Aptamer based E-coli detection in waste waters by portable optical biosensor system

Here, we are presenting a portable optical-fiber based E-coli biosensor system via using an aptamer which can specifically distinguish the E-coliO157:H7 strain from other pathogens. The detection procedure is based on competitive mode detection. A known concentration of fluorescently labeled aptamer and E-coli were mixed and after a certain time filtered. The rest of free aptamers pumped to the system. With hybridization of the free aptamers and their optical-fiber surface immobilized complementary DNA (probe-DNA), we can monitor the fluorescent signal which is proportional to the amount of the E-coli. Thus, we can detect the E-coli without pumping it directly onto the sensing surface and we could protect the optical fiber surface from the aggregation of target bacteria or other pollutants that may come from real waste water samples. After optimization experiments, the linear detection range was determined from 10 to 10⁵cfu/ml with higher than 0.95 R² value. The system was regenerated successfully with 5%SDS solution over 100 times without any significant deterioration of the sensor performance. The developed system had high specificity towards E-coli (less than 20% signal with other pathogens) and it could be applied to real waste water samples with 81 to 93% recovery and 4 to 21% cv values (n=3).