Dual-mode SPR/SERS biosensor utilizing metal nanogratings fabricated via wet etching-assisted direct laser interference patterning

This study introduces a dual-mode biosensor, combining surface plasmon resonance (SPR) and surface-enhanced Raman scattering (SERS), to sensitively detect Human Immunoglobulin (H-IgG) on Au nanogratings. The Au nanogratings were fabricated on a single-crystal silicon surface using wet etching-assisted nanosecond direct laser interference patterning (DLIP), allowing precise control over period and depth. By optimizing the DLIP intersection angle and etching time, the resulting Au nanogratings exhibit remarkable SPR absorption dips in reflection spectra and robust localized SPR, rendering them highly responsive to local refractive index changes and conducive to strong localized electric fields for enhanced SERS activity. Notably, the 765 nm-period grating demonstrates a sensitivity at 751 nm/RIU and a resolution of 2.93 x 10-5 RIU. In SPR mode, protein A immobilization on the Au nanograting surface enables specific H-IgG binding, achieving a limit of detection (LOD) of 23.5 nM. In SERS mode, the biosensor exhibits better sensitivity, with a LOD of 1.176 nM. The SPR mode exhibits high linearity, while the SERS method enables sample identification based on characteristic peaks, enhancing specificity and accuracy. The synergy between these complementary modes offers multiple detection options and enhances result cross-validation, thereby improving assay accuracy and reliability.