Preparation of Excitation‐Independent Photoluminescent Graphene Quantum Dots with Visible‐Light Excitation/Emission for Cell Imaging

Abstract

We report the first pyrrole-ring surface-functionalized graphene quantum dots (p-GQDs) prepared by a two-step hydrothermal approach under microwave irradiation in an ammonia medium. The most distinct feature of the functionalized GQDs is that both the excitation and emission wavelengths fall into the visible-light region. The p-GQDs are excited by visible light at λ(ex) 490 nm (2.53 eV) to emit excitation-independent photoluminescence at a maximum wavelength of λ(em) 550 nm. This is thus far the longest emission wavelength reported for GQDs. Stable photoluminescence is achieved at pH 4-10 with an ionic strength of 1.2 mol L(-1) KCl. These features make the p-GQDs excellent probes for bio-imaging and bio-labeling, which is demonstrated by imaging live HeLa cells.

Tailoring color emissions from N-doped graphene quantum dots for bioimaging applications

“…Our previous investigation showed the pyrrolic ring formed via dehydrolysis between neighbor carboxyl and amide groups 18 . The solid 13 C nuclear magnetic resonance spectrum demonstrated that the pyrrolic ring belongs to pyrrolidone 32,33 . With the pyrrolidone formation, the relative amount of carbonyl (C5O) increases, which is consistent with the results of O 1s high-resolution XPS spectra.…”

“…S3). That means this band is not only related to the n R p* transition of C5O but also the transition of orbitals (HOMO) to the lowest unoccupied molecular orbitals (LUMO) of these groups 14,33 . Comparing the UV-Vis spectra of three kinds of N-GQDs, the adsorption band at 350 nm has a slight red-shift to 360 nm (Figure 3d), indicating that this band affects by the chemical composition of N-GQDs.…”

“…The contribution of p R p* transition also decreases from N-GQDs-B to N-GQDs-Y due to the larger effective conjugation length and edge state. The edge state of N-GQDs is assigned to N state from conjugated pyrrole/pyrrolidone groups, resulting in a red-shift of PL emission and excitation with the increasing amount of pyrrolic N. Wang et al also found the introduction of pyrrole ring into GQDs leads to red-shift PL 33 . Considering the enormous biomedical application of GQDs, the long wavelength-excited emission is highly desired because that will effectively avoid of bioluminescence.…”

Synthesis and Modification of Carbon Nanomaterials utilizing Microwave Heating

“…By functionalizing GQDs, their emission wavelength can be further tuned. Chen et al prepared GQDs of 2 to 6 nm in size, which, subsequent to the exfoliation process, were treated with a surface functionalization step in ammonia solution. This microwave‐assisted treatment resulted in a redshift of the emission maximum to 550 nm.…”

Recent Advances in Graphene Quantum Dots as Bioimaging Probes

“…For instance, Jiang et al [130] synthesized single-or double-layered size-controllable amine-functionalized GQDs by an eco-friendly method with graphene oxide sheets, ammonia and hydrogen peroxide as starting materials, and found a negligible toxicity to HeLa cells for amine-functionalized GQDs. In addition, Chen et al [151] prepared the pyrrole-ring surface-functionalized graphene quantum dots (p-GQDs) by a twostep hydrothermal approach under microwave irradiation of graphene oxide in an ammonia medium. The obtained p-GQDs emittance featured excitation-independent photoluminescence at a maximum wavelength of 550 nm when excited by visible light (490 nm), and stable photoluminescence between pH 4-10 with an ionic strength of 1.2 mol/L KCl was observed.…”