Biosensing with microresonators and fibre nanotips

In the last two decades, a remarkable progress has occurred in the development of biosensor photonic devices and their application in areas ranging from environmental monitoring to food safety, medical diagnostics, drug screening. As an example, recent developments have greatly improved the sensitivity of optical sensors based on metal nanoparticle arrays and single nanoparticles; plasmonic nanosensors seem to offer great potential. Here two more approaches are discussed, concerning biophotonic sensors at different size scale, micrometric or nanometric. The former approach tries to fully exploit the properties of whispering gallery mode (WGM) microresonators; a very promising route is based on the use of hollow microresonators (microbubbles), which make possible an efficient integration of the sensing device and the fluidics. The latter approach is based on the use of optical fibres with nanometric tip, which can allow to take measurements inside a single cell.