Oxygen Vacancy-Enhanced Electrochemiluminescence Sensing Strategy Using Luminol Thermally Encapsulated in Apoferritin as a Transducer for Biomarker Immunoassay

Oxygen vacancies (OVs) enhanced electrochemiluminescence (ECL) biosensing strategy using luminol thermally encapsulated in apoferritin (Lum@apoFt) as an efficient transducer was investigated for ultrasensitive biomarker detection. By applying the oxygen-defect engineering (ODE) strategy, the OVs enriched cobalt-iron oxide (r-CoFe₂O₄) was fabricated as the sensing substrate to boost the electron mobility and catalyze the generation of superoxide anion radical (O₂^•-) for signal amplification. It should be noted that r-CoFe₂O₄ with higher OVs density dramatically accelerated the ECL reaction between O₂^•- and luminol anionic radicals, achieving 6.5-fold stronger ECL output than CoFe₂O₄ with no or low OVs density. Moreover, facile encapsulation of approximate 412 luminol molecules in a single apoFt cavity was first realized by an efficient thermal-induction method. The obtained Lum@apoFt complexes exhibited well-maintained ECL efficiency and excellent biocompatibility for biological modifications. On this basis, a biosensor was developed for early diagnostics of squamous cell carcinomas by detecting its representative biomarker named cytokeratin 19 fragment 21-1 (CYFRA 21-1), from which excellent linearity was achieved in 0.5 pg/mL to 50 ng/mL with a detection limit of 0.14 pg/mL. This work not only put forward a novel idea of creating OVs enriched sensing interface with excellent signal-amplification function but also proposes a facile and robust methodology to design apoFt-based transducers for developing more practical nanoscale biosensors in early diagnostics of diseases.