Paper-based 3D SERS immunoassay array based on self-assembly of AuNBPs@Ag nanorods for ultrasensitive and highly stable detection of α-fetoprotein

Establishing a simple, sensitive, and accurate α-fetoprotein (AFP) detection methods is of great significance for the early diagnosis of hepatocellular carcinoma (HCC). Surface-enhanced Raman spectroscopy (SERS) has been identified as one of the most promising techniques for clinical monitoring. However, accurate detection of AFP is still challenging due to the poor stability of SERS substrate and the low abundance of AFP in the early stages of HCC. Herein, we developed an ultrasensitive and highly stable paper-based 3D SERS immunoassay array for AFP detection, combining the superior advantages of self-assembled AuNBPs@Ag nanorods, filter paper, and sandwich immunoassay. In the immunoassay array, 4-mercaptobenzoic acid (4-MBA) linked to the secondary antibody was employed as the Raman reporter, while the array modified with antibodies was used to capture AFP. The SERS immunoassay array sensor exhibited a wide linear range (3 pg mL−1 to 10 µg mL−1), low detection limit (0.086 pg mL−1), good specificity, and high signal reproducibility (RSD < 5 %). Meanwhile, the sensor is further used for accurate detection of trace AFP in serum, which paves an avenue for the fabrication of SERS substrates with high stability and provides a new outlook for their application in the early diagnosis of cancer.