Green-synthesized magneto-plasmonic nanocomposites for enhanced SPR biosensing of BSA under external magnetic field modulation

In this study, the development of a green-synthesized surface plasmon resonance (SPR) biosensor based on Fe 3 O 4 /Ag nanocomposites (NCs) for bovine serum albumin (BSA) detection through an externally applied magnetic field has been explored. The Fe 3 O 4 nanoparticles (NPs) were synthesized using Moringa oleifera extract and incorporated with Ag NPs. Analysis of structural, optical, and magnetic characterizations confirmed crystalline Fe 3 O 4 /Ag NCs with homogeneous Ag distribution, band-gap narrowing, and near-superparamagnetic behavior. For the SPR measurements, resonance angles of 46.41°, 46.52°, and 46.64° for the integrated Fe 3 O 4 /Ag NCs in prism/Au configuration were observed depending on 1, 3, and 5 mg/mL BSA concentrations, with a detection limit of 0.40 mg/mL and a R-squared value of 0.99. For the magneto-optic SPR (MOSPR) measurements, an increase in resonance angles of 46.61°, 46.60°, and 46.70° was detected with a magnetic field strength of 40, 50, and 60 Oe, respectively, resulting in full width at half maximum broadening and an increase in detection accuracy in MOSPR compared with conventional SPR, while preserving the same detection limit. The transverse magneto-optical Kerr effect response exhibited a higher sensitivity than conventional SPR, resulting in an approximately twofold enhancement in the MOSPR configuration. The quantitative analysis reveals how the response of green-synthesized Fe 3 O 4 /Ag magneto-plasmonic NCs evolves under an applied magnetic field, enabling a magnetically modulated SPR biosensing response for BSA. • Fe 3 O 4 /Ag nanocomposites were synthesized via a green synthesis method using Moringa oleifera extract. • The nanocomposites exhibited narrowed band gaps, enhanced plasmonic activity, and soft ferromagnetic properties. • The SPR sensor with Fe 3 O 4 /Ag provides a low LOD value in detecting target analytes such as bovine serum albumin. • Integration of transverse magneto-optical Kerr effect (TMOKE) modulation further enhanced the SPR sensitivity