Book excerpt: This book introduces the fundamentals and applications of the localized surface plasmon resonance (LSPR) property of noble metallic nanoparticles, with an emphasis on the biosensing applications of plasmonic nanoparticles, especially in living cell imaging and photothermal therapy. It provides an overview of the different operating principles of plasmonic sensors, particularly the single-nanoparticle-based detections, and a series of creative biosensors based on the modulation of different parameters of nanoparticles (particle size, shape, composition and surrounding medium) for label-free detection. The interparticle coupling effect, plasmon resonance energy transfer, electron transfer on plasmonics surface are also covered in this book. This book is intended for graduate students and researchers working in the interdisciplinary field combining chemistry, biology, material science and nanophotonics. Yi-Tao Long is a Professor at the School of Chemistry and Molecular Engineering, East China University of Science and Technology, China.