Structure-switching aptamer triggering signal amplification strategy for tobramycin detection based on hybridization chain reaction and fluorescence synergism

Based on hybridization chain reaction (HCR) and fluorescence synergism, a novel aptasensor for tobramycin was successfully constructed. Tobramycin competed with cDNA-FAM to bind aptamers immobilized on magnetic beads. After magnetic separation, the released cDNA-FAM acted as initiator to trigger HCR amplification, thus the fluorescence was significantly enhanced due to binding of SYBR Green I (SGI) to the formed long doublestranded DNA and the synergistic fluorescence of FAM. In the absence of tobramycin, the initiator was magnetically separated and no HCR occurred, more importantly, graphene oxide can quench the fluorescence of excessive hairpins/SGI and cDNA-FAM, so almost no background signal was detected. This aptasensor can monitor tobramycin in the range of 0.3-50 mu M with low detection limit of 17.37 nM. Due to the potential generality of structure-switching aptamers and effectiveness of fluorescence synergism, this enzyme-free amplification strategy can be extended to other applications by rational design of nucleic acid sequences.