Abstract
We investigate spectroscopic imaging ellipsometry for monitoring biomolecules at surfaces of nanoparticles. For the modeling of polarimetric light scattering off surface-adsorbed core-shell nanoparticles, we employ an extension of the exact solution for the scattering by particles near a substrate presented by Bobbert and Vlieger, which offers insight beyond that of the Maxwell-Garnett effective medium approximation. Varying thickness and refractive index of a model bio-organic shell results in systematic and characteristic changes in spectroscopic parameters [Formula: see text] and [Formula: see text]. The salient features and trends in modeled spectra are in qualitative agreement with experimental data for antibody immobilization and fibronectin biorecognition at surfaces of gold nanoparticles on a silicon substrate, but achieving a full quantitative agreement will require including additional effects, such as nanoparticle-substrate interactions, into the model.
Highlights
Nanoparticles (NPs) are widely used in biomedical applications: biosensing, point-of-care diagnostics, in vivo sensing and imaging, cell tracking and drug delivery, among others [1, 2]
We took advantage of numerical computations to systematically investigate the changes in the ellipsometric parameters Ψ and Δ as a function of characteristics of the core-shell NPs— surface density, shell refractive index and thickness—varied within ranges realistically accessible in experiments; all calculations assumed a fixed gold core diameter of 20 nm and a fixed angle of incidence (AOI) of 65°
We have investigated spectroscopic ellipsometry as a technique for characterization of coreshell metal-organic nanoparticles adsorbed on a substrate
Summary
Nanoparticles (NPs) are widely used in biomedical applications: biosensing, point-of-care diagnostics, in vivo sensing and imaging, cell tracking and drug delivery, among others [1, 2]. We report the Bobbert-Vlieger model that has been adapted to describe light scattering by core-shell metal-organic NPs (metallic core with bio-organic shell) placed on a substrate and can be used to determine their optical properties. This model offers a practical approach, an improvement on models based on the effective medium approximation (EMA), because Bobbert-Vlieger model describes an exact solution of the underlying Maxwell’s equations, while being less complex than the Green’s functions methods. We first construct a theoretical formulation for light scattering by a core-shell metalorganic NP on a substrate, based on exact solutions of Maxwell’s equations provided by the Bobbert-Vlieger model. With appropriate models developed and validated, spectroscopic ellipsometry could become a complementary characterization technique for nanoparticle systems, alongside the more traditional techniques such as TEM, UV-Vis and DLS
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