Discrete dipole approximation simulations of gold nanorod optical properties: Choice of input parameters and comparison with experiment

Abstract

Gold nanorods have interesting optical properties due to surface plasmon resonance effects. A variety of biomedical applications of these particles have been envisaged and feasibilities demonstrated in imaging, sensing, and therapy based on the interactions of light with these particles. In order to correctly interpret experimental data and tailor the nanorods and their environments for optimal use in these applications, simulations of the optical properties of the particles under various conditions are essential. Of various numerical methods available, the discrete dipole approximation (DDA) approach implemented in the publicly available DDSCAT code is a powerful method that had proved popular for studying gold nanorods. However, there is as yet no universal agreement on the shape used to represent the nanorods and on the dielectric function of gold required for the simulations. We systematically study the influence of these parameters on simulated results. We find large variations in the position of plasmon resonance peaks, their amplitudes, and shapes of the spectra depending on the choice of the parameters. We discuss these in the light of experimental optical extinction spectra of gold nanorods synthesized in our laboratory. We show that much care should be taken and prudence applied before DDA results be used to interpret experimental data and to help characterize nanoparticles synthesized.

Accuracy of the discrete dipole approximation for simulation of optical properties of gold nanoparticles

“…The refractive index of gold nanoparticles is a controversial issue [22]. However, although the specific values of the bulk refractive index (and size corrections to account for surface damping) will have a significant impact on simulation results, they are too small to significantly alter the DDA accuracy (as long as the same refractive index is used for the DDA and the reference method -data not shown).…”

“…Agreement between the DDA simulations and experiments for extinction spectra of gold nanoparticles has never been perfect [22,33,34]. However, the disagreement is attributed mostly to uncertainties in particle shape [33,34] and in the gold refractive index [22].…”

“…However, the disagreement is attributed mostly to uncertainties in particle shape [33,34] and in the gold refractive index [22]. Moreover, researchers are mainly interested in position of resonance peaks in the spectrum.…”

Detection of Oxidative Stress Biomarkers Using Novel Nanostructured Biosensors

“…The collective oscillation of local surface plasmons is excited when the distance d between AuNP is: d < 5r, where r is the AuNP radius. Theoretical studies of plasmonic oscillations (Brioude et al, 2005, Draine et al, 1994, Gonzales et al, 2007, Jain et al, 2006, Kooij et al, 2006, Lee et al, 2005, 2006, Prescott et al, 2006, Ungureanu et al, 2009, Yang et al, 1995, Yin et al, 2006 and SP absorbance spectra (Alvarez et al, 1997, Etchegoin et al, 2006, Johnson et al, 1972, Kamat, 2002, Link et al, 1999a, Link et al, 1999b, Mishchenko et al, 2002, Perez-Juste et al, 2005, Ping et al, 2008 have enabled the understanding of mechanisms leading to the absorbance maximum shifts associated with the assembly processes. Extensive studies of the surface plasmon absorbance for various AuNP systems have been carried out by several groups (Alivisatos et al, 1996, Elghanian et al, 1997, Hostetler et al, 1998, Hostetler et al, 1999, Kamat, 2002, Kariuki et al, 2004, Kelly et al, 2003, Lim et al, 2009, Maye et al, 2005, Park et al, 2002, Reynolds et al, 2000, Storhoff et al, 1998, Taton et al, 2000, Taton et al, 2001, Zheng et al, 2000.…”

Microspectroscopic characterisation of gold nanorods for cancer detection

“…Q ext is the extinction efficiency of a particle calculated using the Discrete Dipole Approximation method, DDSCAT, 151,152 and r is the radius of an equivalent sphere obtained from actual size determination from SEM images (data not shown, see Rayavarapu et al 81 ). The PEG-GNR aspect ratio of 2.4 ± 0.2 was derived from analysis of at least 250 particles in each case from SEM images, as was shown by Rayavarapu et al 81 …”