Pathogenic Escherichia coli (E. coli) widely exist in Nature and have always been a serious threat to the human health. Conventional colony forming units counting-based methods are quite time consuming and not fit for rapid detection for E. coli. Therefore, novel strategies for improving detection efficiency and sensitivity are in great demand. Aptamers have been widely used in various sensors due to their extremely high affinity and specificity. Successful applications of aptamers have been found in the rapid detection of pathogenic E. coli. Herein, we present the latest advances in screening of aptamers for E. coli, and review the preparation and application of aptamer-based biosensors in rapid detection of E. coli. Furthermore, the problems and new trends in these aptamer-based biosensors for rapid detection of pathogenic microorganism are also discussed.
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, α-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 × 10 2 colony forming units (CFU)/mL to 5.0 × 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 × 10 2 , 5.0 × 10 5 and 5.0 × 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~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. Appl. Sci. 2019, 9, 295 2 of 15 bacterial colony morphology, color change, and biochemical reactions for quantitative detection. This detection method is economical and relatively simple to operate, but the detection time is generally 48-72 h or even longer, which cannot meet the needs for rapid detection. As an effective molecular biological detection technology, polymerase chain reaction (PCR) and the derived technology of PCR has been widely used in detecting E. coli [4,7]. PCR is based on the principle that DNA templates can denature at high temperatures, reactivate and extend (one cycle) at low temperatures by using appropriate DNA polymerase and primers. As the template DNA amplification product increases exponentially, increasing the number of cycles can magnify the specified DNA sequence by several million-fold in a short time, which greatly improves detection sensitivity [8]. However, PCR technology is costly and prone to produce false negatives [9], which limits the extensive application of PCR. In addition, enzyme-linked immunosorbent assay (ELISA), as a common immunological detection technology, has also been used in bacterial test [5,10]. ELISA technology undergoes a color change by the catalysis of the enzyme in the specific recognition process. Owing to the immune activity between antigen and antibody, ELISA method has superior specificity, high sensitivity and short detection time, and has been used in detection of different subtypes of E. col...
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