Long period grating in double cladding fiber coated with graphene oxide as high-performance optical platform for biosensing

In this work, the development and testing of a novel fiber-optic based label-free biosensor is presented, whose performance were verified through the detection of C-reactive protein (CRP) in serum. The device is based on a long period grating fabricated in a double cladding fiber with a W-shaped refractive index (RI) profile. As a result, the working point of the device was tuned to the mode transition region by chemical etching of the outer fiber cladding, obtaining a significant enhancement of the RI sensitivity and an excellent visibility of the grating resonances due to the mode transition in an all-silica structure. The fiber transducer was coated with a nano metric thin layer of graphene oxide in order to provide functional groups for the covalent immobilization of the biological recognition element. A very low limit of detection of about 0.15 ng/mL was obtained during the detection of CRP in serum, and a large working range (1 ng/mL - 100 mu g/mL) of clinical relevance has been also achieved.

Automated summary

In this study, a novel fiber-optic biosensor was developed and tested for label-free detection of C-reactive protein in serum. The device showed enhanced sensitivity and visibility of grating resonances by tuning the working point to the mode transition region through etching of the outer fiber cladding. Coating the fiber transducer with graphene oxide enabled covalent immobilization of the biological recognition element, resulting in a low detection limit and a wide working range of clinical relevance.