Laser-Induced Periodic Phase-Transition of 2D-MoTe2 Nanograting Template for Frequency-Shift Digital-SERS Immunoassay of Autoimmune Disease.

Fabrication of cross-scaled ultrasensitive surface-enhanced Raman scattering (SERS) substrates ranging from nanogaps for efficient localized surface plasmon resonances (LSPRs) to mm2-size for easy operation is challenging. Here, we propose femtosecond-laser-induced periodic phase-transition (fs-LIPPT) of 1T'-MoTe2 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-MoTe2/SiO2-interlayer waveguide triggers the highly homogeneous periodic 1T' phase-transition pattern. The Au nanoparticles (AuNPs) are subsequently reduced at the 1T' regions in chloroauric acid solution, forming a subwavelength AuNPs@1T'-MoTe2 nanograting with 295.0 ± 8.1 nm in period. The Fano resonances by coupling the narrow-band guided-mode resonances supported in the 1T'-MoTe2/SiO2-interlayer nanograting with the broadband LSPRs in AuNPs promote optical localization, achieving the superior performance with a limit of detection in 10-14 m and a SERS performance factor of 7.5 × 106 for rhodamine 6G (R6G). A paradigm of frequency-shift digital-SERS immunoassay for serological diagnosis is established using the R6G-labeled AuNPs@1T'-MoTe2 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.