Optimization of Optical Absorption of Colloids of SiO2@Au and Fe3O4@Au Nanoparticles with Constraints

Abstract

We study the optical response of monodisperse colloids of core-shell plasmonic nanoparticles and introduce a computational approach to optimize absorption for photothermal applications that require dilute colloids of non-interacting particles with a prescribed volume fraction. Since the volume fraction is held constant, the particle concentration is size-dependent. Optimization is achieved by comparing the absorption spectra of colloids as a function of particle size and structure. We demonstrate the approach via application to colloids of core-shell SiO2@Au and Fe3O4@Au nanoparticles with particle sizes that range from 5–100 nm and with the incident wavelength varying from 600–1200 nm. The absorption spectra are predicted using Mie theory and the analysis shows that there is a unique mix of parameters (core radius, shell thickness, wavelength) that maximize absorption, independent of the value of volume fraction. We show that lossy Fe3O4 cores produce a much broader absorption peak with much less sensitivity to variations in particle structure and wavelength than lossless SiO2 cores. This approach can be readily adapted to colloids of nanoparticles with arbitrary materials, shapes and structure using appropriate numerical methods to compute the absorption spectra. As such, it is useful for the rational design of colloids and process variables for a broad range of photothermal applications.

Hybrid magnetite–gold nanoparticles as bifunctional magnetic–plasmonic systems: three representative cases

“…Also note, that for larger tuning capabilities, NPs with cores ranging between D C = 4-100 nm and shells up to 40 nm can also be prepared. [27][28][29][30][31] For the case of the dumbbell, Fe(Au) composites have been synthesised with minor modifications on the procedures of ref. 32.…”

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“…The monodispersed gold nanoparticles were used as labels to increase the sensitivity of the SPR imaging technique [10]. The amplification effect of antibody gold nanoparticles (AuNPs) and aptamer-AuNPs on the detection by SPR, and the development of a sandwich SPR method for protein detection, had been verified in previous research [2,3,[11][12][13][14].…”

Iron Oxide and Gold Based Magneto-Plasmonic Nanostructures for Medical Applications: A Review

“…Applying Mie theory, the optical spectra of such hetero-structures were calculated for two different particle sizes, 60 and 100 nm, and various ratios between the shell thickness and the core radius, 10%, 20%, 30%, and 40%. The obtained spectra showed that the plasmonic absorption band is red-shifted as the ratio decreased [ 87 ]. This feature was confirmed experimentally by Canet-Ferrer et al [ 88 ], who evidenced that the extinction spectra of Fe 3 O 4 -Au core-shell NSs of 5 nm in diameter, exhibited the highest absorption wavelength (around 700 nm) when the gold thickness was the thinnest (about 1 nm).…”

“… Parametric analysis of optimum normalized absorption vs. λ for two different sized Fe 3 O 4 @Au NPS with various shell-to-radius ratios ξ Au ( a ) D p = 60 nm, ( b ) D p = 100 nm. Reproduced with permission from [ 87 ]. …”