A signal-on electrochemical aptasensor for highly sensitive and specific detection of kanamycin based on target-induced signaling probe shifting mechanism

An electrochemical displacement-based aptasensor was developed for the detection of kanamycin-a (KMY-A). Based on the target-induced signaling probe shifting mechanism, this aptasensor shows a "signal on" change with a simple 3-probe structure. One no-thiolated capture probe and one thiolated assistant probe are attached onto the Au electrode surface in a short duplex state, and one methylene blue (MB)-labelled signaling probe is free in the detection solution. Before adding the KMY-A, a very small background signal is obtained with low efficient electron transfer because of the MB labels on the signaling probe far from the electrode surface. After adding the KMY-A, the more stable capture probe/KMY-A complex formed between the capture probe and the KMY-A undoes the former short duplex to release the assistant probe, which induces the formation of another assistant probe/signaling probe duplex. This structure change can shift the MB labels close to the electrode surface with much higher efficient electron transfer, thereby leading to a big detection signal. Under the optimized fabrication and detection conditions, the sensor features a high sensitivity for KMY-A with the detection limit of 3.3 pM and a fast sensing speed with the response time of similar to 9 min. In addition, it is worth mentioning that the target discrimination ability of sensor can be improved through using longer assistant probe to strengthen the hybridization force between the capture probe and the assistant probe, which is helpful for establishing the special detection system with high specificity requirement.