Andrea Cambiaso

Modelling and simulation of a diffusion limited glucose biosensor

Abstract A mathematical model for an amperometric enzyme sensor is described as a tool to design glucose biosensors, operating in a diffusion limited regimen. This kind of enzyme electrode really comprises a miniature reactor system rather than a classical form of transducer. The equations constituting the model are obtained taking into account both the diffusion process and the enzymatic reaction in the general (not pseudo-stationary) case. The model is numerically integrated in order to obtain the time behaviour of the electrode current. The Michaelis-Menten apparent constant ( K m app ) of the whole system is obtained from the simulation and compared with that computed for a bulk system.

Computer simulations of the responses of passive and active integrated microbiosensors to cell activity

Abstract Detection of cell activity via solid-state microtransducers is a rapidly growing research area. In order to design and test microdevices optimized for specific biological applications, ranging from cell electrophysiology to cell pharmacology, there is an increasing need for systematic computer simulations. As specific examples, the performances of noble-metal microelectrodes, ion-sensitive field-effect transistors (ISFETs) and light-addressable potentiometric sensors (LAPSs) are analysed and discussed by means of computer simulations based on their equivalent circuits.

An H+-FET-based system for on-line detection of microorganisms in waters

Abstract A flow-through system for on-line detection of microorganisms in waters is presented. A Si3N4 ISFET with integrated signal-conditioning electronics, expressly designed for this application, is employed as an H+ sensor. The article describes the system principles, the transducer architecture, a preliminary characterization of the developed sensor chip, and preliminary measurements performed in the presence of microorganisms.

Use of surfactant-modified cellulose acetate for a high-linearity and pH-resistant glucose electrode

Cellulose acetate modified by incorporation of the surfactant Tween-80 is used as an outer membrane in a glucose oxidase based enzyme electrode. The membrane acts as a glucose diffusion restricting barrier, allowing extension of response linearity to 0.4 mol I–1, with sensitivity of 2.5 nA l mmol–1. Response times of <100 s can be achieved by use of initial slope (I/t) measurements. The membrane also provides protection for the enzyme from low pH deactivation for at least 10 min, allowing for re-use in low-pH samples such as citrus fruit.

Detection of cell activity via ISFET devices: Modelling and computer simulations

Abstract The characterization of the electrochemical behaviour of several distinct excitable cells in a population of cultured cells is a key point for the understanding of the development and stabilization of organized networks of cells. This knowledge represents a fundamental step for both basic research areas (neural computation) and clinical applications (functional prostheses). In this paper, we propose the use of ISFET devices for detecting the electrochemical activity of excitable cells cultured in vitro. After a short review of the various kinds of microelectrodes described in the literature, the paper will be focused on modelling and computer simulations of the responses of ISFET devices to cellular activity, under various approximations. An ad hoc modification to the simulation program SPICE is used in order to extend the simulation of integrated devices behaviour to the recording of the activity of a single cell. The values of the simulated drain currents suggest the feasibility of the proposed approach.

Experimental and theoretical surface acoustic wave analysis of thin‐film lipid multilayers

The leaky surface acoustic wave (LSAW) velocity of thin films of lipids on a glass substrate has been investigated, using a reflection acoustic microscope at a frequency of 1 GHz. Multilayers of ω‐tricosenoic acid (28–220 nm in depth), collected with the Langmuir–Blodgett technique have been deposited on silanized glass. V(z) curves have been measured, and the LSAW velocity has been calculated from them. The results point out that the velocity decreases linearly as the lipid‐layer thickness increases. A theory is also presented, which gives a linear dependence between the LSAW velocity and the layer thickness.

An array of H+ FETs for space-resolved electrochemical measurements in microenvironments

Abstract This paper deals with pH measurements based on a 2×2 array of H + -sensitive FETs. The experimental apparatus, including the data-acquisition system, is described and results are reported, which show the effectiveness of the approach in monitoring the evolution of electrochemical phenomena in semi-solid media. Possible future appliclations are briefly discussed.

Acoustical Microscopy Applications for Living Cells Investigations

Several authors 1,2,3 have shown that scanning reflection acoustic microscopy operating in the GHz range is a powerful tool for observing living cells adhering to a substrate in culture; the related procedure is somewhat similar to reflection contrast optical microscopy 4. Acoustic images contain information relevant to cell topography and cell attachment sites. Computer processing of digital acoustic images results in a great enhancement of these two features. Moreover, further information can be gained by comparing experimental data with those obtained by modelling and computer simulating the whole process of acoustic image formation. Such a model will be described in the next section. This description will be followed by specific examples of cell image processing and by comparisons between experimental and computer simulation results.

On the boundary conditions for acoustic waves at a solid–solid or fluid–solid interface

The boundary conditions at a solid–solid interface are analyzed in the transition from a solid–solid interface to a liquid–solid interface. This transition is mathematically performed by means of a limit process, that is, by letting the Lame shear coefficient of one medium tend to zero. The behavior of the reflection coefficient for transverse waves in the transition can be derived from the boundary conditions. In particular, a linear shear‐velocity dependence of its magnitude has been found. As a consequence, the magnitudes of the other reflection and transmission coefficients are also linear. Numerical calculations of the coefficients have been performed. The results confirm the theoretical analysis and point out some critical angles where the linear trend does not occur.

Digital Acoustic Microscopy of Cell-Substrate Attachment: Experiments and Model Predictions

Cell adhesion is an important component of numerous biological responses including growth, differentiation, and motility. In many cultured cell lines, immunofluorescence studies have verified the co-localization of the fibronectin receptors talin and vinculin at specific cell-substrate attachment sites, which have initially been detected by interference reflection microscopy (IRM) and called “focal contacts” (Izzard and Lochner, 1976).