A protein-based biointerfacing route toward label-free immunoassays with long period gratings in transition mode

► Due to divergent design needs, biofunctionalization of polymer optical resonators is difficult. ► Adsorption of bovine serum albumin (BSA) provides an intermediate layer for further functionalization. ► Optimal concentration and exposure time of BSA to glutaraldehyde determined by ELISA and surface plasmon resonance assays. ► Covalent immobilization of IgG to BSA through glutaraldehyde and detection of anti IgG. ► Multiple biomolecular interactions monitored in real time by means of a Long Period Grating in transition mode.