Additivity of light-scattering patterns of aggregated biological particles

Separation-dependent near-field effects in Mie scattering spectra of two optically trapped aerosol droplets

The backscattering of ultraviolet and visible light by a model organic (squalane) aerosol droplet (1.0 Collapse

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Wireless monitoring of cell cultures based on light scattering: A novel optical scheme and portable prototype

Cell cultures are widely used in scientific research, biomedicine, and industry. When culturing, it is important to maintain certain conditions, including the concentration of cells. Monitoring of the culture growth and cell counting is an urgent task for the optimization of technological processes. Most existing methods require sampling from a culture flask. This procedure is time-consuming and associated with the risks of contamination. We present a device able to monitor the growth of cells number in a suspension noninvasively. The device uses a laser beam that pass through the culture flask and measures the intensity of scattered light as a function of coordinate along the beam. This optical scheme allows one to obtain accurate results for both high- and low-scattering samples. We constructed the wireless portable prototype for monitoring of cell culture growth directly in the incubator and demonstrated the applicability of the device for Jurkat cells and Escherichia coli bacteria.

4π light scattering flow cytometry: enhancing the identification and characterization of individual cells

The analysis of individual particles with complex morphologies from light scattering is crucial in disperse systems studies, such as blood cells. Characterization, which assumes determining particle characteristics, has a higher likelihood of succeeding in solving the inverse light-scattering problem if an instrument provides enough light-scattering data. In this study, we demonstrate how we extend the operating angular interval for the 4π Scanning Flow Cytometer (4πSFC), which measures angle-resolved light-scattering profiles (LSPs) of individual particles. The angular interval is extended by additionally measuring light scattering for the backward hemisphere. Currently, the 4πSFC setup uses three lasers, a single optical cell, and three photomultipliers. It enables the measurement of the LSP of individual particles within the angular interval of 10 to 170° for polar angles with integration over azimuth angles, which covers the spatial angle of 98.5% of the 4π angle. We demonstrate the 4πSFC's performance in measuring LSPs from the analysis of polymer beads, mature and spherized erythrocytes, and platelets. The 4πSFC has the potential to be very useful in identifying platelet dimers and granulocytes without labels, characterizing lymphocytes, monocytes, and abnormal erythrocytes.

Flexible scattering order formulation of the discrete dipole approximation

The discrete dipole approximation (DDA) is a well-known method for computation of the scattering of light from nonspherical particles. Here, we present a new scattering order formulation (SOF) of the DDA that allows the user to represent the scattering particle with higher flexibility than in conventional DDAs, while the computer memory required always scales as O(N). In our new SOF, the user can locate each dipole independently, or off-grid, in space, assign each dipole a unique size and a unique dipole shape as appropriate, and assign each dipole a unique magnetoelectric polarizability with no constraints. The cost of this flexibility is that the computation time is increased from O(N l o g N) to O(N 2). To compensate, our model allows the user to vary the range of dipole interaction in a unique manner. We find that, in cases in which the scatterer has at least one dimension that is sufficiently small compared with the wavelength, a relatively small number of iterations is required for convergence of the simulation, and in addition, a small dipole interaction range can be invoked to reduce the computation time to O(N) while still producing results that are sufficiently accurate.

The SSSS scheme: a method for calculating multiple scattering of electromagnetic radiation by a collection of sparsely spaced spherical scatterers of Mie-scattering size based on first principles

We present a method for calculating multiple scattering of electromagnetic radiation by a collection of sparsely spaced spherical scatterers (SSSS) of Mie-scattering size based on first principles rather than radiative transfer theory. In this respect, our methodology is conceptually similar to the superposition T-matrix method. However, our implementation, which we call the SSSS scheme, differs in a number of respects. Overall, the SSSS scheme is simpler, it is better suited numerically to sparse spacing, and the computer memory required is only linearly dependent on the total number of scatterers. We suggest that the SSSS scheme would be particularly useful for examining the effects of different spatial configurations of drops within water clouds in Earth's atmosphere and would also be useful in other fields of research in which the exact configuration of a collection of sparsely spaced Mie-sized scatterers is important.

Blood platelet quantification by light scattering: from morphology to activation

Analysis of blood platelets encounters a number of different preanalytical issues, which greatly decrease the reliability and accuracy of routine clinical analysis. Modern hematology analyzers determine only four parameters relating to platelets. Platelet shape and dose-dependent activation parameters are outside the scope of commercial instruments. We used the original scanning flow cytometer for measurement of angle-resolved light scattering and the discrete dipole approximation for simulation of light scattering from a platelet optical model, as an oblate spheroid, and global optimization with two algorithms: the DATABASE algorithm to retrieve platelet characteristics from light scattering and the DIRECT algorithm to retrieve dose-dependent activation parameters. We developed the original sampling protocol to decrease spontaneous platelet activation. The new protocol allows us to keep most of the platelets in resting and partially activated states before analysis. The analysis delivers 13 content and morphological parameters of the platelets. To analyze platelet shape change during ADP activation we developed a phenomenological model. This model was applied to the analysis of ADP activation of platelets to give 8 dose-dependent activation parameters. To demonstrate the applicability of the developed protocol and analytical method, we analyzed platelets from five donors. This novel approach to the analysis of platelets allows the determination of 21 parameters relating to their content, morphology and dose-dependent activation.

Additivity of integral optical cross sections for a fixed tenuous multi-particle group

We use the volume integral equation formulation of frequency-domain electromagnetic scattering to settle the issue of additivity of the extinction, scattering, and absorption cross sections of a fixed tenuous group of particles. We show that all the integral optical cross sections of the group can be obtained by summing up the corresponding individual-particle cross sections, provided that the single-scattering approximation applies.

Supercontinuum-based nondisruptive scattering analyses of mouse fibroblast L929 cells before and after necrosis

The scattering properties of biological tissue are highly dependent on the structure size, refractive index, and wavelength of the incident light. Furthermore, these scattering characteristics are strongly influenced by movements of the scattering objects. A method is developed to determine the angular- and spectral-resolved scattering properties that enabled the characterization of biological nano- and microscaled cell structures. Nanosecond pulses from a spectrally filtered supercontinuum light source are captured and time-resolved to depress background noise and minimize disruptive effects of the biological cells. The scattering characteristics of a monolayer of mouse fibroblast L929 cells are measured at defined wavelengths in a standard cell culture plate. Because of the size and distribution of the scattering structures, a Fourier transform-based Mie scattering scheme is used to analyze the data. The system is tested to detect structural changes of mouse fibroblast L929 cells before and after poisoning with Triton X100. The final result is the development of a contamination-free method to study pathological changes in cell cultures, necrosis, or other cell-damaging effects.

Method for the simulation of blood platelet shape and its evolution during activation

We present a simple physically based quantitative model of blood platelet shape and its evolution during agonist-induced activation. The model is based on the consideration of two major cytoskeletal elements: the marginal band of microtubules and the submembrane cortex. Mathematically, we consider the problem of minimization of surface area constrained to confine the marginal band and a certain cellular volume. For resting platelets, the marginal band appears as a peripheral ring, allowing for the analytical solution of the minimization problem. Upon activation, the marginal band coils out of plane and forms 3D convoluted structure. We show that its shape is well approximated by an overcurved circle, a mathematical concept of closed curve with constant excessive curvature. Possible mechanisms leading to such marginal band coiling are discussed, resulting in simple parametric expression for the marginal band shape during platelet activation. The excessive curvature of marginal band is a convenient state variable which tracks the progress of activation. The cell surface is determined using numerical optimization. The shapes are strictly mathematically defined by only three parameters and show good agreement with literature data. They can be utilized in simulation of platelets interaction with different physical fields, e.g. for the description of hydrodynamic and mechanical properties of platelets, leading to better understanding of platelets margination and adhesion and thrombus formation in blood flow. It would also facilitate precise characterization of platelets in clinical diagnosis, where a novel optical model is needed for the correct solution of inverse light-scattering problem.

Multiple scattering and scattering cross sections

The scattering cross section for a cluster of scatterers can be calculated using various methods, either exactly or by invoking various approximations. Of special interest are methods in which the scattering properties of individual members of the cluster are used. The underlying question is: Can the contribution to the cluster's cross section from any one member of the cluster be identified? Except for situations in which all effects of multiple scattering are ignored, no such method of identification has been found.