Supra-Carbon Dots Formed by Fe3+-Driven Assembly for Enhanced Tumor-Specific Photo-Mediated and Chemodynamic Synergistic Therapy

Target Functionalized Carbon Dot Nanozymes with Dual-Model Photoacoustic and Fluorescence Imaging for Visual Therapy in Atherosclerosis

Multifunctional nanomedicines have been used in atherosclerosis theranostics. Herein, phosphatidylserine-specific peptide CLIKKPF-functionalized carbon-dots nanozymes (pep-CDs) are reported for specific and efficient noninvasive theranostic of atherosclerosis. Surprisingly, pep-CDs are discovered to not only inherit the inherent properties of carbon dots (CDs), including deep-red fluorescence emission, photoacoustic response, and superoxide dismutase-like antioxidant, and anti-inflammatory activities but also possess the ability to target recognition on foam cells and target localization on plaques due to the specific interaction of CLIKKPF with phosphatidylserine on the membrane outer surface of foam cells. Furthermore, the target localization effect of pep-CDs vastly promotes the efficient accumulation of CDs in plaque, thus maximizing AS theranostic of CDs. Interestingly, pep-CDs could be developed to image plaque for monitoring atherosclerosis pathological progression in real-time resulting from the different content of foam cells. This work on the one hand proposes a simple and feasible strategy to construct theranostic nanoplatform employing only a single functional unit (i.e., multifunctional CDs) to simplify the fabrication procedure, on the other hand, highlights the advantages of the active target auxiliary mode for atherosclerosis theranostic applications.

Advances in Magnetic Carbon Dots: A Theranostics Platform for Fluorescence/Magnetic Resonance Bimodal Imaging and Therapy for Tumors

Theranostics technology that combines tumor diagnosis or monitoring with therapy is an important direction for the future development of tumor treatment. It takes advantage of efficiently observing tumor tissues, monitoring tumor treatment in real time, and significantly improving the cure efficiency. Magnetic carbon dots (CDs) are of wide interest as molecular imaging probes, drug carriers, photosensitizers, and radiosensitizers in the integration of tumor fluorescence/magnetic resonance bimodal diagnosis and treatment because of their small size, good optical stability, magnetic relaxation rate, and biocompatibility. This review first analyzes and compares the synthesis methods and physicochemical properties of magnetic CDs in recent years and then concludes their mechanism in tumor fluorescence/magnetic resonance bimodal imaging and therapy in details. Subsequently, the research progress of their application in tumor theranostics are summarized. Finally, the problems and challenges of magnetic CDs for development at this stage are prospected. This review provides new ideas for their controlled synthesis and application in efficient and precise therapy for tumors.

Optimized strategies of ROS-based nanodynamic therapies for tumor theranostics

Reactive oxygen species (ROS) play a crucial role in regulating the metabolism of tumor growth, metastasis, death and other biological processes. ROS-based nanodynamic therapies (NDTs) are becoming attractive due to non-invasive, low side effects and tumor-specific advantages. NDTs have rapidly developed into numerous branches, such as photodynamic therapy, chemodynamic therapy, sonodynamic therapy and so on. However, the complexity of the tumor microenvironment and the limitations of existing sensitizers have greatly restricted the therapeutic effects of NDTs, which heavily rely on ROS levels. To address the limitations of NDTs, various strategies have been developed to increase ROS yield, which is an urgent aspect for the positive development of NDTs. In this review, the nanodynamic potentiation strategies in terms of unique properties and universalities of NDTs are comprehensively outlined. We mainly summarize the current dilemmas faced by each NDT and the respective solutions. Meanwhile, the NDTs universalities-based potentiation strategies and NDTs-based combined treatments are elaborated. Finally, we conclude with a discussion of the key issues and challenges faced in the development and clinical transformation of NDTs.

Recent strategies of carbon dot-based nanodrugs for enhanced emerging antitumor modalities

Nanomaterial-based cancer therapy has recently emerged as a new therapeutic modality with the advantages of minimal invasiveness and negligible normal tissue toxicity over traditional cancer treatments. However, the complex microenvironment and self-protective mechanisms of tumors have suppressed the therapeutic effect of emerging antitumor modalities, which seriously hindered the transformation of these modalities to clinical settings. Due to the excellent biocompatibility, unique physicochemical properties and easy surface modification, carbon dots, as promising nanomaterials in the biomedical field, can effectively improve the therapeutic effect of emerging antitumor modalities as multifunctional nanoplatforms. In this review, the mechanism and limitations of emerging therapeutic modalities are described. Further, the recent advances related to carbon dot-based nanoplatforms in overcoming the therapeutic barriers of various emerging therapies are systematically summarized. Finally, the prospects and potential obstacles for the clinical translation of carbon dot-based nanoplatforms in tumor therapy are also discussed. This review is expected to provide a reference for nanomaterial design and its development for the efficacy enhancement of emerging therapeutic modalities.

Drug-Primed Self-Assembly of Platinum-Single-Atom Nanozyme to Regulate Cellular Redox Homeostasis Against Cancer

Single-atom nanozymes (SAzymes) with high catalytic activity exhibit the potential to disequilibrate the reactive oxygen metabolic balance in the tumor microenvironment (TME), which contains several endogenous reductive substances such as glutathione (GSH). Herein, a novel nano-assembly (CDs@Pt SAs/NCs@DOX) is first constructed using drug-primed platinum (Pt) single-atom or nanocluster nanozymes with a Pt loading of 34.8%, which exhibits prominent dual enzymatic activities to mimic peroxidase (POD) and glutathione oxidase (GSHOx). The unique GSHOx-like activity can efficiently scavenge GSH with a relatively low Km (1.04 mm) and high Vmax (7.46 × 10-6  m s-1 ), thus avoiding single oxygen (1 O2 ) depletion. CDs@Pt SAs/NCs@DOX simultaneously demonstrates low-temperature photothermal therapy and TME- or laser-controlled disassembly and drug release, which can effectively regulate cellular redox homeostasis and achieve high tumor growth inhibition. These outcomes may provide promising strategies for the preparation of Pt SAzymes with multiple activities and variable-sized nano-assemblies, allowing for broader applications of SAzymes and nano-assemblies in the biomedical field.

Supramolecular Chemistry of Carbon-Based Dots Offers Widespread Opportunities

Carbon dots are an emerging class of nanomaterials that has recently attracted considerable attention for applications that span from biomedicine to energy. These photoluminescent carbon nanoparticles are defined by characteristic sizes of <10 nm, a carbon-based core and various functional groups at their surface. Although the surface groups are widely used to establish non-covalent bonds (through electrostatic interactions, coordinative bonds, and hydrogen bonds) with various other (bio)molecules and polymers, the carbonaceous core could also establish non-covalent bonds (ππ stacking or hydrophobic interactions) with π-extended or apolar compounds. The surface functional groups, in addition, can be modified by various post-synthetic chemical procedures to fine-tune the supramolecular interactions. Our contribution categorizes and analyzes the interactions that are commonly used to engineer carbon dots-based materials and discusses how they have allowed preparation of functional assemblies and architectures used for sensing, (bio)imaging, therapeutic applications, catalysis, and devices. Using non-covalent interactions as a bottom-up approach to prepare carbon dots-based assemblies and composites can exploit the unique features of supramolecular chemistry, which include adaptability, tunability, and stimuli-responsiveness due to the dynamic nature of the non-covalent interactions. It is expected that focusing on the various supramolecular possibilities will influence the future development of this class of nanomaterials.

Carbon-Based Stimuli-Responsive Nanomaterials: Classification and Application

Carbon-based nanomaterials, including carbon nanotubes, carbon nanospheres, and carbon nanofibers, are becoming a research hotspot due to their unique structure and good mechanical, thermal, electrical, optical, and chemical properties. With the development of material synthesis technology, they can be functionalized and used in various fields such as energy, environment, and biomedicine. In particular, stimuli-responsive carbon-based nanomaterials have stood out in recent years because of their smart behavior. Researchers have applied carbon-based nanomaterials to different disease treatments based on their stimulus-response properties. In this paper, based on stimuli-responsive carbon-based nanomaterials' morphology, we categorize them into carbon nanotubes, carbon nanospheres, and carbon nanofibers according to their morphology. Then, their applications in probes, bioimaging, tumor therapy, and other fields are discussed. Finally, we address the advantages and disadvantages of carbon-based stimuli-responsive nanomaterials and discuss their future perspective.

Surface-charge-switch triggered self assembly of vancomycin modified carbon nanodots for enhanced photothermal eradication of vancomycin-resistant Enterococci biofilms

A new type of vancomycin (Van)-modified carbon nanodots (CNDs@Van) with pH-responsive surface charge switchable activity was successfully developed by covalently cross-linking Van on the surface of carbon nanodots (CNDs). Polymeric Van was formed on the surface of CNDs by covalent modification, which enhanced the targeted binding of CNDs@Van to vancomycin-resistant enterococci (VRE) biofilms and effectively reduced the carboxyl groups on the surface of CNDs to achieve pH-responsive surface charge switching. Most importantly, CNDs@Van was free at pH 7.4, but assembled at pH 5.5 owing to surface charge switching from negative to zero, resulting in remarkably enhanced near-infrared (NIR) absorption and photothermal properties. CNDs@Van exhibited good biocompatibility, low cytotoxicity, and weak hemolytic effects under physiological conditions (pH 7.4). Regarding targeted binding to VRE bacteria, CNDs@Van self-assembled in a weakly acidic environment (pH 5.5) generated by VRE biofilms, giving enhanced photokilling effects in in vitro and in vivo assays. Therefore, potentially, CNDs@Van can be used as a novel antimicrobial agent against VRE bacterial infections and their biofilms.

Copper-Nitrogen-Coordinated Carbon Dots: Transformable Phototheranostics from Precise PTT/PDT to Post-Treatment Imaging-Guided PDT for Residual Tumor Cells

Phototheranostics has attracted considerable attention in the fields of cancer diagnosis and treatment. However, the complete eradication of solid tumors using traditional phototheranostics is difficult because of the limited depth and range of laser irradiation. New phototheranostics enabling precise phototherapy and post-treatment imaging-guided programmed therapy for residual tumors is urgently required. Accordingly, this study developed a novel transformable phototheranostics by assembling hyaluronic acid (HA) with copper-nitrogen-coordinated carbon dots (CDs). In this transformable nanoplatform, named copper-nitrogen-CDs@HA, the HA component enables the specific targeting of cluster determinant (CD) 44-overexpressing tumor cells. In the tumor cells, redox glutathione converts Cu(II) (cupric ions) into Cu(I) (cuprous ions), which confers the novel transformable functionality to phototheranostics. Both in vitro and in vivo results reveal that the near-infrared-light-photoactivated Cu^II-N-CDs@HA could target CD44-overexpressing tumor cells for precise synergistic photothermal therapy and photodynamic therapy. This study is the first to observe that Cu^II-N-CDs@HA could escape from lysosomes and be transformed in situ into Cu^I-N-CDs@HA in tumor cells, with the d⁹ electronic configuration of Cu(II) changing to the d¹⁰ electronic configuration of Cu(I), which turns on their fluorescence and turns off their photothermal properties. This transformable phototheranostics could be used for post-treatment imaging-guided photodynamic therapy on residual tumor cells. Thus, the rationally designed copper-nitrogen-coordinated CDs offer a simple in situ transformation strategy for using multiple-stimulus-responsive precise phototheranostics in post-treatment monitoring of residual tumor cells and imaging-guided programmed therapy.

Hypoxia mitigation by manganese-doped carbon dots for synergistic photodynamic therapy of oral squamous cell carcinoma

Photodynamic therapy (PDT) is widely used for cancer treatment due to its non-invasive and precise effectiveness, however, hypoxia in the tumor microenvironment greatly limits the efficacy of photodynamic therapy. Compared with conventional photosensitizers, carbon dots (CDs) have great potential. Therefore, developing a water-soluble, low-toxicity photosensitizer based on CDs is particularly important, especially one that can enhance the photodynamic efficacy using the tumor microenvironment to produce oxygen. Herein, manganese-doped carbon dot (Mn-CDs, ∼2.7 nm) nanoenzymes with excellent biocompatibility were prepared by a solvothermal method using ethylenediaminetetraacetic acid manganese disodium salt hydrate and o-phenylenediamine as precursors. TEM, AFM, HR-TEM, XRD, XPS, FT-IR, ζ potential, DLS, UV-Vis, and PL spectra were used to characterize the Mn-CDs. Cancer resistance was assessed using the CCK-8 kit, calcein AM versus propidium iodide (PI) kit, and the Annexin V-FITC/PI cell apoptosis assay kit. The obtained Mn-CDs have excellent near-infrared emission properties, stability, and efficient ¹O₂ generation. Notably, the manganese doping renders CDs with catalase (CAT)-like activity, which leads to the decomposition of acidic H₂O₂ in situ to generate O₂, enhancing the PDT efficacy against OSCC-9 cells under 635 nm (300 mW·cm^-2) irradiation. Thus, this work provides a simple and feasible method for the development of water-soluble photosensitizers with oxygen production, presenting good biosafety for PDT in hypoxic tumors.

A novel carbon-nanodots-based theranostic nano-drug delivery system for mitochondria-targeted imaging and glutathione-activated delivering camptothecin

Chemotherapy is severely limited by continuously decreased therapeutic efficacy and uncontrolled side effects on normal tissue, which can be improved by constructing a nanoparticle-based drug delivery system (DDS). Nevertheless, no studies have reported on DDS-based on carbon-nanodots (CNDs), combining subcellular organelle-targeted imaging/drug delivery, high drug loading content, and glutathione (GSH)-sensitive drug release into one system. Herein, the as-fabricated CNDs can be covalently conjugated with a mitochondria-targeting ligand (triphenylphosphine, TPP), a smart GSH-responsive disulfide linker (S-S), and the anticancer drug (camptothecin, CPT) to initially prepare a theranostic nano-DDS (TPP-CNDs-S-CPT) with the drug loading efficiency of 64.6 wt%. Owing to excellent water dispersibility, superior fluorescence properties, satisfactory cell permeability, and favorable biocompatibility, TPP-CNDs-S-CPT was successfully used for intracellular mitochondrial-targeted imaging in vitro. High intracellular GSH concentrations in tumor cells caused the cleavage of S-S, resulting in concomitant activation and release of CPT, as well as significant fluorescence enhancement. In vivo, TPP-CNDs-S-CPT exhibited lower biological toxicity and even higher tumor-activatable performance than free CPT, as well as specific cancer therapy with few side effects. The mitochondria-targeted ability and the precise drug-release in tumor make TPP-CNDs-S-CPT a hopeful chemotherapy prodrug, providing significant theoretical basis and data support for in-depth understanding and exploration of chemotherapeutic DDS-based on CNDs.

Chemodynamic Therapy via Fenton and Fenton-Like Nanomaterials: Strategies and Recent Advances

Chemodynamic therapy (CDT), a novel cancer therapeutic strategy defined as the treatment using Fenton or Fenton-like reaction to produce •OH in the tumor region, was first proposed by Bu, Shi, and co-workers in 2016. Recently, with the rapid development of Fenton and Fenton-like nanomaterials, CDT has attracted tremendous attention because of its unique advantages: 1) It is tumor-selective with low side effects; 2) the CDT process does not depend on external field stimulation; 3) it can modulate the hypoxic and immunosuppressive tumor microenvironment; 4) the treatment cost of CDT is low. In addition to the Fe-involved CDT strategies, the Fenton-like reaction-mediated CDT strategies have also been proposed, which are based on many other metal elements including copper, manganese, cobalt, titanium, vanadium, palladium, silver, molybdenum, ruthenium, tungsten, cerium, and zinc. Moreover, CDT has been combined with other therapies like chemotherapy, radiotherapy, phototherapy, sonodynamic therapy, and immunotherapy for achieving enhanced anticancer effects. Besides, there have also been studies that extend the application of CDT to the antibacterial field. This review introduces the latest advancements in the nanomaterials-involved CDT from 2018 to the present and proposes the current limitations as well as future research directions in the related field.