Realization of Enhanced Evanescent Field Long Period Fiber Grating near Turn around Point for Label-Free Immunosensing

Abstract

A long-period fiber grating (LPFG) with maximum enhancement of evanescent field has been designed and fabricated, along with theoretical modeling, by working near the turn-around point (TAP) of the lowest order symmetric cladding mode (LP0.2 cladding mode). The LPFG was fabricated using a point-by-point inscription technique and it was characterized in terms of surrounding refractive index (SRI) within the range of 1.333 to 1.3335 using a thermostated flow-cell. This closed cell, made of poly(methyl methacrylate) (PMMA), was designed for better handling of the sensor, because during the fabrication process, the diameter of the LPFG was reduced up to ~20 µm by chemical etching, for the maximum enhancement of the evanescent field. The sensitivity of dual peak resonance of the LP0.2 cladding mode near TAP was measured and resulted to be ~8751 nm/SRIU with a resolution of the order of 10−5 RIU. The sensor was further used for the label-free immunosensing application by the implementation of Immunoglobulin G (IgG)/anti-Immunoglobulin G (anti-IgG) bioassay in human serum on the grating region inside the thermostated closed flow cell.

Label-Free Anti-Human IgG Biosensor Based on Chemical Modification of a Long Period Fiber Grating Surface

“…2021, 5, 48 2 of 7 mode, followed by self-assembled ssDNA probes [13]. Using a long-period fiber grating (LPFG) platform, Liu et al demonstrated the use of a LPFG coated with graphene oxide (GO) nanosheets using the changes in resonant intensity to measure different concentrations of hemoglobin adsorbed by the GO layer [14]; Chiavaioli et al reported a D-shaped single mode optical fiber (SMF) nanocoated with different metals for IgG/anti-IgG assays, reaching limit of detections (LOD) around to the femtomolar values [15]; and Dey et al presented a sensitivity-enhanced LPFG near the turning point by etching the fiber with hydrofluoric acid to detect anti-mouse IgG [16]. In a similar approach to this work, Liu et al demonstrated an LPFG-coated with silica nanoparticles modified with gold nanoparticles (AuNPs).…”