A new design of a fiber optic sensor based on balloon shaped bending and flattening sensing probe: Application towards an ultra specific and sensitive detection of nitrite using g-C3N4/ZrPO4 nanocomposites coating

[Display omitted] •New high-sensitivity flattened balloon-shaped plastic optical fiber (FBPOF) sensor design has been proposed.•The design underwent optimization for enhanced efficiency as an absorption sensor, using COMSOL.•The optimised design FBPOF was coated with g-C3N4/ZrPO4 to detect NO2− ions.•The proposed design exhibited an LOD of 182 ppb and a sensitivity of 0.03204 µA/µM.•Selectivity for NO2− ions, and temperature insensitivity are also shown. The fabrication and characterization of a flattened balloon shaped fiber optic nitrite sensor using zirconium phosphate supported on graphitic carbon nitrite nanocomposites (g-C3N4/ZrPO4) as a cladding material have been reported. To design the sensing probe, a small portion of the fiber is mechanically hot pressed for flattening and then structured into a balloon shape. The improved sensitivity of the proposed design is ascribed to the better light extraction efficiency to the cladding in the flattened region of the balloon shaped fiber compared with a similar non flattened structure which is explained using numerical simulation. To demonstrate the sensing behavior of the proposed design, a NO2− ion sensing probe is fabricated by coating g-C3N4/ZrPO4 nanocomposite over the flattened portion of the balloon shaped fiber. Experimental results on sensing exhibit a limit of detection (LOD) of 182 ppb and sensitivity 0.03204 µA/µM for NO2− ion. Further, the study is extended towards showing high specificity and fair temperature invariance of the proposed sensor which indicates its improved performance.