A Fluorescent Aptamer Sensor Based on Cu-TCPP/rGO for Homogeneous Screening of G‑Quadruplex Ligands

Single-stranded human telomeric DNA can fold into G-quadruplexes, structures composed of stacked G-quartets. Ligands that target G-quadruplex DNA have received considerable attention because of their potential anticancer activity. We developed a Förster resonance energy transfer (FRET) system to identify drugs that stabilize G-quadruplexes with human telomeric DNA in a homogeneous medium using Cu-4,4,4,4-(Porphine-5,10,15,20-tetrayl) tetrakis (benzoic acid)/reduced graphene oxide (Cu-TCPP/rGO) as fluorescence quencher. Fluorescein-tagged human telomeric G-rich DNA (F-GDNA) exhibited significant fluorescence quenching upon adsorption onto the Cu-TCPP/rGO surface, with fluorescence recovery observed when the ligands were bound to the G-quadruplexes. The ligand stabilized formation of G-quadruplexes was further confirmed using circular dichroism (CD) spectroscopy. Notably, flavonoids and anthraquinones derived from traditional Chinese medicines promoted G-quadruplex formation within the GDNA. The combined results of fluorescence and CD spectroscopy indicate that the proposed FRET-based methodology serves as a cost-effective, facile, and efficient tool for screening G-quadruplex ligands. This approach has significant potential for application in the identification of telomerase-targeting anticancer drugs.