A G-quadruplex-selective luminescent iridium(III) complex and its application by long lifetime

G-Quadruplex-Based Fluorescent Turn-On Ligands and Aptamers: From Development to Applications

Guanine (G)-quadruplexes (G4s) are unique nucleic acid structures that are formed by stacked G-tetrads in G-rich DNA or RNA sequences. G4s have been reported to play significant roles in various cellular events in both macro- and micro-organisms. The identification and characterization of G4s can help to understand their different biological roles and potential applications in diagnosis and therapy. In addition to biophysical and biochemical methods to interrogate G4 formation, G4 fluorescent turn-on ligands can be used to target and visualize G4 formation both in vitro and in cells. Here, we review several representative classes of G4 fluorescent turn-on ligands in terms of their interaction mechanism and application perspectives. Interestingly, G4 structures are commonly identified in DNA and RNA aptamers against targets that include proteins and small molecules, which can be utilized as G4 tools for diverse applications. We therefore also summarize the recent development of G4-containing aptamers and highlight their applications in biosensing, bioimaging, and therapy. Moreover, we discuss the current challenges and future perspectives of G4 fluorescent turn-on ligands and G4-containing aptamers.

Al3+ enhanced room temperature phosphorescence of Pd-porphyrin resided in hybrid supramolecular gels and used for detection of trace Hg2+ ions

Micelle-hybridized supramolecular hydrogels were constructed through the self-assembly of gelator N,N-dibenzoyl-L-cystine (DBC) and micelles formed from a Gemini surfactant (G_12-8-12). A phosphor, palladium meso-tetra (4-carboxyphenyl) porphyrin (Pd-TCPP) and Al³⁺ ions were loaded within the hybrid system. Interestingly, the room temperature phosphorescence (RTP) of Pd-TCPP can be efficiently enhanced and modulated by the concentration of Al³⁺ ions. The enhancement effect could be attributed to the interactions between Al³⁺ and DBC as well as porphyrin, which verified by ¹H NMR analysis. The study of transmission electron microscopy and scanning electron microscopy indicated that a more compact 3D network structure of the gel system was formed upon the addition of Al³⁺. In addition, measurement of critical micelle concentration indicated that Al³⁺ ions increase the surface activity of G_12-8-12 to promote micelle formation, thereby increasing the dispersion of Pd-TCPP in the hybrid gels. Based on the synergistic effect of these results, the non-radiative transition of Pd-TCPP was efficiently inhibited, resulting in highly efficient RTP. Furthermore, the enhanced RTP of as-prepared gel system shows potential application to detect trace Hg²⁺ ions because the RTP can be quenched by Hg²⁺. A linear relationship between RTP against the logarithmic concentration of Hg²⁺ was found over the range of 6 × 10^-8 and 1 × 10^-6 mol/L. The detection limit was found to be 0.017 nmol/L.

Direct visualization of nucleolar G-quadruplexes in live cells by using a fluorescent light-up probe

BACKGROUND

Direct detection of G-quadruplexes in human cells has become an important issue due to the vital role of G-quadruplex related to biological functions. Despite several probes have been developed for detection of the G-quadruplexes in cytoplasm or whole cells, the probe being used to monitor the nucleolar G-quadruplexes is still lacking.

METHODS

Formation of the nucleolar G-quadruplex structures was confirmed by using circular dichroism (CD) spectroscopy. The binding affinity and selectivity of Thioflavin T (ThT) towards various DNA/RNA motifs in solution and gel system were measured by using fluorescence spectroscopy and polyacrylamide gel electrophoresis (PAGE), respectively. G-quadruplex imaging in live cells was directly captured by using confocal laser scanning microscopy (CLSM).

RESULTS

Formation of the rDNA and rRNA G-quadruplex structures is demonstrated in vitro. ThT is found to show much higher affinity and selectivity towards these G-quadruplex structures versus other nucleic acid motifs either in solution or in gel system. The nucleolar G-quadruplexes in living cells are visualized by using ThT as a fluorescent probe. G-quadruplex-ligand treatments in live cells lead to sharp decrease of ThT signal.

CONCLUSIONS

The natural existence of the G-quadruplexes structure in the nucleoli of living cells is directly visualized by using ThT as an indicator.

GENERAL SIGNIFICANCE

The research provides substantive evidence for formation of the rRNA G-quadruplex structures, and also offers an effective probe for direct visualization of the nucleolar G-quadruplexes in living cells.