Fiber optic biosensor for inflammatory markers based on long period grating

Here, we have reported the development and testing of a label-free fiber optic biosensor, for the real-time detection in serum of an inflammatory marker, the C-reactive protein (CRP). It is based on a novel configuration involving a long period grating (LPG) in double cladding fiber, with specific refractive index profile. Optimization of the sensitivity by means of mode transition was obtained through slight chemical etching of the fiber surface. A thin layer of graphene oxide was deposited around the LPG portion, to provide functional groups for the covalent immobilization of the biological recognition element. A large working range of CRP concentrations of clinical relevance was covered and a low limit of detection of 1.1 ng/mL was obtained in serum. The development of biosensors able to guarantee simple and rapid in-situ monitoring approach is quite an actual topic: an example is the SARS-CoV-2 infection.