It has been proposed that new transcription modulations Can be achieved via topological coupling between duplex DNA and DNA secondary structures, such as G-quadruplexes, in gene promoters through super helicity effects. Limited by available methodologies, however, such a coupling has not been quantified directly In this work, Using novel magneto-optical tweezers that combine the nanometer resolution of optical tweezers and the easy manipulation of magnetic tweezers,. We found that the flexibility of DNA increases with positive superhelicity (sigma). More interestingly, we found that the population of G-quadruplex increases linearly from 2.4% at sigma = 0.1 to 12% at sigma = -0.03. The population then rapidly increases to a plateau of 23% at sigma < -0.05. The rapid increase coincides with the melting of dotble-stranded DNA, Suggesting that G-quadmplex formation is correlated with DNA melting. Our results provide evidence fot topology-Mediated transcription modulation at the molecular level. We anticipate that these high-resolution magneto-optical tweezers will be instrumental in studying the interplay between the topology and activity of biological macromolecules from a mechanochemical perspective.