Nucleolus-Targeted Red Emissive Carbon Dots with Polarity-Sensitive and Excitation-Independent Fluorescence Emission: High-Resolution Cell Imaging and in Vivo Tracking

Abstract

Red-emitting carbon dots (CDs) have attracted tremendous attention due to their wide applications in areas including imaging, sensing, drug delivery, and cancer therapy. However, it is still highly challenging for red-emitting CDs to simultaneously achieve high quantum yields (QYs), nucleus targeting, and super-resolution fluorescence imaging (especially the stimulated emission depletion (STED) imaging). Here, it is found that the addition of varied metal ions during the hydrothermal treatment of p-phenylenediamine (pPDA) leads to the formation of fluorescent CDs with emission wavelengths up to 700 nm. Strikingly, although metal ions play a crucial role in the synthesis of CDs with varied QYs, they are absent in the formed CDs, that is, the obtained CDs are metal-free, and the metal ions play a role similar to a “catalyst” during the CD formation. Besides, using pPDA and nickel ions (Ni2+) as raw materials, we prepare Ni–pPCDs which have the highest QY and exhibit various excellent fluorescence properties including excitation-independent emission (at ∼605 nm), good photostability, polarity sensitivity, and ribonucleic acid responsiveness. In vitro and in vivo experiments demonstrate that Ni–pPCDs are highly biocompatible and can realize real-time, wash-free, and high-resolution imaging of cell nuclei and high-contrast imaging of tumor-bearing mice and zebrafish. In summary, the present work may hold great promise in the synthesis and applications of red emissive CDs.

Polyol-Mediated Synthesis of Nitrogen-Containing Carbon-Dots from Tetracyanobenzene with Intense Red Fluorescence

“…The observed lattice distance of 1.91 Å relates to graphite ( d 101 with 2.03 Å, [32,33]) but definitely shows a certain reduction. Such reduced lattice fringe distance was already observed for nitrogen-containing C-dots and is ascribed to the higher polarity of heteroatom-containing graphite layers in comparison to pure graphite layers [6,20,21,22,23,24,25]. In contrast, C-dots prepared via the polyol synthesis with similar conditions but in absence of TCB exhibited a larger lattice fringe distance of 2.05 Å [16,18].…”

“…Although reliable liquid-phase syntheses of C-dots have been established, the realization of C-dots showing intense red emission is still a challenge. Most often red emission was reported for nitrogen- or sulfur-doped C-dots, Eu 3+ -containing C-dots, or C-dots that were modified with plasmonic metal nanoparticles [6,19,20,21,22,23,24,25]. The quantum yield for red emission with 30%–35% is nevertheless comparably low in comparison to the blue and green emission of C-dots (up to 80%) [1,3,4,5,6,7,8].…”

Facile Synthesis of “Boron-Doped” Carbon Dots and Their Application in Visible-Light-Driven Photocatalytic Degradation of Organic Dyes

“…For instance, in Nabid and co-workers' report [74], boron was hardly found in C-dots prepared from hydrothermal treatment at 160 • C using citric acid monohydrate as the carbon source, dicyandiamide and boric acid as nitrogen and boron-doping agents, respectively. In a different study, Wu and co-workers reported that the addition of varied metal ions during the hydrothermal treatment of p-phenylenediamine led to the formation of fluorescent C-dots with emission wavelengths up to 700 nm [75]. Strikingly, although metal ions played a crucial role in the synthesis of C-dots with varied quantum yields, they were absent in the formed C-dots; that is, the obtained C-dots were metal-free, and the metal ions played a role similar to a "catalyst" during the C-dots formation.…”

Nanocarriers used as probes for super-resolution microscopy

“…2). [21][22][23][24][25][26][27][28][29][30][31] In the following section we provide a brief overview of these methods. In STED, a focused excitation beam (cyan) superimposed with a doughnut-shaped depletion beam (red) are scanned over the sample to acquire an image at high resolution (down to ~50-80 nm in live cells).…”

“…Copyright 2017, Nature Publishing Group. (g) Reproduced with permission 28. Copyright 2019, American Chemical Society.…”