Due to the high abundance of K+ in environments and K+-induced high stability of G-quadruplex (G4), developing a selective G4-based fluorescent sensor for other metal ions with K+ tolerance is a great challenge. Herein, we found that even in the presence of 15000-fold excess of K+, Ba2+ exhibits a highly specific binding with a human telomeric G4 (htG4) in comparison with other G4-binding metal ions such as Pb2+ and Sr2+. This specific binding event can be recognized by a natural fluorophore of hypericin with a lighting-up fluorescence response. Interestingly, inverting the polarity of the most 3' G in htG4 can sensitize the Ba2+ response with the retaining Ba2+ specificity and K+ tolerance. This polarity inversion of htG4 causes a G4 conformation change in K+ and the polarity-inverted htG4 tends to favorably dimerize in response to the Ba2+ specific binding. To our knowledge, this is the first report that polarity inversion of G4 can be applied to construct a selective metal sensor with K+ tolerance. Our findings will open a new way to conveniently regulate the G4 conformation and stability by polarity inversion towards developing high-performance sensors.
Keywords: Fluorescence; G-quadruplex; Hypericin; K(+) tolerance; Metal sensor; Polarity inversion.
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