Development of an Electrochemical Biosensor for Rapid and Effective Detection of Pathogenic Escherichia coli in Licorice Extract

An aptamer-based electrochemical biosensor was successfully developed and applied in the rapid detection of pathogenic Escherichia coli (E. coli) in licorice extract. The thiolated capture probes were firstly immobilized on a gold electrode, and then the biotinylated aptamer probes for E. coli were introduced by hybridization with the capture probes. Due to the stronger interaction between the aptamer and the E. coli, a part of the biotinylated aptamers will dissociate from the capture probes in the presence of E. coli. The residual biotinylated aptamer probes can quantitatively bind with streptavidin-alkaline phosphatase. Subsequently, alpha-naphthyl phosphate substrate was catalytically hydrolyzed to generate electrochemical response, which could be recorded by a differential pulse voltammetry. The dependence of the peak current on the logarithm of E. coli concentration in the range from 5.0 x 10(2) colony forming units (CFU)/mL to 5.0 x 10(7) CFU/mL exhibited a linear trend with a detection limit of 80 CFU/mL. The relative standard deviation of 5 successive scans was 5.3%, 4.5% and 1.1% for 5.0 x 10(2), 5.0 x 10(5) and 5.0 x 10(7) CFU/mL E. coli, respectively. In the detection of the licorice extract samples, the results obtained from the proposed strategy and traditional culture counting method were close to each other, but the time consumption was only similar to 1/30 compared with the traditional method. These results demonstrate that the designed biosensor can be potentially utilized for rapid microbial examination in traditional Chinese medicine and relevant fields.