Polymer optic fiber photoluminescent probe for cortisol continuous monitoring with metal-enhanced fluoroimmunoassay

Surface-specific metal-enhanced cortisol fluoroimmunoassy was applied to the plasmonic-active thin film substrate on polymer optical fiber tip and adjacent unclad side surface of it’s core in backscattering optical scheme. Cortisol is required to be monitored in metabolic disorders, chronic inflammation conditions, cardiovascular disease and psychiatric conditions. Fiber sensing area was generated by amination of the unclad core polymer surface with sequential immobilization of spherical Au nanoparticles. This modification allowed us to create island thin film with plasmon resonance band suitable for surface-specific atto633 dye fluorescence intensity enhancement for both, excitation and emission wavelengths. Synthesis of the cortisol-sensitive area include then formulation of the modified surface by direct antibodies physisorption, surface passivation with BSA and application of the synthetic bifunctional protein conjugate – atto633-BSA-3-cmo-cortisol providing reversible adsorption by Au-bound immunoglobulins. Fluoroimmunoassay on the fiber probe surface was conducted then by joining the opposite, intact fiber tip via ferrule type connectors and bundle-waveguide to the portable spectrometer with laser excitation source. Sensitivity of biosensor on fiber is tested by immersing the probes sensing region into the samples containing cortisol in standard concentration range for calibration and fluorescence spectra change over time was recorded. The technique described is aimed towards development of practical applications, one of which is continuous cortisol biosensing in vivo.