Silver Nanotripod Array‐Based Sandwich Immunosensor for Sensitive SERS Detection of SARS‐CoV‐2 Spike Protein and Multiplexed Protein Samples

The COVID‐19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) has significantly impacted public health and social stability, highlighting the urgent need for rapid diagnostic methods to ensure timely clinical intervention. Herein, we develop a sensitive surface‐enhanced Raman scattering (SERS) immunosensor based on a silver nanotripod (AgNT) array sandwich structure for simulating early SARS‐CoV‐2 detection. AgNT arrays modified with SARS‐CoV‐2 antibody serve as a capture substrate; antibody‐modified gold nanoparticles (AuNPs) functionalized with dye molecules act as detection probes. Upon binding to analyte, these components form an AuNPs@AgNT sandwich immunosensor generating enhanced SERS signals for detection. The detection limit of AuNPs@AgNT for SARS‐CoV‐2 spike protein in phosphate‐buffered saline (PBS) samples and saliva samples could reach 0.1 and 0.77 pg mL −1 , respectively. This sandwich immunosensor demonstrates excellent reproducibility with a relative standard deviation lower than 8% and maintains satisfactory detection specificity even in various saliva samples and other proteins. Furthermore, by integrating machine learning technology, the sandwich immunosensor enables accurate discrimination of multi‐target samples. These results illustrate the promise of the SERS sandwich immunosensor for the early SARS‐CoV‐2 spike protein detection, which has a remarkable significance for the virus detection in the future.