(79b) Light Extinction By Agglomerates of Gold Nanoparticles: A Plasmon Ruler for Sub-10 Nm Interparticle Distances

Plasmon rulers relate the shift of resonance wavelength, λ_l, of gold agglomerates to the average distance, s, between their constituent nanoparticles. These rulers are essential for monitoring the dynamics of biomolecules (e.g., proteins and DNA) by determining their small (<10 nm) coating thickness. However, existing rulers for dimers and chains estimate coating thicknesses smaller than 10 nm with rather large errors (more than 200%). Here, the light extinction of dimers, 7- and 15-mers of gold nanoparticles with diameter, d_p = 20 - 80 nm and s = 1 - 50 nm is simulated by interfacing discrete element modeling (Kelesidis et al, 2017) with discrete dipole approximation (Kelesidis and Pratsinis, 2019). The evolution of gold light extinction during agglomeration reveals that λ_l increases up to 680 nm as single gold nanoparticles coagulate to 15-mers, in excellent agreement with data from UV-visible spectroscopy. The λ_l shift of gold dimers, 7- and 15-mers increases with decreasing s and can be described by a universal power law resulting in a new plasmon ruler that enables the estimation of gold nanoagglomerate s (Fig. 1), in excellent agreement with microscopy data. So, the new plasmon ruler obtained here for agglomerates of gold nanoparticles can be used instead of tedious microscopy measurements to determine the thickness of sub-10 nm organic and inorganic coatings, facilitating the detection of biomolecules, such as proteins and DNA (Kelesidis et al., 2022).

References:

Kelesidis, G. A., Goudeli, E., and Pratsinis, S. E. 2017. Morphology and mobility diameter of carbonaceous aerosols during agglomeration and surface growth. Carbon 121:527-535, doi.org/10.1016/j.carbon.2017.06.004.

Kelesidis, G. A., and Pratsinis, S. E. 2019. Soot light absorption and refractive index during agglomeration and surface growth. Proc. Combust. Inst. 37: 1177-1184, doi.org/10.1016/j.proci.2018.08.025.

Kelesidis, G. A., Gao, D., Starsich, F.H.L., and Pratsinis, S. E. 2022. Light Extinction by Agglomerates of Gold Nanoparticles: A Plasmon Ruler for Sub-10 nm Interparticle Distances. Anal. Chem. 94:5310-5316, doi.org/10.1021/acs.analchem.1c05145.

Figure 1. Au agglomerate λ_l as a function of normalized interparticle separation, s/d_p, estimated by DDA using dimers of monodisperse (squares and inverse triangles) and bidisperse (circles) nanoparticles and DEM-derived 7- (diamonds) and 15-mers (triangles) of monodisperse NPs with d_p = 20–50 (squares, circles, diamonds, and triangles) or 75 and 80 nm (inverse triangles) and s = 1–50 nm. A new plasmon ruler (solid line and shaded area) is derived by regressing the DDA-derived λ_l evolution.