Activatable Core-Shell Metallofullerene: An Efficient Nanoplatform for Bimodal Sensing of Glutathione

Zero-Dimensional Carbon Nanomaterials for Fluorescent Sensing and Imaging

Advances in nanotechnology and nanomaterials have attracted considerable interest and play key roles in scientific innovations in diverse fields. In particular, increased attention has been focused on carbon-based nanomaterials exhibiting diverse extended structures and unique properties. Among these materials, zero-dimensional structures, including fullerenes, carbon nano-onions, carbon nanodiamonds, and carbon dots, possess excellent bioaffinities and superior fluorescence properties that make these structures suitable for application to environmental and biological sensing, imaging, and therapeutics. This review provides a systematic overview of the classification and structural properties, design principles and preparation methods, and optical properties and sensing applications of zero-dimensional carbon nanomaterials. Recent interesting breakthroughs in the sensitive and selective sensing and imaging of heavy metal pollutants, hazardous substances, and bioactive molecules as well as applications in information encryption, super-resolution and photoacoustic imaging, and phototherapy and nanomedicine delivery are the main focus of this review. Finally, future challenges and prospects of these materials are highlighted and envisaged. This review presents a comprehensive basis and directions for designing, developing, and applying fascinating fluorescent sensors fabricated based on zero-dimensional carbon nanomaterials for specific requirements in numerous research fields.

Transforming Passive into Active: Multimodal Pheophytin-Based Carbon Dots Customize Protein Corona to Target Metastatic Breast Cancer

Formation of protein corona on nanomaterials surface in vivo is usually considered as an unpredictable event for a predefined targeted delivery system for malignant cancers. In most situations, these protein coronas substantially change targeting efficiency or even cause adverse reactions which both hinder the clinical translation of the cargo-delivery systems. Active customization of protein corona onto nanomaterials surfaces can benefit their biomedical performances and open up new opportunities in construction of targeted delivery systems. Herein, lipid-PEG/pheophytin carbon dots (LPCDs) are prepared from natural chlorophyll and integrate seamlessly with positron emission tomography imaging, near-infrared fluorescence imaging, and photodynamic therapy capacity. In vitro measurements demonstrate that the LPCDs can actively absorb apolipoproteins into the protein corona to enhance their uptakes in breast cancer cells. In vivo studies confirm that LPCDs can give accurate delineation of metastatic breast cancer foci from surrounding normal tissues with multimodal biomedical functions. The feasibility of using LPCDs as a multimodal imaging and cancer-targeting nanoplatform may provide impetus for developing precise yet facile protein corona-targeted delivery systems for future clinical practice.

Multifunctional carbon nanomaterials for diagnostic applications in infectious diseases and tumors

Infectious diseases (such as Corona Virus Disease 2019) and tumors pose a tremendous challenge to global public health. Early diagnosis of infectious diseases and tumors can lead to effective control and early intervention of the patient's condition. Over the past few decades, carbon nanomaterials (CNs) have attracted widespread attention in different scientific disciplines. In the field of biomedicine, carbon nanotubes, graphene, carbon quantum dots and fullerenes have the ability of improving the accuracy of the diagnosis by the improvement of the diagnostic approaches. Therefore, this review highlights their applications in the diagnosis of infectious diseases and tumors over the past five years. Recent advances in the field of biosensing, bioimaging, and nucleic acid amplification by such CNs are introduced and discussed, emphasizing the importance of their unique properties in infectious disease and tumor diagnosis and the challenges and opportunities that exist for future clinical applications. Although the application of CNs in the diagnosis of several diseases is still at a beginning stage, biosensors, bioimaging technologies and nucleic acid amplification technologies built on CNs represent a new generation of promising diagnostic tools that further support their potential application in infectious disease and tumor diagnosis.

Near infrared imaging of intracellular GSH by AuNCs@MnO2 core-shell nanoparticles based on the absorption competition mechanism

Dynamically monitoring intracellular glutathione (GSH), a crucial biomarker of oxidative stress, is of significance for the diagnosis and treatment of certain diseases. Although manganese dioxide (MnO2) based GSH fluorescent sensors have exhibited high sensitivity and good selectivity owing to the specific reactivity between GSH and MnO2, near-infrared (NIR) MnO2 based nanoprobes for GSH detection are scarce. Herein, we have developed a NIR activatable fluorescence nanoprobe for the imaging and determination of intracellular GSH based on a core-shell nanoparticle, consisting of NIR emitted gold nanocluster doped silica as the fluorescent core and manganese dioxide as the GSH-responsive shell (named AuNCs@MnO2). Due to the absorption competition mechanism, the outer MnO2 shell rather than the inner AuNCs core preferentially absorbed the excitation light, thus leading to fluorescence quenching of the inner AuNCs core. Upon addition of GSH, the fluorescence of the nanoprobe restored along with the reduction of MnO2 to Mn2+ because of the absorption competition disappearance-induced emission. The activatable fluorescence linearly increased upon changing the GSH concentration in the range of 2 to 5000 μM with a detection limit of 0.67 μM. The cytotoxicity test shows that the AuNCs@MnO2 nanoprobes have a good biocompatibility. After entering the cancer cells, the intracellular GSH degraded the outermost MnO2 shell and initiated the NIR fluorescence restoration of AuNCs, which can be used to monitor the dynamic change of intracellular GSH. This strategy provides an NIR-activatable way to detect GSH levels in living cells and offers a promising platform for the diagnosis and treatment of GSH-related diseases.

Stimuli-activatable nanomaterials for phototherapy of cancer

Phototherapy including photothermal therapy (PTT) and photodynamic therapy (PDT), as non-invasive therapy approaches, have gained accumulated attention for cancer treatment in past years. PTT and PDT can generate local hyperthermia effects and reactive oxygen species (ROS) respectively, for tumor eradication. To improve the therapeutic performance while minimizing the reverse side effects of phototherapy, extensive efforts have been devoted to developing stimuli-activatable (e.g. pH, redox, ROS, enzyme, etc) nanomaterials for tumor-specific delivery/activation of the phototherapeutics. In this review, we first overviewed the recent advances of the engineered stimuli-responsive nanovectors for the phototherapy of cancer. We particularly summarized the progress of stimuli-activatable nanomaterials-based combinatory therapy strategies for augmenting the performance of phototherapy. We further discuss challenges for the clinical translation of nanomaterials-based phototherapy.

Design and synthesis of highly fluorescent and stable fullerene nanoparticles as probes for folic acid detection and targeted cancer cell imaging

Rational design and construction of fullerene derivatives play significant roles in the development of applications for sensing, marking and imaging in biomedical fields. In the present work, a novel type of C₆₀ fluorescent nanoparticle (C₆₀ FNP) was synthesized by a combination of thiol-ene chemistry and modification with folic acid (FA). The as-prepared C₆₀ FNPs exhibited intense blue luminescence with a relatively high quantum yield of 26%, which is higher than that of any other reported fluorescent fullerene-based nanomaterial. Moreover, they revealed superior photobleaching resistance under constant UV lamp illumination for 5 h and excellent photostablity after 9 months of storage in water. Due to the mutual hydrogen bond interaction, the obtained C₆₀ FNPs were capable of acting as a sensitive and specific probe for FA detection and quantification, with a liner range of 0 to 80 μM and a detection limit of 0.24 μM. Satisfactory recoveries (95.4%-105.2%) were obtained from a series of actual samples, further confirming the feasibility of this nanoprobe. Additionally, taking advantage of the FA moiety, the C₆₀ FNPs had easy access to penetrate into cancer cells with higher expression levels of folate receptors, thereby achieving the function of targeted cellular imaging.

A pH-Activatable MnCO3 Nanoparticle for Improved Magnetic Resonance Imaging of Tumor Malignancy and Metastasis

Engineered magnetic nanoparticles have been extensively explored for magnetic resonance imaging (MRI) diagnosis of a tumor to improve the visibility. However, most of these nanoparticles display "always-on" signals without tumor specificity, causing insufficient contrast and false positives. Here, we provide a new paradigm of MRI diagnosis using MnCO₃ nanorhombohedras (MnNRs) as an ultrasensitive T₁-weighted MRI contrast agent, which smartly enhances the MR signal in response to the tumor microenvironment. MnNRs would quickly decompose and release Mn²⁺ at mild acidity, one of the pathophysiological parameters associated with cancer malignancy, and then Mn²⁺ binds to surrounding proteins to achieve a remarkable amplification of T₁ relaxivity. In vivo MRI experiments demonstrate that MnNRs can selectively brighten subcutaneous tumors from the edge to the interior may be because of the upregulated vascular permeation at the tumor edge, where cancer cell proliferation and angiogenesis are more active. Specially, benefiting from the T₂ shortening effect in normal liver tissues, MnNRs can detect millimeter-sized liver metastases with an ultrahigh contrast of 294%. The results also indicate an effective hepatic excretion of MnNRs through the gallbladder. As such, this pH-activatable MRI strategy with facility, biocompatibility, and excellent efficiency may open new avenues for tumor malignancy and metastasis diagnosis and holds great promise for precision medicine.

A novel "off-on-off" fluorescent-nanoprobe based on B, N co-doped carbon dots and MnO2 nanosheets for sensitive detection of GSH and Ag. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2021;244:118831. [PMID: 32860994 DOI: 10.1016/j.saa.2020.118831]

In this study, a new "off-on-off" fluorescence strategy for detecting glutathione (GSH) and silver ions (Ag⁺) is presented. The constructed nanoprobe is composed of B, N co-doped carbon dots (B, N-CDs) and manganese dioxide nanosheets (MnO₂ nanosheets), where MnO₂ nanosheets serve as a kind of efficient fluorescence quencher. The sensing mechanism of the system is based on the inner filter effect (IFE) and destruction-protection strategy. The assay strategy includes three processes: fluorescence quenching of B, N-CDs by MnO₂ nanosheets, the deconstruction of MnO₂ nanosheets by GSH, the combination between GSH and Ag⁺. The MnO₂ nanosheets are reduced to Mn²⁺ because of the addition of GSH and restoring the fluorescence intensity of the system, while the formation of the complex between GSH and Ag⁺ inhibit the reduction of MnO₂ nanosheets on account of the addition of Ag⁺, leading to the decrease in fluorescence of the probe. This strategy allows the quantitative detection of GSH and Ag⁺ with detection limit of 0.32 μmol·L^-1 and 0.24 μmol·L^-1, respectively. Moreover, this approach displays good sensitivity, selectivity and broad linear range, which could be broadly applicable for practical applications.

Biomass carbon dots derived from Wedelia trilobata for the direct detection of glutathione and their imaging application in living cells

The development of long-wavelength emission carbon dots as a label-free sensing platform for the direct detection of glutathione (GSH) is still of great challenge. Herein, novel rose-red fluorescence carbon dots (wCDs) with a long-wavelength emission of 654 nm were successfully synthesized by a one-step microwave-solvothermal treatment of biomass Wedelia trilobata. The biomass-based wCDs could sensitively respond to copper ions (Cu2+) with a limit of detection (LOD) of 0.22 μM, which could be utilized as the fluorescence turn off-on sensor for the detection of GSH through recovering their fluorescence quenched by Cu2+. Moreover, the label-free wCDs with abundant active functional groups could be used to construct a direct quenching platform for the sensitive and selective detection of GSH by the dynamic quenching effect within 20 s without further modification, displaying a good linear range of 0-3.0 mM with a LOD of 35 μM that fits well with the GSH content in living cells (0.5-10 mM). Additionally, confocal imaging of living cells indicates that as-prepared wCDs with high photobleaching resistance and favorable biocompatibility possess the capacity for real-time monitoring of the variations of intracellular Cu2+ and GSH levels, and distinguishing cancerous cells from normal cells owing to the overexpression of GSH in cancerous cells. This study opens a new vision for developing an efficient and sensitive fluorescent sensor for the detection of GSH, and demonstrates the great prospects for wCDs in ion/molecule tracking, bioimaging and cancer diagnosis.

Responsive Trimodal Probes for In Vivo Imaging of Liver Inflammation by Coassembly and GSH-Driven Disassembly

Noninvasive in vivo imaging of hepatic glutathione (GSH) levels is essential to early diagnosis and prognosis of acute hepatitis. Although GSH-responsive fluorescence imaging probes have been reported for evaluation of hepatitis conditions, the low penetration depth of light in liver tissue has impeded reliable GSH visualization in the human liver. We present a liver-targeted and GSH-responsive trimodal probe (GdNPs-Gal) for rapid evaluation of lipopolysaccharide- (LPS-) induced acute liver inflammation via noninvasive, real-time in vivo imaging of hepatic GSH depletion. GdNPs-Gal are formed by molecular coassembly of a GSH-responsive Gd(III)-based MRI probe (1-Gd) and a liver-targeted probe (1-Gal) at a mole ratio of 5/1 (1-Gd/1-Gal), which shows high r ₁ relaxivity with low fluorescence and fluorine magnetic resonance spectroscopic (¹⁹F-MRS) signals. Upon interaction with GSH, 1-Gd and 1-Gal are cleaved and GdNPs-Gal rapidly disassemble into small molecules 2-Gd, 2-Gal, and 3, producing a substantial decline in r ₁ relaxivity with compensatory enhancements in fluorescence and ¹⁹F-MRS. By combining in vivo magnetic resonance imaging (¹H-MRI) with ex vivo fluorescence imaging and ¹⁹F-MRS analysis, GdNPs-Gal efficiently detect hepatic GSH using three independent modalities. We noninvasively visualized LPS-induced liver inflammation and longitudinally monitored its remediation in mice after treatment with an anti-inflammatory drug, dexamethasone (DEX). Findings highlight the potential of GdNPs-Gal for in vivo imaging of liver inflammation by integrating molecular coassembly with GSH-driven disassembly, which can be applied to other responsive molecular probes for improved in vivo imaging.

Fullerenes as an Effective Amyloid Fibrils Disaggregating Nanomaterial

Nowadays, determining the disassembly mechanism of amyloids under nanomaterials action is a crucial issue for their successful future use in therapy of neurodegenerative and overall amyloid-related diseases. In this study, the antiamyloid disassembly activity of fullerenes C₆₀ and C₇₀ dispersed in 1-methyl-2-pyrrolidinone (NMP) toward amyloid fibrils preformed from lysozyme and insulin was investigated using a combination of different experimental techniques. Thioflavin T fluorescence assay and atomic force microscopy were applied for monitoring of disaggregation activity of fullerenes. It was demonstrated that both types of fullerene-based complexes are very effective in disassembling preformed fibrils, and characterized by the low apparent half-maximal disaggregation concentration (DC₅₀) in the range of ∼22-30 μg mL^-1. Small-angle neutron scattering was employed to monitor the different stages of the disassembly process with respect to the size and morphology of the aggregates. Based on the obtained results, a possible disassembly mechanism for amyloid fibrils interacting with fullerene/NMP complexes was proposed. The study is a principal step in understanding of the fullerenes destruction mechanism of the protein amyloids, as well as providing valuable information on how macromolecules can be engineered to disassemble unwanted amyloid aggregates by different mechanisms.

Carnosine-Modified Fullerene as a Highly Enhanced ROS Scavenger for Mitigating Acute Oxidative Stress

Fullerenes are known as highly efficient scavengers for reactive oxygen species (ROSs). In this study, a carnosine-modified fullerene derivative (C₆₀-Car) was synthesized via a one-step nucleophilic addition reaction. C₆₀-Car forms nanoparticles (NPs) readily in water at neutral pH and room temperature through self-assembly. The C₆₀-Car NPs were found to possess good water solubility, biocompatibility, and excellent ROSs scavenging capability. The scavenging efficiency of ROSs is as high as 92.49% and significantly better than that of hydroxyfullerene (C₆₀-OH NPs, 70.92%) and l-carnosine. Furthermore, C₆₀-Car NPs showed strong cytoprotective ability against H₂O₂-induced damage to the normal human fetal hepatocyte cells (L-02) and human epidermal keratinocytes-adult (HEK-a) cells at a lower concentration of 2.5 μM. In contrast, C₆₀-OH NPs showed a minor cytoprotective effect on cells at a high concentration of 10 μM. The excellent properties of such a fullerene derivative, C₆₀-Car, can be attributed largely to the involvement of l-carnosine with biological activity and antioxidant property, which make it better for biomedicine, and it may provide a new strategy for mitigating acute oxidative stress based on fullerene materials.