(559h) Colorimetric Detection of Ionizing Radiation Using Polypeptide-Templated Gold Nanoparticles

Ionizing radiation, including gamma rays and X-rays, has numerous applications in nuclear energy, astrophysics, food technology¹, biomedical imaging², and cancer therapy³ However, ionizing radiation causes DNA damage in cells⁵ leading to carcinogenesis, and can also cause deleterious effects on the environment⁶. Consequently, the necessity for detecting ionizing radiation has led to development of methods based on fluorescence⁷, quantum dots⁸ and inorganic films⁹. Most of these detection methods suffer from serious drawbacks of being expensive and hard to fabricate on a large scale. Here, we describe a detection system in which  cysteine-containing elastin-like polypeptides (C_nELPs; n=2,12; C=cysteine) were used to reduce colorless metal salts to colored metallic nanoparticles.  C_nELPs were used to template gold and silver nanoparticles from metal salts upon exposure to different doses of ionizing radiation. Nanoparticle formation was visualized colorimetrically by the naked eye, and spectroscopically by detecting the plasmonic peak of gold at 520 nm and silver at 420 nm. While gold and silver nanoparticles were formed at doses starting at 175 and 50 Gy, respectively, nanoparticle was not observed when free cysteine’s were used, indicating the key role of the polypeptide in this detection system. Transmission Electron Microscopy (TEM) indicated formation of 10-20 nm metallic cores, while dynamic light scattering studies indicated the formation of nanoparticles with hydrodynamic diameters of 80-150nm, following exposure to ionizing radiation. Nanoparticle hydrodynamic diameters reduced with an increase in radiation dose, likely to the loss of integrity of the polypeptide under these conditions. These studies indicate a straightforward colorimetric method for detecting ionizing radiation based on nanoparticle formation from colorless metal salts, and also describes a facile method of nanoparticle formation in which, nanoparticle size can be tailored based on radiation dose and C_nELP type.

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