Labelling of Cellular Targets Using Promising Two-Photon Contrast Agent Based on Sorted Nitrogen-Doped Graphene Quantum Dot-Polymer Conjugates Exhibiting Exictation-Wavelength-Independent Photoluminescence

In this study, high-uniformity sorted nitrogen-doped graphene quantum dots (N-GQDs) with different sizes displayed the phenomenon of excitation-wavelength-independent photoluminescence emission. The electronic properties and mechanisms involved in quantum-confined photoluminescence can serve as the foundation for the application of oxygenated graphene in photonics, and biology. Further, the sorted N-GQDs were then conjugated with polyethylenimine exposed under two-photon excitation, resulting in good biocompatibility and a higher photoluminescence quantum yield, two-photon absorption, two-photon luminescence emission, absolute cross section of two-photon excitation, ratio of radiative decay rate/non-radiative decay rate, stability and a change in lifetime that could be served as promising two-photon contrast probes. These exceptionally bright, highly photostable, and multiplexing-compatible sorted N-GQD-polymer materials are suitable for employment as fluorescence probes in biological and biomedical applications for analyzing multiplexed targets.