Novel hybrids based on graphene quantum dots covalently linked to glycol corroles for multiphoton bioimaging

Abstract

Graphene quantum dots (GQDs) possess excellent optical properties, high photostability, aqueous solubility and bio-compatibility. The presence of carboxyl and hydroxyl groups on GQDs surface and edges provides an excellent opportunity to explore them as anchoring units for covalent functionalization. In addition, the nonlinear optical response of GQDs allows the development of optical sensors operating in biological media. To evaluate the possibility of using GQDs to introduce a hydrophobic sensing unit inside animal cells and to add a nonlinear response to the sensing unit we prepared a novel hybrid based on GQDs covalently linked to corrole units bearing a glycol branch. Covalent functionalization was supported by X-ray photoelectron spectroscopy (XPS), Raman and Fourier transform infrared (FTIR) spectroscopy. Both the height and the diameter of the hybrid showed distributions peaking below 4 nm. The UV–vis absorption and emission spectra of the hybrids were additive with respect to that of the GQDs and the corrole. Insights about the most stable conformation of the corrole with respect to the GQDs core was provided by in silico studies using a model structure. The internalization and distribution of the hybrids in live animal cells was evaluated in human breast adenbocarcinoma cell line (MCF-7 cells) using confocal and multiphoton microscopy. Notably, multiphoton microscopy allowed for image collection using nonlinear excitation in the near-infrared and emission in the red part of the visible spectra.