A selective and sensitive fluorescent aptasensor for detection of kanamycin based on catalytic recycling activity of exonuclease III and gold nanoparticles

Kanamycin is an aminoglycoside antibiotic used in human and veterinary medicine. Sensitive and selective methods to detect kanamycin residues for food safety and clinical diagnosis are of great interest. In this study a fluorescent aptasensor was designed to detect kanamycin based on exonuclease III activity (Exo III), gold nanoparticles (AuNPs) and FAM-Labeled complimentary strand of aptamer (CS). In the absence of kanamycin, aptamer binds to its CS to form a double-stranded DNA (dsDNA) with 3′-overhang end at aptamer and 3′-blunt end at CS. The formed dsDNA leaves the surface of AuNPs. Upon addition of Exo III, aptamer is recycled from dsDNA and the cycle goes on, leading to a very strong fluorescence emission. In the presence of kanamycin, aptamer binds to its target and CS remains on the surface of AuNPs, resulting in a weak fluorescence emission. The designed aptasensor showed high selectivity toward aminoglycoside antibiotics, including kanamycin and gentamicin, with a limit of detection (LOD) as low as 321 pM for kanamycin. This aptasensor was successfully used to detect kanamycin in milk and serum.