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.
Yao et al. (2026) studied this question.