Abstract
Plasmonics has provided one of the commercially proven label-free biosensing platforms to date. Traditional surface plasmon resonance (SPR) sensors, however, suffer from moderate sensitivity because of the label-free nature. In this chapter, we review various recent approaches that have attempted to produce improved detection characteristics with unique strengths and weaknesses. We first explore plasmonic field localization for self-aligned overlap or colocalization between localized near-fields and target molecules developed for dramatically enhanced detection performance. Localized SPR sensors based on metallic nanoparticles for amplification of plasmonic optical signatures measured by target molecular interactions have also been reviewed. Phase-sensitive SPR configurations based on optical path difference as well as temporal difference control have been explored for sensitivity improvement compared with conventional intensity-based SPR sensors with measurement of angular and frequency characteristics. Relatively new analytical methods based on whispering gallery mode sensors coupled to nanostructures that support localized surface plasmon to achieve ultrahigh sensitivity that may enable single molecular detection were also described. We have also included the use of SPR imaging for high-throughput labelfree detection. Finally, surface-enhanced Raman spectroscopy using plasmonic nearfield enhancement was discussed for the amplification of molecular signals. This chapter highlights many exciting research directions that have been unraveled to develop high-performance optical label-free biosensors based on diverse plasmonic platforms.
Keywords: Field enhancement, Label-free optical biosensor, Plasmonic localization, Phase-sensitive measurement, Surface plasmon resonance, Surfaceenhanced Raman spectroscopy.
