Graphene Quantum Dot Oxidation Governs Noncovalent Biopolymer Adsorption

Abstract

<jats:title>Abstract</jats:title><jats:p>The graphene quantum dot (GQD) is a carbon allotrope with a planar surface amenable for functionalization and nanoscale dimensions that confer photoluminescent properties. Collectively, these properties render GQDs an advantageous platform for nanobiotechnology applications, including as optical biosensors and delivery platforms. In particular, noncovalent functionalization offers a route to reversible modification and preservation of the pristine GQD substrate. However, a clear paradigm for GQD noncovalent functionalization has yet to be realized. Herein, we demonstrate the feasibility of noncovalent polymer adsorption to the GQD surface, with a specific focus on single-stranded DNA (ssDNA). We study how GQD oxidation level affects the propensity for polymer adsorption by synthesizing and characterizing four types of GQD substrates and investigating noncovalent polymer association to these substrates. Distinct adsorption methods are developed for successful ssDNA attachment based upon the GQD’s initial level of oxidation. ssDNA adsorption to the GQD is confirmed by atomic force microscopy, by inducing ssDNA desorption, and with molecular dynamics simulations. ssDNA is determined to adsorb strongly to no-oxidation GQDs, weakly to low-oxidation GQDs, and not at all for heavily oxidized GQDs. We hypothesize that high GQD oxygen content disrupts the graphitic carbon domains responsible for stacking with the aromatic ssDNA bases, thus preventing the formation of stable polymer-GQD complexes. Finally, we develop a more generic adsorption platform and assess how the GQD system is tunable by modifying both the polymer sequence and type.</jats:p>

Photoluminescence brightening of single-walled carbon nanotubes through conjugation with graphene quantum dots

“…While SWCNTs are reported to quench the fluorescence of GQDs, investigating the change in the fluorescence of SWCNTs when conjugated with GQDs is lacking. Jeong et al28 recently demonstrated that GQDs could interact with ssDNA strands depending on their oxidation level; ssDNA was adsorbed on the surface of GQDs with no or low oxidation, while no adsorption occurred in GQDs with medium and high oxidation levels. To avoid the interactions between GQDs and ssDNA, we synthesized three different types of mediumoxidation GQDs, compared their influence on the QY of ssDNA-SWCNTs of different chiralities, and explored the related mechanisms.…”