Nanoplasmonic Sensors with Various Photonic Coupling Effects for Detecting Different Targets

© 2015 American Chemical Society. Nanoplamsonic sensors have been utilized to effectively detect molecules or biological structures with diverse sizes. Their performances can be engineered through various photonic and plasmonic coupling strategies; however, the coupling effects modify the surface electric field and complicate the interrelationship between the resonance line width, the sensitivity, and the decay length of the electric field. This makes rational sensor design challenging. We provide insight into the nanoplasmonic sensing performances by using the finite difference time domain method to numerically study the sensing behavior for three types of coupling strategies: (1) coupling to a Fabry-Perot cavity, (2) diffractive coupling in periodic arrays, and (3) coupling to propagating surface plasmons. The sensitivity analysis is based on the recently proposed second-order surface sensitivity, and the results are distinguished for different targets such as the bulk index change, thin surface monolayer, and thicker layer that is larger than the typical decay length. The resonance line width, sensitivities to different targets, figure of merit, and decay length are systematically compared. The important role of the decay length in the sensor evaluation is also clarified. Our results offer guidance to the nanoplasmonic sensor design for a variety of applications.status: publishe