(700b) A Colorimetric Plasmonic Nanosensor for Dosimetry of Therapeutic Levels of Ionizing Radiation

Of the several types of cancer prevalent in men today in the US, prostate cancer is the second most commonly occurring with an estimated 220,800 new cases by the American Cancer Society in 2015. Hypofractionated radiotherapy as a treatment procedure for the ablation of cancerous tumors, delivers the total dose planned by the therapists over several sittings. However, owing to repeated radiation there is a high possibility of accidental damage to the nearby tissues and organs during treatment. It is extremely difficult to reduce the associated risk in this procedure, taking into consideration the absence of an in vivo dosimeter which could quantify the exact dose received by the rectum and the tissues. Moreover, the commercial dosimeters available for use are often bulky and require extensive post processing for data readout. Here, we present a simple technique to detect therapeutically relevant doses of ionizing radiation based on nanoparticle formation. We were successful in achieving this by holding gold in its univalent state and stabilizing it using a cationic surfactant. This precursor solution presents potential to be employed within an inflatable endorectal balloon which is often times used during radiotherapy to support the prostate and detect the dose received by the rectal wall. Upon irradiation of the precursor solution, free radicals are generated which subsequently reduce the univalent gold to Au(0), forming nanoparticles. The shape and size of the resultant nanoparticles give rise to characteristic colors while the concentration results in differential intensities of color which is a pseudo measure of the incident radiation. Characterization of the resultant nanoparticles was carried out using UV-Vis absorbance spectroscopy, Dynamic Light Scattering and Transmission Electron Microscopy. We also investigated the role of different cationic surfactants in assisting nanoparticle formation by maintaining the same head group, counter ion and varying the chain lengths. The nanosensor we synthesized is sensitive to radiation levels as low as 1 Gy and being therapeutically relevant, could potentially be used to validate the doses during radiotherapy.