Nanoscale Optical Biosensor:  Short Range Distance Dependence of the Localized Surface Plasmon Resonance of Noble Metal Nanoparticles

Silver and gold nanotriangles were fabricated by nanosphere lithography (NSL) and their localized surface plasmon resonance (LSPR) spectra were measured by UV−vis extinction spectroscopy. It is demonstrated that the short range (viz., 0−2 nm) distance dependence of the electromagnetic fields that surround these nanoparticles when resonantly excited can be systematically tuned by changing their size, structure, and composition. This is accomplished by measuring the shift in the peak wavelength, λmax, of their LSPR spectra caused by the adsorption of hexadecanethiol as a function of nanoparticle size (in-plane width, out-of-plane height, and aspect ratio), shape (truncated tetrahedron versus hemisphere), and…