Target-switched triplex nanotweezer and synergic fluorophore translocation for highly selective melamine assay

摘要： This paper describes a triplex DNA nanotweezer to specifically capture melamine (MEL). The triplex-forming oligonucleotide (TFO) arm can be switched from the open state to the closed state once MEL binds to the abasic site (AP site) in duplex via the bifacial hydrogen bonding with thymines. Following this nanotweezer operation, the AP site-bound fluorophore is translocated to the terminal triplet to subsequently light up the nanotweezer. The TFO arm is found to be pivotal for permitting the AP site binding. The synergic processes of target competition and fluorophore translocation support a high selectivity for the MEL assay even against the inherent adenosine and the MEL hydrolysis products. Chelerythrine is employed as the fluorescent probe. The detection limit of MEL was estimated to be about 140 nM assuming a signal-to-noise ratio of 3. It was applied to the determination of MEL in spiked milk samples without any separation procedure. Conceivably, this method opens a new avenue towards highly selective triplex-based sensors by making use of other commercially available DNA modifications for recognizing other analytes.