Metal nanoparticles support localized surface plasmon resonances, collective oscillations of conduction electrons that strongly couple to light at specific wavelengths and produce extremely high electromagnetic fields near the nanoparticle surface. Surface Enhanced Raman Scattering (SERS) can increase the Raman signal by more than 6 orders of magnitude. Fluorescent molecules near the metal particle surface can also be enhanced and can be protected from photobleaching. (Surface Enhanced Fluorescence; SEF)
For SERS applications, plasmonic nanoparticles with areas of high curvature produce the largest field enhancements (e.g. rod, cubic, pyramidal, or plate geometries). Controlled aggregation of particles into doublets or triplets also produce high enhancements, especially when the SERS molecule can be trapped in the junction between the particles. For SEFS, the fluorescent molecules also need to be in high localized field but if the fluorescent molecule is too close to the metal surface, its emission can be “quenched”. Thus, SEFS particles typically are designed to position the fluorescent molecule a few nm away from the surface.
nanoComposix has between developing SERS and SEFS particles for more than 10 years. Plasmonic nanoparticles with resonance wavelengths from 400 nm to 1000 nm that have ultra-clean bare surfaces ideal for SERS applications are available as stock product and other size and wavelength variants are available as custom orders. For SEFS, there is a requirement that the molecules be separated from the metal surface by a fixed amount (typically 5 to 10 nm). Silica shelled plasmonic nanoparticles are often used for this barrier layer and custom loading of fluorescent molecules into silica shelled plasmonic nanoparticles is available on request.
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