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Multifunctional nanoplatforms based on mesoporous silica coated with alumina were successfully and sustainably synthesized using sodium silicate extracted from rice husk ash (RHA), demonstrating the potential for cancer theranostics. The hybrid nanostructures produced (C2-600 and C4-600) from two different calcination times exhibited distinct morphologies, textural parameters, and degrees of mesoscopic organization. As expected, the Al 2 O 3 coating on the mesoporous silica nanoparticles (MSNs) reduced the specific surface area from 720 m2/g to 122 m2/g (C2-600) and 57 m2/g (C4-600), while preserving their mesoporous structure. Additionally, both C2-600 and C4-600 showed relatively good stability across a wide pH interval, with a zeta potential of ζ = −15 mV and hydrodynamic diameter (D h) ranging from 160 to 670 nm, depending on the pH of the medium. These peculiar characteristics resulted in high encapsulation efficiency (EE ≈ 90 %) for the doxorubicin (DOX) anticancer drug, as well as sustained drug release in simulated gastric fluid (SGF, pH 1.2) and simulated intestinal fluid (SIF, pH 7.4). Appreciably, C4-600-DOX released approximately 83 % of the drug over 96 h and demonstrated significant biodegradation in simulated biological media. Furthermore, the hybrid nanoplatforms exhibited strong optical absorption between 250 and 420 nm, along with broad and intense photoluminescence (PL) in the near-infrared (NIR) region (680–900 nm), which is highly desirable for NIR-fluorescence diagnostic imaging. Notably, the hybrid nanoplatforms without DOX were non-cytotoxic to fibroblast and Caco-2 cells, while the DOX-loaded nanoplatforms exhibited selectivity and potent anticancer activity, inhibiting approximately 80 % of Caco-2 colorectal cancer cells after 72 h. These findings demonstrate that C2-600 and C4-600 are innovative, multifunctional and biodegradable nanoplatforms with powerful potential as drug carriers and fluorescence imaging agents, making them promising candidates for cancer theranostics. [Display omitted] • Hybrid nanoplatforms based on mesoporous silica from RHA coated by Al 2 O 3 were synthesized for biomedical applications. • C2-600 and C4-600 exhibit different structural characteristics and both present PL emission in the Vis-NIR region. • C2-600 and C4-600 exhibited encapsulation efficiency (EE%) of 88 % and sustained DOX release. • Hybrid nanoplatforms are not cytotoxic for cells, but when loaded DOX, they inhibit nearly 80 % of Caco-2 cancerous cells. • Hybrid nanostructures are promising nanoplatforms to be employed for theranostics of cancer. [ABSTRACT FROM AUTHOR]