Cell properties assessment using optimized dielectrophoresis-based cell stretching and lumped mechanical modeling

Cells mechanical property assessment has been a promising label-free method for cell differentiation. Several methods have been proposed for single-cell mechanical properties analysis. Dielectrophoresis (DEP) is one method used for single-cell mechanical property assessment, cell separation, and sorting. DEP method has overcome weaknesses of other techniques, including compatibility with microfluidics, high throughput assessment, and high accuracy. However, due to the lack of a general and explicit model for this method, it has not been known as an ideal cell mechanical property evaluation method. Here we present an explicit model using the most general electromagnetic equation (Maxwell Stress Tensor) for single-cell mechanical evaluation based on the DEP method. For proof of concept, we used the proposed model for differentiation between three different types of cells, namely erythrocytes, peripheral blood mononuclear cells (PBMC), and an epithelial breast cancer cells line (T-47D). The results show that, by a lumped parameter that depends on cells' mechanical and electrical properties, the proposed model can successfully distinguish between the mentioned cell types that can be in a single blood sample. The proposed model would open up the chance to use a mechanical assessment method for cell searching in parallel with other methods.

Effective optical constants n and κ and extinction coefficient of silica aerogel

In this work the normal reflectance, R, at a planar silica aerogel interface and the normal transmittance, T, of a silica aerogel slab were measured using a Fourier Transform Infrared Spectrometer. Two procedures were used to obtain the effective optical constants, i.e., the refractive index n and the absorption index κ, of silica aerogel. One procedure determined κ from the measured transmittance T and then determined n from the results for κ and from the measured reflectance R using the Kramers–Kronig relation; the other procedure determined n and κ of silica aerogel from n and κ of fully dense silica glass by using the Clausius–Mossotti equation, Maxwell Garnett formula, and Bruggeman formula. The first procedure has a relatively large error due to the inaccuracy of the transmission and reflection measurements. The second procedure, especially the Clausius–Mossotti equation, yields values of n that are consistent with experiments and may be used for the calculation of the effective optical constants and the extinction coefficient of silica aerogel.

Thermodynamics of the Volta effect for surface films

An explicit thermodynamic analysis of the Volta effect for a system including adsorbed films or spread monolayers is presented in terms of surface variables. From an appropriate fundamental equation, Maxwell relations are obtained describing the effect of an applied electric field on some of the parameters characterizing surface films. It is shown that the assumptions of Bridgman, Kelvin & Lorentz (B.K.L.) concerning the properties of the Volta and compensation potentials are strictly incorrect, but that in many cases of practical interest the errors introduced by these assumptions are negligible, and lie well within current experimental accuracy. Measurable effects associated with the breakdown of the B.K.L. assumptions are predicted at high fields corresponding to phenomena such as field desorption. New experiments are suggested by the demonstration that in the transition region of a two dimensional first-order phase change, the B.K.L. assumptions can break down significantly when the chemical potentials of the adsorbed components are among the variables to be kept constant, but much less so at constant average surface densities of all surface active components. Finally, a possible method is suggested for obtaining the slopes of the isotherms for spread monolayers in regions in which they are too small to measure by conventional means.