Fluorescein-Stabilized i‑Motif DNA and ItsUnfolding Leading to a Stronger Adsorption Affinity

Several previous studies have indicated that poly-deoxycytidine (poly-C) DNA has an anomalously high affinity for different types of surfaces. It was hypothesized that the formation of an i-motif structure could be a factor responsible for this enhanced affinity, but this is against the notion that a folded molecule should have less interactions with a surface. Herein, the properties of poly-C DNA were examined in detail, focusing on the presence or absence of a FAM (carboxyfluorescein) label and its subsequent adsorption on graphene oxide. Fluorescence and CD spectroscopy studies indicated that the FAM can stabilize an i-motif structure in C15 DNA. In particular, the fluorescence of FAM is drastically quenched when the DNA is folded. This structure is irreversibly unfolded upon heating. Furthermore, the unfolded structure has an even higher affinity to graphene oxide compared to the folded structure. Finally, a large portion of the folded C15 unfolds upon desorption from graphene oxide, and unfolding cou...