A G-triplex-based label-free fluorescence switching platform for the specific recognition of chromium species

A HtG3 fluorescent switching sensing platform for Cr 3+ qualitative identification based on binding-induced G3 structural breaking and COR fluorescence recovery. • A G-triplex (HtG3) fluorescence switch-on sensor was constructed for metal-ion (Cr 3+ ) qualitative identification. • A fluorescence label-free method based on the competitive binding of COR and Cr 3+ with HtG3. • The structural flexibility and tunability of HtG3 contributed to its better performance on Cr 3+ responsing. • This report extended the practical application of G3 in the sensing fields. G-triplex (G3), as an intermediate of G-quardruplex (G4), is a typical non-classical DNA topology with three G-tracts, formed by folding guanine-riched DNA sequences. The flexibility and tunability of G3-folding structures can provide a versatile platform for analytes sensing. However, current researches about G3s on sensing applications, especially on metal ion sensing, are relatively rare. Herein, we first develop a label-free fluorescence switch-on sensing platform based on the G-triplex topology (HtG3) for the specific qualitative identification of chromium species. Coralyne (COR), a molecule probe whose fluorescence can be inhibited by HtG3, is employed to monitor the Cr 3+ binding events with the principle that Cr 3+ could break the parallel HtG3-folding structure to result in COR releasing from HtG3 and its fluorescence recovery. Furthermore, this HtG3 sensing platform we constructed also can be used to indirectly identify CrO 4 2- through reducing it to Cr 3+ with ascorbic acid (AA). Our work will extend the practical application of G3 as a biosensor and inspire wide interests in exploring more non-classical DNA structures.