Gold NanoUrchins exhibit distinctive optical properties compared to spherical gold nanoparticles of equivalent core diameter. The spiky and uneven surface induces a red shift in the surface plasmon peak, and there is a greater enhancement of the electromagnetic field at the tips of the Gold NanoUrchin spikes when compared to spherical particles.
For instance, 100 nm spherical gold nanoparticles have a surface plasmon resonance (SPR) peak at 570 nm, while 100 nm Gold NanoUrchins display an SPR peak around 680 nm.
TEM of 100 nm Gold NanoUrchins. Image Credit: Merck
Left - UV-VIS spectra of 100 nm Gold NanoUrchins (blue) and 100 nm standard gold nanoparticles (green). Note the red-shift in the SPR-peak. Right - UV-VIS spectra of Gold NanoUrchins ranging in size from 50 nm to 100 nm in diameter. Image Credit: Merck