Absolute real-time measurement of particle size distribution with the flying light-scattering indicatrix method

Methods to Measure Water Permeability

Water permeability is a key feature of the cell plasma membranes, and it has seminal importance for several cell functions such as cell volume regulation, cell proliferation, cell migration, and angiogenesis to name a few. The transport of water occurs mainly through plasma membrane water channels, aquaporins. Aquaporins have very important function in physiological and pathophysiological states. Due to the above, the experimental assessment of the water permeability of cells and tissues is necessary. The development of new methodologies of measuring water permeability is a vibrant scientific field that constantly develops during the last three decades along with the advances in imaging mainly. In this chapter we describe and critically assess several methods that have been developed for the measurement of water permeability both in living cells and in tissues with a focus in the first category.

Multiplex single particle analysis in microfluidics

A method to combine precise particle alignment in-flow and light scattering profile characterization for micrometric sized particles is reported.

Asymmetry coefficient for large optically soft spherical particles

The basic mechanisms describing radiation scattered by large optically soft spheres are presented in this paper. The contributions of different components of geometrical optics to formation of the integral indicatrix have been estimated. The asymptotic equations for the asymmetry coefficient have been obtained.

Calibration-free method to determine the size and hemoglobin concentration of individual red blood cells from light scattering

At present, hemoglobin concentration and the volume of an erythrocyte can be determined from the intensities of light scattered by an individual cell at fixed angular intervals. This method is used in modern hemoglobin analyzers, but it requires calibration of optical and electronic units by certified particles of known size and refractive index. We describe a method that is based on the parametric solution of an inverse light-scattering problem and does not require a calibration procedure. The method is based on the use of parameters of the entire angular light-scattering pattern, called an indicatrix here. These parameters do not depend on the absolute intensity of light scattering. The indicatrix parameters form approximating equations that relate these parameters to the size and the phase-shift parameters of the particle. The applicability of the method is demonstrated by measurement of the indicatrices of individual sphered erythrocytes. The indicatrices of the individual erythrocytes were measured with a scanning flow cytometer at an angular range of from 15 to 55 deg. The volume and the hemoglobin concentration have been calculated by use of the developed method and by fitting of the experimental indicatrices to the indicatrices calculated from the Mie theory.

Individual Escherichia coli cells studied from light scattering with the scanning flow cytometer

BACKGROUND

Flow cytometry is a powerful tool for the analysis of individual particles in a flow. Differential light scattering (an indicatrix) was used for many years to obtain morphologic information about microorganisms. The indicatrices play the same role for individual particle recognition as a spectrum for substance characterization. We combined two techniques to analyze the indicatrix of the cells for the purpose of developing a database of light-scattering functions of cells.

METHODS

The scanning flow cytometer (SFC) allows the measurement of the entire indicatrix of individual particles at polar angles ranging from 5 degrees to 100 degrees. In this work, light-scattering properties of Escherichia coli have been studied both experimentally and theoretically with the SFC and the T-matrix method, respectively. The T-matrix method was used because of the nonspherical shape of E. coli cells, which were modeled by a prolate spheroid.

RESULTS

The indicatrices of E. coli cells were stimulated with T-matrix method at polar angles ranging from 10 degrees to 60 degrees. The absolute cross-section of light scattering of E. coli has been determined comparing the cross section of polystyrene particles modeled by a homogeneous sphere. The E. coli indicatrices were compared for logarithmic and stationary phases of cell growth.

CONCLUSIONS

The indicatrices of E. coli were reproducible and could be used for identification of these cells in biologic suspensions. The angular location of the indicatrix minimum can be used in separation of cells in logarithmic and stationary phases. To use effectively the indicatrices for that purpose, the light-scattering properties of other microorganisms have to be studied.

Particle classification from light scattering with the scanning flow cytometer

BACKGROUND

The differential light-scattering pattern, an indicatrix, provides the most complete characterization of the optical properties of a particle. Particle classification can be performed on the basis of particle parameters retrieved from the indicatrices. This classification extends the ability of flow cytometry in particle recognition.

METHODS

The scanning flow cytometer (SFC) permits an acquisition of traces of light scattering signals, i.e., native SFC traces, from single particles. The acquired native SFC traces are transformed into indicatrices. The performance of the SFC in measurements of indicatrices has been demonstrated for the following particles: lymphocytes, erythrocytes, polystyrene particles, and milk-fat particles.

RESULTS

The structure and profile of the indicatrix for each particle type have been found to be unique. Classification of polystyrene particles has been performed on the basis of the map formed by particle refractive index and size. The polystyrene particles were classified using this map into different size categories ranging from 1.4-7 microm, with a size deviation of 0.07 microm.

CONCLUSIONS

The method based on analysis of native SFC traces shows better performance in particle classification than the method based on the particle refractive index and size map. The classification performance of the SFC will be useful, for example, for particle sorting and particle identification, and with additional fluorescent measurements may have applications in multiparameter particle-based immunoassay.

Light-scattering properties of individual erythrocytes

We have studied the light-scattering properties of human erythrocytes both experimentally and theoretically. In the experimental study measurements were performed with a Scanning Flow Cytometer (SFC). The SFC can measure the light-scattering pattern (indicatrix) of an individual particle over an angular range of 10-60 degrees. We have observed polymorphism in the measured set of indicatrices. To understand the reason for this polymorphism, we have made a theoretical study of the scattering properties of erythrocytes. The Wentzel-Kramer-Brillouin approximation has been employed to calculate indicatrices of individual erythrocytes in different orientations relative to the incident light beam. The indicatrices were calculated over an angular range of 15-35 degrees. A comparison of the experimentally measured and theoretically calculated indicatrices shows that the polymorphism is due mainly to the different orientation of the erythrocytes in the flow. The effect caused by the Poiseuille profile of the flow on an individual erythrocyte within the SFC cuvette capillary was studied theoretically by use of the Stokes approximation. Rotation of an erythrocyte was predicted by this theoretical analysis, and this prediction was further verified by comparison with experimental results.

Parametric solution of the inverse light-scattering problem for individual spherical particles

We analyze the relation between spherical particle parameters (size parameter ? and relative refractive index m ) and light-scattering indicatrix parameters (fringe pitch and visibility) for ?and m ranging from 7 to 88 and from 1.025 to 1.2, respectively. We consider formation of the indicatrix structure under variation of size parameter ? and phase-shift parameter ? =2 ?(m - 1). We show that indicatrix visibility depends basically on the phase-shift parameter whereas fringe pitch depends on the size parameter. An analysis of these dependencies allows us to determine the region in the ? x ? map where particle parameters can be derived unambiguously from indicatrix parameters. We clarify errors in determination of particle characteristics on the basis of the approximating equations that relate particle size and phase shift to indicatrix parameters.