Moxifloxacin-conjugated graphene oxide: Antimicrobial, anti-adhesive and cell-selective properties supporting its potential for future biomedical coatings

Graphene oxide (GO) provides a versatile platform for the development of antimicrobial and anti-adhesive materials, particularly when combined with covalently immobilized bioactive compounds but translating antibiotic activity into a stable layer without clinically relevant drug leaching remains challenging. Here, we report a covalently engineered GO-moxifloxacin (GO-MOX) composite obtained by grafting MOX onto ethylenediamine-functionalized GO via carbodiimide coupling. The successful functionalization was supported by complementary physicochemical analyses, including FTIR, NMR, Raman, XPS, TGA, SEM/EDS and XRD. TGA indicated a high MOX loading of approximately 44.75 wt%, while HPLC analysis revealed that extractable/free MOX represented only 0.0586% of the total MOX content, supporting the predominantly covalent and minimally releasing character of the material. GO-MOX showed pronounced antimicrobial activity against representative ESKAPEE pathogens, with MIC values of 7.81 μg/mL against E. coli and 62.5 μg/mL against the tested Gram-positive strains. In the antimycobacterial assay, GO-MOX markedly inhibited the growth of both drug-susceptible and rifampicin/isoniazid-resistant Mycobacterium tuberculosis strains under the tested conditions. Anti-adherence activity was observed at sub-inhibitory concentrations, with MBEC values of 1.95 μg/mL for E. coli and 7.81 μg/mL for S. aureus, suggesting interference with early bacterial attachment. Additional analyses on mature biofilms formed on titanium substrates showed that GO-based treatments, particularly GO-MOX, affected biofilm viability, promoted membrane permeabilization, and altered extracellular matrix components, including extracellular proteins, nucleic acids/eDNA-like fractions and polysaccharides. In vitro cellular assays showed that normal MRC-5 fibroblasts recovered metabolic activity to ≥80% after 72 h, whereas A549 cells displayed a concentration- and time-dependent decrease in viability. ROS generation and Caspase-3 activity further suggested that the selective antiproliferative response observed in A549 cells may be associated, at least in part, with oxidative stress-mediated apoptotic mechanisms. In silico target prediction and structural inspection of MOX-topoisomerase complexes suggested that GO-MOX may retain a MOX-related contribution involving bacterial DNA gyrase/topoisomerase IV, while GO may provide additional contact-associated interfacial effects. Overall, GO-MOX emerges as a promising antimicrobial and anti-adhesive nanoplatform with cell-selective antiproliferative effects, supporting its further investigation for the future development of biomedical antimicrobial surfaces and coatings.