Novel impedimetric aptasensor for label-free detection of Escherichia coli O157:H7

© 2017 Elsevier B.V. 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 Escherichia coli O157:H7, which can cause important diseases, are 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 are 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 the surface conductivity. A DNA aptamer, which 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 impedimetric aptasensor for detection and quantification of pathogenic E. coli O157:H7 with a low detection limit, good selectivity and short detection time. The developed sensor shows a linear response (R2 = 0.977), proportional to the logarithm of bacterial concentration present in the sample, with the limit of detection (LOD) of about 102 cfu mL−1. No response of the aptasensor was registered in the presence of other bacterial strains (E. coli k12, Salmonella typhimurium, Staphylococcus aureus), which confirms the selectivity of the suggested detection method. Additionally, the methodology of the aptasensor regeneration was developed, 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.