We report herein the specific sensing of dimeric H45 G-quadruplex DNA via a fluorescence light-up response using fluorescent tetrazolylpyrene nucleoside (TzPyBDo) as a probe. The strong binding of the probe via an intercalative stacking interaction inside the connecting loop of two G-quadruplex units of H45 and the discrimination to other monomeric and long DNA duplexes are accompanied by a drastic enhancement of the emission intensity without compromising the conformation and stability.