This work demonstrates the significant fluorescence enhancement of thioflavin T (ThT) when binding to G-quadruplexes possessing hybrid structures by using UV–vis absorption spectra, fluorescence spectra, and T m experiments to confirm the binding events. ThT binding does not disturb native G-quadruplex structures preformed in Na+ and K+ solutions. The fluorescence enhancement is caused by the rotation restriction of benzothiazole (BZT) and dimethylaminobenzene (DMAB) rings in the ThT excited state upon its G-quadruplex binding. This molecular rotor mechanism as a means of fluorescence enhancement is confirmed using a nonrotor analogue of ThT. Hydroxylation and electrolyte experiments demonstrate that ThT stacks on the tetrad of the hybrid G-quadruplexes, whereas electrostatic forces contribute more to ThT binding for other G-quadruplex structures. By stacking on the tetrad, the ThT binding favors selective identification of DNA hybrid G-quadruplex structures with enhanced fluorescence and can serve as a conformation probe to monitor G-quadruplex structure conversion between hybrid and other structures. Using these properties, we developed a selective and label-free fluorescent K+ sensor with a detection limit of 1 mM for K+ in the presence of 100 mM Na+. The coexistence of other metal ions produces a fluorescence response comparable to K+ alone. We believe that ThT can potentially provide structure identification of hybrid G-quadruplexes and aid in the construction of G-quadruplex-based sensors.

Dual control: Hybrid silica–nanocrystal–organic dye superstructures comprising fluorescein isothiocyanate (FITC)‐doped silica cores, embedded CdTe quantum dots, and an outer silica shell display well‐resolved dual fluorescence emission. Multicolor encoding fluorescent probes are generated by modulating the fluorescence intensity ratio of the dual emission by a simple post‐encoding strategy (see picture).

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Highly blue fluorescence carbon dots were synthesized by one-step hydrothermal treatment of potatoes. The as-obtained C-dots have been applied to bioimaging of HeLa cells, which shows their excellent biocompatibility and low cytotoxicity. The results reveal that C-dots are promising for real cell imaging applications. In addition, the carbon dots can be utilized as a probe for sensing phosphate.

This work reports a scalable synthesis of water-dispersible fluorescent carbon nanodots based on the simple hydrothermal method (180 °C for 6 h) of kitchen wastes (grape peel for example). We discuss the feasibility of synthesis from kitchen wastes both experimentally and theoretically, and the as-prepared nanodots have high selectivity for Fe(3+) ions based on fluorescence quenching which is due to the complexes between nanodots and metal ions.