Fluorescent probes can handle rigors of spaceflight

Kevin Robinson

Two common fluorescent probes may be one step closer to a flight to Mars now that researchers have determined that the probes can withstand high doses of radiation with little degradation of their ability to fluoresce. That is good news for scientists and engineers who want to use these probes and others like them to hunt for life on other planets.

Little is known about how well fluorescein and Alexa Fluor 633 would stand up to the potentially high levels of radiation involved in deep spaceflight. So as part of a larger effort to prepare instruments for a European Mars mission to search for life, researchers from the Space Research Centre at the University of Leicester, from the Cranfield Biotechnology Centre at Cranfield University, and from the University of Birmingham, all in the UK, put the fluorophores to the test. Typically, the fluorophores are bound to antibodies and used to label bacteria in a solution.

Researchers exposed fluorophores to cyclotron radiation to mimic the radiation of space. They used special sample blocks with 15-μl wells to hold the liquid fluorophore before evaporating the water. Courtesy of Daniel P. Thompson.

The researchers put solutions of the fluorophores into holders specially constructed to allow multiple 15-μl wells to be put into a cyclotron beam and evaporated the water from the solution so that only dried fluorophore remained.

“If the reagents are carried to Mars in solution, we expect significant radiation damage to the materials,” explained Daniel P. Thompson of the University of Leicester. “This is due to the radiation generating chemically reactive species from the water that could chemically attack our reagents.”

The researchers calculated the anticipated radiation exposure for a trip to Mars during peak solar flare season and exposed the dried fluorophores to alpha and proton radiation from the cyclotron. To ensure that the results would cover the range of exposures, they did not account for any spacecraft shielding and used 1, 10, 100 and 10,000 times the expected exposure. After exposure, the fluorophores were rehydrated and tested using a Cary Eclipse fluorescence spectrophotometer from Varian Inc. of Palo Alto, Calif. The results showed very little degradation, even at 10,000 times the expected exposure.

Thompson said that the researchers have conducted further experiments using gamma radiation from a cobalt-60 radionucleotide source and that they plan to subject the fluorophores to vacuum heat testing and, possibly, to heavier ion testing from iron, carbon, silicon or oxygen. They also are considering tests using higher-energy protons, and they want to test other fluorophores.

To label bacteria, the fluorophores must be bound to antibodies, so Thompson said the investigators also are testing the effects of radiation on antibodies and plan to test the stability of antibody-fluorophore conjugates. They hope to conduct tests during the 2007 ESA Biopan mission, which would allow them to test the effects of multiple variables at once by sending materials into the space environment of low Earth orbit.

Thompson said that as the design of the spacecraft becomes clearer, the group can be more precise in its testing. However, the results of these early tests could allow engineers to worry less about shielding the fluorescent reagents from solar and cosmic radiation.

Analytical Chemistry, published online Feb. 24.