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Microreactor produces radioactive probe in a jiffy.



A miniature chemical reactor Chemical reactor

A vessel in which chemical reactions take place. A combination of vessels is known as a chemical reactor network. Chemical reactors have diverse sizes, shapes, and modes and conditions of operation based on the nature of the reaction system
 that whips up a diagnostic tool could widen the availability of positron-emission tomography (PET) scans, say the reactor's inventors.

PET uses radioactive molecules to image metabolism or other physiological functions. The most commonly administered probe is a radioactive version of glucose that reveals tumors, which take up more of this nutrient than regular cells do.

Making radioactive probes requires expensive machinery. Radioactive elements are generated by particle accelerators known as cyclotrons. Commercial synthesizers costing about $14,0,000 then chemically incorporate the radioelement ra·di·o·el·e·ment  
n.
A naturally occurring or artificially produced radioactive element.
 into a desired molecule.

Furthermore, probe production must be quick because the activity of their radioactive elements decreases rapidly. One half of a quantity of fluorine-18 decays in 110 minutes, but commercial synthesizers take about 50 minutes to make the PET-glucose probe that contains fluorine-18.

To come up with a faster, more versatile synthesizer synthesizer

Machine that electronically generates and modifies sounds, frequently with the use of a digital computer, for use in the composition of electronic music and in live performance.
, a multi-institute research team from California designed a silicone microchip with a pattern of tunnels, valves, and pumps. The pattern permits a series of reactions to take place sequentially in closed regions of the chip, preventing cross-contamination of reactants. A computer controls the order of the reactions and pumps in reagents through tubing connected to the chip.

The five-step chemical reaction that synthesizes the glucose probe requires several different solvents. Vapors can escape through the chip's porous silicone, so the researchers can heat fluid in the chip to burn off one solvent before introducing another, says Stephen R. Quake of Stanford University Stanford University, at Stanford, Calif.; coeducational; chartered 1885, opened 1891 as Leland Stanford Junior Univ. (still the legal name). The original campus was designed by Frederick Law Olmsted. David Starr Jordan was its first president. . He and his colleagues describe their device in the Dec. 16 Science.

A standard clinical dose of the radioactive glucose probe has an activity of 10 millicuries (mCi). With their first microreactor, the researchers made 190 microcuries of the material in 14, minutes. But a second-generation chip synthesized 1.74 mCi of the probe in under 20 minutes. That's more than enough to image a tumor tumor: see neoplasm.  in a mouse.

With additional chip designs, the production of multiple radioactive probes will be as easy as swapping chips, say Quake and coauthor Hsian-Rong Tseng of the University of California, Los Angeles UCLA comprises the College of Letters and Science (the primary undergraduate college), seven professional schools, and five professional Health Science schools. Since 2001, UCLA has enrolled over 33,000 total students, and that number is steadily rising. . The low cost of the materials that go into the system, which is being explored for commercialization, should mean more medical facilities can make their probes on-site, says Tseng.

"You have to be within striking distance of a cyclotron cyclotron: see particle accelerator.
cyclotron

Particle accelerator that accelerates charged atomic or subatomic particles in a constant magnetic field.
," says Quake, but these machines are fairly well distributed across the United States United States, officially United States of America, republic (2005 est. pop. 295,734,000), 3,539,227 sq mi (9,166,598 sq km), North America. The United States is the world's third largest country in population and the fourth largest country in area. .

The system offers the potential for "radioisotopes on demand, customized to biologically relevant molecules," says mechanical engineer Todd Thorsen of the Massachusetts Institute of Technology Massachusetts Institute of Technology, at Cambridge; coeducational; chartered 1861, opened 1865 in Boston, moved 1916. It has long been recognized as an outstanding technological institute and its Sloan School of Management has notable programs in business, . He notes that the microchip could benefit basic research as well as medical diagnosis.

But the silicone material does limit the types of reactions the chip can perform, cautions Quake. Some widely used solvents would cause the silicone to swell and close off the tunnels.
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Author:Cunningham, A.
Publication:Science News
Geographic Code:1USA
Date:Dec 17, 2005
Words:464
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