||Alex Pronschinske, Philipp Pedevilla, Colin J. Murphy, Ben Coughlin, Emily A. Lewis, Felicia R. Lucci, Garth Brown, George Pappas, Angelos Michaelides & E. Charles H. Sykes
||1) Deptartment of Chemistry, Tufts University, 62 Talbot Avenue, Medford, MA 02155, USA.
2) Thomas Young Centre, London Centre for Nanotechnology and Department of Chemistry, University College London, London WC1E 6BT, UK. 3PerkinElmer, Inc., 331 Treble Cove Road, North Billerica, MA 01862.
||Pronschinske, A. et al. Nature Mater. http://dx.doi.org/10.1038/nmat4323 (2015)
Radioactive decay and its accompanying high-energy radiation are well understood and have been utilized for decades. However, the role of low-energy electrons created during irradiation has only recently begun to be appreciated. Low-energy electrons are the most important component of radiation damage in biological environments because they have subcellular ranges and interact destructively with chemical bonds. Their short ranges make them ideal for targeted cancer therapies, yet methods for generating them locally do not exist. To address this we synthesized one atom thick films of the radioactive isotope 125I on gold that are stable under ambient conditions. Low temperature scanning tunnelling microscopy, supported by electronic structure simulations, allowed us to directly observe the nuclear transmutation of individual 125I atoms into 125Te atoms, and explain the surprising stability of the 2-D film as it underwent radioactive decay. Electron spectroscopy revealed that the interface geometry induces a 500% amplification of low-energy electron emission (< 50 eV) as compared to a bulk emitter. The interface-induced enhancement of the low-energy electron flux arises from high-energy electron scattering within the Au surface, a fundamental process that will persist in a radioisotope/metal nano-structure of any complexity. These 2-D radioactive films offer a platform for understanding the microscopic details of electron-induced processes and provide a route to nano-scale electron emitters. Most significantly, 125I is commonly used in medical imaging, radiation therapy and biological assays and the 125I-Au sample preparation methods described here are highly compatible with Au nanoparticles. Therefore, this interface enhancement of biologically active low energy electrons will offer nano-scale specificity for highly targeted nanoparticle therapies.
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