Biocompatible Hollow Gadolinium Oxide Nanocarriers for the Transport of Bioactive Molecules to Cells

Integrating imaging and therapeutic capabilities into a single entity can offer enhanced diagnostic accuracy and treatment efficacy in clinically effective formulations. Due to the diversity of chemical structures and/or limited solubility of inhibitors or fluorophores, it is essential to employ a robust delivery carrier that can facilitate drug absorption and distribution during its circulation in the blood. This study explores the potential of hollow gadolinium oxide (Gd2O3) nanocarriers in imaging and drug delivery applications. The citric acid (CA)-capped hollow gadolinium oxide nanocarriers were synthesized via urea-assisted precipitation and hydrothermal methods using carbon spheres as sacrificial templates. The resulting nanosized hollow spheres displayed a spherical morphology and demonstrated relaxation rates in the longitudinal and transverse directions, as indicated by their r1 and r2 values of 1.8 and 5.3 s–1 mM–1, respectively. To mimic the physiological conditions, the hollow gadolinium oxide spheres were loaded separately with antibiotic sparfloxacin and the azo dye Congo red at neutral pH (7.4) and body temperature (37 °C). The CR-loaded nanospheres exhibited a time-dependent internalization behavior with HeLa cells, suggesting their imaging potential for intracellular drug delivery. Furthermore, the SP-loaded nanospheres demonstrated antimicrobial activity against both Gram-positive and Gram-negative bacteria, demonstrating their therapeutic potential against bacterial infections. To mitigate the risk of leaching of Gd3+ ions and their inherent toxicity, a CA coating was applied to hollow gadolinium oxide surface which resulted in outstanding cell viability of the surface functionalized nanocarriers. In addition, the CA coating offered additional support for the increased encapsulation and continuous release of drug molecules until 1 week (168 h). The characterization data provide evidence for the potential of CA-capped hollow gadolinium oxide spheres as positive MR contrast agents and their applicability as safe and controlled drug carriers.