Laser‐Induced Periodic Phase‐Transition of 2D‐MoTe ₂ Nanograting Template for Frequency‐Shift Digital‐SERS Immunoassay of Autoimmune Disease

ABSTRACT Fabrication of cross‐scaled ultrasensitive surface‐enhanced Raman scattering (SERS) substrates ranging from nanogaps for efficient localized surface plasmon resonances (LSPRs) to mm ² ‐size for easy operation is challenging. Here, we propose femtosecond‐laser‐induced periodic phase‐transition ( fs ‐LIPPT) of 1T’‐MoTe ₂ nanograting template, inducing Au nanostructures for frequency‐shift digital‐SERS immunoassay. The interference between the incident transverse electric wave and propagation wave in the 2H‐MoTe ₂ /SiO ₂ ‐interlayer waveguide triggers the highly homogeneous periodic 1T’ phase‐transition pattern. The Au nanoparticles (Au NP s) are subsequently reduced at the 1T’ regions in chloroauric acid solution, forming a subwavelength Au NP s@1T’‐MoTe ₂ nanograting with 295.0 ± 8.1 nm in period. The Fano resonances by coupling the narrow‐band guided‐mode resonances supported in the 1T’‐MoTe ₂ /SiO ₂ ‐interlayer nanograting with the broadband LSPRs in Au NP s promote optical localization, achieving the superior performance with a limit of detection in 10 ⁻¹⁴ m and a SERS performance factor of 7.5 × 10 ⁶ for rhodamine 6G (R6G). A paradigm of frequency‐shift digital‐SERS immunoassay for serological diagnosis is established using the R6G‐labeled Au NP s@1T’‐MoTe ₂ nanograting conjugated with immunoglobulin G of rheumatoid arthritis, by which the discrimination accuracy is unexpectedly close to unity. The present work provides a novel protocol for SERS serum immunoassay, opening opportunities for early diagnosis and accurate prognosis of autoimmune diseases by blood test in the future.