Ovarian cancer remains a leading cause of cancer-related mortality due to its asymptomatic progression and late diagnosis. Herein, we present an ultrasensitive ratiometric fluorescence assay for detecting cancer antigen 125 (CA125), a key biomarker of ovarian cancer. This assay integrates a photoluminescent aluminum-based metal-organic framework (Al-MOF), antibody-conjugated gold nanoparticles (AuNPs), and cleavable silica nanocapsules (CSNs). The Al-MOF functions as both a recognition probe and an acidic environment generator, emitting fluorescence at 426 nm, while AuNPs serve as Förster resonance energy transfer (FRET) quenchers. CSNs encapsulate cadmium telluride quantum dots (CdTe QDs; λem = 496 nm) and CA125 antigens within a silica shell crosslinked by pH-sensitive diiminodialkyl silane linkers. Upon antigen binding, the CA125 bridges the Al-MOF and AuNPs, inducing proximity-dependent FRET quenching of Al-MOF fluorescence. Concurrently, the acidic environment cleaves the diimine linkers, releasing the encapsulated QDs and antigens. This dual mechanism generates inversely correlated signals including quenched Al-MOF emission at 426 nm and enhanced QD fluorescence at 496 nm under 370 nm excitation. The assay achieves a detection limit of 37.5 nU/mL for Al-MOF/AuNPs and 0.7 nU/mL for the ratiometric readout (F496/F426), demonstrating an 86-fold sensitivity enhancement over single emission systems. High specificity in human serum samples and strong resistance to interference highlight its potential for early and reliable ovarian cancer diagnostics. The dual‑signal immunoassay was further validated against electrochemiluminescence (ECL), confirming its analytical robustness.
