Direct conjugation of distinct carbon dots as Lego-like building blocks for the assembly of versatile drug nanocarriers

N, S-Codoped Carbon Dots-Based Reusable Solvatochromic Organogel Sensors for Detecting Organic Solvents

The visualization and analysis of organic solvents using fluorescent sensors are crucial, given their association with environmental safety and human health. Conventional fluorescent sensors are typically single-use sensors and they often require sophisticated measurement instruments, which limits their practical and diverse applications. Herein, we develop solvatochromic nitrogen and sulfur codoped carbon dots (NS-CDs)-based organogel sensors that display color changes in response to different solvents. NS-CDs are synthesized using a solvothermal method to produce monodispersed particles with exceptional solubility in various organic solvents. NS-CDs exhibit distinct photoluminescent emission spectra that correlate with the solvent polarity, and the solvent-dependent photoluminescent mechanism is investigated in detail. To highlight the potential application of solvatochromic NS-CDs, portable and low-cost NS-CDs-embedded organogel sensors are fabricated. These sensors exhibit highly robust solvatochromic performance despite repeated solvent switches, thus ensuring consistent and reliable measurements in practical applications. This study provides valuable insights into the solvatochromism of carbon dots and opens up new avenues for designing real-time organic solvent sensing platforms.

Progress in drug delivery and diagnostic applications of carbon dots: a systematic review

Carbon dots (CDs), which have particle size of less than 10 nm, are carbon-based nanomaterials that are used in a wide range of applications in the area of novel drug delivery in cancer, ocular diseases, infectious diseases, and brain disorders. CDs are biocompatible, eco-friendly, easy to synthesize, and less toxic with excellent chemical inertness, which makes them very good nanocarrier system to deliver multi-functional drugs effectively. A huge number of researchers worldwide are working on CDs-based drug delivery systems to evaluate their versatility and efficacy in the field of pharmaceuticals. As a result, there is a tremendous increase in our understanding of the physicochemical properties, diagnostic and drug delivery aspects of CDs, which consequently has led us to design and develop CDs-based theranostic system for the treatment of multiple disorders. In this review, we aim to summarize the advances in application of CDs as nanocarrier including gene delivery, vaccine delivery and antiviral delivery, that has been carried out in the last 5 years.

Dual emission N-doped carbon dots as a ratiometric fluorescent and colorimetric dual-signal probe for indigo carmine detection

Novel dual-emission fluorescent nitrogen-doped carbon dots (N-CDs) were synthesized by a facile one-pot hydrothermal method using ascorbic acid and rhodamine B as precursors and melamine as nitrogen source. The obtained N-CDs exhibited dual-emitting peaks at 435 nm and 578 nm under the single excitation of 350 nm. The fluorescence at 578 nm was more effectively quenched by indigo carmine (IC) based on the internal filtration effect and aggregation-induced emission quenching. Meanwhile, the apparent color change of N-CDs from pink to blue-purple after adding various concentrations of IC could be clearly observed with the naked eye. Therefore, a ratiometric fluorescent and colorimetric dual-signal probe based on N-CDs was developed for IC detection with high selectivity and sensitivity. The addition of IC caused the ratiometric fluorescent value (F₄₃₅/F₅₇₈) to increase linearly within the range from 0 to100 µM with a detection limit (LOD) of 0.18 µM and the colorimetric signal presented a linear response in the range of 0-133 µM with a LOD of 57.4 nM. Furthermore, the IC in juice drink, candy, and water was successfully detected. Besides, the N-CDs were also designed as a ratiometric temperature probe, and the ratiometric fluorescence signal (F₄₃₅/F₅₇₈) was linearly and reversibly responsive to temperature in the range of 20-75 °C.

An Overview on Carbon Quantum Dots Optical and Chemical Features

Carbon quantum dots are the materials of a new era with astonishing properties such as high photoluminescence, chemical tuneability and high biocompatibility. Since their discovery, carbon quantum dots have been described as nanometric high-fluorescent carbon nanoparticles, but this definition has become weaker year after year. Nowadays, the classification and the physical explanation of carbon quantum dots optical properties and their chemical structure remain matter of debate. In this review, we provide a clear discussion on these points, providing a starting point for the rationalization of their classification and a comprehensive view on the optical and chemical features of carbon quantum dots.

Recent advances in carbon dots: synthesis and applications in bone tissue engineering

Bone tissue engineering (BTE), based on the perfect combination of seed cells, scaffold materials and growth factors, has shown unparalleled potential in the treatment of bone defects and related diseases. As the site of cell attachment, proliferation and differentiation, scaffolds composed of biomaterials play a crucial role in BTE. Over the past years, carbon dots (CDs), a new type of carbon-based nanomaterial, have attracted extensive research attention due to their good biocompatibility, unique optical properties, and abundant functional groups. This paper reviews recent research progress in the use of CDs in the field of BTE. Firstly, different preparation methods of CDs are summarized. Then, the properties and categories of CDs applied in BTE are described in detail. Subsequently, the applications of CDs in BTE, including osteogenesis, fluorescence tracing, phototherapy and antibacterial activity, are presented. Finally, the challenges and future perspectives of CDs in BTE are briefly discussed to give a comprehensive picture of CDs. This review provides a theoretical basis and advanced design strategies for the application of CDs in BTE.

Neurological manifestations of SARS-CoV-2 infections: towards quantum dots based management approaches

Developing numerous nanotechnological designed tools to monitor the existence of SARS-CoV-2, and modifying its interactions address the global needs for efficient remedies required for the management of COVID-19. Herein, through a multidisciplinary outlook encompassing different fields such as the pathophysiology of SARS-CoV-2, analysis of symptoms, and statistics of neurological complications caused by SARS-CoV-2 infection in the central and peripheral nervous systems have been testified. The anosmia (51.1%) and ageusia (45.5%) are reported the most frequent neurological manifestation. Cerebrovascular disease and encephalopathy were mainly related to severe clinical cases. In addition, we focus especially on the various concerned physiological routes, including BBB dysfunction, which transpired due to SARS-CoV-2 infection, direct and indirect effects of the virus on the brain, and also, the plausible mechanisms of viral entry to the nerve system. We also outline the characterisation, and the ongoing pharmaceutical applications of quantum dots as smart nanocarriers crossing the blood-brain barrier and their importance in neurological diseases, mainly SARS-CoV-2 related manifestations Moreover, the market status, six clinical trials recruiting quantum dots, and the challenges limiting the clinical application of QDs are highlighted.

Structure-Property-Activity Relationships in Carbon Dots

Carbon dots (CDs) are one of the most versatile nanomaterials discovered in the 21st century. They possess many properties and thus hold potentials in diverse applications. While an increasing amount of attention has been given to these novel nanoparticles, the broad scientific community is actively engaged in exploring their limits. Recent studies on the fractionalization and assembly of CDs further push the limits beyond just CDs and demonstrate that CDs are both a mixture of heterogeneous fractions and promising building blocks for assembly of large carbon-based materials. With CDs moving forward toward both microscopic and macroscopic levels, a good understanding of the structure-property-activity relationships is essential to forecasting the future of CDs. Hence, in this Perspective, structure-property-activity relationships are highlighted based on the repeatedly verified findings in CDs. In addition, studies on CD fractionalization and assembly are briefly summarized in this Perspective. Eventually, these structure-property-activity relationships and controllability are essential for the development of CDs with desired properties for various applications especially in photochemistry, electrochemistry, nanomedicine, and surface chemistry. In summary, in our opinion, since 2004 until the present, history has witnessed a great development of CDs although there is still some room for more studies. Also, considering many attractive properties, structure-property-activity relationships, and the building block nature of CDs, a variety of carbon-based materials of interest can be constructed from CDs with control. They can help reduce blind trials in the development of carbon-based materials, which is of great significance in materials science, chemistry, and any fields related to the applications.

Sensitive, Selective and Reliable Detection of Fe3+ in Lake Water via Carbon Dots-Based Fluorescence Assay

In this study, C-dots were facilely synthesized via microwave irradiation using citric acid and ethylenediamine as carbon precursors. The fluorescence emissions of the C-dots could be selectively quenched by Fe³⁺, and the degree of quenching was linearly related to the concentrations of Fe³⁺ presented. This phenomenon was utilized to develop a sensitive fluorescence assay for Fe³⁺ detection with broad linear range (0–250, 250–1200 μmol/L) and low detection limit (1.68 μmol/L). Most importantly, the assay demonstrated high reliability towards samples in deionized water, tap water and lake water, which should find potential applications for Fe³⁺ monitoring in complicated environments.

The Transformation of 0-D Carbon Dots into 1-, 2- and 3-D Carbon Allotropes: A Minireview

Carbon dots (CDs) represent a relatively new type of carbon allotrope with a 0-D structure and with nanoparticle sizes < 10 nm. A large number of research articles have been published on the synthesis, characteristics, mechanisms and applications of this carbon allotrope. Many of these articles have also shown that CDs can be synthesized from “bottom-up” and “top-down” methods. The “top-down” methods are dominated by the breaking down of large carbon structures such as fullerene, graphene, carbon black and carbon nanotubes into the CDs. What is less known is that CDs also have the potential to be used as carbon substrates for the synthesis of larger carbon structures such as 1-D carbon nanotubes, 2-D or 3-D graphene-based nanosheets and 3-D porous carbon frameworks. Herein, we present a review of the synthesis strategies used to convert the 0-D carbons into these higher-dimensional carbons. The methods involve the use of catalysts or thermal procedures to generate the larger structures. The surface functional groups on the CDs, typically containing nitrogen and oxygen, appear to be important in the process of creating the larger carbon structures that typically are formed via the generation of covalent bonds. The CD building blocks can also ‘aggregate’ to form so called supra-CDs. The mechanism for the formation of the structures made from CDs, the physical properties of the CDs and their applications (for example in energy devices and as reagents for use in medicinal fields) will also be discussed. We hope that this review will serve to provide valuable insights into this area of CD research and a novel viewpoint on the exploration of CDs.

ZIF-based carbon dots with lysosome-Golgi transport property as visualization platform for deep tumour therapy via hierarchical size/charge dual-transform and transcytosis

The poor penetration of nanomaterials in solid tumours and difficulty in monitoring their penetration depth are major obstacles in their application for the treatment of solid tumours. Herein, pH-responsive carbon dots (ZCD) based on a zeolitic imidazolate framework (ZIF-8) were fabricated to achieve the deep delivery of the chemotherapeutic doxorubicin (DOX) via a hierarchical size/charge dual-transformation and transcytosis. The as-prepared ZCD accumulated in the solid tumour and the acidic tumour microenvironment further triggered its decomposition. Firstly, ZCD was decomposed by the weakly acidic extracellular microenvironment of the solid tumour, enabling it to transform into small and neutrally charged particles. Subsequently, these particles were endocytosed by lysosomes, and further disintegrated into smaller and positively charged particles, which could target the Golgi apparatus. Consequently, ZCD delivered DOX deep into the solid tumour via a size-shrinking strategy and Golgi-mediated transcytosis, thus significantly improving its antitumour efficacy. In addition, carbonization endowed ZCD with superior fluorescence property, which was enhanced in the acidic microenvironment, thus improving the sensitivity and accuracy of ex vivo monitoring of the penetration depth of the nanomedicine in real time. Collectively, our results confirmed that the carbon dots obtained via the direct carbonization of ZIF-8 simultaneously exhibited enhanced deep penetration into solid tumours and fluorescence, which could be monitored, and that the carbonization of functional materials is effective to enhance their fluorescence, and further broaden their applications.

Carbon Nanotubes, Graphene, and Carbon Dots as Electrochemical Biosensing Composites

Carbon nanomaterials (CNMs) have been extensively used as electrochemical sensing composites due to their interesting chemical, electronic, and mechanical properties giving rise to increased performance. Due to these materials' unknown long-term ecological fate, care must be given to make their use tractable. In this review, the design and use of carbon nanotubes (CNTs), graphene, and carbon dots (CDs) as electrochemical sensing electrocatalysts applied to the working electrode surface are surveyed for various biosensing applications. Graphene and CDs are readily biodegradable as compared to CNTs. Design elements for CNTs that carry over to graphene and CDs include Coulombic attraction of components and using O or N atoms that serve as tethering points for attaching electrocatalytically active nanoparticles (NPs) and/or other additives.

Biomass-Based Carbon Dots: Current Development and Future Perspectives

Carbon dots have been considered as a solution to the challenges that semiconductor quantum dots have encountered because they are more biocompatible and can be synthesized from abundant and nontoxic materials such as biomass. This review will highlight the advantages of these biomass-based carbon dots in terms of synthesis, properties, and applications in the biomedical field. Furthermore, future applications especially in the biomedical field of biomass-based carbon dots as well as the challenges of semiconductor quantum dots such as biocompatibility, photobleaching, environmental challenges, toxicity, and poor solubility will be discussed in detail. Biomass-derived quantum dots, a subsection of carbon dots that are the most desirable for future research, will be focused upon including from synthesis to applications. Finally, the future development of biomass derived quantum dots in the biomedical field will be discussed and evaluated to unlock the potential for their applications.

Microbial inhibition and biosensing with multifunctional carbon dots: Progress and perspectives

Carbon dots (CDs) and their doped counterparts including nitrogen-doped CDs (N@CDs) have been synthesized by bottom-up or top-down approaches from different precursors. The attractiveness of such emerging 2D‑carbon-based nanosized materials is attributed to their excellent biocompatibility, preparation, aqueous dispersibility, and functionality. The antimicrobial, optical, and electrochemical properties of CDs have been advocated for two important biotechnological applications: bacterial eradication and sensing/biosensing. CDs as well as N@CDs act as antimicrobial agents as their surfaces encompass functional hydroxyl, carboxyl, and amino groups that generate free radicals. As a new class of photoluminescent nanomaterials, CDs can be employed in diversified analytics. CDs with surface carboxyl or amino groups form nanocomposites with nanomaterials or be conjugated with biorecognition molecules toward the development of sensors/biosensors. The deployment of conductive CDs in electrochemical sensing has also increased significantly because of their quantum size, excellent biocompatibility, enzyme-mimicking activity, and high surface area. The review also addresses the ongoing challenges and promises of CDs in pathogenesis and analytics. Perspectives on the future possibilities include the use of CDs in microbial viability assay, wound healing, antiviral therapy, and medical devices.

Carbon Dots: A Future Blood-Brain Barrier Penetrating Nanomedicine and Drug Nanocarrier

Drug delivery across the blood-brain barrier (BBB) is one of the biggest challenges in modern medicine due to the BBB's highly semipermeable property that limits most therapeutic agents of brain diseases to enter the central nervous system (CNS). In recent years, nanoparticles, especially carbon dots (CDs), exhibit many unprecedented applications for drug delivery. Several types of CDs and CD-ligand conjugates have been reported successfully penetrating the BBB, which shows a promising progress in the application of CD-based drug delivery system (DDS) for the treatment of CNS diseases. In this review, our discussion of CDs includes their classification, preparations, structures, properties, and applications for the treatment of neurodegenerative diseases, especially Alzheimer's disease (AD) and brain tumor. Moreover, abundant functional groups on the surface, especially amine and carboxyl groups, allow CDs to conjugate with diverse drugs as versatile drug nanocarriers. In addition, structure of the BBB is briefly described, and mechanisms for transporting various molecules across the BBB and other biological barriers are elucidated. Most importantly, recent developments in drug delivery with CDs as BBB-penetrating nanodrugs and drug nanocarriers to target CNS diseases especially Alzheimer's disease and brain tumor are summarized. Eventually, future prospects of the CD-based DDS are discussed in combination with the development of artificial intelligence and nanorobots.

Sodium selenite-carbon dots nanocomposites enhance acaricidal activity of fenpropathrin: Mechanism and application

As an essential trace element, selenium can be used to protect crops from pests, while, in nature, most crops cannot accumulate enough selenium from the soil to reach the effective dose for pest control. In this study, carbon dots modified with arginine in nano-scale was prepared and characterized, then, it was combined with sodium selenite to form selenium-carbon dots (Se-CDs). Function evaluation of Se-CDs showed that it could increase the absorption of selenium in plant leaves, promote the control efficiency of fenpropathrin, and protect plant from damage caused by Tetranychus cinnabarinus. In addition, we found that expressions of P450 genes and activity of P450 enzyme both decreased in selenium treated mites. In vivo, the acaricidal activity of fenpropathrin increased significantly when one of the P450 genes, CYP389B1, was silenced, and the recombinant protein of CYP389B1 could metabolize fenpropathrin in vitro. The results suggested that inhibiting the expression of P450 gene and repressing the detoxification of T. cinnabarinus was the molecular mechanism that how selenium promoted the acaricidal activity of fenpropathrin. The application of Se-CDs in the field will decrease the use of chemicals acaricides, reduce chemical residues, and ensure the safety of agricultural products.

Gel-like carbon dots: A high-performance future photocatalyst

To protect water resources, halt waterborne diseases, and prevent future water crises, photocatalytic degradation of water pollutants arouse worldwide interest. However, considering the low degradation efficiency and risk of secondary pollution displayed by most metal-based photocatalysts, highly efficient and environmentally friendly photocatalysts with appropriate band gap, such as carbon dots (CDs), are in urgent demand. In this study, the photocatalytic activity of gel-like CDs (G-CDs) was studied using diverse water pollution models for photocatalytic degradation. The degradation rate constants demonstrated a remarkably enhanced photocatalytic activity of G-CDs compared with most known CD species and comparability to graphitic carbon nitride (g-C₃N₄). In addition, the rate constant was further improved by 1.4 times through the embedment of g-C₃N₄ in G-CDs to obtain CD-C₃N₄. Significantly, the rate constant was also higher than that of g-C₃N₄ alone, revealing a synergistic effect. Moreover, the use of diverse radical scavengers suggested that the main contributors to the photocatalytic degradation with G-CDs alone were superoxide radicals (O₂^-) and holes that were, however, substituted by O₂^- and hydroxyl radicals (OH) due to the addition of g-C₃N₄. Furthermore, the photocatalytic stabilities of G-CDs and CD-C₃N₄ turned out to be excellent after four cycles of dye degradation were performed continuously. Eventually, the nontoxicity and environmental friendliness of G-CDs and CD-C₃N₄ were displayed with sea urchin cytotoxicity tests. Hence, through various characterizations, photocatalytic degradation and cytotoxicity tests, G-CDs proved to be an environmentally friendly and highly efficient future photocatalyst.

Carbon Dots as Promising Tools for Cancer Diagnosis and Therapy

Simple Summary

Diagnostic approaches and chemotherapeutic delivery based on nanotechnologies, such as nanoparticles (NPs), could be promising candidates for the new era of cancer research. Recently great attention has been received by carbon-based nanomaterials such as Carbon Dots (CDs), due their variegated physical-chemical properties that makes these systems appealing for multiple use from bioimaging, biosensing, nano-carriers for drug delivery systems to innovative therapeutic agents in photodynamic (PDT) and photothermal therapy (PTT). In this review, we report the last evidence on the application and prospects of CDs as useful nano theranostics tools for cancer diagnosis and therapy.

Abstract

Carbon Dots (CDs) are the latest members of carbon-based nanomaterials, which since their discovery have attracted notable attention due to their chemical and mechanical properties, brilliant fluorescence, high photostability, and good biocompatibility. Together with the ease and affordable preparation costs, these intrinsic features make CDs the most promising nanomaterials for multiple applications in the biological field, such as bioimaging, biotherapy, and gene/drug delivery. This review will illustrate the most recent applications of CDs in the biomedical field, focusing on their biocompatibility, fluorescence, low cytotoxicity, cellular uptake, and theranostic properties to highlight above all their usefulness as a promising tool for cancer diagnosis and therapy.

The Role of Carbon Quantum Dots in Organic Photovoltaics: A Short Overview

Carbon quantum dots (CDs) are a new class of fluorescent carbonaceous nanomaterials that were casually discovered in 2004. Since then, they have become object of great interest in the scientific community because of their peculiar optical properties (e.g., size-dependent and excitation wavelength-dependent fluorescence), which make them very similar to the well-known semiconductor quantum dots and suitable for application in photovoltaic devices (PVs). In fact, with appropriate structural engineering, it is possible to modulate CDs photoluminescence properties, band gap, and energy levels in order to realize the band matching suitable to enable the desired directional flow of charge carriers within the PV device architecture in which they are implanted. Considering the latest developments, in the present short review, the employment of CDs in organic photovoltaic devices (OPVs) will be summarized, in order to study the role played by these nanomaterials in the improvement of the performances of the devices. After a first brief summary of the strategies of structural engineering of CDs and the effects on their optical properties, the attention will be devoted to the recent highlights of CDs application in organic solar cells (OSCs) and in dye sensitized solar cells (DSSCs), in order to guide the users towards the full exploitation of the use of these nanomaterials in such OPV devices.

Recent Developments of Carbon Dots in Biosensing: A Review

Early diagnosis of diseases is of great importance because it increases the chance of a cure and significantly reduces treatment costs. Thus, development of rapid, sensitive, and reliable biosensing techniques is essential for the benefits of human life and health. As such, various nanomaterials have been explored to improve performance of biosensors, among which, carbon dots (CDs) have received enormous attention due to their excellent performance. In this Review, the recent advancements of CD-based biosensors have been carefully summarized. First, biosensors are classified according to their sensing strategies, and the role of CDs in these sensors is elaborated in detail. Next, several typical CD-based biosensors (including CD-only, enzymatic, antigen-antibody, and nucleic acid biosensors) and their applications are fully discussed. Last, advantages, challenges, and perspectives on the future trends of CD-based biosensors are highlighted.

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

Carbon dots (C-dots) were facilely fabricated via a hydrothermal method and fully characterized. Our study shows that the as-synthesized C-dots are nontoxic, negatively charged spherical particles (average diameter 4.7 nm) with excellent water dispersion ability. Furthermore, the C-dots have a rich presence of surface functionalities such as hydroxyls and carboxyls as well as amines. The significance of the C-dots as highly efficient photocatalysts for rhodamine B (RhB) and methylene blue (MB) degradation was explored. The C-dots demonstrate excellent photocatalytic activity, achieving 100% of RhB and MB degradation within 170 min. The degradation rate constants for RhB and MB were 1.8 × 10⁻² and 2.4 × 10⁻² min⁻¹, respectively. The photocatalytic degradation performances of the C-dots are comparable to those metal-based photocatalysts and generally better than previously reported C-dots photocatalysts. Collectively considering the excellent photocatalytic activity toward organic dye degradation, as well as the fact that they are facilely synthesized with no need of further doping, compositing, and tedious purification and separation, the C-dots fabricated in this work are demonstrated to be a promising alternative for pollutant degradation and environment protection.