Photodynamic therapy (PDT) is a cancer treatment that combines a chemical compound, called a photosensitizer, with a particular type of light to kill cancer cells. The treatment works like this: the photosensitizing agent is injected into the bloodstream. The agent is absorbed by cells all over the body, but stays in cancer cells longer than it does in normal cells. One to three days after injection, when most of the agent has left normal cells but remains in cancer cells, the tumor is exposed to light. The photosensitizer in the tumor absorbs the light and produces an active form of oxygen (singlet oxygen) that destroys nearby cancer cells. PDT has been used for the past 30 years and is a treatment that works. PDT takes very little time, is often done as an outpatient, can be accurately targeted to the affected area, can be repeated, and has no long-term side effects. It also isn't as expensive or invasive as some other cancer treatment options. The limitation of this form of cancer treatment is that the light needed to activate most photosensitizers cannot pass through more than one centimeter of tissue. For this reason, PDT is usually used to treat tumors on or just under the skin or on the lining of internal organs or cavities. PDT is also less effective in treating large or deep tumors, because the light cannot pass far into these tumors. Researchers have now proposed a new PDT system in which the light is generated by x-ray scintillation nanoparticles with attached photosensitizers. When the nanoparticle-photosensitizer conjugates are targeted to tumors and stimulated by x-rays during radiotherapy, the particles generate visible light that can activate the photosensitizers for photodynamic therapy. Therefore, the radiation and photodynamic therapies are combined and occur simultaneously, and the tumor destruction can be more efficient. More importantly, it can be used for deep tumor treatment as x-rays can penetrate through tissue.
Electron microscopy is a delicate balancing act between using the highest energy electrons possible in order to obtain the best image while avoiding destruction of the sample under investigation. Trouble is, the electron beam does not just observe, it also interacts with the structure that is observed. This can be critical for fragile samples such as nanostructures: the transfer of energy from the electron beam can be sufficient that atoms are knocked right out of the material. In the worst case the sample is destroyed in front of your eyes. Scientists in Orsay, France have turned this problem to their advantage. They have developed a new approach to shaping nanomaterials atom by atom, using a scanning transmission electron microscope (STEM) as a nanometrically precise cutting tool. In this way they 'carve' their materials, such as carbon nanotubes, by removing individual atoms from specifically chosen locations. This technique has the added advantage that scientists can observe what they are doing at the same time. The new technique demonstrates a 'nanoelectron- lithography' of single walled nanotubes, a top down approach to locally control their nanostructures.
Diatoms are a major group of hard-shelled algae and one of the most common types of phytoplankton. A characteristic feature of diatom cells is that they are encased within a unique cell wall made of silica. Silicate materials are very important in nature and they are closely related to the evolution of living organisms. Diatom walls show a wide diversity in form, some quite beautiful and ornate, but usually consist of two symmetrical sides with a split between them, hence the group name. There is great potential for the use of diatoms in nanotechnology. This potential lies in the pores and channels which give rise to a greatly increased surface area, and the silica structure which lends itself to chemical modification. In addition there is a huge variety in the sizes and shapes of diatoms available, providing scope for the selection of a particular species of diatom tailored to a particular requirement. Researchers in the UK have demonstrated that the silica walls of diatoms can be used for the attachment of active biomolecules, such as antibodies, using either primary amine groups or the carbohydrate moiety. These modified structures can, therefore, be used for antibody arrays or for use in techniques such as immunoprecipitation.
Nanopores function as membrane channels in all living systems, where they serve as sensitive electro-mechanical devices that regulate electrical potential, ionic flow, and molecular transport through the cell membrane. Scientists are studying nanopore construction with the goal of making man-made cell membranes and single molecule detectors. So far, nanoporous membrane-based separations simply use the difference in size of the analytes relative to pore size in the membrane. Here, for a nanopore to be useful as a single molecule detector, its diameter must not be much larger than the size of the molecule to be detected. When a single molecule enters a nanopore in an insulating membrane, it causes changes in the nanopore's electrical properties, which then can be detected and measured. In order to bring about selectivity beyond size, it is necessary that methods for functionalizing the membrane pores are available. To that end, researchers have developed a very simple, but versatile, method for decorating the nanoporous membranes with functional groups. By uniformly modifying the internal cavities of nanopores with various polymers they were able to demonstrate selectivities based on size, charge and hydrophobicity of the molecule passing through the nanopore.
Walk into an intensive care unit and you're likely to see many of the patients sporting a 'central line' - a plastic tube placed in a large vein that goes to the heart. A central line is a very efficient way to pump nutrients, antibiotics or other drugs directly into the bloodstream. Unfortunately it is also a cause for bloodstream infections (sepsis) and central lines remain an important cause for hospital deaths. An estimated 200,000 bloodstream infections occur each year in the U.S. alone, the majority associated with the presence of an intravascular catheter. The Institute for Healthcare Improvement (IHI) estimates the yearly death toll from blood infections related to intravenous lines to be as high as 28,000. Numerous pathogens can cause sepsis and the death toll could be reduced if the specific pathogen could be identified more quickly than it is usually done today using blood cultures (the laboratory examination of a blood sample to detect the presence of disease-causing microorganisms). One solution would be to determine the pathogen's DNA, requiring a rapid DNA assay with the potential for mutant identification and multiplexing. Current DNA assays are based on thermal dehybridization or melting of the DNA duplex helix - the melting temperature of DNA is determined by its base sequence - a process that can take up to an hour. Researchers in Germany have developed a novel technique that allows for DNA analysis in the millisecond range. Their method has great potential to vastly improve the speed of pathogen detection.
More and more carbon nanotube (CNT) applications are moving from the research lab into commercial products. For example, CNTs can be found already in tennis rackets and bicycles, displays and TV screens, and numerous resins used by aerospace, defense, health care, and electronics companies. Not surprisingly, CNT production is growing by hundreds of metric tons a year. One of the large suppliers alone, Bayer, is talking about having 3,000 metric tons of production capacity in place by 2012. As a result of the increasing supply, prices are dropping fast. While a kilogram of multi-walled CNTs (MWCNTs) sold for tens of thousands of dollars just a few years ago (and single-walled CNTs still do), the price for some types of MWCNTs has fallen to hundreds of dollars per kg. Recent market analyses forecast sales of all nanotubes to reach $1 billion to $2 billion annually within the next four to seven years. In terms of dollar value, electronics devices will be the largest end-use category, although composite materials in automotive applications may account for greater volumes. These volumes are expected to approach several thousand metric tons per year. This means that the exposure to CNTs, especially by factory workers, will increase substantially over the next few years. Since the jury is still out as to the toxicity of nanotubes it appears prudent to at least develop suitable sensor technology to detect CNTs, especially in the workplace.
The vision of revolutionary bottom-up nanotechnology is based on a concept of molecular assembly technologies where nanoscale materials and structures self-assemble to microscale structures and finally to macroscopic devices and products. We are a long way from realizing this vision but researchers are busily laying the foundation for nanoscale engineering. Assembling nanoscopic components into macroscopic materials is an appealing goal but one of the enormous difficulties lies in bridging approximately six orders of magnitude that separate the nanoscale from the macroscopic world. Until machinery capable of automated and industrial-scale nano-assembly can be built, the parallelism of chemical synthesis and self-assembly is necessary when controlling materials at the nanoscale. An obvious direct approach to molecular nanotechnology therefore is to start with organic molecules as building blocks. Modest from the viewpoint of molecular manufacturing visionaries, but quite fascinating to a lot of scientists, research into nanofibers, as a modification of organic crystals, is making good progress. New research results coming out of Denmark offer the basis for a novel organic-molecule-based nanotechnological concept that allows for a multitude of applications in fundamental research and in device applications. Essentially, this concept is based on three steps: 1) directed self-assembled surface growth of nanofibers from functionalized molecules; 2) transfer and manipulation of individual fibers as well as of ordered arrays; and 3) device integration.
'Smart' is the key buzz word used by materials engineers when they describe the future of coatings, textiles, building structures, vehicles and just any material that you can think of. Materials are made 'smart' when they are engineered to have properties that change in a controlled manner under the influence of external stimuli such as mechanical stress, temperature, humidity, electric charge, magnetic fields etc. Nature of course is full with 'smart' materials that are capable of adapting to new tasks, are self-healing, and can self-assemble autonomously simply out of a solution of building blocks. Duplicating this feat with man-made materials will one day become a reality thanks to nanotechnology. Scientists not only dream about self-repairing cars or building walls that turn transparent like windows, they are actively working on the first steps towards these goals. Simple smart materials (that are not nanotechnology based) are already a reality, such as piezoelectric materials and shape memory alloys. Emerging nanotechnologies are now about to give scientists the tools to take smart materials to the next performance level. For instance, the European project Inteltex is developing a new, multifunctional textile that could be used as a wallpaper to detect temperature changes or chemical leakage or that could be used in medical and protective wear to monitor body temperature and mechanical stress. MIT's Institute for Soldier Nanotechnologies works on smart surfaces that switch properties. Nanotechnology-enabled smart materials are still very early days but basic progress is being made. Another small building block towards smart materials was recently reported by Italian researchers who demonstrated photo-switchable nanofibers based on the reversible transformation between two molecular photochemical states, exhibiting different chemico-physical characteristics.