accounts for the strong (101) signal in the XRD. Since the lattice parameters are determined by the mole ratio, and the mole ratio depends on the growth temperature, careful adjustment of all parameters that influence the temperature is critical.
This is one demonstration of tree-like nanostructures composed of different materials in the branches and stem. The method should in principle work for other material combinations. However, some relationship between the lattice parameters of the stem and the branches is required in order to grow branches instead of a core-shell structure. In addition, the deposition temperature of the branch material must be below that of the stem material to prevent the destruction of the stem in the last preparation step. An alternative method for nanoparticle synthesis involves solvothermal growth. There have been a handful of reports about tree-like composite NTs synthesized by solvothermal methods. Compared with solvothermal methods, solvent-free CVD is more environmentally friendly and enables the preparation of materials with higher purity. However, CVD also has some limitations. CVD is usually operated at high temperatures to vaporize precursors, and prepared samples may have different compositions at elevated temperatures.
In summary, we prepared a novel ZnO/CdSSe vertically aligned tree-like nanostructure. Both the ZnO stems and the CdSSe branches were predominantly in wurtzite structure. TCSPC measurements show fast charge transfer from the CdSSe branches to the ZnO stems. The tunable BG of the CdSSe branches, the transparent ZnO stems, and the efficient charge transfer between both makes ZnO/CdSSe NTs a promising material for optical, photovoltaic, and photoelectrochemical applications.

ZnO is a II-VI semiconductor featuring a band gap (BG) of 3.3 eV, a high electron mobility, and a large exciton binding energy1,2. It is an abundant semiconducting material with a plethora of present and future applications in optical devices, solar cells, and photocatalysis. However, ZnO is transparent, which limits its application in the visible spectral range. Therefore, materials absorbing visible light, such as narrow-gap semiconductors3, dye molecules4, and photosensitive polymers5, have frequently been employed for sensitizing ZnO to visible light absorption.
CdS (BG 2.43 eV) and CdSe (BG 1.76 eV) are common II-VI narrow-gap semiconductors and have been intensively investigated. The BG and lattice parameters of the ternary alloy CdSSe can be adjusted by varying the mole ratios of the VI components6,7. ZnO/CdSSe nanocomposites have been reported to result in efficient photovoltaic energy conversion8,9.
Combining the efficient electron transport pathway of vertically aligned ZnO nanowires towards a substrate with the improved visible light absorption of the CdSSe branches led to efficient electron transfer between the stem and branches9,10. Thus, we synthesized a new tree-like ZnO/CdSSe nanostructure, where vertically aligned ZnO nanowires are decorated with CdSSe branches. This composite material can act as a building block for novel solar energy conversion devices.
This protocol describes how ZnO nanowire arrays are grown on a sapphire substrate by one-step chemical vapor deposition (CVD) from ZnO and C powders, following a procedure that has previously been published11. Following the growth of ZnO nanowires, a second step of CVD is employed to grow CdSSe branches on the ZnO nanowires. We employ X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) to measure the crystal structures, morphology, and composition of the ZnO/CdSSe nanotrees (NTs). The optical properties and charge carrier transfer mechanism between the branches and stem have been investigated by photoluminescence (PL) spectroscopy and time-resolved PL lifetime measurements.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>ZnO</td>
			<td>Sigma Aldrich</td>
			<td>1314-13-2</td>
			<td></td>
		</tr>
		<tr>
			<td>Activated Carbon</td>
			<td>Alfa</td>
			<td>231-153-3</td>
			<td></td>
		</tr>
		<tr>
			<td>CdSe</td>
			<td>Sigma Aldrich</td>
			<td>1306-24-7</td>
			<td></td>
		</tr>
		<tr>
			<td>CdS</td>
			<td>Sigma Aldrich</td>
			<td>1306-23-6</td>
			<td></td>
		</tr>
		<tr>
			<td>Sapphire</td>
			<td>MTI</td>
			<td>2SP</td>
			<td>a-plane, 10 &#215; 10 &#215; 1 mm</td>
		</tr>
		<tr>
			<td>Furnace</td>
			<td>Lindberg Blue M</td>
			<td>SSP</td>
			<td></td>
		</tr>
		<tr>
			<td>Scanning electron microscope</td>
			<td>Hitachi</td>
			<td>S5700</td>
			<td>assembled with an Oxford Inca X-act detector</td>
		</tr>
		<tr>
			<td>X-ray powder diffractometer&#160;</td>
			<td>Rigaku&#160;</td>
			<td>MiniFlex</td>
			<td>filtered Cu K&#945; radiation (&#955;=1.5418 &#197;)</td>
		</tr>
		<tr>
			<td>Amplified Ti:sapphire oscillator&#160;</td>
			<td>Coherent Mantis</td>
			<td>Coherent Legend-Elite</td>
			<td></td>
		</tr>
		<tr>
			<td>Single photon detection module&#160;</td>
			<td>ID Quantique</td>
			<td>ID-100</td>
			<td></td>
		</tr>
		<tr>
			<td>Sputter coater</td>
			<td>Cressington</td>
			<td>308</td>
			<td>assembled with gold target</td>
		</tr>
		<tr>
			<td>Fiber probe spectrometer</td>
			<td>Photon Control</td>
			<td>SPM-002</td>
			<td></td>
		</tr>
		<tr>
			<td>Colored Glass Filter</td>
			<td>Thorlabs</td>
			<td>FGB37-A - &#216;25 mm BG40</td>
			<td>AR Coated: 350 - 700 nm&#160;</td>
		</tr>
		<tr>
			<td>Compressed argon gas</td>
			<td>Keen</td>
			<td>7440-37-1</td>
			<td></td>
		</tr>
	</tbody>
</table>

synthesis of hierarchical zno/cdsse heterostructure nanotrees

A two-step chemical vapor deposition procedure is here employed to prepare tree-like hierarchical ZnO/CdSSe hetero-nanostructures. The structures are composed of CdSSe branches grown on ZnO nanowires that are vertically aligned on a transparent sapphire substrate. The morphology was measured via scanning electron microscopy. The crystal structure was determined by X-ray powder diffraction analysis. Both the ZnO stem and CdSSe branches have a predominantly wurtzite crystal structure. The mole ratio of S and Se in the CdSSe branches was measured by energy dispersive X-ray spectroscopy. The CdSSe branches result in strong visible light absorption. Photoluminescence (PL) spectroscopy showed that the stem and branches form a type-II heterojunction. PL lifetime measurements showed a decrease in the lifetime of emission from the trees when compared to emission from individual ZnO stems or CdSSe branches and indicate fast charge transfer between CdSSe and ZnO. The vertically aligned ZnO stems provide a direct electron transport pathway to the substrate and allow for efficient charge separation after photoexcitation by visible light. The combination of the abovementioned properties makes ZnO/CdSSe nanotrees promising candidates for applications in solar cells, photocatalysis, and opto-electronic devices.

Figure 1 shows the growth mechanism of ZnO/CdSSe NTs. The procedure involved a catalytic vapor-liquid-solid (VLS) process followed by a non-catalytic vapor-solid (VS) growth. In the first VLS step, ZnO and C react in the Ar atmosphere, resulting in metallic Zn and carbon oxide. Zn is subsequently dissolved in the gold precursor on the sapphire substrate. ZnO nanowires grow from the dissolved Zn and residual oxygen. In the second step, exposure to air results in the growth of long ZnO nanowires by VLS-VS on top of the short ZnO seeds. The VLS-VS mechanism has been discussed in detail previously11,12. In the last step, the CdSSe branches grow directly, without a catalyst, on the ZnO nanowire.
SEM images of the ZnO nanowires obtained after the first step (Protocol 1.2) are shown in Figure 2(a). SEM images of tree-like nanostructures obtained after the second step (Protocol 1.3) are shown in Figure 2(b) and (c). We employed EDS to determine the composition of the NTs. The branches contained S and Se, with a mole percentage ratio of around 0.53:0.47. EDS element scans were performed at three different positions on the NT, indicated in Figure 2(c). Figures 2(d), (e), and (f) show the composition of the stem, the branch, and the cap, respectively. An element line scan mapping along the line in Figure 2(g) is shown in Figure 2(h). The element scan shows that the cap and stem can be clearly distinguished in the scan that shows only contributions from Zn and O in the area of the stem. The crystal structures of the NTs were measured via XRD. They are compared to the crystal structures of pure ZnO and CdSSe nanowires, shown in Figure 3. Pure ZnO and CdSSe nanowires show the expected hexagonal wurtzite structure, with characteristic peaks at (100), (002), (101), and (102)13,15. A very strong and narrow peak at (002) for ZnO can be explained by the one-directional growth of the vertically aligned ZnO nanowires. The XRD measurement of the NTs shows a combination of ZnO and CdSSe wurtzite structures. According to Vegard&#39;s law, the mole ratio of S:Se was determined from the XRD data to be 0.54:0.46, which corresponds to the EDS result. The CdSSe in the NTs showed an additional peak that is assigned with the (111) plane of the zincblende phase and is discussed later.
PL spectra and time-resolved PL measurements employing TCSPC are shown in Figure 4(a) and (b), respectively. In Figure 4(a), the fluorescence emissions of ZnO, CdSSe, and ZnO/CdSSe have maxima at 514 nm, 646 nm, and 627 nm, respectively. A 500-nm bandpass filter was chosen for the ZnO PL lifetime measurement, while a 650-nm filter was used for measuring the emission from CdSSe and ZnO/CdSSe NTs. Time-resolved PL measurements were fitted using single- or bi-exponential functions. In Figure 2(b), the PL lifetime of ZnO/CdSSe NTs (0.11 nsec) is shorter than the lifetimes of either ZnO (3.67 nsec) or CdSSe (1.06 nsec) at a 400-nm excitation. This can be explained by fast electron transfer from the conduction band (CB) of CdSSe to the CB of ZnO. In the isolated nanowires, excited electrons recombine radiatively on a nanosecond time scale. If the CdSSe branches are in contact with the ZnO stem, excited electrons can transfer non-radiatively from CdSSe to ZnO, with a time scale that depends on the interface and that can be much faster than the radiative lifetime. Therefore, the PL lifetime of ZnO/CdSSe NTs is reduced by electron transfer across the interface.
<img alt="Figure 1" src="/files/ftp_upload/54675/54675fig1.jpg" /> 
Figure 1. Schematic synthesis of ZnO/CdSSe NTs. The set-up inside the furnace is shown on the left. The following images show the three steps of NT preparation involving: the VLS process in Ar, the VLS-VS process in air, and the deposition of CdSSe branches. Reproduced from Ref. 17. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54675/54675fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/54675/54675fig2.jpg" /> 
Figure 2. SEM images and EDS spectra. a) SEM image of ZnO nanowires prepared via CVD; b) and c) SEM images of ZnO/CdSSe NTs prepared via CVD; EDS spectra of the ZnO stem, CdSSe cap, and CdSSe branch of ZnO/CdSSe NTs are shown in d), e), and f), respectively; h) The element line scan along the line shown in g), reproduced from Ref. 17. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54675/54675fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/54675/54675fig3.jpg" /> 
Figure 3. XRD Spectra of ZnO, CdSSe, ZnO/CdSSe NTs. (100), (002), (101), and (102) peaks, characteristic of the ZnO and CdSSe wurtzite structure for the bare nanowires, are shown. The additional peaks from the NTs can be identified with the (111) plane of CdSSe in the zincblende structure, as discussed in the text. Reproduced from Ref. 17. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54675/54675fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/54675/54675fig4.jpg" /> 
Figure 4. PL spectra and TSCPC measurements. PL spectra (a) and TSCPC measurements fitted with single-exponential decay (b) of ZnO, CdSSe, and ZnO/CdSSe NTs excited with a 400-nm-wavelength laser. The PL spectra show fluorescence of ZnO, CdSSe, and ZnO/CdSSe at 514 nm, 646 nm, and 627 nm, respectively. Lifetimes of ZnO, CdSSe, and ZnO/CdSSe are 3.67 nsec, 1.32 nsec, and 0.72 nsec, respectively. Reproduced from Ref. 17. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54675/54675fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Synthesis of Hierarchical ZnO/CdSSe Heterostructure Nanotrees at JoVE.com

Synthesis of Hierarchical ZnO/CdSSe Heterostructure Nanotrees

Here, we prepare and characterize novel tree-like hierarchical ZnO/CdSSe nanostructures, where CdSSe branches are grown on vertically aligned ZnO nanowires. The resulting nanotrees are a potential material for solar energy conversion and other opto-electronic devices.

A two-step chemical vapor deposition procedure is here employed to prepare tree-like hierarchical ZnO/CdSSe hetero-nanostructures. The structures are ...

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Nanyang Technological University

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JoVE Journal

Chemistry

9.9K Views.  University of Delaware. Here, we prepare and characterize novel tree-like hierarchical ZnO/CdSSe nanostructures, where CdSSe branches are grown on vertically aligned ZnO nanowires. The resulting nanotrees are a potential material for solar energy conversion and other opto-electronic devices.

Video: Synthesis of Hierarchical ZnO/CdSSe Heterostructure Nanotrees

Synthesis of Immunotargeted Magneto-plasmonic Nanoclusters

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

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

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

Synthesis and Characterization of Functionalized Metal-organic Frameworks

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and technological applications. Their signature property is their ultrahigh porosity, which however imparts a series of challenges when it comes to both constructing them and working with them. Securing desired MOF chemical and physical functionality by linker/node assembly into a highly porous framework of choice can pose difficulties, as less porous and more thermodynamically stable congeners (e.g., other crystalline polymorphs, catenated analogues) are often preferentially obtained by conventional synthesis methods. Once the desired product is obtained, its characterization often requires specialized techniques that address complications potentially arising from, for example, guest-molecule loss or preferential orientation of microcrystallites. Finally, accessing the large voids inside the MOFs for use in applications that involve gases can be problematic, as frameworks may be subject to collapse during removal of solvent molecules (remnants of solvothermal synthesis). In this paper, we describe synthesis and characterization methods routinely utilized in our lab either to solve or circumvent these issues. The methods include solvent-assisted linker exchange, powder X-ray diffraction in capillaries, and materials activation (cavity evacuation) by supercritical CO2 drying. Finally, we provide a protocol for determining a suitable pressure region for applying the Brunauer-Emmett-Teller analysis to nitrogen isotherms, so as to estimate surface area of MOFs with good accuracy.

Synthesis, activation, and characterization of intentionally designed metal-organic framework materials is challenging, especially when building blocks are incompatible or unwanted polymorphs are thermodynamically favored over desired forms. We describe how applications of solvent-assisted linker exchange, powder X-ray diffraction in capillaries and activation via supercritical CO2 drying, can address some of these challenges.

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and ...

Synthesis of Indoxyl-glycosides for Detection of Glycosidase Activities

Indoxyl glycosides proved to be valuable and versatile tools for monitoring glycosidase activities. Indoxyls are released by enzymatic hydrolysis and are rapidly oxidized, for example by atmospheric oxygen, to indigo type dyes. This reaction enables fast and easy screening in vivo without isolation or purification of enzymes, as well as rapid tests on agar plates or in solution (e.g., blue-white screening, micro-wells) and is used in biochemistry, histochemistry, bacteriology and molecular biology. Unfortunately the synthesis of such substrates proved to be difficult, due to various side reactions and the low reactivity of the indoxyl hydroxyl function. Especially for glucose type structures low yields were observed. Our novel approach employs indoxylic acid ester as key intermediates. Indoxylic acid esters with varied substitution patterns were prepared on scalable pathways. Phase transfer glycosylations with those acceptors and peracetylated glycosyl halides can be performed under common conditions in high yields. Ester cleavage and subsequent mild silver mediated glycosylation yields the peracetylated indoxyl glycosides in high yields. Finally deprotection is performed according to Zempl&#233;n.

Indoxyl glycosides are well-established and widely used tools for enzyme screening and enzyme activity monitoring. Especially for glucose type structures previous syntheses proved to be challenging and low yielding. Our novel approach employs indoxylic acid esters as precious intermediates to yield a considerable number of indoxyl glycosides in good yields.

Indoxyl glycosides proved to be valuable and versatile tools for monitoring glycosidase activities. Indoxyls are released by enzymatic hydrolysis and are ...

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.

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

Hydroquinone Based Synthesis of Gold Nanorods

Gold nanorods are an important kind of nanoparticles characterized by peculiar plasmonic properties. Despite their widespread use in nanotechnology, the synthetic methods for the preparation of gold nanorods are still not fully optimized. In this paper we describe a new, highly efficient, two-step protocol based on the use of hydroquinone as a mild reducing agent. Our approach allows the preparation of nanorods with a good control of size and aspect ratio (AR) simply by varying the amount of hexadecyl trimethylammonium bromide (CTAB) and silver ions (Ag+) present in the "growth solution". By using this method, it is possible to markedly reduce the amount of CTAB, an expensive and cytotoxic reagent, necessary to obtain the elongated shape. Gold nanorods with an aspect ratio of about 3 can be obtained in the presence of just 50 mM of CTAB (versus 100 mM used in the standard protocol based on the use of ascorbic acid), while shorter gold nanorods are obtained using a concentration as low as 10 mM.

This paper describes a protocol for the synthesis of gold nanorods, based on the use of hydroquinone as reducing agent, plus the different mechanisms for controlling their size and aspect ratio.

Gold nanorods are an important kind of nanoparticles characterized by peculiar plasmonic properties. Despite their widespread use in nanotechnology, the ...

Synthesis and Mass Spectrometry Analysis of Oligo-peptoids

Peptoids are sequence-controlled peptide-mimicking oligomers consisting of N-alkylated glycine units. Among many potential applications, peptoids have been thought of as a type of molecular information storage. Mass spectrometry analysis has been considered the method of choice for sequencing peptoids. Peptoids can be synthesized via solid phase chemistry using a repeating two-step reaction cycle. Here we present a method to manually synthesize oligo-peptoids and to analyze the sequence of the peptoids using tandem mass spectrometry (MS/MS) techniques. The sample peptoid is a nonamer consisting of alternating N-(2-methyloxyethyl)glycine (Nme) and N-(2-phenylethyl)glycine (Npe), as well as an N-(2-aminoethyl)glycine (Nae) at the N-terminus. The sequence formula of the peptoid is Ac-Nae-(Npe-Nme)4-NH2, where Ac is the acetyl group. The synthesis takes place in a commercially available solid-phase reaction vessel. The rink amide resin is used as the solid support to yield the peptoid with an amide group at the C-terminus. The resulting peptoid product is subjected to sequence analysis using a triple-quadrupole mass spectrometer coupled to an electrospray ionization source. The MS/MS measurement produces a spectrum of fragment ions resulting from the dissociation of charged peptoid. The fragment ions are sorted out based on the values of their mass-to-charge ratio (m/z). The m/z values of the fragment ions are compared against the nominal masses of theoretically predicted fragment ions, according to the scheme of peptoid fragmentation. The analysis generates a fragmentation pattern of the charged peptoid. The fragmentation pattern is correlated to the monomer sequence of the neutral peptoid. In this regard, MS analysis reads out the sequence information of the peptoids.

A protocol is described for the manual synthesis of oligo-peptoids followed by sequence analysis by mass spectrometry.

Peptoids are sequence-controlled peptide-mimicking oligomers consisting of N-alkylated glycine units. Among many potential applications, peptoids have ...

Synthesis of Substrate-Bound Au Nanowires Via an Active Surface Growth Mechanism

Advancing synthetic capabilities is important for the development of nanoscience and nanotechnology. The synthesis of nanowires has always been a challenge, as it requires asymmetric growth of symmetric crystals. Here, we report a distinctive synthesis of substrate-bound Au nanowires. This template-free synthesis employs thiolated ligands and substrate adsorption to achieve the continuous asymmetric deposition of Au in solution at ambient conditions. The thiolated ligand prevented the Au deposition on the exposed surface of the seeds, so the Au deposition only occurs at the interface between the Au seeds and the substrate. The side of the newly deposited Au nanowires is immediately covered with the thiolated ligand, while the bottom facing the substrate remains ligand-free and active for the next round of Au deposition. We further demonstrate that this Au nanowire growth can be induced on various substrates, and different thiolated ligands can be used to regulate the surface chemistry of the nanowires. The diameter of the nanowires can also be controlled with mixed ligands, in which another &#34;bad&#34; ligand could turn on the lateral growth. With the understanding of the mechanism, Au nanowire-based nanostructures can be designed and synthesized.

We report a solution-based method to synthesize substrate-bound Au nanowires. By tuning the molecular ligands used during the synthesis, the Au nanowires can be grown from various substrates with different surface properties. Au nanowire-based nanostructures can also be synthesized by adjusting the reaction parameters.

Advancing synthetic capabilities is important for the development of nanoscience and nanotechnology. The synthesis of nanowires has always been a ...

Solid-phase Synthesis of [4.4] Spirocyclic Oximes

A convenient synthetic route for spirocyclic heterocycles is well sought after due to the molecule&#39;s potential use in biological systems. By means of solid-phase synthesis, regenerating Michael (REM) linker strategies, and 1,3-dipolar cycloaddition, a library of structurally similar heterocycles, both with and without a spirocyclic center, can be constructed. The main advantages of the solid-support synthesis are as follows: first, each reaction step can be driven to completion using a large excess of reagents resulting in high yields; next, the use of commercially available starting materials and reagents keep the costs low; finally, the reaction steps are easy to purify via simple filtration. The REM linker strategy is attractive because of its recyclability and traceless nature. Once a reaction scheme is completed, the linker can be reused multiple times. In a typical solid-phase synthesis, the product contains either a part of or the whole linker, which can prove undesirable. The REM linker is &#34;traceless&#34; and the point of attachment between the product and the polymer is indistinguishable. The high diastereoselectivity of the intramolecular 1,3-dipolar cycloaddition is well documented. Limited by the insolubility of the solid support, the reaction progression can only be monitored by a change in the functional groups (if any) via infrared (IR) spectroscopy. Thus, the structural identification of intermediates cannot be characterized by conventional nuclear magnetic resonance (NMR) spectroscopy. Other limitations to this method stem from the compatibilities of the polymer/linker to the desired chemical reaction scheme. Herein we report a protocol that allows for the convenient production of spirocyclic heterocycles that, with simple modifications, can be automated with high-throughput techniques.

Here we present a protocol to demonstrate an efficient method for the synthesis of spirocyclic heterocycles. The five-step process utilizes solid-phase synthesis and regenerating Michael linker strategies. Generally difficult to synthesize, we present a customizable method for the synthesis of spirocyclic molecules otherwise inaccessible to other modern approaches.

A convenient synthetic route for spirocyclic heterocycles is well sought after due to the molecule&#39;s potential use in biological systems. By means of ...

Synthesis and Characterization of Amphiphilic Gold Nanoparticles

Gold nanoparticles covered with a mixture of 1-octanethiol (OT) and 11-mercapto-1-undecane sulfonic acid (MUS) have been extensively studied because of their interactions with cell membranes, lipid bilayers, and viruses. The hydrophilic ligands make these particles colloidally stable in aqueous solutions and the combination with hydrophobic ligands creates an amphiphilic particle that can be loaded with hydrophobic drugs, fuse with the lipid membranes, and resist nonspecific protein adsorption. Many of these properties depend on nanoparticle size and the composition of the ligand shell. It is, therefore, crucial to have a reproducible synthetic method and reliable characterization techniques that allow the determination of nanoparticle properties and the ligand shell composition. Here, a one-phase chemical reduction, followed by a thorough purification to synthesize these nanoparticles with diameters below 5 nm, is presented. The ratio between the two ligands on the surface of the nanoparticle can be tuned through their stoichiometric ratio used during synthesis. We demonstrate how various routine techniques, such as transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), and ultraviolet-visible (UV-Vis) spectrometry, are combined to comprehensively characterize the physicochemical parameters of the nanoparticles.

Amphiphilic gold nanoparticles can be used in many biological applications. A protocol to synthesize gold nanoparticles coated by a binary mixture of ligands and a detailed characterization of these particles is presented.

Gold nanoparticles covered with a mixture of 1-octanethiol (OT) and 11-mercapto-1-undecane sulfonic acid (MUS) have been extensively studied because of ...

Hierarchical and Programmable One-Pot Oligosaccharide Synthesis

This article presents a general experimental protocol for programmable one-pot oligosaccharide synthesis and demonstrates how to use Auto-CHO software for generating potential synthetic solutions. The programmable one-pot oligosaccharide synthesis approach is designed to empower fast oligosaccharide synthesis of large amounts using thioglycoside building blocks (BBLs) with the appropriate sequential order of relative reactivity values (RRVs). Auto-CHO is a cross-platform software with a graphical user interface that provides possible synthetic solutions for programmable one-pot oligosaccharide synthesis by searching a BBL library (containing about 150 validated and &#62;50,000 virtual BBLs) with accurately predicted RRVs by support vector regression. The algorithm for hierarchical one-pot synthesis has been implemented in Auto-CHO and uses fragments generated by one-pot reactions as new BBLs. In addition, Auto-CHO allows users to give feedback for virtual BBLs to keep valuable ones for further use. One-pot synthesis of stage-specific embryonic antigen 4 (SSEA-4), which is a pluripotent human embryonic stem cell marker, is demonstrated in this work.

This protocol demonstrates how to use the Auto-CHO software for hierarchical and programmable one-pot synthesis of oligosaccharides. It also describes the general procedure for RRV determination&#160;experiments and one-pot glycosylation of SSEA-4.

This article presents a general experimental protocol for programmable one-pot oligosaccharide synthesis and demonstrates how to use Auto-CHO software for ...