Nucleolus tracking and nucleus-targeted photodynamic therapy are attracting increasing attention due to the importance of nucleolus and the sensitivity of nucleus to various therapeutic stimuli. Herein, a new class of multifunctional fluorescent carbon quantum dots (or carbon dots, CDs) synthesized via the one-pot hydrothermal reaction of m-phenylenediamine and l-cysteine was reported to effectively target nucleolus. The as-prepared CDs possess superior properties, such as low-cost and facile synthesis, good water dispersibility, various surface groups for further modifications, prominent photostability, excellent compatibility, and rapid/convenient/wash-free staining procedures. Besides, as compared with SYTO RNASelect (a commonly used commercial dye for nucleolus imaging) that can only image nucleolus in fixed cells, the CDs can realize high-quality nucleolus imaging in not only fixed cells but also living cells, allowing the real-time tracking of nucleolus-related biological behaviors. Furthermore, after conjugating with protoporphyrin IX (PpIX), a commonly used photosensitizer, the resultant CD-PpIX nanomissiles showed remarkably increased cellular uptake and nucleus-targeting properties and achieved greatly enhanced phototherapeutic efficiency because the nuclei show poor tolerance to reactive oxygen species produced during the photodynamic therapy. The in vivo experiments revealed that the negatively charged CD-PpIX nanomissiles could rapidly and specifically target a tumor site after intravenous injection and cause efficient tumor ablation with no toxic side effects after laser irradiation. It is believed that the present CD-based nanosystem will hold great potential in nucleolus imaging and nucleus-targeted drug delivery and cancer therapy.

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.

Ultrasmall quaternized CDs are used to visualize Gram-positive and Gram-negative bacterial biofilms, and selectively eradicate and inhibit Gram-positive bacterial biofilms.

Copper-containing nanomaterials have been applied in various fields because of their appealing physical, chemical, and biomedical properties/functions. Herein, for the first time, a facile, room-temperature, and one-pot method of simply mixing copper ions and sulfur-doped carbon dots (CDs) is developed for the synthesis of copper/carbon quantum dot (or CD)-crosslinked nanosheets (CuCD NSs). The thus-obtained CuCD NSs with the size of 20-30 nm had a high photothermal conversion efficiency of 41.3% and good photothermal stability. Especially, after coating with thiol-polyethylene glycol and fluorescent molecules, the resultant CuCD NSs could selectively target tumor tissues and realize multimodal (photoacoustic, photothermal, and fluorescence) imaging-guided cancer therapy. More importantly, our CuCD NSs exhibited laser-triggered cytosolic delivery, lysosomal escape, and nuclear-targeting properties, which greatly enhanced their therapeutic efficacy. The significantly enhanced tumor accumulation of CuCD NSs after in situ tumor-site laser irradiation was also observed in in vivo experiments. These in vitro and in vivo events occurring during the continuous laser irradiation have not been observed. Overall, this work develops a CD-assisted synthetic method of photothermal nanoagents for triple-modal imaging-guided phototherapy and deepens our understanding of the action mechanism of photothermal therapy, which will promote the development of nanomedicine and beyond.

Carbon dots (or carbon quantum dots) are small (less than 10 nm) and luminescent carbon nanoparticles with some form of surface passivation. As an emerging class of nanomaterials, carbon dots have found wide applications in medicine, bioimaging, sensing, electronic devices, and catalysis. In this review, we focus on the recent advancements of carbon dots for sensing and killing microorganisms, including bacteria, fungi, and viruses. Synthesis, functionalization, and a toxicity profile of these carbon dots are presented. We also discuss the underlying mechanisms of carbon dot-based sensing and killing of microorganisms.