Marcelo Otero

A new algorithmic strategy which permits an unambiguous extraction of the effective surface mass density, loss tangent and characteristic impedance of the first coating layer in AT cut quartz crystal resonators (QCR) is introduced. A preliminary analysis of the propagating error in the determination of these effective physical parameters, due to practical errors in the admittance measuring system or due to a lack of precision in the admittance model for describing the real admittance of the sensor, is presented as well. This analysis makes clear the necessity of a standard indicating the specifications of the measuring system including the cell interface for an appropriate sensor characterization.

We describe quartz crystal electroacoustic admittance studies in thickness shear mode resonators loaded with self-assembled multilayers composed of alternate layers of glucose oxidase (GOx) and poly(allylamine) covalently attached to [Os(bpy)2ClPyCOH]- , (PAH-Os), deposited on a 3-mercaptopropanesulfonic acid (MPS)-modified gold on the quartz crystal. The complex acoustic impedance parameters, R(S) and X(LS) of a lumped-element Butterworth-Van Dyke (BVD) resonator have been determined for organized thin films of different thickness obtained by varying the number of enzyme layers, n, in (PAH-Os)n(GOx)n structures. The ellipsometric film thickness and mass for dry enzyme multilayer films and films in contact with water were evaluated, and the average film density was estimated. By combination of the estimated film thickness and density, the expression for the surface mechanical impedance of the lumped-element modified resonator (Granstaff and Martin model), and the liquid density and viscosity, we simulate the layer-by-layer film growth on the basis of the measured electroacoustic impedance. The complex impedance X(LS) and R(S) increase with film thickness and the enzyme films can be regarded as acoustically thin in the reduced state for films thinner than 600 nm. We have also measured electroacoustic parameters for PAH-Os/GOx self-assembled multilayers under electrochemical perturbation in a buffer electrolytic solution. The electrostatically self-assembled multilayers behaved as lossy viscoelastic films at 10 MHz with G'f and G''f on the order of 10(6) Pa. The films became viscoelastic upon oxidation to Os(III), resulting in an increase of R(S) and X(LS) in the oxidized state with the number of (PAH-Os)(GOx) bilayers due to film swelling and an increase in the shear moduli during oxidation.

ABSTRACT Here, we present and discuss a compartmental stochastic model for Aedes aegypti conceived as a math- ematical structure able to interpolate and extrapolate (predict) biological phenomena, and direct the attention to biological matters that need experimental elucidation. The model incorporates weather information in the form of daily temperatures and rain and pays particular attention to determining factors in temperate climates. Sufficiently large rains trigger egg hatching, which in turn leads to peaks in larval densities. Hatching is inhibited by the absence of bacteria (Gillett effect), a mechanism of rel- evance during the winter season and in seasons with isolated rains. The model also incorporates egg hatching independent of rains. Both egg hatching and larval development depend on the availability of food, which is modeled as bacteria produced at rates that depend on the temperature. Larval mortality and pupation rates depend on the larvae to bacteria ratio. The results of the model for egg laying activ- ity were compared with field records during a normal season and a drought. Both the model and the records indicate that the egg laying activity of Ae. aegypti is not zero during the drought and recovers quickly when normal weather is reestablished. We studied the sensitivity of the model to different sets of physiological parameters published for a few different local populations of this species, and found that there is an important sensitivity to local characteristics that will affect some predictions of the model. We emphasize that if the information is going to be used to evaluate control methods, the life cycle of the mosquito must be studied for the local strain under the local environmental conditions (including food). We showed that the adult populations produced by the model are insensitive to certain combinations of parameters and that this insensitivity is related to the variability reported for different strains obtained from closely located places. When the model is considered in a larger biological context, it indicates that some standard procedures performed to measure the life cycle of Ae. aegypti in the laboratory might have a determining influence in the results.

ABSTRACT This chapter describes recent advances of electrodes that are chemically modified with integrated biomolecules and molecular wires. Both hydrogels and self-assembled organized multilayer platforms are treated. Electrode reactions provide a switch between two phases of different electrical conductivity, that is, a metal electrode with electronic conductivity and an electrolyte with ionic conductivity. Chemically modified electrodes are electrode surfaces modified by suitable molecules or polymers with known specific interaction towards a target analyte molecule that enhance the specificity, and at the same time provide mechanisms for electron transfer to or from the underlying electrode. Theoretical aspects of the amperometric modified electrodes are evaluated and compared with the experimental results. Another relevant approach involving redox enzymes integrated on modified electrodes is presented for RNA and DNA detection. A different approach for integration of biomolecules on modified electrodes is possible through electropolymerization of conducting polymers. Among chemically modified electrodes, integrated chemical systems with a high degree of organization in supramolecular architectures have been developed with enzymes in ordered monolayers and multilayer systems using different assembling techniques: Langmuir-Blodgett, self-assembled monolayers, step-by-step electrostatic adsorption of alternate multilayers, antigen-antibody interaction, avidinbiotin interaction, surfactant films, electrostatic adsorption of hyperbranched polyelectrolytes, and redox-modified dendrimers.