8:00 PM - EL01.20.19
Evolution of Gold Nanoparticle Light Absorption During Agglomeration
Daniel Gao1,Georgios Kelesidis1,Sotiris Pratsinis1
Particle Technology Laboratory (PTL) ETH Zurich1
Gold nanoparticles are very attractive for biomedical applications due to their enhanced light absorption by collective oscillations of their surface electrons at the surface plasmon resonance wavelength, λSPR . For example, their high λSPR sensitivity on the refractive index of the medium shows great potential for detection of small organic molecules and proteins . The λSPR shifts from the visible light range (e.g. 530 nm) for single spheres to the near infrared spectrum (e.g. 780 nm) for non-spherical particles, such as nanorods. The λSPR sensitivity to refractive index of the medium also increases as with decreasing particle sphericity, ranging from 44 nm per refractive index unit (RIU) for single spheres to 224 nm/RIU for rods .
Here, discrete element modeling (DEM) is coupled with discrete dipole approximation (DDA)  to investigate numerically the evolution of gold light absorption during nanoparticle agglomeration. The DDA model is validated against simulations and experiments for single spheres and nanorods . The DEM-derived agglomerate sphericity is quantified by the fractal dimension, Df, evolving from 3 for single spheres to 1.91 for ramified agglomerates having more than 15 monomers. The gold λSPR shifts from 530 to about 650 nm during agglomeration due to plasmonic coupling effects , in good agreement with data . The evolution of λSPR sensitivity to the medium is elucidated as a function of agglomerate size and benchmarked against those of single spheres and rods .
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