OICC Press Journal of Nanostructure in Chemistry 2193-8865 16 1 2026 02 28 New forms of Graphitic Carbon Nitride: The Case of S-gC3N4-Au and the Perspectives of a Theragnostic 10.57647/jnsc.2026.1601.02 EN Jéssica Ingrid Faria De Souza Brazilian Nuclear Energy Commission, Nuclear Engineering Institute, Laboratory of Nanoradiopharmacy and Synthesis of New Radiopharmaceuticals, Rio de Janeiro-RJ, 21941906, Brazil Natália Cristina Gomes-da-Silva Brazilian Nuclear Energy Commission, Nuclear Engineering Institute, Laboratory of Nanoradiopharmacy and Synthesis of New Radiopharmaceuticals, Rio de Janeiro-RJ, 21941906, Brazil Natália Mayumi Andrade Yoshihara Brazilian Nuclear Energy Commission, Nuclear Engineering Institute, Laboratory of Nanoradiopharmacy and Synthesis of New Radiopharmaceuticals, Rio de Janeiro-RJ, 21941906, Brazil Giulia Sigete-Lobo Brazilian Nuclear Energy Commission, Nuclear Engineering Institute, Laboratory of Nanoradiopharmacy and Synthesis of New Radiopharmaceuticals, Rio de Janeiro-RJ, 21941906, Brazil Francisco Dheyson de Quadro Carvalho Group of Chemistry of Advanced Materials (GQMat)- Department of Analytical Chemistry and Physical-Chemistry, Federal University of Ceará, Fortaleza-CE, 451-970, Brazil Pedro Hilton Lima Baracho Group of Chemistry of Advanced Materials (GQMat)- Department of Analytical Chemistry and Physical-Chemistry, Federal University of Ceará, Fortaleza-CE, 451-970, Brazil Leticia Nogueira Xavier Group of Chemistry of Advanced Materials (GQMat)- Department of Analytical Chemistry and Physical-Chemistry, Federal University of Ceará, Fortaleza-CE, 451-970, Brazil Lillian Maria Uchôa Dutra Fechine Group of Chemistry of Advanced Materials (GQMat)- Department of Analytical Chemistry and Physical-Chemistry, Federal University of Ceará, Fortaleza-CE, 451-970, Brazil Tiago Melo Freire Group of Chemistry of Advanced Materials (GQMat)- Department of Analytical Chemistry and Physical-Chemistry, Federal University of Ceará, Fortaleza-CE, 451-970, Brazil Luciana Magalhães Rebelo Alencar Federal University of Maranhão, Department of Physics, Biophysics Laboratory, Campus Bacanga, São Luís-MA, 65080-805, Brazil Alan Silva Menezes Federal University of Maranhão, Department of Physics, Biophysics Laboratory, Campus Bacanga, São Luís-MA, 65080-805, Brazil Pierre Basílio Almeida Fechine Group of Chemistry of Advanced Materials (GQMat)- Department of Analytical Chemistry and Physical-Chemistry, Federal University of Ceará, Fortaleza-CE, 451-970, Brazil Ralph Santos-Oliveira Brazilian Nuclear Energy Commission, Nuclear Engineering Institute, Laboratory of Nanoradiopharmacy and Synthesis of New Radiopharmaceuticals, Rio de Janeiro-RJ, 21941906, Brazil; State University of Rio de Janeiro, Laboratory of Nanoradiopharmacy and Strategic Biomaterials, Rio de Janeiro-RJ, 220000, Brazil https://orcid.org/0000-0002-0905-481X Journal Article 2026 02 28 This study aimed to develop and characterize a sulfur-doped graphitic carbon nitride (S-g-C₃N₄) nanosystem functionalized with gold (S-g-C₃N₄-Au) for potential applications in cancer therapy. The focus was to evaluate its physicochemical properties, cytotoxicity against breast and prostate cancer cells, pharmacokinetics, biodistribution, and biochemical impact in vivo. To carry out the study, S-g-C₃N₄-Au was synthesized by thermal polymerization of melamine and ammonium sulfate with incorporation of gold seeds. Characterization techniques included SEM, XRD, FTIR, and UV-Vis DRS. Cytotoxicity was evaluated by MTT assays in MDA-MB-231 (breast cancer) and DU-145 (prostate cancer) cell lines. The nanosystem was radiolabeled with technetium-99m for biodistribution and pharmacokinetic studies in Balb/c mice after intraperitoneal administration. Biochemical analyses were conducted to evaluate systemic effects on the liver, kidneys, and metabolic markers. The results obtained demonstrated that the S-g-C₃N₄-Au nanosystem exhibited a porous, layered morphology with uniformly distributed gold nanoparticles. XRD and FTIR confirmed structural integrity, and SEM, STEM, and EDS confirmed successful gold incorporation. Cytotoxicity assays demonstrated significant, dose-dependent reductions in cell viability in both cancer cell lines, with the effects more pronounced at higher concentrations. In vivo, the nanosystem exhibited predominant accumulation in the liver and small intestine, with low systemic clearance and a plasma elimination half-life of 5.53 hours. Biochemical analysis indicated decreased ALT and glucose levels, but elevated AST, LDH-P, and lipase activities, suggesting stress on liver and digestive tissues. This set of results demonstrates that the S-g-C₃N₄-Au nanosystem exhibits favorable physicochemical properties and cytotoxic potential against cancer cells. Its organ-specific biodistribution and prolonged retention highlight its promise for targeted therapy and metabolic modulation. Notably, its ability to be radiolabeled with technetium-99m (99mTc) allows its application in nuclear imaging, further reinforcing its potential as a theranostic platform that integrates diagnostics and therapy in a single nanostructure. However, the observed biochemical alterations reinforce the need for comprehensive toxicological evaluations to ensure safety and enhance therapeutic efficacy.