Magnetite-Based Surface Plasmon Resonance Sensor for Pseudomonas Bacteria Detection

Rapid and precise detection of Pseudomonas bacteria is essential for medical diagnostics, water quality monitoring, and environmental applications. In this study, we propose a highly sensitive plasmonic biosensor incorporating magnetite (Fe<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf>) into a gold (Au) grating-based structure to enhance detection performance. The finite element method (FEM) was implemented to examine the sensor’s loss spectrum, wavelength sensitivity (W<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sn</inf>) and amplitude sensitivity (A<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sn</inf>) across a refractive index (RI) ranging from 1.36 to 1.42. The results demonstrated that Fe<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> significantly enhanced the electric field intensity at the metal-dielectric interface, resulting in improved sensitivity and resolution. The proposed sensor achieved an exceptional W<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sn</inf> of 5000 nm/RIU with an ultra-low detection resolution of 2×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−7</sup> RIU, enabling accurate detection of Pseudomonas bacteria. A red shift in resonance wavelength was observed with increasing RI, confirming strong interactions between bacterial analytes and surface plasmon polaritons (SPPs). The Au layer thickness (D<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">au</inf>) was optimized at 65 nm for maximum sensitivity while A<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sn</inf> reached a peak of 76.4 RIU<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> at RI 1.41. The proposed Au/(Fe<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf>) sensor highlighted the superior performance of over existing optical sensors. These findings suggest that the proposed plasmonic biosensor holds great promise for real-time bacterial detection. Future work will focus on experimental validation and practical implementation to further establish its applicability in clinical and environmental biosensing.