Comparative assessment of the performance of long period fiber grating-based biosensors

Evanescent wave-based optical fiber biosensors consisting of long period grating (LPG) are presented. A chemical or a biochemical interaction taking place on a conveniently treated surface causes a refractive index (RI) change that can be evaluated using optical approaches. By implementing the same antibody/antigen (IgG/anti-IgG) assay protocol in the same experimental conditions, a comparative assessment of the biosensor performance was carried out by using different types of LPGs (standard, turn-around point and coated) in which the coupling occurred with different cladding modes. These sensors were firstly characterized in terms of volume (or bulk) RI sensitivity, which just provides an indication of the biosensor performance, and then of detection limit (LOD), which in turn represents a real and effective analytical parameter of biosensors extrapolated from their calibration curves. LODs of the order of μg L^-1 (10^-11 M) were achieved for turn-around point and coated LPGs both in buffer and in serum as real and complex matrix, thus also proving the biosensor specificity.