Sunday, December 18, 2011

'Label-free' imaging tool tracks nanotubes in cells, blood for biomedical research

 Researchers have demonstrated a new imaging tool for tracking structures called carbon nanotubes in living cells and the bloodstream, which could aid efforts to perfect their use in biomedical research and clinical medicine.

The structures have potential applications in drug delivery to treat diseases and imaging for cancer research. Two types of nanotubes are created in the manufacturing process, metallic and semiconducting. Until now, however, there has been no technique to see both types in living cells and the bloodstream, said Ji-Xin Cheng, an associate professor of biomedical engineering and chemistry at Purdue University.

The imaging technique, called transient absorption, uses a pulsing near-infrared laser to deposit energy into the nanotubes, which then are probed by a second near-infrared laser.

The researchers have overcome key obstacles in using the imaging technology, detecting and monitoring the nanotubes in live cells and laboratory mice, Cheng said.

"Because we can do this at high speed, we can see what's happening in real time as the nanotubes are circulating in the bloodstream," he said.

Findings are detailed in a research paper posted online Dec. 4 in the journal Nature Nanotechnology.

The imaging technique is "label free," meaning it does not require that the nanotubes be marked with dyes, making it potentially practical for research and medicine, Cheng said.

"It's a fundamental tool for research that will provide information for the scientific community to learn how to perfect the use of nanotubes for biomedical and clinical applications," he said.

The conventional imaging method uses luminescence, which is limited because it detects the semiconducting nanotubes but not the metallic ones.

The nanotubes have a diameter of about 1 nanometer, or roughly the length of 10 hydrogen atoms strung together, making them far too small to be seen with a conventional light microscope. One challenge in using the transient absorption imaging system for living cells was to eliminate the interference caused by the background glow of red blood cells, which is brighter than the nanotubes.

The researchers solved this problem by separating the signals from red blood cells and nanotubes in two separate "channels." Light from the red blood cells is slightly delayed compared to light emitted by the nanotubes. The two types of signals are "phase separated" by restricting them to different channels based on this delay.

Researchers used the technique to see nanotubes circulating in the blood vessels of mice earlobes.

"This is important for drug delivery because you want to know how long nanotubes remain in blood vessels after they are injected," Cheng said. "So you need to visualize them in real time circulating in the bloodstream."

The structures, called single-wall carbon nanotubes, are formed by rolling up a one-atom-thick layer of graphite called graphene. The nanotubes are inherently hydrophobic, so some of the nanotubes used in the study were coated with DNA to make them water-soluble, which is required for them to be transported in the bloodstream and into cells.

The researchers also have taken images of nanotubes in the liver and other organs to study their distribution in mice, and they are using the imaging technique to study other nanomaterials such as graphene.

The paper was written by doctoral student Ling Tong; postdoctoral research associate Yuxiang Liu; doctoral students Bridget D. Dolash and Yookyung Jung; biomedical engineering research scientist Mikhail N. Slipchenko; Donald E. Bergstrom, the Walther Professor of Medicinal Chemistry; and Cheng.

The research is funded by the National Science Foundation.

Story Source:

The above story is reprinted from materials provided by Purdue University. The original article was written by Emil Venere.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Ling Tong, Yuxiang Liu, Bridget D. Dolash, Yookyung Jung, Mikhail N. Slipchenko, Donald E. Bergstrom, Ji-Xin Cheng. Label-free imaging of semiconducting and metallic carbon nanotubes in cells and mice using transient absorption microscopy. Nature Nanotechnology, 2011; DOI: 10.1038/nnano.2011.210

Note: If no author is given, the source is cited instead.

New solar-powered classroom brings science to schools in developing countries

 An innovative project led by a chemistry academic at the University of Southampton is using solar generators to provide IT resources and 'hands-on' science for students in developing countries.

A major difficulty in teaching science subjects in developing countries, especially in rural schools, is that students are rarely able to get 'hands-on' experience of experiments. This could be partly due to a lack of equipment, chemicals and facilities but mainly because of a lack of electricity and running water.

Now, Professor Tony Rest, a visiting Chemistry academic at the University of Southampton, and Keith Wilkinson, formerly a teacher at the International School at Lusaka in Zambia, have devised a solar-powered solution based on a digital projector and low-cost solar energy panels so that students can gain access to IT and other modern teaching methods.

Professor Rest says: "The lack of electricity is a particularly serious matter for rural schools and this situation is unlikely to get better in the near to medium future. With drawbacks to petrol generators, due to difficulties in getting supplies and safety hazards, solar energy generators have become available at cost-effective prices and provide a sustainable answer as rural schools have an abundance of the basic energy source required to power them -- sunshine.

Most data/video projectors require 200-300 watt and cannot be economically sustained by solar power in rural villages. However, the advent of mini-projectors, which require about 50 watts of power, has revolutionised the situation and made battery powered projection feasible.

The solar energy generators, which consist of solar panels, batteries and inverters, can be linked to the projector for students to get practical classes via multimedia resources to show laboratory experiments and stress practical techniques.

Professor Rest adds: "These experiences can be extended to other science subjects from physics, biology and maths, to subjects involving practical elements, such as engineering, and to craft subjects, including plumbing, carpentry, and catering, where students need see how to acquire skills. By extending the breadth of subjects benefiting from the use of IT, the overall cost of using a solar energy generator is reduced. Another spin-off is that students in rural schools gain access to valuable IT skills."

The project has been developed by the 'Chemistry Aid' project, the Chemistry Video Consortium based at the University of Southampton, with support from the Royal Society of Chemistry, which has provided multimedia teaching resources.

Story Source:

The above story is reprinted from materials provided by University of Southampton.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Chemists become molecular sculptors, synthesizing tiny, molecular traps

 Using clever but elegant design, University at Buffalo chemists have synthesized tiny, molecular cages that can be used to capture and purify nanomaterials.

Sculpted from a special kind of molecule called a "bottle-brush molecule," the traps consist of tiny, organic tubes whose interior walls carry a negative charge. This feature enables the tubes to selectively encapsulate only positively charged particles.

In addition, because UB scientists construct the tubes from scratch, they can create traps of different sizes that snare molecular prey of different sizes. The level of fine tuning possible is remarkable: In the Journal of the American Chemical Society, the researchers report that they were able to craft nanotubes that captured particles 2.8 nanometers in diameter, while leaving particles just 1.5 nanometers larger untouched.

These kinds of cages could be used, in the future, to expedite tedious tasks, such as segregating large quantum dots from small quantum dots, or separating proteins by size and charge.

"The shapes and sizes of molecules and nanomaterials dictate their utility for desired applications. Our molecular cages will allow one to separate particles and molecules with pre-determined dimensions, thus creating uniform building blocks for the fabrication of advanced materials," said Javid Rzayev, the UB assistant professor of chemistry who led the research.

"Just like a contractor wants tile squares or bricks to be the same size so they fit well together, scientists are eager to produce nanometer-size particles with the same dimensions, which can go a long way toward creating uniform and well-behaved materials," Rzayev said.

To create the traps, Rzayev and his team first constructed a special kind of molecule called a bottle-brush molecule. These resemble a round hair brush, with molecular "bristles" protruding all the way around a molecular backbone.

After stitching the bristles together, the researchers hollowed out the center of each bottle-brush molecule, leaving behind a structure shaped like a toilet paper tube.

The carving process employed simple but clever chemistry: When building their bottlebrush molecules, the scientists constructed the heart of each molecule using molecular structures that disintegrate upon coming into contact with water. Around this core, the scientists then attached a layer of negatively charged carboxylic acid groups.

To sculpt the molecule, the scientists then immersed it water, in effect hollowing the core. The resulting structure was the trap -- a nanotube whose inner walls were negatively charged due to the presence of the newly exposed carboxylic acid groups.

To test the tubes' effectiveness as traps, Rzayev and colleagues designed a series of experiments involving a two-layered chemical cocktail.

The cocktail's bottom layer consisted of a chloroform solution containing the nanotubes, while the top layer consisted of a water-based solution containing positively charged dyes. (As in a tequila sunrise, the thinner, water-based solution floats on top of the denser chloroform solution, with little mixing.)

When the scientists shook the cocktail for five minutes, the nanotubes collided with and trapped the dyes, bringing the dyes into the chloroform solution. (The dyes, on their own, do not dissolve in chloroform.)

In similar experiments, Rzayev and his team were able to use the nanotubes to extract positively charged molecules called dendrimers from an aqueous solution. The nanotubes were crafted so that dendrimers with a diameter of 2.8 nanometers were trapped, while dendrimers that were 4.3 nanometers across were left in solution.

To remove the captured dendrimers from the nanotubes, the researchers simply lowered the pH of the chloroform solution, which shuts down the negative charge inside the traps and allows the captured particles to be released from their cages.

The research on nanotubes is part of a larger suite of studies Rzayev is conducting on bottle-brush molecules using a National Science Foundation CAREER award. His other work includes the fabrication of bottle-brush-based nanomembranes that could be adapted for water filtration, and the assembly of layered, bottle-brush polymers that reflect visible light like the wings of a butterfly do.

Story Source:

The above story is reprinted from materials provided by University at Buffalo.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Kun Huang, Javid Rzayev. Charge and Size Selective Molecular Transport by Amphiphilic Organic Nanotubes. Journal of the American Chemical Society, 2011; 133 (42): 16726 DOI: 10.1021/ja204296v

Note: If no author is given, the source is cited instead.

Carving at the nanoscale

 Researchers at the Catalan Institute of Nanotechnology (ICN) have successfully demonstrated a new method for producing a wide variety of complex hollow nanoparticles.

A common theme in nanoscience research is the recycling of "old" processes and protocols that were once applied crudely on bulk materials in trades and industrial settings, but which can now be applied to nano-sized structures with high precision and resolution using newly available instruments and know-how.

After several years of research, scientists of the Catalan Institute of Nanotechnology (ICN), Dr. Edgar Emir González (currently at Instituto Geofísico Universidad Javeriana y Universidad Santo Tomás) and ICREA Prof. Victor Puntes in collaboration with ICREA Prof. Jordi Arbiol of the Institute of Materials Science of Barcelona (ICMAB-CSIC), have refined methods based on traditional corrosion techniques (the Kirkendall effect and galvanic, pitting, etching and de-alloying corrosion processes).

They show that these methods, which are far more aggressive at the nanoscale than in bulk materials due to the higher surface area of nanostructures, provide interesting pathways for the production of new and exotic materials. By making simple changes in the chemical environment it is possible to tightly control the reaction and diffusion processes at room temperatures, allowing for high yields and high consistency in form and structure. This should make the processes particularly attractive for commercial applications as they are easily adapted to industrial scales.

A wide range of structures can be formed, including open boxes, bimetallic and trimetallic double-walled open boxes with pores, multiwalled/multichamber boxes, double-walled, porous and multichamber nanotubes, nanoframes, noble metal fullerenes, and others.

Story Source:

The above story is reprinted from materials provided by Institut Catala de Nanotecnologia.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

E. Gonzalez, J. Arbiol, V. F. Puntes. Carving at the Nanoscale: Sequential Galvanic Exchange and Kirkendall Growth at Room Temperature. Science, 2011; 334 (6061): 1377 DOI: 10.1126/science.1212822