Effects of cellular fine structure on scattered light pattern.

Biological cells are complex in both morphological and biochemical structure. The effects of cellular fine structure on light scattered from cells are studied by employing a three-dimensional code named AETHER which solves the full set of Maxwell equations by using the finite-difference time-domain method. It is shown that changes in cellular fine structure can cause significant changes in the scattered light pattern over particular scattering angles. These changes potentially provide the possibility for distinguishability of cellular intrastructures. The effects that features of different intrastructure have on scattered light are discussed from the viewpoint of diagnosing cellular fine structure. Finally, we discuss scattered light patterns for lymphocyte-like cells and basophil-like cells.

A miniaturized wide-angle 2D cytometer.

BACKGROUND: We present an optical waveguide based cytometer that is capable of simultaneously collecting the light scattered by cells over a wide range of solid angles. Such comprehensive scattering data are a prerequisite for the microstructural characterization of cells. METHODS: We use latex beads as cell mimics, and demonstrate the ability of this new cytometer to collect back-scattered light in two dimensions (2D). This cytometer is based on a liquid-core optical waveguide, excited by prism coupling, that also serves as the microfluidic channel. In principle, our use of a hemispherical lens allows the collection of scattered light from 0 to 180 degrees in 2D. RESULTS: The experimentally observed positions of the intensity peaks of the back-scattered light agree well with theoretical prediction of scattering from both 4.0- and 9.6-mum diameter latex beads. The position of the bead, relative to the axes of the hemispherical lens and the microchannel, strongly affects the scattering pattern. We discuss a computational method for determining these offsets. CONCLUSIONS: We show that wide-angle 2D light scattering patterns of cell-sized latex beads can be observed in a microfluidic-based optical cytometer that uses leaky waveguide mode excitation. This chip-based system is compatible with emerging chip-based technologies.

3-D simulation of light scattering from biological cells and cell differentiation.

A 3-D code for solving the set of Maxwell equations with the finite-difference time-domain method is developed for simulating the propagation and scattering of light in biological cells under realistic conditions. The numerical techniques employed in this code include the Yee algorithm, absorbing boundary conditions, the total field/scattered field formulation, the discrete Fourier transformation, and the near-to-far field transform using the equivalent electric and magnetic currents. The code is capable of simulating light scattering from any real cells with complex internal structure at all angles, including backward scattering. The features of the scattered light patterns in different situations are studied in detail with the objective of optimizing the performance of cell diagnostics employing cytometry. A strategy for determining the optimal angle for measuring side scattered light is suggested. It is shown that cells with slight differences in their intrastructure can be distinguished with two-parameter cytometry by measuring the side scattered light at optimal angles.