Optical whispering gallery mode resonators for label-free detection of water contaminants

Water pollution is a severe worldwide problem that urgently requires development of novel sensing concepts allowing for monitoring in situ a variety of contaminants at very low concentrations in a cost-effective and multiplexed format. Whispering Gallery Mode (WGM) resonators represent novel and promising tools for the development of high-performance sensing platforms for environmental monitoring. Here we report an overview of WGM platforms for monitoring different classes of water contaminants. The theoretical basis of these novel sensing platforms are presented. Several chemical/biochemical strategies for binding specific chemo/bio-receptors on the surface of the optical resonators are discussed. Finally, the main issues that currently hinder these devices from leaving research laboratories towards the development of high compact and sensitive tools to be launched on the market are reviewed and discussed together with future perspectives.