Localized Surface Plasmon Resonance (LSPR)

Last week’s papers raised some confusion about the term SPR used in connection to UV/Vis for characterizing gold nano particles.

My confusion was the term “Plasmon Resonance”. How is a resonance possible in a colloid with concentrations of 0.01-1 mg/ml? The distances between particles would be too large for them to couple their surface plasmons!

I calculated the average distance of gold colloids in typical UV/Vis solutions, which turned out to be ~ 40 μm; way too large for coupling. (See my calculations in UV-Vis and gold colloids)

A LLM told me that it is a localized phenomenon; not a collective one. This means that each nanoparticle can resonate with the light independently, leading to the characteristic peaks in the UV/Vis spectrum without requiring particle-to-particle coupling.

This morning I came across the term LSPR, which stands for Localized Surface Plasmon Resonance. It turns out that LSPR is a specific type of surface plasmon resonance that occurs in small metallic nanoparticles, where the conduction electrons on the nanoparticle surface oscillate in resonance with incident light. This localized resonance gives rise to the strong absorption and scattering properties observed in UV/Vis spectroscopy of nanoparticles.

LSPR vs SPR

• LSPR should be used for resonances at the scale of individual nanoparticles, typically less than 100 nm in size. This is what we see in SPR spectra from UV-Vis measurements.
• SPR should be reserved for propagating plasmons on flat surfaces, as described in Surface Plasmon Resonance (SPR)