<p> A&#xa0;surface plasmon resonance imaging (SPRi) biosensor&#xa0;is presented which facilitates rapid and sensitive detection of the ovarian cancer biomarker carbohydrate antigens 125 (CA125). The CA125 protein was specifically captured and directly recognized by polyadenylic (polyA)-modified DNA aptamer on the surface of a Au chip. The biosensor demonstrated a&#xa0;linear range of direct detection of CA125 based on SPRi from 20&#xa0;nM to 0.5&#xa0;nM, with a detection limit of 0.47&#xa0;nM. Furthermore, Fe₃O₄ nanoparticles were synthesized in situ on the carboxyl-functionalized two-dimensional (2D) material Ti₃C₂ to obtain MXC/Fe₃O₄ nanocomposites. The large surface area of Ti₃C₂ provides ample binding sites for the in situ generation of Fe₃O₄ and this&#xa0;facilitates subsequent immobilization of DNA aptamers. The amino-modified DNA aptamer interacted with carboxylate sites activated on the surface of Ti₃C₂, and the aptamer was immobilized on the MXC/Fe₃O₄ nanocomposite surface. Due to the magnetic properties of Fe₃O₄ nanoparticles within the composite material, CA125 protein in serum can be effectively captured and separated under an external magnetic field. The captured protein forms a sandwich amplification structure with the DNA adapter on the surface of the Au chip, thereby enhancing the detection signal of CA125. The biosensor demonstrates a linear detection range from 0.5&#xa0;pM to 1000&#xa0;pM, with a detection limit as low as 81 fM. The unique separation capability of the composite nanomaterials enables the biosensor to detect CA125 protein as low as 1&#xa0;pM in complex liquid matrices such as serum, achieving exceptional selectivity, accuracy, and sensitivity in detecting the ovarian cancer marker. This capability significantly supports the early diagnosis of ovarian cancer.</p> Graphical abstract <p></p>