Marcela Ovalle

Leptospirillum ferrooxidans based Fe2+ sensor.

A novel electrochemical biosensor integrating the strictly autotrophic bacterial strain Leptospirillum ferrooxidans as a recognition element and a Clark type oxygen probe as a transducer was designed, metrologically and analytically characterized and applied for the specific Fe(2+) determination. The bacterial Fe(2+) oxidation involves O(2) consumption, thus the quantification was performed registering the decrease of the oxygen reduction current. The limit of detection was found to be 2.4 micromol L(-1) and the sensitivity of the determinations-3.94 nAL micromol(-1). The response time of the biosensor is 18s for Fe(2+) concentrations of 10(-5) to 10(-4) mol L(-1). The biosensor was applied as well for the indirect determination of Fe(2+) oxidizing species such as Cr(2)O(7)(2-), reaching a sensitivity of 2.47 nAL micromol(-1). The transducer characteristics were evaluated and optimized to obtain short response time and high sensitivity. The analytical performances of the biosensor subject of the present work were found to be similar to that of the At. ferrooxidans based one developed by the authors earlier, avoiding however the sulfur compounds interference, because of the substrate specificity of the applied bacterial strain.

Electrochemical Study on the Kinetic Behavior of the Immobilized Acetylcholinesterase

A mathematical model for the behavior of amperometric stationary enzymes electrodes, applying digital simulation, has been developed by Mell and Maloy (16). The steady-state current response has been predicted, respectively, in the limits of catalysis and diffusion control. However, the lack of well defined boundary conditions to describe the mass transport restrains the application of the stationary enzymes electrodes to evaluate the kinetic and diffusion properties of the immobilized enzymes systems. A reliable mathematical model predicting the kinetic parameters of the immobilized enzymes has been proposed by Shu and Wilson (17), taking advantage of the well defined diffusion behavior of the rotating disk electrode. It has been demonstrated that the steady-state current under mass transport limiting conditions at low substrate concentrations could be expressed by the equation:

Electrochemical Biosensors for Food Quality Control

The electrochemical biosensors are analytical devices designed by coupling biological recognition elements and electrochemical transducers. The transducer converts the analytical signal produced as a result of the biochemical and electrochemical interactions into measurable electrical one (Thevenot et al., 1999). The electrochemical biosensors are self-contained, simple to handle, and able to provide specific, sensitive, accurate and cost-effective in situ and on line measurements in real time, without or with a minimum sample preparation. Because of these advantages over the conventional analytical methods, they are well suited for the detection of a large spectrum of compounds, entering food and subjects of analytical control. The present work is intended to demonstrate the applicability of the electrochemical biosensors for arsenic determination in beverages.