This paper presents a functionalized magnetic nanoparticle (Fe3O4@Au MNPs) combined with surface-enhanced Raman spectroscopy (SERS) technique for sensitive detection of colorectal cancer (CRC) protein biomarker carbohydrate antigen 19-9 (CA19-9). Fe3O4@Au MNPs was constructed by PEI-mediated seed growth method. Then, the signal molecule 5-5'-Dithiobis (succinimidoyl-2-nitrobenzoic acid) was used as a bridging agent to link CA19-9 antibody, and the SERS sensor was prepared. Using this sensor, detection of CA19-9 can be realized with only one step sampling reaction. Fe3O4@Au MNPs combines the advantages of magnetic materials and noble metal nanoparticles, effectively amplifying the signal by creating numerous "hot spots" within the Au particle gaps and enhancing magnetic enrichment. Consequently, this approach lowers the detection limit (LOD) and enhances detection sensitivity. The ratio of characteristic peak intensities I1392/I1069 was selected for calculation, and a linear equation was constructed with LOD as low as 0.27 U/mL by quantitative detections of standard antigen. Finally, the sensor was used to analyze the clinical serum samples from CRC patients and healthy individuals, and the detection results were consistent with the actual results. This method exhibits notable advantages, including simple, high sensitivity, specificity, stability and reproducibility. It is expected to provide a new promising analytical method for clinical CA19-9 immunoassay.

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