Microfluidics unveil nucleation and growth in the radiolytic synthesis of colloidal silver and allow X-ray detection with nanoclusters

Abstract

We developed a two-stage microfluidic reactor consisting of one hot and one cold region to systematically investigate a radiolytic method to synthesize colloidal silver and to improve the sensitivity of radiation dosimeters based on the Ag nanoparticles plasmon intensity. The microfluidic approach avoided growth during the heating stage, resulting in the total absence of a plasmon band for non-irradiated samples, greater control of the particle size distribution, and decreased minimal detectable dose. Doses as low as 0.2 Gy could be detected with sensitivities higher than the reported in the literature. This is a great achievement once most chemical dosimeters, besides 3D gels, are not sensitive to such low doses. Samples prepared in the microreactor and exposed to doses from 0 to 0.75 Gy presented an unexpected absorption band above 500 nm and a fluorescence emission around 380 nm, evidencing the presence of Ag nanoclusters (AgNCs). Both, absorption and emission bands from AgNCs, increase in the 0-0.75 Gy range, suggesting that nucleation predominates in the microreaction stage and in the radiolytic step for doses below 1 Gy. Decreased fluorescence intensity and undetected absorption above 500 nm indicate that growth prevails for doses ≥1 Gy. Thus, our work presents a novel way to measure doses based on silver nanoclusters, including both absorption and emission as dosimetric parameters. Besides unveiling nucleation and growth mechanisms associated to nano clusters and particles formation in this radiolytic microreaction, the results put the spotlight on new possibilities for enhanced radiation detection employing AgNCs.