Exonuclease I-assisted fluorescence aptasensor for tetrodotoxin

A fluorescence aptasensor for the highly specific and sensitive determination of tetrodotoxin was established with tetrodotoxin-aptamer as the recognition unit, berberine as the signal reporter and exonuclease I as the elimination agent for the background. Berberine has a weak fluorescence emission at 540 nm, and it can form the tetrodotoxin-aptamer/berberine complex, resulted in an increased fluorescence. After introducing exonuclease I, it can degrade the single strand oligonucleotides of tetrodotoxin-aptamer into the single nucleotide in the absence of tetrodotoxin, which lead to dramatic fluorescence quenching, and reduce the background signal of sensing system. Once tetrodotoxin is in the presence, tetrodotoxin-aptamer is converted into the stable neck ring conformation, which resists the degradation of exonuclease I and provides a more rigid micro-environment for the excited state of berberine, and then the strong fluorescence is observed. Based on the above properties, an ultrasensitive label-free fluorescence aptasensor for tetrodotoxin is established. The fluorescence aptasensor shows good analytical performance with the linear increase of fluorescence intensity at the tetrodotoxin concentration from 0.030 nM to 6.0 x 10(3) nM. The detection limit of 11.0 pM is much lower than that of other reported sensor methods.