Pontos quânticos de carbono dopados com nitrogênio e enxofre aplicados como sensores de radiação ionizante

Abstract

Carbon quantum dots (CDs) are nanomaterials with unique properties such as photoluminescence (PL), water solubility, biocompatibility, and low toxicity. These characteristics make CDs promising materials for various applications, including ionizing radiation detection. In this research, nitrogen-doped CDs (N-CDs) and nitrogen- and sulfur-doped CDs (N,S-CDs) were synthesized via hydrothermal synthesis, characterized, and applied as fluorimetric sensors to measure X-ray and gamma-ray (γ) radiation. N-CDs and N,S-CDs exhibited spherical morphologies with diameters of 3.1 nm and 3.0 nm, respectively. Additionally, they showed PL independent of excitation wavelength, with blue emission for NCDs and red emission for N,S-CDs. Both CDs demonstrated sensitivity to Fe3+ ions with PL quenching. N,S-CDs exhibited a quantum efficiency of 5%, while NCDs showed a quantum efficiency of 95.0%. When mixed with the Fricke solution, N-CDs proved to be radiation-sensitive. Under optimized conditions and gammaray irradiation, they displayed sensitivities of -40,0 ± 7,6 Gy-1 for doses below 2.5 Gy and 12.7 ± 0.7 Gy-1 for doses between 5.0 and 30.0 Gy, with a linear doseresponse for both intervals. For the X-ray irradiation range of 0.0 to 100.0 Gy, three linear regions with different sensitivities were observed. Between 0.0 and 3.0 Gy, the R2 and sensitivity coefficient were 0.994 and -40.7 ± 1.7 Gy-1 , respectively. Between 5.0 and 30.0 Gy, the sensitivity coefficient was -26.5 ± 0.8 Gy-1 , and for 30.0 and 100.0 Gy, a sensitivity of -15.9 ± 0.5 Gy-1 was noted, without observing dose saturation in this range. The calculated minimum dose was 0.23 Gy, exhibiting an excellent detection limit and stability over extended storage periods. Suspensions of N,S-CQDs with Fe2+ ions also proved sensitive to ionizing radiation. FL intensity increased with escalating radiation doses. The sensitivity of N,S-CDs was 0.37 ± 0.02 Gy-1 for doses between 2.5 and 24.0 Gy. The addition of Fe3+ ions or H2O2 to the Fe2+ -N,S-CD suspension led to fluorescence reduction, the inverse process of gamma-ray irradiation.