In this study, we demonstrate a multicore fiber interferometer applied for insulin biosensing. This interferometer was produced by splicing a segment of a multicore fiber (MCF) fused to a standard single-mode fiber (SMF). Our investigation depicted that the interferometer's response to changes in refractive index (RI) was influenced by polarization when a thin gold layer was deposited at the end facet of the multicore fiber (MCF). The most significant sensitivity to RI was achieved when using P-polarized light with a ~10 nm-thick gold-coated sample. This gold-coated interferometer was subsequently functionalized for biosensing purposes and employed in the detection of insulin, successfully identifying insulin at a concentration level of 10−8 g/ml.
Graphene oxide (GO) thin films fabricated by the vacuum filtration method were deposited on bare tilted fiber Bragg grating for refractometry measurements. Two different layer thicknesses (100 nm and 200nm) were used to prepare the samples. The amplitude spectra of the GO-coated TFBGs (GO-TFBGs) were measured with linearly polarized light for different refractive index values of LiCl solutions (1.3333-1.3342). We show that when polarized light is used, the 200 nm GO-TFBGs achieve similar behavior as plasmonic gold-coated TFBGs (Au-TFBGs). This latter exhibits a characteristic attenuation in the amplitude spectrum when P-polarized light excites a surface plasmon resonance (SPR). This behavior suggests that GO is present as a mix of discontinuous and stratified flakes favorable for plasmon-plasmon hybridization, which can be generated for both P and/or S-polarization of the light.
In this work, we report on the refractometric sensing properties of an interferometer produced by fusion-splicing a segment of a seven coupled-core fiber to a standard single-mode fiber. We demonstrate that for a ~10 nm-thick gold layer deposited on the multicore facet, the interferometer amplitude and response to refractive index changes is polarization dependent. We thereby show that refractometric sensitivity is maximum for the polarization-induced minimum amplitude spectrum.
This study investigates a fiber-optic biosensor based on a tilted fiber Bragg grating (TFBG) partially-coated with a thin gold film on its axis and around its cross-section. The effects induced in the TFBG transmitted amplitude spectrum were analyzed for different input light directions for surrounding refractive index (SRI) changes in the range 1.3356 – 1.3370. Partially-coated gratings present the potential ability to sense both volume and surface refractive index changes, which is interesting in biosensing to enhance the signal-to-noise ratio. The gold film was bio-functionalized by human epidermal growth factor receptor (HER2) aptamers using thiol chemistry. The detection of HER2 proteins (a relevant cancer biomarker) at 10-9 g/mL, 10-8 g/mL and 10-6 g/mL demonstrated the advantage to identify environmental perturbations through the bare area of the TFBG. The non-specific drifts that could exist in samples are eliminated and a wavelength shift only related to the surface modification is obtained.
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