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Biosensors based on electronic conducting polymers appear particularly well suited to the requirements of modern biological analysis--multi-parametric assays, high information density, and miniaturization. We describe a new methodology for the preparation of addressed DNA matrices. The process includes an electrochemically directed copolymerization of pyrrole and oligonucleotides bearing on their 5' end a pyrrole moiety. The resulting polymer film deposited on the addressed electrode consists of pyrrole chains bearing covalently linked oligonucleotides (ODN). An oligonucleotide array was constructed on a silicon device bearing a matrix of 48 addressable 50 x 50 microns gold microelectrodes. This technology was successfully applied to the genotyping of hepatitis C virus in blood samples. Fluorescence detection results show good sensitivity and a high degree of spatial resolution. In addition, gravimetric studies carried out by the quartz crystal microbalance technique provide quantitative data on the amount of surface-immobilized species. In the case of ODN, it allows discrimination between hybridization and nonspecific adsorption. The need for versatile processes for the immobilization of biological species on surfaces led us to extend our methodology. A biotinylated surface was obtained by coelectropolymerization of pyrrole and biotin-pyrrole monomers. The efficiency for recognition (and consequently immobilization) of R-phycoerythrin-avidin was demonstrated by fluorescence detection. Copolymerization of decreasing ratios of pyrrole-biotin over pyrrole allowed us to obtain a decreasing scale of fluorescence.

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In this work, the electrochemical determination of glutathione (GSH) using β‐cyclodextrin (β‐CD) modified carbon electrodes was carried out. Different methodologies were used to modify the electrodes. In the first part of this paper, we analyze and compare the ability of the electrodes to determine GSH using the different β‐CD‐modified electrodes and cyclic voltammetry. We found that the carbon paste electrode modified by potential sweeping was the best electrode for GSH determination; in addition, we found that an inclusion complex formed between β‐CD deposited on the electrode surface and GSH. The formation constant for this complex was 2498.54 M−1 at 25 °C. Furthermore, we have also calculated thermodynamic parameters for the formation of the inclusion complex. In the second part of this paper, we analyze the effect of sweep rate and pH on the determination of GSH. The best results were obtained at a rate of 50 mV s−1 and a pH of 2.2. The β‐CD‐modified carbon paste electrode exhibits a linear response in a concentration range of 20 to 157 µM with a sensitivity of 1083.65 µA mM−1cm−2 and a detection limit of 3.92 µM. Finally, the electrode was used to determine the GSH concentration in Eichhornia crassipes root extract, and the concentration determination accuracy was validated by a well‐known spectroscopic method.

The sorption of Cd2+ onto nonliving Typha latifolia roots was investigated using carbon paste electrodes modified with a powder formed from the ground dried root. The equilibria, kinetics, and proton exchange processes associated with the biosorption process were determined. Cd2+ was found to accumulate on the root‐modified electrode under open circuit conditions, and the electrode was transferred to an electrochemical cell for square wave anodic stripping voltammetry measurements. The measured currents were proportional to the amount of Cd2+ adsorbed onto the root, which permitted the biosorption process to be measured as a function of cadmium solution concentration, time, and pH. The equilibrium values were fit to the Langmuir or Freundlich equations, and that the Langmuir isotherm model was found to provide a better fit than the Freundlich model. The pH‐dependent sorption curves showed that the accumulation of cadmium proceeded with proton exchange, and each adsorbed cadmium ion resulted in expulsion of two protons. The sorption kinetics were studied, the data obtained were fit to two models: a pseudo‐second‐order model and an intraparticle diffusion model. The pseudo‐second‐order model provided the best description of the bioadsorption data. These results indicated that these methodologies have clear advantages over existing methods, because the amount of reagents and sorbent used for the experiments are much less than are required for batch experiments.

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