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 oligonucleotide biosensor based on dual-peak long period fiber grating
