Portable SPR-based optical fibre sensing platform for detection of cortisol and Escherichia coli

The optical detection of analytes in aqueous solutions was the focus of this study. Polymer optical fibre D-shape sensors based on surface plasmon resonance (SPR) were employed in a portable platform to measure the levels of the stress hormone cortisol and the bacterial strain <i>Escherichia coli</i>. The sensors were reliable in identifying increasing cortisol levels but responded slightly worse to the <i>Escherichia coli</i> pathogen. The sensitivity of <i>Escherichia coli</i> sensors was -0.38&plusmn;0.06 nm/log(CFU/mL), which is comparable to the sensitivity of cortisol sensors, which was -0.41&plusmn;0.04 nm/log(ng/mL). With a cortisol limit of detection (LOD) of 1.73×10⁻⁴ pg/mL and <i>Escherichia coli</i> detection limit of 3.72×10⁻⁷ CFU/mL, the biosensors' LODs were lower than those found in the literature. Atomic Force Microscopy (AFM) revealed tiny topographical profile variations of 2.0–3.4 nm, which is comparable to the thickness of the used antibodies and indicates that they were deposited parallel to the gold surface. Future research should focus on techniques that could guarantee antibody verticality.