Single plasmonic nanoparticles as ultrasensitive sensors.

Plasmonic nanoparticles, especially Au and Ag, exhibit unique and tuneable optical properties due to their localized surface plasmon resonance, which have been widely applied in cell imaging, biocatalysis and biosensing. Notably, dark-field microscopy enables the observation of the scattering spectra of single nanoparticles and therefore has been intensively used in the construction of various nanosensors. In this mini review, we will briefly introduce the recent applications of plasmonic nanoparticles based on dark-field microscopy. Ultrasensitive sensors at the single-nanoparticle level are mainly focused by Rayleigh scattering spectroscopy, which is sensitive to their geometry, plasmon coupling, plasmon resonance energy transfer and assembly. Fabrication methods for the nanomaterials and new analysis techniques will also be discussed in detail.