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Peptide-Decorated Tunable-Fluorescence Graphene Quantum Dots Bedanga B. Sapkota, Abdelkrim Benabbas, Hao-Yu Greg Lin, Wentao Liang, Paul M. Champion, and Meni Wanunu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b16364 • Publication Date (Web): 02 Mar 2017 Downloaded from http://pubs.acs.org on March 3, 2017
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ACS Applied Materials & Interfaces
Peptide-Decorated Tunable-Fluorescence Graphene Quantum Dots Bedanga Sapkota,1 Abdelkrim Benabbas,1 Hao-Yu Greg Lin,2 Wentao Liang,3 Paul Champion,1 and Meni Wanunu1,‡,* 1 2
Department of Physics, Northeastern University, Boston, Massachusetts 02115
Center for Nanoscale Systems, Harvard University, Cambridge, Massachusetts 02138 3 ‡
Department of Biology, Northeastern University, Boston, Massachusetts 02115
Department of Chemistry and Chemical Biology, Northeastern University, Boston, Massachusetts 02115
ABSTRACT: We report here on the synthesis of graphene quantum dots with tunable size, surface chemistry, and fluorescence properties. In the size regime 15-35 nm, these quantum dots maintain strong visible light fluorescence (mean quantum yield of 0.64) and a high two-photon absorption (TPA) cross section (6,500 Göppert-Mayer units). Further, through non-covalent tailoring of the chemistry of these quantum dots we obtain water-stable quantum dots. For example, quantum dots with lysine groups bind strongly to DNA in solution and inhibit polymerase-based DNA strand synthesis. Finally, by virtue of their mesoscopic size, the quantum dots exhibit good cell permeability into living epithelial cells, while they do not enter the cell nucleus.
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KEYWORDS: Graphene quantum dots, tunable fluorescence, peptides, DNA binding, biological imaging, two-photon fluorescence.
INTRODUCTION: Growing efforts have been focused on the use of graphene for biomedical applications such as drug/gene delivery,1-2 imaging,3-4 biological sensing,4-7 and use of graphene as a biocompatible scaffold for cell culture and tissue engineering.8-9 Reducing the size of a graphene sheet to the nanoscale results in a graphene quantum dot (GQD), which has sparked excitement due to several significant merits desirable for bioimaging/biotargeting such as its optical properties, small size that is commensurate with biomolecules, and ease of functionalization. GQDs exhibit superior brightness10 and excellent photostability against photobleaching and blinking as compared to organic dyes and semiconductor quantum dots (QDs).11-12 Also, their chemical composition is more mild than the traditional semiconductor QDs, which exhibit heavy metal ion toxicity issues. However, despite their mild chemical composition, toxicity is GQD-size dependent. Earlier studies have shown that ultrasmall particles (
