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From the Labs: Nanotechnology

New publications, experiments and breakthroughs in nanotechnology–and what they mean.
April 22, 2008

Self-Assembling Transistors
Organic materials crystallize on a flexible chip for high-performance electronics

An organic semiconductor crystallizes between metal contacts (top). Without a pretreatment, the material does not crystallize (bottom).

Source: “Contact-Induced Crystallinity for High-Performance Soluble Acene-Based Transistors and Circuits”
David Gundlach et al.
Nature Materials 7: 216-221

Results: Researchers at the National Institute of Standards and Technology, Penn State University, and the University of Kentucky have developed a chemical process that helps molecules of an organic semiconductor form transistors on a flexible electronic chip. The molecules crystallize only in the areas between electrical contacts, bridging the gaps between them. In other areas, the organic semiconductor does not crystallize, instead acting as an electrical insulator that prevents unwanted cross talk between transistors.

Why it matters: The process could provide a cheaper way to make high-performance, flexible electronics. Current techniques require either precisely printing semiconductors onto a flexible surface or depositing a semiconductor and etching circuitry into it. Now either step can be skipped. The semiconductor can simply be deposited across the entire surface, and it will self-organize to take on different electronic properties in the appropriate areas.

Methods: The researchers use conventional methods to deposit metallic electrodes on a flexible polyimide substrate. Then they dip the substrate in pentafluorobenzene thiol, which sticks only to the electrodes. Next, they layer the entire surface with an organic semiconductor solution. As the solution dries, it crystallizes on or near the thiol-coated electrodes.

Next steps: The researchers will continue to study the chemistry and kinetics of the semiconductor to better understand what causes it to crystallize. They are also trying to duplicate the process using other semiconductor materials.

Molecular Nanovalves
Tiny valves can release drugs from nano containers for targeted treatments

Source: “PH-Responsive Supramolecular Nanovalves Based on Cucurbit[6]uril Pseudorotaxanes”
Sarah Angelos et al.
Angewandte Chemie 47: 2222-2226

Results: Researchers at the University of California, Los Angeles, have used a complex of molecules to create nanoscale valves for porous silica nanoparticles. The researchers demonstrated that the molecules can seal a fluorescent dye inside the nanoparticles. When the pH of water surrounding a particle changes, part of the nanovalve detaches, allowing the dye to escape.

Why it matters: The nanoparticles could eventually be used to deliver drugs to diseased cells within the body, which differ in pH from healthy cells. A diseased cell that ingested a nanoparticle would cause it to release a drug. Such targeted drug delivery could decrease the side effects of existing treatments and allow the use of drugs that would be either ineffective or lethal if delivered throughout the body. Other nanovalves have been made in the past, but they were activated by special solvents and thus wouldn’t work in the body.

Methods: The researchers made porous silica nanoparticles and chemically treated them, attaching linker mole­cules to them. After loading the nanoparticles with a fluorescent dye, they sealed the pores by binding molecular complexes to the linkers. Then they placed the nanoparticles in water, raised the pH by adding sodium hydroxide, and monitored the release of the dye.

Next steps: The current system works only at harsh pH levels. The researchers are working to develop a system that responds to the gentler pH levels of diseased cells within the body, a crucial modification if the system is to be used for actual drug delivery.

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