Unified Mie and fractal scattering by cells and experimental study on application in optical characterization of cellular and subcellular structures

Abstract

A unified Mie and fractal model for light scattering by biological cells is presented. This model is shown to provide an excellent global agreement with the angular dependent elastic light scattering spectroscopy of cells over the whole visible range (400 to 700 nm) and at all scattering angles (1.1 to 165 deg) investigated. Mie scattering from the bare cell and the nucleus is found to dominate light scattering in the forward directions, whereas the random fluctuation of the background refractive index within the cell, behaving as a fractal random continuous medium, is found to dominate light scattering at other angles. Angularly dependent elastic light scattering spectroscopy aided by the unified Mie and fractal model is demonstrated to be an effective noninvasive approach to characterize biological cells and their internal structures. The acetowhitening effect induced by applying acetic acid on epithelial cells is investigated as an example. The changes in morphology and refractive index of epithelial cells, nuclei, and subcellular structures after the application of acetic acid are successfully probed and quantified using the proposed approach. The unified Mie and fractal model may serve as the foundation for optical detection of precancerous and cancerous changes in biological cells and tissues based on light scattering techniques.

Plum pudding random medium model of biological tissue toward remote microscopy from spectroscopic light scattering

“…Thorough measurements on various tissue types within visible and near-infrared spectral range [9,10] have revealed unexpectedly contradictory trends in, in particular, g, to the above theoretical prediction as well observed by Jacques in his recent review of optical properties of biological tissues [6]. A pure continuum light scattering model has also been found to be insufficient in an extensive study of angular light scattering of water suspensions of human cervical squamous carcinoma epithelial (HiLa) cells over a wide range of wavelengths (400 to 700nm) [8,26].…”

“…Microstructures in biological tissue range from organelles 0.2 − 0.5μm or smaller, mitochondria 1 − 4μm in length and 0.3 − 0.7μm in diameter, nuclei 3 − 10μm in diameter, to mammalian cells 10 − 30μm in diameter. The refractive index variation is about 0.04 − 0.10 for soft tissue with a background refractive index n 1.35 − 1.37 [7,8]. When the wavelength, λ, of the probing light increases, light is less scattered by tissue [5,6] and the reduced scattering coefficient (μ s ) decreases.…”

“…where S core (q) represents the scattering amplitude function of the prominent distinctive scattering "cores" and S bg (q) represents the random fluctuation of the background refractive index described, for example, by the fractal random medium model (6) or the Whittle-Matern model (8). Now consider light scattering by the prominent distinctive cores in tissue.…”

“…The latter incorporates smaller scattering structures such as organelles and refractive index vari-ations throughout the tissue continuum. The total squared scattering amplitude, according to the superposition principle of light scattering in composite particles [8,27], can be written as:…”

“…Denote S bg (q) the scattering amplitude due to the random fluctuation of the background refractive index. The squared background scattering amplitude is specified by [8] …”