Magazine article Science News

Microreactor Produces Radioactive Probe in a Jiffy

Magazine article Science News

Microreactor Produces Radioactive Probe in a Jiffy

Article excerpt

A miniature chemical reactor 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 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, 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. …

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