Defect-Engineered Europium-Doped Ceria Nanomaterial for Oxygen-Vacancy Modulation and Dual-Emission Ratiometric Detection of Spermine

Europium-doped ceria nanomaterials (Ce 1– X Eu X O 2; X = 0, 0.05, and 0.10) were synthesized via a solution-combustion strategy to develop a defect-tunable dual-emissive nanoplatform for selective detection of spermine, which is a prostate cancer biomarker. Structural investigations confirmed phase-pure cubic fluorite CeO 2 with successful substitution of Eu 3+, accompanied by systematic oxygen-vacancy generation. Controlled defect engineering markedly enhanced the optical performance, producing simultaneous defect-related blue emission (∼470 nm) and characteristic Eu 3+ red emission (∼610 nm). Among the compositions, Ce 0.9 Eu 0.1 O 2 exhibited the highest defect density and superior sensing efficiency. The nanomaterial demonstrated pronounced ratiometric fluorescence modulation toward spermine with high selectivity over competing biomolecules, polyamines, and electrolytes. Temperature-dependent studies revealed fluorescence signal amplification at elevated temperatures, while high-ionic-strength conditions did not suppress sensing performance. Electrochemical measurements further confirmed concentration-dependent interfacial responses, yielding a detection limit of 12.15 μM and sensitivity of 0.643 mA mM –1 cm –2 . The sensor demonstrates selective detection in diluted biological matrices (5% urine and 1% serum), indicating its potential for operation in complex media. This study establishes Eu-doped, defect-engineered CeO 2, as an effective material for dual-mode biomarker sensing in complex biological matrices.