G-Quadruplex Conformational Switching for miR-155-3p Detection Using a Ligand-Based Fluorescence Approach

MicroRNA-155-3p (miR-155-3p) is an important biomarker in various pathological conditions, including cancer, making the development of sensitive and specific detection methods crucial. Here, we present a molecular beacon (MB-G4) that underwent a conformational switch upon hybridization with miR-155-3p, enabling the formation of a G-quadruplex (G4) structure. This G4 was recognized by the fluorogenic ligand N-methyl mesoporphyrin IX (NMM), producing a fluorescence signal proportional to the target concentration, making it a new detection method. The conformational dynamics of MB-G4 were characterized through circular dichroism (CD) spectroscopy and native polyacrylamide gel electrophoresis (PAGE), confirming the transition from a hairpin structure to an RNA-DNA hybrid duplex that facilitated G4 formation. The optimization of the experimental conditions, including the potassium chloride (KCl) and NMM concentrations, ensured selective detection with minimal background signal. The detection limit (LOD) was determined to be 10.85 nM, using a linear fluorescence response curve, and the specificity studies demonstrated a clear distinction between miR-155-3p and miR-155-5p. Furthermore, MB-G4 was studied with total RNA extracted from the lung cancer cell line A549 to evaluate its detection in a more complex environment and was able to detect its target, validating its potential for biological sample analysis.