In the bizarre realm of quantum physics, the impossible stairs depicted in M.C. Escher's 1960 lithograph, Ascending and Descending, may take on new resonance. In the picture, a continuous staircase seems to go both up and down. At the University of Chicago, physicists have emulated Escher's stairs -- using corkscrews of light.
The value of these so-called optical vortices may be anything but illusory, though. Indeed, they could help speed the commercial development of the amazingly intricate micromachines that engineers are now sculpting from silicon. Problems arise when such devices require a motor -- to propel a microscopic robot, say, or to power a lilliputian chemical factory. Many elegant micromachine motors have been designed, but most have a fatal flaw, notes Chicago physicist David G. Grier: They wear out quickly.
An optical-vortex system wouldn't wear out. Like Escher's staircase, it has quantum steps leading both up and down. The vortex can apply force to a tiny "gear" suspended in a fluid, descending a quantum step down the corkscrew, then recover enough energy from the fluid's heat to descend another level -- or hop back up to the top. Using an array of four vortices, Grier's team has created a pump that fits in a sphere less than 10% the width of a human hair. So life really does imitate art. Scientists at Georgia Institute of Technology and Emory University are developing a clever way to spot cancer cells and viruses. Hailed as a potentially fast and foolproof diagnostic test, it uses so-called molecular beacons to tag a specific pathogen's messenger RNA (mRNA) -- molecules in chromosomes that help cells translate DNA instructions into proteins.
Schematically, the beacons resemble tiny hairpins. At one end is a fluorescent dye molecule; at the other is a "quencher" molecule that absorbs the dye's light. In between is a hinge of genetic material engineered to pair up with mRNA that is unique to a particular disease. When the hinge latches on to its mRNA quarry -- in a cancer cell, say, or a virus -- it opens, separating the two ends so the beacon's light can shine forth.
In case the hinge breaks and generates a false positive signal, the Georgia team, led by biomedical researcher Gang Bao, recently added a new detector. It's designed to spot only the light from two fluorescent sources very close together -- indicating they are attached to mRNA belonging to a single cancer cell or virus. With the help of venture funding from Georgia Tech, Bao has founded a company, Vivonetics, to commercialize the technology. But he admits that years of testing and refinement remain. Terahertz radiation is the final frontier in the electromagnetic spectrum. It lies between microwaves and infrared light, with frequencies of around 1 trillion cycles per second. Worldwide, only a handful of laboratories were exploring terahertz light, or T-rays, before September 11. Since then, research has shifted into high gear.
Compared with X-rays, T-rays promise sharper, more detailed views of what's inside luggage or hidden under clothing. Hit with a terahertz beam, molecules in explosives give off a distinctive optical "signature." The same is true for cancer cells, illicit drugs, and most other substances. And T-rays don't seem to damage living tissue, so they could make for safer mammograms and dental exams.
T-ray systems now cost a lot more than X-ray equipment, but that's changing. University of Delaware scientists, led by electrical engineer James Kolodzey, have fashioned a T-ray detector the size of a cell phone -- as opposed to early refrigerator-size gear. Delaware's gadget detects T-rays with silicon-germanium chips "printed" with so-called optical waveguides. Another low-cost approach is in the works across the Atlantic. The European Space Agency's Star Tiger project is developing a T-ray detector akin to the cheap silicon-chip sensors that trigger the release of air bags in cars. So terahertz tech now seems headed down the path blazed by computer chips over the past 40 years. -- Scientists have long studied the protein secretions that let mussels stick to rocks amid pounding waves. Some have tried to derive new adhesives from those proteins, but Northwestern University biomedical engineer Phillip B. Messersmith is pursuing a novel twist: repellents. He says that the proteins' ability to bind tightly to different surfaces makes them an ideal base for coatings on implantable medical devices. With an outer layer of protein- and cell-resistant polymers, these coatings could prevent the potentially life-threatening buildup of blood clots or bacterial colonies on cardiac stents or urinary catheters.
-- Tomorrow's contact lenses could dispense drugs in precise doses to treat diseases such as glaucoma. University of Florida researchers are embedding microscopic capsules in soft contact lenses. The capsules, which are too small to affect the optics of a lens, slowly release their contents to avoid a common problem with eye drops: Inserted in the eye, most of these medications get carried off by tears, says chemical engineer Anuj Chauhan. Worse, tears drain into the nasal cavity, and from there the medication can move into the bloodstream and end up causing serious side effects. For example, Timolol Ophthalmic, a treatment for glaucoma, can trigger heart problems.