Nuclear Glow

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Science  26 Jun 2009:
Vol. 324, Issue 5935, pp. 1619-1621
DOI: 10.1126/science.324_1619d

Traditional methods of detecting radioactivity rely on sampling the stream of photons and particles that are actually being radiated. The decay of unstable atomic nuclei sends forth a burst of fast-moving charges—at times accompanied by high-energy, very-short-wavelength gamma rays—and multiple sensing technologies are available to capture them. At the same time, the underlying nuclear transformation also leaves behind a slow heavy co-product, and it is this latter decay signature which Berezin et al. target for sensing. They present an indole-based dye that fluoresces in the near-infrared (760 nm peak emission wavelength) with an efficiency that varies depending on the identity of a coordinated metal ion. Copper (Cu) quenches the fluorescence, whereas zinc enhances it; nickel has little impact. Thus, decay of the unstable 64Cu isotope to a mixture of nickel and zinc can give rise to a significant shift in the fluorescence intensity of the chelating dye. The approximately 12-hour half-life of this nucleus facilitated experimentation; the nuclear decay process does not disrupt coordination of the product ions, nor does it appear to damage the dye scaffold, which retains its primary absorption features throughout. Energy and charge transfer are put forward as the most likely mechanisms for the Cu-induced fluorescence quenching. The authors envision multiple molecular imaging applications.

J. Am. Chem. Soc. 131, 10.1021/ja903685b (2009).

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