Graphene quantum dots (GQDs) are an allotrope of carbon possessing a planar surface amenable for functionalization and nanoscale dimensions that confer photoluminescence. Collectively, these material and optical characteristics render GQDs an advantageous platform for nanobiotechnology applications, including delivery and biosensing. Towards this purpose, noncovalent functionalization offers a route to reversibly modify and preserve the pristine GQD substrate properties. However, a clear paradigm for noncovalent GQD modification has yet to be realized. Herein, we demonstrate the feasibility of noncovalent polymer adsorption to GQD surfaces, specifically focusing 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. Adsorption of ssDNA quenches intrinsic GQD fluorescence for low-oxidation GQDs and enables fluorescence emission via aqueous dispersion of otherwise-insoluble no-oxidation GQDs. ssDNA-GQD complexation is confirmed by atomic force microscopy, by inducing ssDNA desorption, and with molecular dynamics simulations. ssDNA is found 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 show the generality of the adsorption platform and assess how the GQD system is tunable by modifying polymer sequence and type.

Developing noncovalent biopolymer adsorption on graphene quantum dots

ACS Fall 2020 Virtual Meeting

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