The authors would like to acknowledge the support from the Department of Earth Sciences, Uppsala University for supporting part of this research.

1. Functionalization of Multiwalled Carbon Nanotubes
<ol>
	<li>Perform the entire functionalization step inside a fume hood, using safety eye glasses, gloves and lab coat. Measure 24 ml of sulfuric acid and 8 ml of nitrate acid using a graduated cylinder, and then transfer them into a beaker. Add 32 mg of untreated MWCNTs into a beaker using tin foil container at an analytical balance (final concentration should be 1 mg/ml of acid mixture).</li>
	<li>First, keep the beaker with MWCNT and acid mixture in the ultrasonic cleaner (bath) for 2 hr at RT. Then, heat and stir the MWCNT-acid solution for 5 hr at 90 &#176;C using a hot plate.</li>
	<li>Filter the CNT suspension with a 0.2 &#181;m pore diameter PTFE filter membrane placed on a filter holder, and use vacuum to help filtration. Perform the filtration portion by portion and use several filter membranes (approximately 1/4th of above mixture per portion for one filter). Add boiling water during filtration process to filter out the acid solution until the pH of the mixture becomes greater than 5.</li>
	<li>Always break the vacuum before it is turned off and not to introduce anything into the vacuum system. Use a conical beaker to collect the waste liquid.</li>
	<li>Pour filtrated acid into a waste container (send the waste container to a waste handling facility or dilute the liquid before dumping it into the sink by adding at least ten times of tap water).</li>
	<li>Transfer the filter membranes with retained MWCNTs into evaporating dishes and put the dishes into the desiccator (contains approximately 100 g of silica gel) and create a vacuum environment (leave the vacuum on for about 1 hr) for CNT to complete drying (about 24 hr).
	<ol>
		<li>Scrape the CNTs out of the membranes carefully using spatula and transfer the particles into a clean container. Weigh the MWCNTs powder and label the container for future use.</li>
	</ol>
	</li>
</ol>
2. Porous Media for Transport Experiments
<ol>
	<li>Prepare 0.1 M HCl solution for acid washing of silica sand.
	<ol>
		<li>Perform all these steps inside a fume hood with safety eye glasses, gloves, and lab coat. Add 1 L de-ionized water to a 2 L flask. Measure 8 ml of 37% HCl using a graduated cylinder.</li>
		<li>Add the HCl into the de-ionized water carefully. Shake the flask carefully to help mixing.</li>
	</ol>
	</li>
	<li>Wash the sand with the prepared HCl solution.
	<ol>
		<li>Weigh about 1,000 g sand. Add 1/3 of sand into the flask with the HCl solution and shake the flask twice to help mixing then add rest of the sand (1/3 of the sand each time).</li>
		<li>Shake the flask three times and leave the acid with sand for 30 min.</li>
		<li>Pour the liquid out of the flask to acid waste container and rinse the sand with de-ionized water at least 8 times.</li>
	</ol>
	</li>
	<li>Wash the sand with a H2O2 solution.
	<ol>
		<li>Add 700 ml of de-ionized water into the flask with sand then measure 40 ml of 30% H2O2 solution using a graduated cylinder.</li>
		<li>Add the H2O2 solution into flask with sand and shake twice to help mixing. Then add another 40 ml of 30% H2O2 solution 3 times until there is 160 ml H2O2 total in the flask.</li>
		<li>Shake and mix the solution and sand each time and leave the H2O2 solution with sand for 40 min to allow the reaction to be completed. Shake the flask and stir the sand with a plastic rod every 10 min.</li>
		<li>Decant the liquid down to the sink and run tap water for 30 sec.</li>
	</ol>
	</li>
	<li>Rinse and dry the sand.
	<ol>
		<li>Rinse sand with de-ionized water at least 8 times to get rid of any solution or left over reaction products. Shake and stir thoroughly when rinsing.</li>
		<li>Put flask with rinsed sand into an oven (105 &#176;C) for 24 hr to dry, then take sand out of the oven using oven-mitten and leave at the counter for 2 hr for the sand to cool down.</li>
		<li>Transfer the clean sand into a plastic container. Mark the container and place it in an appropriate shelf to be ready for use.</li>
	</ol>
	</li>
</ol>
3. Column Experiments
<ol>
	<li>Preparation of background solution.
	<ol>
		<li>Prepare appropriate background solution chemistry for the column experiment.</li>
		<li>Use 0.1 M HCl and 0.1 M NaOH solutions to adjust the pH and NaCl salt to achieve appropriate ionic strength for the following experiment.</li>
	</ol>
	</li>
	<li>Column selection.
	<ol>
		<li>Choose a glass column of 2.5 cm diameter and 15 cm length for this experiment (pH: 5 and ionic strength: 2 mM in the current study). Use a steel mesh filter (0.2 mm) on both sides of the glass column.</li>
		<li>Flush the tubes connected to the column and fill with background solution (or MWCNTs solution until the 3-way valve to control the type of liquid flow (MWCNTs solution or background solution) as shown in Figure 1.</li>
	</ol>
	</li>
	<li>Wet-packing of the column.
	<ol>
		<li>Weigh the clean sand on a scale and take 124 g of clean sand for the selected column size.</li>
		<li>Use a high precision peristaltic pump. Calibrate the pump to achieve 2 ml/min of liquid flow.</li>
		<li>Start the pump to fill the column from the bottom until the water level is a couple of centimeters above the bottom of the column. Put approximately 1/10th of the measured sand at a time into the column but make sure that the sand level doesn&#8217;t come above the water level in the column. Continue the water flow to the column continuously to stay above the sand level.</li>
		<li>Close the column cap with appropriate filter mesh after complete filling.</li>
		<li>Allow the packed column to flow for at least 1 hr. The individual parameters of the column are indicated in Table 1.</li>
	</ol>
	</li>
	<li>Tracer test.
	<ol>
		<li>Start the column experiment with a tracer test prior to the MWCNT solution experiments.</li>
		<li>Switch the 3-way valve to the tracer solution (using food color tracer at 20 mg/L) to start the experiment.</li>
		<li>Collect the outflow samples from the column at every 2 min (i.e., 4 ml/samples in each sampling tube) using the connected fraction collector as shown in Figure 1.</li>
		<li>Continue to inject the tracer solution for a 4.32 pore volume (i.e., solution passes 4.32 times of the total empty pore space in the sand packed column), which is also called phase I of the experiment.</li>
		<li>Switch the 3-way valve to flow background solution (DI water in the case of tracer experiment) for another 4.32 pore volume.</li>
	</ol>
	</li>
	<li>Preparation of MWCNT solution.
	<ol>
		<li>Make a dispersed, functionalized MWCNTs solution by placing 15 mg of functionalized MWCNTs in a 300 ml beaker containing 200 ml of aqueous solution (with desired solution chemistry i.e., pH 5 and 2 mM ionic strength in the current experimental condition) and using an ultrasonic homogenizer probe placed in the beaker (with 40% power output for 15 min). Mix the dispersed MWCNTs solution with another 800 ml of the same aqueous solution to achieve the MWCNT concentration of 15 mg/L.</li>
		<li>Perform scanning electron microscopy (SEM) image analysis of stock solution for their size and shape of the nanoparticle after functionalization.</li>
	</ol>
	</li>
	<li>MWCNT transport experiment.
	<ol>
		<li>Switch the 3-way valve to MWCNT solution to start the column experiment.</li>
		<li>Collect the outflow samples from the column at every 2 min using the connected fraction collector.</li>
		<li>Inject the MWCNT solution for a 4.32 pore volume (phase I of the experiment).</li>
		<li>Switch the 3-way valve to flow background solution for another 4.32 pore volume, which is called phase II of the experiment.</li>
		<li>Change the injection tube of background solution into DI water bottle (after stopping the pump for a moment to avoid the entrance of air from the tube) and continue the flow for another 4.32 pore volume, which is called phase III of the experiment.</li>
	</ol>
	</li>
	<li>Sample analysis.
	<ol>
		<li>Transfer all the tube samples from fraction collector into a tube rack.</li>
		<li>Prepare a UV/VIS spectrophotometer for sample analysis, i.e., find out the appropriate scanning wavelength for the quantification of the collected samples. Use 400 nm for a MWCNT solution and a 333 nm wavelength for tracer solution.</li>
		<li>Scan all the samples collected from the column during phases I, II, and III using a cuvette at 400 nm wavelength (or a different wavelength if deemed more appropriate in the previous step) and store the data.</li>
		<li>Collect the data from the spectrophotometer and plot them vs time or pore volume to obtain breakthrough curves as shown in the representative results (for example, Figure 3).</li>
		<li>Perform size analysis (hydrodynamic diameter) of inflow and outflow samples using zeta sizer and conduct the visualization studied for both inflow and outflow samples using scanning electron microscopy.</li>
	</ol>
	</li>
</ol>

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The authors declare that they have no competing financial interests.

Effect of MWCNT Functionalization
As Figure 2 confirms the stability of functionalized MWCNTs, the observed difference in eluted volume of MWCNT was due to functionalization and particularly due to the addition of carboxyl (-COOH) groups to the surface of the MWCNTs (Figures 3 and 4). In the similar functionalization process, the presence of oxygen was confirmed by X-ray photoelectron spectroscopy14. It has been fou...

With the recent development in nanotechnology that uses various types of nanoparticles to improve a number of technologies in industries such as information technology, energy, environmental science, medicine, homeland security, food safety, and transportation; a thorough understanding of the&#160;transport&#160;and&#160;retention&#160;of nanoparticles in soil and groundwater is critical for risk assessment as well as environmental applications of engineered nanoparticles1-3. Carbon nanotubes (CNTs) are one of the most produced carbon-based nanoparticles2,4. CNTs are the long and cylindrical form of graphene with a diameter typically below 100 nm and a length in the range of 100 nm to 50 &#181;m. They have unique properties, which have accelerated their use in many applications, such as electronics, optics, cosmetics, and biomedical technology (e.g., composite materials)5. With increased use, there is also an increased risk to human exposure and effect on health as well as adverse ecological consequences following CNT and other carbon based nanomaterials disposal to the environment5-8.
With no surface modifications (unfunctionalized), CNTs are extremely hydrophobic and tend to aggregate in an aqueous solution. Functionalized CNTs can, however, remain dispersed and stable in aqueous solutions and are used for biomedical purposes such as drug delivery9. Here it is essential that the CNTs remain dispersed and mobilized, so the drug can be delivered within the human body10. On the other hand, to reduce environmental risks, there is a need for studies focusing on how to immobilize the CNTs in order to avoid their entrance into aquifers and drinking water resources11. Recent studies have reported the toxic effect of CNTs on living organisms and also risks to ecosystems in terms of CNTs entering and accumulating in the food chains, since CNTs are hard to biodegrade5,8. Even with barrier systems in landfills containing CNTs, it may be possible for CNTs to pass through the barriers. In such cases CNTs could enter into groundwater reservoirs and surface water bodies. As CNT disposal regulations are not well defined and transport mechanisms are poorly understood, an improved understanding of mobility of CNTs is necessary to formulate and design appropriate disposal systems12. Therefore, it is important to study and understand the fate and transport of CNTs in porous media and the effect of physical and chemical factors commonly present in the subsurface environment on surface modified CNT retention.
A number of research has been carried out about the effect of collector grain size13-15, flow rate16, and surface properties of the grains17 on transport of nanoparticles in porous media. However, systematic investigations on the effect of solution chemistry (such as pH and ionic strength) on possible deposition onto the collector surfaces are still limited18-20. Additionally, the combined impact of physical factors, solution chemistry of the medium, and surface properties of carbon nanotubes is not well understood and vary in different literature. In this study, a preparation method for surface modification of MWCNTs will be demonstrated along with a systematic laboratory-scale column packed with acid-cleaned quartz sand will be used to investigate the transport, retention and remobilization of surface-modified CNTs in saturated porous media.

<table><tbody><tr><td>MWCNT</td><td>Cheap Tubes Inc., USA</td><td>sku-03040304</td><td>Purchased as semi-functionlized powder</td></tr><tr><td>Quartz sand</td><td>Sibelco Nordic, Baskarp, Sweden</td><td>B44</td><td>Purchased with more than 91% silica sand</td></tr><tr><td>H&lt;sub&gt;2&lt;/sub&gt;SO&lt;sub&gt;4&lt;/sub&gt;</td><td>VWR</td><td>1.01833.2500</td><td>95%-97% purity</td></tr><tr><td>HNO&lt;sub&gt;3&lt;/sub&gt;</td><td>VWR</td><td>1.00441.1000</td><td>70% purity</td></tr><tr><td>HCl</td><td>VWR</td><td>1.00317.2500</td><td>37%-38% purity</td></tr><tr><td>H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt;</td><td>VWR</td><td>23615.248</td><td>30% purity</td></tr><tr><td>NaCl</td><td>VWR</td><td>1.06404.0500</td><td>99.5% purity</td></tr><tr><td>NaOH</td><td>Sigma-Aldrich</td><td>S8045-500G</td><td>99.99% pur pellets&amp;nbsp;</td></tr><tr><td>Ultrasonic Homogenizer</td><td>Biologics Inc. Manassas, Virginia</td><td>Model 3000, 0-127-0002</td><td>Operated for fix time interval</td></tr><tr><td>Sonicator (bath)</td><td>Kerry Ultrasonic Ltd</td><td>1808</td><td>Common bath sonicator</td></tr><tr><td>Peristaltic pump</td><td>Ismantec, Glattbrugg, Switzerland</td><td>ISM931</td><td>Work with tygon tubing in the pump</td></tr><tr><td>Spectrophotometer</td><td>Hach Lange</td><td>DR500, LPV408.99.0001</td><td>Operate with manual cuvette as well as automated sampling</td></tr><tr><td>pH meter</td><td>Metrohm</td><td>781</td><td>pH analysis</td></tr><tr><td>Glass column</td><td>Chromaflex</td><td>420830-1510</td><td>Column with adjustable cap</td></tr><tr><td>Fraction collector</td><td>Spectrum Labs Europe</td><td>CF-2, 124846</td><td>Fixed at regular interval of time</td></tr><tr><td>Fraction collector tubes</td><td>VWR</td><td>212-9599</td><td>6 ml volume glass tube</td></tr><tr><td>Hot plate stir</td><td>Thermo Scientific</td><td>SP131320-33</td><td>Adjustable tempurature</td></tr><tr><td>Oven</td><td>Elektro Helios</td><td>259</td><td>For oven dry of sand</td></tr><tr><td>Balance</td><td>Mettler Toledo</td><td>AE 160</td><td>For accurate weight</td></tr></tbody></table>

transport of surface-modified carbon nanotubes through a soil column

Carbon nanotubes (CNTs) are widely manufactured nanoparticles, which are being utilized in a number of consumer products, such as sporting goods, electronics and biomedical applications. Due to their accelerating production and use, CNTs constitute a potential environmental risk if they are released to soil and groundwater systems. It is therefore essential to improve the current understanding of environmental fate and transport of CNTs. The transport and retention of CNTs in both natural and artificial media have been reported in literature, but the findings widely vary and are thus not conclusive. There are a number of physical and chemical parameters responsible for variation in retention and transport. In this study, a complete procedure of selected multiwalled carbon nanotubes (MWCNTs) is presented starting from their surface modification to a complete set of laboratory column experiments at critical physical and chemical scenarios. Results indicate that the stability of the commercially available MWCNTs are critical with their attached surface functional group which can also influence the transport and retention of MWCNT through the surrounding medium.

Effect of MWCNT Functionalization
The functionalized and dispersed MWCNT solution was sealed in the beaker to allow the solution to reach equilibrium. There was neither sedimentation nor aggregation observed in the stock solution after sonication, as the hydrodynamic diameter of MWCNT (1,619 &#177; 262 nm) in the solution remained the same for six months of sonication (Figure 2). To investigate the effect of functionalization of MWCNTs on their mobility, two s...

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Transport of Surface-modified Carbon Nanotubes through a Soil Column

Surface properties of a nanoparticle are important for their interaction with the surrounding medium. Therefore the surface modification of carbon nanotubes can be critical for their transport and retention through porous media. Here, lab scale column experiments are used to understand the possible transport and retention of these nanoparticles.

Carbon nanotubes (CNTs) are widely manufactured nanoparticles, which are being utilized in a number of consumer products, such as sporting goods, ...

transport-of-surface-modified-carbon-nanotubes-through-a-soil-column

Research

JoVE Journal

Chemistry

9.4K Views.  Nalanda University. Surface properties of a nanoparticle are important for their interaction with the surrounding medium. Therefore the surface modification of carbon nanotubes can be critical for their transport and retention through porous media. Here, lab scale column experiments are used to understand the possible transport and retention of these nanoparticles. 

Video: Transport of Surface-modified Carbon Nanotubes through a Soil Column

Fabrication, Densification, and Replica Molding of 3D Carbon Nanotube Microstructures

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip devices, and their applications. In particular, capabilities for cost-effective fabrication of polymer microstructures were transformed by the advent of soft lithography and other micromolding techniques 1, 2, and this led a revolution in applications of microfabrication to biomedical engineering and biology. Nevertheless, it remains challenging to fabricate microstructures with well-defined nanoscale surface textures, and to fabricate arbitrary 3D shapes at the micro-scale. Robustness of master molds and maintenance of shape integrity is especially important to achieve high fidelity replication of complex structures and preserving their nanoscale surface texture. The combination of hierarchical textures, and heterogeneous shapes, is a profound challenge to existing microfabrication methods that largely rely upon top-down etching using fixed mask templates. On the other hand, the bottom-up synthesis of nanostructures such as nanotubes and nanowires can offer new capabilities to microfabrication, in particular by taking advantage of the collective self-organization of nanostructures, and local control of their growth behavior with respect to microfabricated patterns. 
Our goal is to introduce vertically aligned carbon nanotubes (CNTs), which we refer to as CNT "forests", as a new microfabrication material. We present details of a suite of related methods recently developed by our group: fabrication of CNT forest microstructures by thermal CVD from lithographically patterned catalyst thin films; self-directed elastocapillary densification of CNT microstructures; and replica molding of polymer microstructures using CNT composite master molds. In particular, our work shows that self-directed capillary densification ("capillary forming"), which is performed by condensation of a solvent onto the substrate with CNT microstructures, significantly increases the packing density of CNTs. This process enables directed transformation of vertical CNT microstructures into straight, inclined, and twisted shapes, which have robust mechanical properties exceeding those of typical microfabrication polymers. This in turn enables formation of nanocomposite CNT master molds by capillary-driven infiltration of polymers. The replica structures exhibit the anisotropic nanoscale texture of the aligned CNTs, and can have walls with sub-micron thickness and aspect ratios exceeding 50:1. Integration of CNT microstructures in fabrication offers further opportunity to exploit the electrical and thermal properties of CNTs, and diverse capabilities for chemical and biochemical functionalization 3.

We present methods for fabrication of patterned microstructures of vertically aligned carbon nanotubes (CNTs), and their use as master molds for production of polymer microstructures with organized nanoscale surface texture. The CNT forests are densified by condensation of solvent onto the substrate, which significantly increases their packing density and enables self-directed formation of 3D shapes.

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip ...

Engineering

Synthesis and Functionalization of Nitrogen-doped Carbon Nanotube Cups with Gold Nanoparticles as Cork Stoppers

Nitrogen-doped carbon nanotubes consist of many cup-shaped graphitic compartments termed as nitrogen-doped carbon nanotube cups (NCNCs). These as-synthesized graphitic nanocups from chemical vapor deposition (CVD) method were stacked in a head-to-tail fashion held only through noncovalent interactions. Individual NCNCs can be isolated out of their stacking structure through a series of chemical and physical separation processes. First, as-synthesized NCNCs were oxidized in a mixture of strong acids to introduce oxygen-containing defects on the graphitic walls. The oxidized NCNCs were then processed using high-intensity probe-tip sonication which effectively separated the stacked NCNCs into individual graphitic nanocups. Owing to their abundant oxygen and nitrogen surface functionalities, the resulted individual NCNCs are highly hydrophilic and can be effectively functionalized with gold nanoparticles (GNPs), which preferentially fit in the opening of the cups as cork stoppers. These graphitic nanocups corked with GNPs may find promising applications as nanoscale containers and drug carriers.

We discussed the synthesis of individual graphitic nanocups using a series of techniques including chemical vapor deposition, acid oxidation and probe-tip sonication. By citrate reduction of HAuCl4, the graphitic nanocups were effectively corked with gold nanoparticles due to the chemically reactive edges of the cups.

Nitrogen-doped carbon  nanotubes consist of many cup-shaped graphitic compartments termed as  nitrogen-doped carbon nanotube cups (NCNCs).  These ...

A Whole Cell Bioreporter Approach to Assess Transport and Bioavailability of Organic Contaminants in Water Unsaturated Systems

Bioavailability of contaminants is a prerequisite for their effective biodegradation in soil. The average bulk concentration of a contaminant, however, is not an appropriate measure for its availability; bioavailability rather depends on the dynamic interplay of potential mass transfer (flux) of a compound to a microbial cell and the capacity of the latter to degrade the compound. In water-unsaturated parts of the soil, mycelia have been shown to overcome bioavailability limitations by actively transporting and mobilizing organic compounds over the range of centimeters. Whereas the extent of mycelia-based transport can be quantified easily by chemical means, verification of the contaminant-bioavailability to bacterial cells requires a biological method. Addressing this constraint, we chose the PAH fluorene (FLU) as a model compound and developed a water unsaturated model microcosm linking a spatially separated FLU point source and the FLU degrading bioreporter bacterium Burkholderia sartisoli RP037-mChe by a mycelial network of Pythium ultimum. Since the bioreporter expresses eGFP in response of the PAH flux to the cell, bacterial FLU exposure and degradation could be monitored directly in the microcosms via confocal laser scanning microscopy (CLSM). CLSM and image analyses revealed a significant increase of the eGFP expression in the presence of P. ultimum compared to controls without mycelia or FLU thus indicating FLU bioavailability to bacteria after mycelia-mediated transport. CLSM results were supported by chemical analyses in identical microcosms. The developed microcosm proved suitable to investigate contaminant bioavailability and to concomitantly visualize the involved bacteria-mycelial interactions.

A whole cell bioreporter assay with Burkholderia sartisoli RP037-mChe was developed to detect fractions of an organic contaminant (i.e., fluorene) available for bacterial degradation after active transport by mycelia bridging air-filled pores in a water unsaturated model system.

Bioavailability of contaminants is a prerequisite for their effective biodegradation in soil. The average bulk concentration of a contaminant, however, is ...

Environment

Facile Preparation of Internally Self-assembled Lipid Particles Stabilized by Carbon Nanotubes

We present a facile method to prepare nanostructured lipid particles stabilized by carbon nanotubes (CNTs). Single-walled (pristine) and multi-walled (functionalized) CNTs are used as stabilizers to produce Pickering type oil-in-water (O/W) emulsions. Lipids namely, Dimodan U and Phytantriol are used as emulsifiers, which in excess water self-assemble into the bicontinuous cubic Pn3m phase. This highly viscous phase is fragmented into smaller particles using a probe ultrasonicator in presence of conventional surfactant stabilizers or CNTs as done here. Initially, the CNTs (powder form) are dispersed in water followed by further ultrasonication with the molten lipid to form the final emulsion. During this process the CNTs get coated with lipid molecules, which in turn are presumed to surround the lipid droplets to form a particulate emulsion that is stable for months. The average size of CNT-stabilized nanostructured lipid particles is in the submicron range, which compares well with the particles stabilized using conventional surfactants. Small angle X-ray scattering data confirms the retention of the original Pn3m cubic phase in the CNT-stabilized lipid dispersions as compared to the pure lipid phase (bulk state). Blue shift and lowering of the intensities in characteristic G and G&#39; bands of CNTs observed in Raman spectroscopy characterize the interaction between CNT surface and lipid molecules. These results suggest that the interactions between the CNTs and lipids are responsible for their mutual stabilization in aqueous solutions. As the concentrations of CNTs employed for stabilization are very low and lipid molecules are able to functionalize the CNTs, the toxicity of CNTs is expected to be insignificant while their biocompatibility is greatly enhanced. Hence the present approach finds a great potential in various biomedical applications, for instance, for developing hybrid nanocarrier systems for the delivery of multiple functional molecules as in combination therapy or polytherapy.

We report on a smart application of carbon nanotubes for kinetic stabilization of lipid particles that contain self-assembled nanostructures in their cores. The preparation of lipid particles requires rather low concentrations of carbon nanotubes permitting their use in biomedical applications such as drug delivery.

We present a facile method to prepare nanostructured lipid particles stabilized by carbon nanotubes (CNTs). Single-walled (pristine) and multi-walled ...

Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology

We demonstrate a method for the low temperature growth (350 &#176;C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive thin-films. Due to the low growth temperature, the process allows integration with modern low-&#954; dielectrics and some flexible substrates. The process is compatible with standard semiconductor fabrication, and a method for the fabrication of electrical 4-point probe test structures for vertical interconnect test structures is presented. Using scanning electron microscopy the morphology of the CNT bundles is investigated, which demonstrates vertical alignment of the CNT and can be used to tune the CNT growth time. With Raman spectroscopy the crystallinity of the CNT is investigated. It was found that the CNT have many defects, due to the low growth temperature. The electrical current-voltage measurements of the test vertical interconnects displays a linear response, indicating good ohmic contact was achieved between the CNT bundle and the top and bottom metal electrodes. The obtained resistivities of the CNT bundle are among the average values in the literature, while a record-low CNT growth temperature was used.

A method for the growth of low temperature vertically-aligned carbon nanotubes, and the subsequent fabrication of vertical interconnect electrical test structures using semiconductor fabrication is presented.

We demonstrate a method for the low temperature growth (350 &#176;C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive ...

Functionalization of Single-walled Carbon Nanotubes with Thermo-reversible Block Copolymers and Characterization by Small-angle Neutron Scattering

We demonstrate a protocol for single-walled carbon nanotube functionalization using thermo-sensitive PEO-PPO-PEO triblock copolymers in an aqueous solution. In a carbon nanotube/PEO105-PPO70-PEO105 (poloxamer 407) aqueous solution, the amphiphilic poloxamer 407 adsorbs onto the carbon nanotube surfaces and self-assembles into continuous layers, driven by intermolecular interactions between constituent molecules. The addition of 5-methylsalicylic acid changes the self-assembled structure from spherical-micellar to a cylindrical morphology. The fabricated poloxamer 407/carbon nanotube hybrid particles exhibit thermo-responsive structural features so that the density and thickness of poloxamer 407 layers are also reversibly controllable by varying temperature. The detailed structural properties of the poloxamer 407/carbon nanotube particles in suspension can be characterized by small-angle neutron scattering experiments and model fit analyses. The distinct curve shapes of the scattering intensities depending on temperature control or addition of aromatic additives are well described by a modified core-shell cylinder model consisting of a carbon nanotube core cylinder, a hydrophobic shell, and a hydrated polymer layer. This method can provide a simple but efficient way for the fabrication and in-situ characterization of carbon nanotube-based nano particles with a structure-tunable encapsulation.

A method for the functionalization of carbon nanotubes with structure-tunable polymeric encapsulation layers and structural characterization using small-angle neutron scattering is presented.

We demonstrate a protocol for single-walled carbon nanotube functionalization using thermo-sensitive PEO-PPO-PEO triblock copolymers in an aqueous ...

Repression of Multiple Myeloma Cell Growth In Vivo by Single-wall Carbon Nanotube (SWCNT)-delivered MALAT1 Antisense Oligos

The single-wall carbon nanotube (SWCNT) is a new type of nanoparticle, which has been used to deliver multiple kinds of drugs into cells, such as proteins, oligonucleotides, and synthetic small-molecule drugs. The SWCNT has customizable dimensions, a large superficial area, and can flexibly bind with drugs through different modifications on its surface; therefore, it is an ideal system to transport drugs into cells. Long noncoding RNAs (lncRNAs) are a cluster of noncoding RNA longer than 200 nt, which cannot be translated to protein but play an important role in biological and pathophysiological processes. Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) is a highly conserved lncRNA. It was demonstrated that higher MALAT1 levels are related to the poor prognosis of various cancers, including multiple myeloma (MM). We have revealed that MALAT1 regulates DNA repair and cell death in MM; thus, MALAT1 can be considered as a therapeutic target for MM. However, the efficient delivery of the antisense oligo to inhibit/knockdown MALAT1 in vivo is still a problem. In this study, we modify the SWCNT with PEG-2000 and conjugate an anti-MALAT1 oligo to it, test the delivery of this compound in vitro, inject it intravenously into a disseminated MM mouse model, and observe a significant inhibition of MM progression, which indicates that SWCNT is an ideal delivery shuttle for anti-MALAT1 gapmer DNA.

Repression of Multiple Myeloma Cell Growth In Vivo by Single-wall Carbon Nanotube SWCNT-delivered MALAT1 Antisense Oligos

This manuscript describes the synthesis of a single-wall carbon nanotube (SWCNT)-conjugated MALAT1 antisense gapmer DNA oligonucleotide (SWCNT-anti-MALAT1), which demonstrates the reliable delivery of the SWCNT and the potent therapeutic effect of anti-MALAT1 in vitro and in vivo. Methods used for synthesis, modification, conjugation, and injection of SWCNT-anti-MALAT1 are described.

The single-wall carbon nanotube (SWCNT) is a new type of nanoparticle, which has been used to deliver multiple kinds of drugs into cells, such as ...

Cancer Research

Localization and Relative Quantification of Carbon Nanotubes in Cells with Multispectral Imaging Flow Cytometry

Carbon-based nanomaterials, like carbon nanotubes (CNTs), belong to this type of nanoparticles which are very difficult to discriminate from carbon-rich cell structures and de facto there is still no quantitative method to assess their distribution at cell and tissue levels. What we propose here is an innovative method allowing the detection and quantification of CNTs in cells using a multispectral imaging flow cytometer (ImageStream, Amnis). This newly developed device integrates both a high-throughput of cells and high resolution imaging, providing thus images for each cell directly in flow and therefore statistically relevant image analysis. Each cell image is acquired on bright-field (BF), dark-field (DF), and fluorescent channels, giving access respectively to the level and the distribution of light absorption, light scattered and fluorescence for each cell. The analysis consists then in a pixel-by-pixel comparison of each image, of the 7,000-10,000 cells acquired for each condition of the experiment. Localization and quantification of CNTs is made possible thanks to some particular intrinsic properties of CNTs: strong light absorbance and scattering; indeed CNTs appear as strongly absorbed dark spots on BF and bright spots on DF with a precise colocalization.
This methodology could have a considerable impact on studies about interactions between nanomaterials and cells given that this protocol is applicable for a large range of nanomaterials, insofar as they are capable of absorbing (and/or scattering) strongly enough the light.

In this study, the main purpose was to monitor the cellular uptake and eventual exocytosis of carbon nanotubes (CNTs). From this perspective, we proposed here a unique method using multispectral imaging flow cytometry allowing a quantification and localization of CNTs in a statistically relevant number of cells.

Carbon-based nanomaterials, like carbon nanotubes (CNTs), belong to this type of nanoparticles which are very difficult to discriminate from carbon-rich ...

Bioengineering

Precision Milling of Carbon Nanotube Forests Using Low Pressure Scanning Electron Microscopy

A nanoscale fabrication technique appropriate for milling carbon nanotube (CNT) forests is described. The technique utilizes an environmental scanning electron microscope (ESEM) operating with a low pressure water vapor ambient. In this technique, a portion of the electron beam interacts with the water vapor in the vicinity of the CNT sample, dissociating the water molecules into hydroxyl radicals and other species by radiolysis. The remainder of the electron beam interacts with the CNT forest sample, making it susceptible to oxidation from the chemical products of radiolysis. This technique may be used to trim a selected region of an individual CNT, or it may be used to remove hundreds of cubic microns of material by adjusting ESEM parameters. The machining resolution is similar to the imaging resolution of the ESEM itself. The technique produces only small quantities of carbon residue along the boundaries of the cutting zone, with minimal effect on the native structural morphology of the CNT forest.

Low pressure scanning electron microscopy in a water vapor ambient is used to machine nanoscale to microscale features in carbon nanotube forests.

A nanoscale fabrication technique appropriate for milling carbon nanotube (CNT) forests is described. The technique utilizes an environmental scanning ...

Using Carbon Nanofiber Arrays for Efficient Biomolecule and Dye Delivery to Plants

Using Vertically Aligned Carbon Nanofiber Arrays on Rigid or Flexible Substrates for Delivery of Biomolecules and Dyes to Plants

The delivery of biomolecules and impermeable dyes to intact plants is a major challenge. Nanomaterials are up-and-coming tools for the delivery of DNA to plants. As exciting as these new tools are, they have yet to be widely applied. Nanomaterials fabricated on rigid substrate (backing) are particularly difficult to successfully apply to curved plant structures. This study describes the process for microfabricating vertically aligned carbon nanofiber arrays and transferring them from a rigid to a flexible substrate. We detail and demonstrate how these fibers (on either rigid or flexible substrates) can be used for transient transformation or dye (e.g., fluorescein) delivery to plants. We show how VACNFs can be transferred from rigid silicon substrate to a flexible SU-8 epoxy substrate to form flexible VACNF arrays. To overcome the hydrophobic nature of SU-8, fibers in the flexible film were coated with a thin silicon oxide layer (2-3 nm). To use these fibers for delivery to curved plant organs, we deposit a 1 &#181;L droplet of dye or DNA solution on the fiber side of VACNF films, wait 10 min, place the films on the plant organ and employ a swab with a rolling motion to drive fibers into plant cells. With this method, we have achieved dye and DNA delivery in plant organs with curved surfaces.

Author Spotlight: Unlocking Plant Transformation by Innovating with Carbon Nanofiber Arrays 

Here we describe methods for microfabricating vertically aligned carbon nanofibers (VACNFs), transferring VACNFs to flexible substrates, and applying VACNFs on both rigid and flexible substrates to plants for biomolecule and dye delivery.

The delivery of biomolecules and impermeable dyes to intact plants is a major challenge. Nanomaterials are up-and-coming tools for the delivery of DNA to ...

Transport of Surface-modified Carbon Nanotubes through a Soil Column

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