Microbial safety of drinking water constitutes a major concern in countries at all levels of economic development. Thus, rapid, sensitive and cost effective methods of pathogenic bacteria detection, like common like Escherichia coli O157:H7, which can cause important diseases, is highly required. In this work an impedimetric transducer modified with E. coli specific aptamer is studied. To enhance the sensitivity a three-dimensional interdigitated electrode array (3D-IDEA) impedimetric transducer in which the electrodes separated by insulating barriers was used. In this sensor, chemical reactions at the surface of the barrier provoke electrical charge redistribution which causes changes in surface conductivity. A DNA aptamer that recognizes specifically the outer membrane proteins of the E. coli O157:H7 was selected as the biorecognition moiety. Here we report a novel label-free impedance aptasensor for detection and quantification of pathogenic E. coli O157:H7 with a low detection limit, good selectivity and short detection times. The developed sensor shows a linear response (R 2 =0.977), proportional to the logarithm of bacterial concentration present in the sample, with a limit of detection (LOD) of about 10 2 cfu•mL-1. No response was registered when the aptasensor was incubated with other bacterial strains, confirming the selectivity of suggested method. Additionally, the possibility of the sensor regeneration is shown, so that the detection may be performed several times with the same sensor. Moreover, suitability of the aptasensor for bacteria detection in real samples was demonstrated with a new approach involving bacteria pre-concentration.
Current output of microbial fuel cells (MFCs) depends on a number of engineering variables mainly related to the design of the fuel cell reactor and the materials used. In most cases the engineering of MFCs relies on the premise that for a constant biomass, current output correlates well with the metabolic activity of the cells. In this study we analyze to what extent, MFC output is also affected by the mode of operation, emphasizing how discontinuous operation can affect temporal patterns of current output. The experimental work has been carried out with Shewanella oneidensis MR-1, grown in conventional two-chamber MFCs subject to periodic interruptions of the external circuit. Our results indicate that after closure of the external circuit, current intensity shows a peak that decays back to basal values. The result suggests that the MFC has the ability to store charge during open circuit situations. Further studies using chronoamperometric analyses were carried out using isolated biofilms of Shewanella oneidensis MR-1 developed in a MFC and placed in an electrochemistry chamber in the presence of an electron donor. The results of these studies indicate that the amount of excess current over the basal level released by the biofilm after periods of circuit disconnection is proportional to the duration of the disconnection period up to a maximum of approximately 60 min. The results indicate that biofilms of Shewanella oneidensis MR-1 have the ability to store charge when oxidizing organic substrates in the absence of an external acceptor.
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