<p>A&#xa0;chemiluminescent aptamer sensor (CL aptasensor) is&#xa0; proposed for ultrasensitive determination of CYFRA21-1 as a lung cancer biomarker. The sensing mechanism of the CL aptasensor is&#xa0; based on the incorporation of luminol into a cobalt-based metal–organic framework (MOF), also called ZIF-67, to generate a composite of the luminol@ZIF-67. This composite was then functionalized with a CYFRA21-1 specific aptamer (luminol@ZIF-67-apt) as signal probe. ssDNA was immobilized on PVP/NiO nanocomposite, allowing hybridization with the aptamer by complementary base pairing. In the presence of CYFRA 21–1, the luminol@ZIF-67-apt/PVP/NiO-ssDNA ternary complex could be assembled and induced intense chemiluminescence emission. Under the optimized conditions, the sensor showed a broad linear detection range&#xa0; from 10⁻⁵ to 10⁴&#xa0;ng/mL, with a detection limit (LOD) of 3.7 × 10⁻⁵&#xa0;ng/mL. Reproducibility (RSD = 3.81%) and long-term stability were observed, with signals retained to 98.22% and 97.87% over 20 and 33&#xa0;days, respectively. Recovery experiments in spiked human serum samples ranged from 96.00% to 99.30%, and RSDs from 3.41% to 4.07%, indicating good stability and potential in complex biological matrices. Such a strategy holds great promise for ultrasensitive detection of CYFRA 21–1 for clinical bioanalysis.</p> Graphical Abstract <p></p>