Opal particles, with diameter ca. 80 nm, were synthesized by the Stöber method. Samples were exposed to 100 Gy of beta particle irradiation and its thermoluminescence (TL) emission was recorded. TL response presents good reproducibility, standard deviation 1 %. The glow curve displays two TL peaks 86 and 400 °C and the afterglow (AG) phenomenon is observed immediately after irradiation (< 150°C). The synthetic opal-C exhibits a linear dependence of AG response as function of dose from 0.25 to 8 Gy. This dose range is of interest for personal and clinical dosimetry. Moreover, a previous study indicates that cytotoxic and genotoxic effects caused by opal nanoparticles, did not induce unrepairable DNA damage neither a cellular harm. Therefore, our results show synthetic opal-C is a material useful for in vivo radiation dosimetry.