An exonuclease I-assisted quencher-free 2-aminopurine aptasensor based on a multipath paper-based device for ultrasensitive detection of kanamycin

Abstract

A quencher-free multipath microfluidic paper-based analytical device (µPAD) was constructed for ultrasensitive detection of kanamycin based on exonuclease I (Exo I)-assisted signal enhancement of 2-aminopurine (2-AP). Here, Exo I, a single-stranded DNA-specific nuclease, was introduced to fully liberate 2-AP mononucleotides to greatly enhance biosensing sensitivity. 2-AP, a fluorescent adenine analogue embedded in single-stranded DNA (ssDNA), was employed as the detection signal source. The fluorescence of 2-AP is strong in the mononucleotide state, while it can have low fluorescence and even no fluorescence in ssDNA and dsDNA, respectively. The 2-AP fluorescence probe included 2-AP DNA and kanamycin aptamer. When kanamycin was present, binding occurred between kanamycin and the aptamer, leading to ssDNA, which was further digested by Exo I. In this case, free 2-AP mononucleotides were liberated, indicating strong fluorescence. In addition, the captured kanamycin was released for binding with the new aptamer, which resulted in the formation of a binding-hydrolysis-release cycle with the aid of Exo I. Under optimal conditions, this µPAD exhibited sensitive and multipath detection of kanamycin at concentrations as low as 1.26 × 10−14 M with a wide range of 10−13–10−7 M. Furthermore, satisfactory results were achieved for analysing spiked kanamycin in milk and honey samples. This strategy is a very promising tool for monitoring antibiotics and evaluating the safety of animal-derived foods.