Starting from the traditional enzyme-based biosensing method to functionalized nanostructure-based sensors, this book provides a detailed overview of some of the advanced sensing methodologies based on photonic crystal cavity-based sensing devices. The authors have compiled the book keeping in mind the extraordinary success history of nanomaterials, their current strategical exploitation, and an unprecedented pool of possibilities they hold for the future. The book looks at the various sensors, such as for biosensing, electrochemical sensing, gas sensing, photo-electrochemical sensing, and colorimetric sensing, all of which have shown potential.