Immunosensing With Electro-active Photonic Devices
The field of immunosensors, in which an affinity ligand-based immunochemical reaction is coupled to a highly responsive transducer, is growing rapidly. In this chapter we describe the development of two novel photonic strategies for label-free human viral pathogen immunosensing. Two electrically-modulated photonic technologies, named single-mode electro-active integrated optical waveguide (SM-EA-IOW) and electrochemical surface plasmon resonance (EC-SPR) have been developed for specific immunosensing detection. Both sensing photonic strategies are based on incorporating a sandwich immunoassay onto the surfaces of the electro-active photonic devices. To do so, the electro-active photonic platforms are mounted in a micro-electrochemical flow cell where it is functionalized with a monoclonal antibody aimed at a specific target pathogen antigen. Once the target is bound to the device surface, it promotes the capturing of a secondary polyclonal antibody conjugated with a redox-active methylene blue (MB) dye. The methylene blue displays a reversible change in optical absorption throughout a reduction–oxidation transition, which provides an optical signal that can be driven electrically and interrogated with high sensitivity by spectroelectrochemical responses. As a proof of principle, the strategy was applied for the detection of hemagglutinin (HA) protein from the H5N1 avian influenza A virus onto two electro-active photonic devices, the SM-EA-IOW and EC-SPR platforms. The experimental results of the electro-active based immunosensors showed a remarkable limit of detection, ensuring a promising future for these emerging technologies. Their experimental benefits and their intrinsic trade-offs are discussed here.