Grating-coupled magneto-optical surface plasmon resonance biosensor for biomolecular detection

Abstract

This work demonstrates a lithography-free and cost-effective grating-coupled magneto-optical surface plasmon resonance (MOSPR) biosensing platform based on a Blu-ray disc (BD-R) grating. The periodic grating obtained from a commercial BD-R through a controlled delamination process serves as the plasmonic coupler by providing the additional in-plane momentum required for surface plasmon polariton excitation, thereby avoiding both prism coupling and lithography-defined nanostructures. An Ag/Co/Ag trilayer was subsequently deposited onto the grating to support surface plasmon excitation and enable transverse magneto-optical Kerr effect (TMOKE) modulation under an externally applied alternating magnetic field. By employing a differential modulation detection scheme combined with a lock-in amplifier, environmental noise and light-source fluctuations were effectively suppressed, resulting in approximately fourfold improvement in signal-to-noise ratio (SNR) compared with the conventional surface plasmon resonance (SPR) measurement. Experimental characterization at a wavelength of 632.8 nm yielded a refractive index sensitivity of 94.4°/RIU and an enhanced figure of merit (FOM) of 130–150 RIU −1 . The biosensing capability of the platform was further validated through real-time monitoring of the specific interaction between immobilized Human immunoglobulin G (Human IgG) and Goat anti-human IgG, achieving a statistically estimated limit of detection (LoD) of 0.337 μg/mL for Goat anti-human IgG detection. These results demonstrate that the proposed MOSPR platform provides a simple, scalable, and cost-effective approach for high-resolution biochemical sensing.