Evanescent wave aptasensor for continuous and online aminoglycoside antibiotics detection based on target binding facilitated fluorescence quenching

The biosensors capable for on-site continuous and online monitoring of pollutants in environment are highly desired due to their practical importance and convenience. The group specific detection of pollutants is especially attractive due to the diversity of environmental pollutants. Here we devise an evanescent wave aptasensor based on target binding facilitated fluorescence quenching (FQ-EWA) for the online continuous and group-specific detection of aminoglycoside antibiotics (AMGAs). In FQ-EWA, a fluorophore labeled DNA aptamer selected against kanamycin was used for both the target recognition in solution and signal transduction on optical fiber of EWA. The aptamers form multiple-strand complex (M-Apt) in the absence of AMGAs. The binding between AMGA and the aptamer disrupts M-Apt and leads to the formation of AMGA -aptamer complex (AMGA-Apt). The photo-induced electron transfer between the fluorophore and AMGA partially quenches the fluorescence of AMGA-Apt. The structure-selective absorption of AMGA-Apt over M-Apt on the graphene oxide further quenches the fluorescence of AMGA-Apt. Meanwhile, the unbound aptamers in solution assemble with the unlabeled aptamers immobilized on the fiber to form M-Apt. The amount of M-Apt on the fiber is inversely proportional to the concentration of AMGAs, enabling the signal-off detection of AMGAs from 200 nM to 200 μM with a detection limit of 26 nM. The whole detection process is carried out in an online mode without any offline operation, providing a great benefit for system automation and miniaturization. FQ-EWA also shows great surface regeneration capability and enables the continuous detection more than 60 times.