V ₂ CT _<i>x</i> MXene‐powered handheld SERS biosensor for the viral antigen test

Abstract The intrinsic property of MXenes to adsorb dyes with high Raman scattering cross‐sections makes them promising candidates for surface‐enhanced Raman scattering (SERS) biosensors. In the study, we report a vanadium carbide MXene (V 2 CT x )‐based SERS biosensor tag, V 2 CT x @Thi (thionine)@Au NPs (gold nanoparticles)‐Ab (antibody), owing to its large interlayer spacing and superior dye adsorption capacity. The tag V 2 CT x @Thi@Au NPs‐Ab was fully characterized and validated, demonstrating a significantly enhanced Raman signal through both electromagnetic and chemical enhancement mechanisms. Using a handheld Raman spectrometer as a readout tool, the developed handheld SERS biosensor was successfully applied for the detection of viral antigens. The biosensor exhibited excellent linearity (1.562–100 nM) and achieved a low limit of detection (LOD) 1.562 nM. Moreover, the biosensor demonstrated good selectivity and stability for detecting the target S protein in saliva samples. Our study highlights the potential of V 2 CT x MXene as a powerful material for handheld SERS biosensors, paving the way for portable and efficient viral diagnostics.