It appears from published literature, that an individual Au nanocage produces about an order of magnitude higher absorption cross-section than an individual Au nanorod (considering 750-850 nm spectral range and corresponding dimensions of the nanoparticles). Does anybody know if there was some other shape that can do even better than nanocages? I'm looking for strong dominant absorbers (absorption>>scattering).
Basically, the absorption and scattering depends on particle size. If you use spherical gold nanoparicles with small diameters, say 10 nm, the absorption dominates. You can do a simple Mie calculations to verify that. You can check this website for some information: http://chenglongresearch.weebly.com/1/post/2013/12/mie-scattering-calculation-python-code.html
Chenqlong,
Wouldn't you get the plasmon resonance for spherical Au nanoparticles of this size around 510-530 nm or so? One can't really tune much their plasmon resonances. They will be always
Hi Serge,
Got your point. You are right, the plasmonic resonance of single gold sphere alone is hard to go beyond 600 nm. Maybe dimer (two gold sphere close together) can go well into near infrared since the strong coupling between two gold spheres will red shift the plasmonic resonance. I think the key design point is you design the particle combination so that a dark mode is excited. I guess the dark mode may give you large absorption since it radiate less in principle.
I advise you to take a look on the following references:
http://www.opticsinfobase.org/boe/abstract.cfm?uri=boe-3-3-590
and also "Optimized Nanocage for Cancer Photothermal Therapy and
Comparison with Other Nanoparticles"
Dear Serge,
I think the best option is to consider the case of interpenetrated or crossing randomly distributed gold NWs. There are various publications which report the enhancement of optical responses by crossed geometry. Prokes et al showed such a case for the crossed Ag NWs.
@ O.C.Aktas,
That's interesting. Thanks! I guess it would require some assembling effects taken into account and leading to a formation of such crossings. I was thinking more in terms of independent NPs. For example, during a cellular uptake of the same number of NPs those with higher absorption cross-sections would provide higher mu_a and as a result, be more efficient absorbers of NIR radiation. Then, they can be considered as more efficient optical contrast agents for diagnostic purposes.
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