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We analyze the sensitivity of electrical measurements to lysis of biological cells in suspensions. We aim at discerning the electrical parameter and measuring conditions that are more convenient to monitor the kinetics of a lysis process. We consider single-frequency measurements of the capacitance and resistance of an electrical capacitor containing a suspension of biological cells at mid-radiofrequencies. We use well-established models to estimate the relative sensitivities to variations of the volume fraction of cells during a lysis process. Then we estimate values for the resolution in measuring the fraction of cells that have been lysed with commercially available LCR meters. Unexpectedly, our results indicate that, despite the total number of ions in solution remains constant during a lysis process, in general, the electrical resistance provides a more appropriate signal for sensing the evolution of cell lysis than the capacitance. This is contrary to the case when the cell's volume fraction without lysis is to be measured. We predict that, with single-frequency resistance measurements, a resolution better than 0.1% in volume fraction of lysed cells should be attainable without much difficulty. Keywords: Electrical sensing, Biological-cell suspensions, Lysis, Resistance, Capacitance, Effective dielectric function

The purpose of this article is to calculate the generalized nonlocal conductivity tensor of a spherical particle made of isotropic and linear materials. The generalized conductivity tensor is a crucial element in the formulation of the mean-field theories of the electromagnetic response of random particulate systems. This is equivalent to what is called the T-Matrix in multiple scattering theories. Here, a new method is proposed for finding explicit expressions for this tensor directly from its definition including the magnetic response of the spheres. Its relation with the S-Matrix in the theory of single scattering is stated as a generalization. Several approximations and limit cases of possible interest in specific systems are analyzed and the results of some calculations are presented as a numerical example.

In this work, we solve the problem of modeling the generation of an acoustic pulse produced by the incidence of a pulsed laser light upon an elastic material. Our concern is about the heat transport during the absorption of electromagnetic radiation. We assume that the pulse duration is of the order of nanoseconds, and asses if under these conditions the contribution of the heat transport in the sample is an essential consideration in the description of the phenomena or if we can ignore it in the model. We begin with the energy balance analysis over the initial interaction of radiation with matter in the context of the formulation Meixner-Prigonine which is called the linear irreversible thermodynamics to describe the induced temperature field. Then we carry a momentum balance which yields the macroscopic elasticity equations with a heat source for the induced pressure field. Once established the equations for temperature and displacement fields, we solve them for the one-dimensional case, showing that the induced pressure has two components, one fast component and one slow component which is due to heat transport in the sample, which is one of the main contributions of the paper.

We model theoretically the voltage response to an acoustic pulse of a multilayer system forming a low noise capacitive sensor including a Polyvinylidene Fluoride piezoelectric film. First we model a generic piezoelectric detector consisting of a piezoelectric film between two metallic electrodes that are the responsible to convert the acoustic signal into a voltage signal. Then we calculate the pressure-to-voltage transfer function for a N-layer piezo-electric capacitor detector, allowing to study the effects of the electrode and protective layers thickness in typical layered piezoelectric sensors. The derived transfer function, when multiplied by the Fourier transform of the incident acoustic pulse, gives the voltage electric response in the frequency domain. An important concern regarding the transfer function is that it may have zeros at specific frequencies, and thus inverting the voltage Fourier transform of the pulse to recover the pressure signal in the time domain is not always, in principle, possible. Our formulas can be used to predict the existence and locations of such zeroes. We illustrate the use of the transfer function by predicting the electric signal generated at a multilayer piezoelectric sensor to an ultrasonic pulse generated photoacoustically by a laser pulse at a three media system with impedance mismatch. This theoretical calculations are compared with our own experimental measurements.

We present the viability of obtaining the particle size and surface coverage in a monolayer of polystyrene particles adsorbed on a glass surface from optical coherent reflectance data around the critical angle in an internal reflection configuration. We have found that fitting a CSM to optical reflectivity curves in an internal reflection configuration around the critical angle with a dilute random monolayer of particles adsorbed on the surface can in fact provide the particle's radius and surface coverage once the particles are sufficiently large., Conference Date: Sunday 24 May 2009 Conference Location: Quebec, Canada Conference Title: Photonics North 2009 Conference Chairs: Real Vallee

"We discuss and analyze a practical methodology for the determination of the dielectric constant of a macroscopic solid sample in a nondestructive way. The technique consists in measuring the capacitance between a pointer electrode and the dielectric surface as a function of the separation distance in a scale comparable to the radius of curvature of the tip's apex. The changes in capacitance that must be measured will commonly be in the atto-farad scale and require specialized instrumentation which we also describe here. The technique requires two calibration standards and the sample needs to have a portion of its surface flat and some minimum dimensions, but otherwise it can have an arbitrary shape. We used a simple model based on the method of images to explain the methodology and present experimental results with the proposed methodology."

International audience; We present the design of an innovating integrated planar structure adapted for intensity or phase measurements. It is based on the evanescent prism decoupling of the optical signal from a waveguide used as the sensing element. The device is formed by successive thin film sputtering deposition. A TiO2 crystalline layer forms the gas sensing element from which light is coupled out by a planar high refractive index prism. We experimentally validate the structure.