G-triplex (G3) has been recognized as a popular intermediate during the folding of G-quadruplex (G4). This has raised interest to anticipate the ultimate formation of G3 by shortening the G4-forming oligonucleotides with the remaining three G-tracts. Some G3 structures have been validated and their stability has been found to be affected by the loop sequences similar to G4s. In this work, however, we first found that an intermolecular parallel G4 structure was preferred in K+ for the oligonucleotide 5′-TGGGTAGGGCGGG-3′ (DZ3) containing only three G-tracts. We screened auramine O (AO) as the appropriate fluorophore with a molecular rotor feature to target this G4 structure. AO bound with DZ3 in a 1 : 4 ratio, as confirmed by isothermal titration calorimetry experiments, suggesting the formation of a tetramolecular G4 structure (4erG4). The excimer emission from the labelled pyrene and the DNA melting behavior at various pHs in the presence of Ag+ proved the formation of the 4erG4 structure rather than the prevalent intramolecular G3 folding. This work demonstrates that one should be cautious while putatively predicting a G3 structure from an oligonucleotide containing three G-tracts.
Molecular logic gates possess great potential for multi-parameter sensing, intelligent diagnostics, and molecular computation. One remaining challenge was to construct novel new logic gates based on smart nanomaterials and functional nucleic acids. In this study, two novel new logic devices were constructed utilizing ion-tuned DNA/copper nanoclusters (CuNCs), which were dual-responsive to K + and H + . By merely altering the arrangement of a specific sequence of the DNA stabilizer, two kinds of well-designed DNA probes permuted by G-tracts, C-tracts, and poly-T were designed as the building blocks of the logic device. Poly-T acted as the template for the formation of CuNCs. G-tracts and C-tracts enabled a K + /H + -responsive conformational switch into G-quadruplex (G4) and i-motif structures. Such a conformational conversion significantly modulated the fluorescence behaviors of CuNCs. This study discovered the unique interaction between the logic device and graphene oxide (GO). The logic devices were implemented for the analysis of K + and microRNA.
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