Nanosensors for Environmental Analysis Based on Plasmonic Nanoparticles

Abstract

Interesting optical properties of gold and silver nanoparticles have been known for a fairly long time. Intensive colour of suspensions of such nanoparticles is a consequence of the excitation of a collective oscillation of surface conduction electrons (called surface plasmons) when electromagnetic radiation interacts with metal nanoparticles with a negative real and small positive imaginary dielectric constant (such as nanoparticles of gold or silver). The plasmonic optical properties of metal nanostructures are dependent on their shape and size, the dielectric properties of the metal and the surroundings, and on the possible electromagnetic coupling with the localized surface plasmons in nearby other plasmonic objects. The other important consequence of the excitation of surface plasmons is a local significant enhancement of the electromagnetic field at some places of the illuminated nanoparticles. Mentioned above specific plasmonic properties of gold and silver nanoparticles allowed on development of many sensors for chemical analysis, including sensors dedicated for environmental analysis. Some of these sensors are so sensitive, that recording of the reliable analytical signal even from a single molecule of an analyte is possible.