Sulfonamide-Terminated Phosphonic Acid-Based Double Hydrophilic Block Copolymers Forming Phosphate-Resistant Lanthanide-Coordinated Hybrid Polyionic Nanostructures with Antibacterial Activity

Sulfonamide-terminated double hydrophilic block copolymers (DHBCs) composed of poly(oligo(ethylene glycol) acrylate) (POEGA) and poly(vinylphosphonic acid) (PVPA) were synthesized by RAFT polymerization and used to form hybrid polyionic complexes (HPICs) with trivalent lanthanide ions (Gd3+ or Eu3+). These HPICs self-assembled into stable, well-defined colloidal nanostructures under physiological conditions, driven by strong PVPA–lanthanide coordination. Eu3+ luminescence studies revealed a robust coordination environment resistant to competitive phosphate ions, in contrast with poly(acrylic acid) (PAA)-based analogues. Both the functionalized polymers and their HPICs exhibited antibacterial activity against Pseudomonas aeruginosa and Staphylococcus aureus. Moreover, the Gd3+-based HPICs showed high longitudinal relaxivity values comparable to clinical MRI contrast agents and remained stable over a wide pH range, highlighting their potential as multifunctional theranostic nanoplatforms.