I have seen that most of the researchers use a 785nm wavelength LASER for SERS investigation of gold nanoparticles. What is the reason behind this? Is it due to the LSPR frequency of the gold nanoparticle?
Because plasmon banda of gold NP is located in this rtegion. Also if the prove have some fluorescence, this phenomenon can be avoid by excitation in IR region.
Besides: For biological applications it is better to use NIR-LASER to avoid damages in cells/tissues...
Same laser has been used for silver NPs SERS also. I was wondering if its related to plasmon band location than how it can be used for silver NPs. @traian lliescu
If Ag nanoparticles (as well as Au) are aggregated the plasmon band can shift to NIR. Another interesting point why you can sometimes use NIR-LASER (also for non-aggregated nanoparticles with no significant plasmon band in NIR region) is the dark modes effect which becomes stronger in NIR.
The SPR of gold nanoparticles is ~520 nm (depending on the size), due to their spherical nature. However, if one axis of the particle becomes elongated so that the particle becomes rod-shaped, then a longitudinal axis produces the LSPR around 785 nm (depending on the aspect ratio). Likewise, if 2 or more particles align themselves, then it is as if they are one entity, and the LSPR presents itself around the 785 nm wavelength.
When using green laser the SP absorption leads to release of thermal energy and scattering(Rayleigh /Mie:Depend on size of GNP). Around 400 nm and below wavelength induce fluorescence in nano rods. To minimize other optical responses and get enhances raman signals 785 nm laser is preferable
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