Plasmonic and magnetoplasmonic interferometry for sensing

[Introduction and background] Nowadays, we are surrounded by sensors in our daily lives, in industrial processes, medical diagnosis systems, environmental monitoring, etc. The development of sensors with higher sensitivity and smaller dimensions to be integrated in miniaturized systems is then of highest importance for our society. Within all different kinds of sensors, optical sensors are advantageous because they are highly versatile, non-invasive and they can be used in aggressive conditions. In particular, sensors based on surface plasmons, known as surface plasmon resonance (SPR) sensors, have become increasingly popular in biosensing in recent decades due to their high sensitivity and ease of use. Different SPR configurations, such as modulation techniques, have been proposed and demonstrated in order to increase their sensitivity, and attempts to obtain miniaturized SPR sensors have been carried out, the development of plasmonic interferometry sensors being a promising path.[Main results] We have compared theoretically the performance of three implementations of plasmonic sensors: the standard SPR configuration, plasmonic interferometry and magnetically modulated plasmonic (magnetoplasmonic) interferometry. Our results show that the sensitivity of plasmonic interferometers surpasses that of standard SPR methods for long enough except the micrometer-sized interferometers. Moreover, when plasmonic interferometers are magnetically modulated, the direct measurement of the induced modulation in the surface plasmon wavevector allows one to further increase the system sensitivity.[Wider implications] These results show that the development of plasmonic interferometers for sensing, either plain or magnetically modulated, is an interesting route to obtain miniaturized surface plasmon based sensors with higher sensitivity. Moreover, the extended knowledge of immobilization protocols in gold already developed for standard SPR sensors will remain applicable.We acknowledge funding from the Spanish MINECO ('MAPS' MAT2011-29194-C02-01 and 'FUNCOAT' CONSOLIDER INGENIO 2010 CSD2008-00023) and the Comunidad de Madrid ('MICROSERES-CM' S2009/TIC-1476).Peer Reviewe