Long Period Grating based Biosensing Technology for the Detection of Vitamin D3

The label-free detection of vitamin D by employing fiber optic biosensor is reported in this work. Here, the long period grating (LPG) which is inscribed into a specialty fiber i.e., double cladding fiber (DCF) having W-type refractive index profile, is basically employed as a foundation for biosensing. The wet-chemical etching is performed to the outer cladding of the fiber to induce mode transition phenomenon which resulted in an enhanced sensitivity of -1400 run/RIU towards surrounding medium along with significant visibility (> 15 dB) of grating's resonance band. The sensing surface of an LPG device is then coated with a graphene oxide (GO) layer of nanometric thickness providing carboxylic functional groups for grafting of 25-OH-D3 specific antibody for vitamin D3. Finally, the detection of vitamin D3 was tested using concentrations in buffer solutions within the clinical range of 1-100 ng/mL resulting a limit of detection (LOD) lower than 1 ng/mL.