Label-free optical biosensors based on a planar optical waveguide

We review optical label-free biosensing platforms based on planar optical waveguides with their operation principles and performance characteristics. As the building blocks of refractometric optical transducers and plasmonic optical devices, optical planar waveguides are widely adopted to be core sensing platforms for label-free optical assay of biological and chemical interactions due to the high sensitivity with their invulnerability to external noise such as electromagnetic interference. The review scope includes the sensing schemes of conventional dielectric waveguides, the reverse symmetry waveguides, the anti-resonant reflecting optical waveguides (ARROW), and metal-clad leaky waveguides (MCLW). The configurations of the sensing systems with their operation features will be discussed together with the recent development and progress. In particular, we address in more detail the reverse symmetry waveguide and the MCLW based biosensors which have a capability of detecting micrometer-scale biological objects.