Sugar moiety driven adsorption of nucleic acid on graphene quantum dots: Photophysical, thermodynamic and theoretical evidence

Abstract

Integration of biologically important molecules with graphene quantum dots (GQDs) as a new class of luminescent water-soluble carbon materials, has drawn considerable attention for recent exciting progress on its biomedical applications. In order to avoid toxic semiconductor QDs, GQDs have shown great promise in detection of DNA and other biological applications and hence, fundamental understanding of processes of interactions is important and necessary. The present work establishes the significant role of sugar residue of nucleic acids in adsorption of graphene materials through experimental estimation of binding thermodynamics concomitant with density functional theoretical (DFT) simulation and a detailed evaluation of photophysical parameters. Maximum quenching efficiency of adenosine moiety coupled with the shift in the vibrations of the five-member ring of D-ribose demonstrates the adsorption of DNA on GQDs framework through sugar moieties. The observed experimental results are consistent with the favorable Gibb’s free energy calculated through theoretical simulation. DFT presenting orbital interactions and bonding mechanism of DNAs on GQDs confirms that adsorption on GQDs surface involves charge transfer from nucleobases to GQDs and adenosine, in particular, binds strongly through charge transfer of 0.032e from nitrogen atom to carbon of GQDs. The present investigation will provide insights in understanding the possible role of GQDs in cellular imaging, biosensing and as carriers in targeted drug delivery.