Electrochemical Detection of Growth of Escherichia coli with sensors based on platinum electrodes S. Pavoni 1 , H. Cobas 1 , R. Contreras 2 , Á. Zayas 2 , E. Álvarez 2 1 Centro de Investigaciones en Microelectrónica., km 8½ Antigua Carretera de Vento. Capdevila.Boyeros, Ciudad de La Habana, Cuba. P.O.Box 8016. 2 Centro Nacional de Investigaciones Científicas, Diagnóstico Microbiológico – CNIC, Ave. 25 esq. 158, No. 15202, Cubanacán, Playa, Ciudad Habana, Cuba. *Corresponding author: S. Pavoni, (537) 2663047, sonnia.pavoni@electrica.cujae.edu.cu Abstract The experimental characterization and comparison of two microelectrochemical sensors based on platinum electrodes fabricated on thin-film and thick-film technologies, for the detection of Escherichia coli growth are described. Experimental measurements of cyclic voltammetry and linear sweep voltammetry were made by placing one drop of inoculated culture medium onto the sensor area. Similar voltammetric behaviours were obtained with the two sensors. Voltammograms with anodic peak current were observed for samples with concentration higher than a threshold of about 3E+8 cell/ml. A linear relationship was established between logarithms of initial inoculum size and the time elapsed to the first anodic peak current was detected. Keywords: bacteria, sensor, thin-film sensor, thick-film sensor, voltammetry. Introduction The diagnosis of infectious diseases is one of the most important purposes of microbiology laboratories. In the group of bacteria, Escherichia coli is one that shows more interest. The presence of this microorganism in the drinkable water or in food could indicated faecal pollution and provoke diseases in the human been. One way to detect infections is by measuring the growing of the bacterial population. During this process the bacterial culture composition undergoes modifications and changes in electrical parameters of the system take place. Electrochemical methods have been applied to microbial cultures [1, 2]. Since 1978, almost all electrochemical methods reported for microbiological applications have been used mainly impedimetric and conductimetric approaches [3-5]. These methods are based on the measure of components of impedance that appears between two electrodes submerged into a container with the inoculated culture. Potentiometric approaches have also been reported. Wilkins and co-workers [6, 7] reported the detection of the increase in voltage between two electrodes due to the hydrogen evolution of the test organisms. In the direct application of the voltammetric techniques to cells culture, Matsunaga and co- workers were leaders [8]. In their assays of cyclic voltammetry with yeast and bacteria solutions, they found oxidative peak currents in potential of 0,7 V vs. SCE. The use of this technique has also been reported to study fungus [9] and for the classification of gram-negative and gram-positive bacteria [10]. Of course, the successfully of all electrochemically techniques depends on the characteristics of the used electrodes. The progress of fabrication technologies for electronic devices has been useful for the construction of planar microelectrodes for microelectrochemical sensors. Recently Pavoni et al. reported the use of thin-film planar microsensor to voltammetric analysis of microbiological cultures [11]. Anodic peak currents were observed for samples leaving lag growth phase. In this work the experimental characterization and comparison of two microelectrochemical sensors based on platinum electrodes fabricated on thin- film and thick-film technologies, for the detection of growth of microvolumes of cultures of Escherichia coli are presented. This investigation is a contribution to the development of sensors devices and measuring procedures for microbiological diagnosis applications.