Direct visualization of molecular scale chemical adsorptions on solids using plasmonic nanoparticle arrays

The fast and sensitive detections of chemicals adsorption onto solid substrates are of importance to many fields. Ordered arrays of gold or silver nanoparticles with strong surface plasmon resonances allow directly visualized detections of molecular scale adsorptions of polymer multilayers, an explosive derivative, and mercury vapor on solid substrates. The adsorbed species change local dielectric constants surrounding plasmonic nanoparticles, leading to shifts of plasmon resonance peaks into either long or short wavelength direction depending on interactions of chemicals with nanoparticles. The magnitude of peak shifts is proportional to the amount of adsorbed chemicals in certain range, and is sufficiently large so that color changes can be seen directly by naked eyes. The ordered nanoparticles can be made over a large area at high yield, allowing a quantitative, passive, and sensitive detection of molecular species.