Carbon-Based Quantum Dots with Solid-State Photoluminescent: Mechanism, Implementation, and Application

Metal-organic framework (MOF)/C-dots and covalent organic framework (COF)/C-dots hybrid nanocomposites: Fabrications and applications in sensing, medical, environmental, and energy sectors

Developing new hybrid materials is critical for addressing the current needs of the world in various fields, such as energy, sensing, health, hygiene, and others. C-dots are a member of the carbon nanomaterial family with numerous applications. Aggregation is one of the barriers to the performance of C-dots, which causes luminescence quenching, surface area decreases, etc. To improve the performance of C-dots, numerous matrices including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and polymers have been composited with C-dots. The porous crystalline structures, which are constituents of metal nodes and organic linkers (MOFs) or covalently attached organic units (COFs) provide privileged features such as high specific surface area, tunable structures, and pore diameters, modifiable surface, high thermal, mechanical, and chemical stabilities. Also, the MOFs and COFs protect the C-dots from the environment. Therefore, MOF/C-dots and COF/C-dots composites combine their features while retaining topological properties and improving performances. In this review, we first compare MOFs with COFs as matrices for C-dots. Then, the recent progress in developing hybrid MOFs/C-dots and COFs/C-dots composites has been discussed and their applications in various fields have been explained briefly.

Facile Synthesis of B/P Co-Doping Multicolor Emissive Carbon Dots Derived from Phenylenediamine Isomers and Their Application in Anticounterfeiting

Carbon dots (CDs) possess a considerable number of beneficial features for latent applications in biotargeted drugs, electronic transistors, and encrypted information. The synthesis of fluorescent carbon dots has become a trend in contemporary research, especially in the field of controllable multicolor fluorescent carbon dots. In this study, an elementary one-step hydrothermal method was employed to synthesize the multicolor fluorescent carbon dots by co-doping unique phenylenediamine isomers (o-PD, m-PD, and p-PD) with B and P elements, which under 365 nm UV light exhibited signs of lavender-color, grass-color, and tangerine-color fluorescence, respectively. Further investigations reveal the distinctness in the polymerization, surface-specific functional groups, and graphite N content of the multicolor CDs, which may be the chief factor regarding the different optical behaviors of the multicolor CDs. This new work offers a route for the exploration of multicolor CDs using B/P co-doping and suggests great potential in the field of optical materials, important information encryption, and commercial anticounterfeiting labels.

Symmetry-Triggered Tunable Phosphorescence Lifetime of Graphene Quantum Dots in a Solid State

Studying the phosphorescent mechanisms of carbon nanostructures synthesized by the "bottom-up" approach is key to understanding the structure modulation and the interfacial properties of carbon nanostructures. In this work, the relationships among symmetry of precursors in the "bottom-up" synthesis, structures of products, and phosphorescence lifetimes of graphene quantum dots (GQDs) are studied. The symmetry matching of precursors in the formation of a D6h graphene-like framework is considered the key factor in controlling the separability of sp2 domains in GQDs. As the separability of sp2 domains in GQDs increases, the phosphorescence lifetimes (14.8-125.5 ms) of GQDs in the solid state can be tuned. Machine learning is used to define the degree of disorder (S) of the GQD structure, which quantitatively describes the different space groups of precursors. The negative correlation between S and the oscillator strength of GQDs is uncovered. Therefore, S can be recognized as reflective of oscillator strength in the GQD structure. Finally, based on the correlations found between the structures and phosphorescence lifetimes of GQDs, GQDs with an ultralong phosphorescence lifetime (28.5 s) are obtained. Moreover, GQDs with visible phosphorescence emission (435-618 nm) are synthesized.

Effective Detection of Cu(II) Ions Based on Carbon Dots@Exfoliated Layered Double Hydroxides Composites Fluorescence Probe

A series of carbon dots@exfoliated layered double hydroxides (CDs@LDH) composites were hydrothermally fabricated by Mg/Al LDH and formamide. The results of FTIR, UV-vis, and XPS spectra in company with HRTEM images showed that crystalline nano CDs formed on the single layer of LDH by Mg-C bond. With the increase of solvothermal reaction time from 2 to 6 h, the band gap and the binding energy of aminic and graphitic N species of CDs@LDH composites decreased, whereas the crystallinity increased. The fluorescence peaks of CDs@LDH composites could be deconvoluted into short-wavelength (416 nm) and large-wavelength (443 nm) components by Gaussian function, and the fluorescence intensities of both components enhanced with the extension of the solvothermal reaction time. The simultaneous enhancements of fluorescence lifetime and quantum yield resulted from the relatively high electron density in graphitic nitrogen of CDs@LDH, whereas the reduction of nonradiative rate was due to the high crystallinity in the carbon core of CDs@LDH. A strong exciton-lattice interaction also has been validated based on the excitation and emission spectra of CDs@LDH, so the fluorescence emission of CDs@LDH composite was heavily related to its crystalline carbon core and nitrogen-containing groups. CDs@LDH with high nitrogen-containing exhibited a superior detection property for Cu2+ ion sensing with the linear range of 26.90 ~ 192.20 μM and a limit of detection of 0.1957 μM. The photo-induced electron transfer (PET) process dominated the fluorescence quenching of CDs@LDH by Cu2+ ion since the fluorescence lifetime decreased with the increase of Cu2+ ion concentration.

Antimicrobial Hydrogels: Potential Materials for Medical Application

Microbial infections based on drug-resistant pathogenic organisms following surgery or trauma and uncontrolled bleeding are the main causes of increased mortality from trauma worldwide. The prevalence of drug-resistant pathogens has led to a significant increase in medical costs and poses a great threat to the normal life of people. This is an important issue in the field of biomedicine, and the emergence of new antimicrobial materials hydrogels holds great promise for solving this problem. Hydrogel is an important material with good biocompatibility, water absorption, oxygen permeability, adhesion, degradation, self-healing, corrosion resistance, and controlled release of drugs as well as structural diversity. Bacteria-disturbing hydrogels have important applications in the direction of surgical treatment, wound dressing, medical device coating, and tissue engineering. This paper reviews the classification of antimicrobial hydrogels, the current status of research, and the potential of antimicrobial hydrogels for one application in biomedicine, and analyzes the current research of hydrogels in biomedical applications from five aspects: metal-loaded hydrogels, drug-loaded hydrogels, carbon-material-loaded hydrogels, hydrogels with fixed antimicrobial activity and biological antimicrobial hydrogels, and provides an outlook on the high antimicrobial activity, biodegradability, biocompatibility, injectability, clinical applicability and future development prospects of hydrogels in this field.

Structural Features of Carbon Dots and Their Agricultural Potential

Carbon dots (CDs) have drawn attention due to their enticing physical, chemical, and surface properties. Besides, good conductivity, low toxicity, environmental friendliness, simple synthetic routes, and comparable optical properties are advantageous features of CDs. Further, recently, CDs have been explored for biological systems, including plants. Among biological systems, only plants form the basis for sustainability and life on Earth. In this Review, we reviewed suitable properties and applications of CDs, such as promoting the growth of agricultural plants, disease resistance, stress tolerance, and target transportation. Summing up the available studies, we believe that the applications of CDs are yet to be explored significantly for innovation and technology-based agriculture.

The emergence and prospects of carbon dots with solid-state photoluminescence for light-emitting diodes

The significant features of carbon dots (CDs), such as bright and tunable photoluminescence, high thermal stability, and low toxicity, endow them with tremendous potential for application in next generation optoelectronics. Despite great progress achieved in the design of high-performance CDs so far, the practical applications in solid-state lighting and displays have been retarded by the aggregation-caused quenching (ACQ) effect ascribed to direct π-π interactions. This review provides a comprehensive overview of the recent progress made in solid-state CD emitters, including their synthesis, optical properties and applications in light-emitting diodes (LEDs). Their triplet-excited-state-involved properties, as well as their recent advances in phosphor-converted LEDs and electroluminescent LEDs, are mainly reviewed here. Finally, the prospects and challenges of solid-state CD-based LEDs are discussed with an eye on future development. We hope that this review will provide critical insights to inspire new exciting discoveries on solid-state CDs from both fundamental and practical standpoints so that the realization of their potential in optoelectronic areas can be facilitated.

Bright solid-state luminescence and high-temperature resistance of Ga-doped carbon dots with ultra-wideband white emission for light-emitting diodes

Fluorescent CDs tend to undergo solid-state aggregation quenching in powder form. This is caused by the stacking of π-π conjugate structures and excessive resonant energy transfer. Moreover, various forms of N play an important role in white CDs suitable for LED applications. White, single-component, non-N-doped CDs have never been reported for LED application. In this study, to overcome this limitation, we developed Ga-doped CD powders containing no N element that exhibit ultra-wideband white emission in the range of 420-800 nm for LED applications and were able to resist solid-state aggregation quenching. Furthermore, the Ga-doped CD powders demonstrated excellent luminescence stability under high temperatures. Another strength of the Ga-doped CD powders is their large Stokes shift, where the peak center of white emission shifts from 550 nm to 650 nm under 365 nm excitation as the Ga doping concentration is adjusted from 0.05 to 0.6 (Ga : H2O, mass ratio). The full width at half-maximum can reach 262 nm. Additionally, the Ga-doped CD powders exhibit good luminescence stability under long-time exposure to an air atmosphere. Their luminescent intensity retained 70%-74% of the initial values even after being left in natural placement for 100 days. Moreover, the Ga-doped CDs demonstrate afterglow features.

Preparation and application of carbon quantum dot fluorescent probes combined with rare earth ions

Globally, antibiotic abuse, organic contamination, and excessive heavy metal ion pollution pose serious threats to human health. In this case, ratiometric fluorescent probes can eliminate the errors caused by environmental factors and provide more accurate detection results than single-emission intensity nanoprobes. Accordingly, based on the excellent biocompatibility and abundant surface functional groups of carbon quantum dots (CQDs) and the properties of large Stokes shifts and narrow emission bands of rare earth ions (RE3+), RE-CQD fluorescent probes have attracted widespread attention. Herein, firstly we review the combination of carbon quantum dots with rare earth ions (rare earth complexes) using various functionalization approaches to improve the defects of rare earth complexes and realize the functionalization of carbon quantum dots and their applications in many fields, such as biology and environmental science. In addition, we classify the methods for the synthesis of RE-CQD hybrids into three groups according to the different binding modes of the RE and CQDs, including doping, covalent grafting, and direct coordination. The excellent properties of these fluorescent probes are also briefly described. Finally, a comprehensive overview of the important applications of RE-CQD fluorescent probes in the fields of public safety sensing, chemical sensing, biomedical sensing, temperature sensing, and pH sensing is presented. In this review, the recent research progress in the field of ratiometric fluorescence sensing based on carbon quantum dots and rare earth ions is summarized and an outlook on the future development of RE-CQD fluorescent probes regarding their construction and potential applications is provided.

Lignocellulosic Biomass-Based Carbon Dots: Synthesis Processes, Properties, and Applications

Carbon dots (CDs), a new type of carbon-based fluorescent nanomaterial, have attracted widespread attention because of their numerous excellent properties. Lignocellulosic biomass is the most abundant renewable natural resource and possesses broad potential to manufacture different composite and smart materials. Numerous studies have explored the potential of using the components (such as cellulose, hemicellulose, and lignin) in lignocellulosic biomass to produce CDs. There are few papers systemically aiming in the review of the state-of-the-art works related to lignocellulosic biomass-derived CDs. In this review, the significant advances in synthesis processes, formation mechanisms, structural characteristics, optical properties, and applications of lignocellulosic biomass-based CDs such as cellulose-based CDs, hemicellulose-based CDs and lignin-based CDs in latest research are reviewed. In addition, future research directions on the improvement of the synthesis technology of CDs using lignocellulosic biomass as raw materials to enhance the properties of CDs are proposed. This review will serve as a road map for scientists engaged in research and exploring more applications of CDs in different science fields to achieve the highest material performance goals of CDs.

Synthesis of N,Si co-doped carbon dots to establish a fluorescent sensor for Hg(II) detection with triple signal output

Mercury is a heavy metal with extreme toxicity. Thus, it is of significance to develop an effective method for mercury ion detection with high performance. In this study, carbon dots doped with nitrogen and silicon (N,Si/CQDs) were successfully prepared from folic acid and N-[3-(trimethoxysily)propyl]-ethylenediamine. The N,Si/CQDs show an obvious cyan fluorescence of 460 nm with the radiation of 350 nm. The existence of mercury ions induces the fluorescence quenching of N,Si/CQDs due to photoinduced electron transfer, which was applied for the sensitive sensing of Hg(II). More importantly, the practical application of the N,Si/CQD probe was confirmed by measurements of Hg(II) in real samples of lake water, sorghum and rice. In addition, the N,Si/CQD nanoprobe was integrated on a sensing strip for specific detection of Hg(II). Quantitative measurement of Hg(II) was realized by the outstanding linearity between the diameter (or fluorescence intensity) of the fluorescence quenching ring and the concentration of mercury ions. The sensor shows potential for rapid detection with a triple signal readout on-site and represents a larger step towards practical applications.

Laser-Induced Graphene-based Flexible Substrate with Photothermal Conversion and Photoresponse Performance on Polyimide Film

Graphene-based flexible electronic devices are widely used in photoelectric components and photodetectors. However, it remains a huge challenge to fabricate graphene-based flexible devices efficiently and economically. Compared with the flexible electronic devices made by combining the flexible film with metal and semiconductor materials, the graphene-based flexible substrate (GFS) can be efficiently and conveniently induced by laser direct writing on the flexible film. In this paper, the GFS with a resistance of as low as 15 Ω was successfully induced by CO2 laser on a polyimide (PI) film in one step, and the GFS surface covered with carbon nanoparticles (GFSC) with a resistance of 25 Ω was further induced by femtosecond (fs) laser reprocessing. Benefiting from the laser-induced porous graphene structure, the absorptivity of GFS is up to 90% in the wavelength range of 200-2000 nm. The formation of carbon nanoparticles on the GFSC surface further improves the absorptivity to 97.5% in a wide spectral range. Under white light irradiation of 1 sun, the surface temperature of GFS reaches 65.7 °C and that of GFSC is up to 70.8 °C within 2 min. Under the irradiation of a light-emitting diode (LED) with a central wavelength of 365 nm, the highest photoresponsivity of GFS and GFSC was 8.8 and 1.3 mA/W, respectively. The response time and recovery time of GFS are 8 and 7.3 s, and those of GFSC are 8.3 and 6.7 s, respectively. Importantly, GFSC has a more stable photoresponse performance due to the better electron capture and transfer capability of carbon nanoparticles. It is believed that GFS and GFSC have great application potential in flexible photodetectors and sensors.

Boosting Plant Photosynthesis with Carbon Dots: A Critical Review of Performance and Prospects

Artificially augmented photosynthesis in nano-bionic plants requires tunable nano-antenna structures with physiochemical and optoelectronic properties, as well as unique light conversion capabilities. The use of nanomaterials to promote light capture across photosystems, primarily by carbon dots, has shown promising results in enhancing photosynthesis through tunable uptake, translocation, and biocompatibility. Carbon dots possess the ability to perform both down and up-light conversions, making them effective light promoters for harnessing solar energy beyond visible light wavelengths.This review presents and discusses the recent progress in fabrication, chemistry, and morphology, as well as other properties such as photoluminescence and energy conversion efficiency of nano-antennas based on carbon dots. The performance of artificially boosted photosynthesis is discussed and then correlated with the conversion properties of carbon dots and how they are applied to plant models. The challenges related to the nanomaterial delivery and the performance evaluation practices in modified photosystems, consideration of the reliability of this approach, and the potential avenues for performance improvements through other types of nano-antennas based on alternative nanomaterials are also critically evaluated. It is anticipated that this review will stimulate more high-quality research in plant nano-bionics and provide avenues to enhance photosynthesis for future agricultural applications.

Supramolecular Liquid Crystal Carbon Dots for Solvent-Free Direct Ink Writing

Recent years have witnessed the major advances of nanolights with extensive exploration of nano-luminescent materials like carbon dots (CDs). However, solvent-free processing of these materials remains a formidable challenge, impeding endeavors to develop advanced manufacturing techniques. Herein, in response to this challenge, liquid crystallization is demonstrated as a versatile and robust approach by deliberately anchoring flexible alkyl chains on the CDs surface. Alkyl chain grafting on the CDs surface is observed to substantially depress the common aggregation-caused quenching effect, and results in a shift of self-assembly structure from the crystalline phase to smectic liquid crystalline phase. The liquid-crystalline phase-transition temperature is ready to adjust by varying the alkyl chain length, endowing low-temperature (<50 °C) melt-processing capabilities. Consequently, the first case of direct ink writing (DIW) with liquid crystal (LC) carbon dots is demonstrated, giving rise to highly emissive objects with blue, green and red fluorescence, respectively. Another unexpected finding is that DIW with the LC inks dramatically outperforms DIW with isotropic inks, further highlighting the significance of the LC processing. The approach reported herein not only exhibits a fundamental advance by imparting LC functions to CDs, but also promises technological utility in DIW-based advanced manufacturing.

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.

Polymer-Derived Carbon Nanofiber and Its Photocurrent-Switching Responses of Carbon Nanofiber/Cu Nanocomposite in Wide Ranges of Excited Light Wavelength

Transformation into electric or photoelectric functional composite from non-conjugated polymers is a great challenge due to the presence of a large number of locative states. In this paper, carbon nanofiber was synthesized via hydrothermal carbonization utilizing carboxymethyl cellulose as a precursor, and the carbon nanofiber/Cu nanocomposite was constructed for defect passivation. The results indicated that the resulting nanocomposites exhibited good absorbance in visible light range and NIR (near-infrared). The photoconductive responses to typical weak visible light (650 nm et al.) and NIR (808, 980, and 1064 nm) were studied based on Au gap electrodes on flexible polymer substrates. The results exhibited that the nanocomposite's solid thick film showed photocurrent-switching behaviors to visible light and NIR, the switch-ratio was depending on the wavelengths and power of incident lights. The positive and negative photoconductance responses phenomenon was observed in different compositions and changing excited wavelengths. Their photophysical mechanisms were discussed. This illustrated that the nanocomposites easily produce free electrons and holes via low power of incident light. Free electrons and holes could be utilized for different purposes in multi-disciplinary fields. It would be a potential application in broadband flexible photodetectors, artificial vision, simulating retina, and bio-imaging from visible light to NIR. This is a low-cost and green approach to obtain nanocomposite exhibiting good photocurrent response from the visible range to NIR.

Plasma-Enabled Graphene Quantum Dot Hydrogels as Smart Anticancer Drug Nanocarriers

One of the major challenges on the way to low-cost, simple, and effective cancer treatments is the lack of smart anticancer drug delivery materials with the requisite of site-specific and microenvironment-responsive properties. This work reports the development of plasma-engineered smart drug nanocarriers (SDNCs) containing chitosan and nitrogen-doped graphene quantum dots (NGQDs) for drug delivery in a pH-responsive manner. Through a customized microplasma processing, a highly cross-linked SDNC with only 4.5% of NGQD ratio can exhibit enhanced toughness up to threefold higher than the control chitosan group, avoiding the commonly used high temperatures and toxic chemical cross-linking agents. The SDNCs demonstrate improved loading capability for doxorubicin (DOX) via π-π interactions and stable solid-state photoluminescence to monitor the DOX loading and release through the Förster resonance energy transfer (FRET) mechanism. Moreover, the DOX loaded SDNC exhibits anticancer effects against cancer cells during cytotoxicity tests at minimum concentration. Cellular uptake studies confirm that the DOX loaded SDNC can be successfully internalized into the nucleus after 12 h incubation period. This work provides new insights into the development of smart, environmental-friendly, and biocompatible nanographene hydrogels for the next-generation biomedical applications.

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.

Controlled Growth of MoS2 on Dendritic Ferric Oxide to Enhance Electrochemiluminescence of Nitrogen-Doped Carbon Quantum Dots for Sensitive Immunoassay

The essential expansion of electrochemiluminescence (ECL) technology into clinical detection relies on sensitive and stable signal and maintenance of the activity of the immune molecules during the analysis. This poses a critical challenge for an ECL biosensor as a luminophore in general requires high potential excitation resulting in a strong ECL signal; nevertheless, it has an irreversible effect on the activity of the antigen or antibody. Herein, a novel electrochemiluminescence (ECL) biosensor utilizing nitrogen-doped carbon quantum dots (N-CQDs) as emitters and molybdenum sulfide/ferric oxide (MoS₂@Fe₂O₃) nanocomposites as a coreaction accelerator was developed for detection of neuron-specific enolase (NSE), a biomarker of small cell lung cancer. The doping of nitrogen allows the CQDs to exhibit ECL signals with low excitation potential, with a more viable activity possible for immune molecules. MoS₂@Fe₂O₃ nanocomposites exhibit superior coreaction acceleration characteristics in hydrogen peroxide than any single component of them, and the highly branched dendrite microstructure provides a large number of binding sites for immune molecular, which is an inevitable factor for trace detection. In addition, ion beam sputtering gold particle technology is introduced into the sensor fabrication via an Au-N bond, which will provide sufficient density orientation for capturing the antibody load via the Au-N bonds. With excellent repeatability, stability, and specificity, the as-purposed sensing platform showed differentiated ECL responses of NSE range from 10.00 fg/mL to 500 ng/mL, and the limit of detection (LOD) was calculated of 6.30 fg/mL (S/N = 3). The proposed biosensor is prospective to provide a new avenue for the analysis of NSE or other biomarkers.

Emerging Trends of Carbon-Based Quantum Dots: Nanoarchitectonics and Applications

Carbon-based quantum dots (QDs) have emerged as a fascinating class of advanced materials with a unique combination of optoelectronic, biocompatible, and catalytic characteristics, apt for a plethora of applications ranging from electronic to photoelectrochemical devices. Recent research works have established carbon-based QDs for those frontline applications through improvements in materials design, processing, and device stability. This review broadly presents the recent progress in the synthesis of carbon-based QDs, including carbon QDs, graphene QDs, graphitic carbon nitride QDs and their heterostructures, as well as their salient applications. The synthesis methods of carbon-based QDs are first introduced, followed by an extensive discussion of the dependence of the device performance on the intrinsic properties and nanostructures of carbon-based QDs, aiming to present the general strategies for device designing with optimal performance. Furthermore, diverse applications of carbon-based QDs are presented, with an emphasis on the relationship between band alignment, charge transfer, and performance improvement. Among the applications discussed in this review, much focus is given to photo and electrocatalytic, energy storage and conversion, and bioapplications, which pose a grand challenge for rational materials and device designs. Finally, a summary is presented, and existing challenges and future directions are elaborated.

Wet-spinning fluorescent alginate fibres achieved by doping PEI modified CPDs for multiple anti-counterfeiting

Carbonized polymer dots (CPDs) with satisfactory excitation-dependent-emission and biocompatibility had great potential in anti-counterfeiting fibres field. However, it was difficult for CPDs to combined into the fibres due to the unstable interaction between CPDs and spinnable polymer matrix. Polyethyleneimine (PEI) was used to modify CPDs (namely PEI-CPDs) for achieving stable interactions with sodium alginate (SA) by a simple method, which including the physical interaction between the amino groups of PEI-CPDs and carboxyl groups of SA and the chain entanglement between two types of polymer chains. Then alginate fibres based on PEI-CPDs (PEI-CPDs/CaALG fibres) were successfully prepared by wet-spinning for the first time with less loss of PEI-CPDs. The high mechanical strength, excellent thermal stability and good biocompatibility achieved by PEI-CPDs/CaALG fibres. Furthermore, the fibres exhibited the excitation-dependent-emission property. Anti-counterfeiting of the fibres was conducted on both textile and papers, which showed higher security than the existing anti-counterfeiting fibres.

Solid-state Fluorescence from Carbon Dots Widely Tunable from Blue to Deep Red through Surface Ligand Modulation

Carbon dots (CDs) find widespread attention due to their remarkable fluorescent and electronic properties. However, aggregation-caused quenching currently limits the application of CDs in colored displays. The construction of CDs with color-tunable solid-state fluorescence (SSF) is rarely reported, since the preparation of SSF CDs is technically challenging. Herein, through surface ligand modulation, SSF CDs with an emission-color span of almost 300 nm (from blue to deep red) were obtained. In-depth structure-property studies reveal that intra- and inter-molecular hydrogen-bonding inside SSF CDs provokes the emission properties in the aggregated state. Photodynamic characterizations demonstrate emission wavelengths can be switched smoothly by deliberately altering conjugation ability between substituent ligands and CDs core. Three-dimensional printing patterning is used to create a range of emissive objects, demonstrating the commercial potential for use in optical lamps.

Recent Advances of Carbon Dots with Afterglow Emission

Carbon dots (CDs) have gradually become a new generation of nano-luminescent materials, which have received extensive attention due to excellent optical properties, wide source of raw materials, low toxicity, and good biocompatibility. In recent years, there are many reports on the luminescent phenomenon of CDs, and great progress has been achieved. However,there are rarely systematic summaries on CDs with persistent luminescence. Here, a summary of the recent progress on persistent luminescent CDs, including luminous mechanism, synthetic strategies, property regulation, and potential applications, is given. First, a brief introduction is given to the development of CDs luminescent materials. Then, the luminous mechanism of afterglow CDs from room temperature phosphorescence (RTP), delayed fluorescence (DF), and long persistent luminescence (LPL) is discussed. Next, the constructed methods of luminescent CDs materials are summarized from two aspects, including matrix-free self-protected and matrix-protected CDs. Moreover, the regulation of afterglow properties from color, lifetime, and efficiency is presented. Afterwards, the potential applications of CDs, such as anti-counterfeiting, information encryption, sensing, bio-imaging, multicolor display, LED devices, etc., are reviewed. Finally, an outlook on the development of CDs materials and applications is proposed.

Immunoinducible Carbon Dot-Incorporated Hydrogels as a Photothermal-Derived Antigen Depot to Trigger a Robust Antitumor Immune Response

Immunogenic tumor cell death (ICD) induced by photothermal therapy (PTT) fails to elicit a robust antitumor immune response partially due to its inherent immunosuppressive microenvironment and poor antigen presentation. To address these issues, we developed an immunoinducible carbon dot-incorporated hydrogel (iCD@Gel) through a dynamic covalent Schiff base reaction using mannose-modified aluminum-doped carbon dots (M/A-CDs) as a cross-linking agent. The M/A-CDs possessed superior photothermal conversion efficiency and served as nanocarriers to load cytosine-phosphate-guanine oligodeoxynucleotides (CpG ODNs) for inducing the maturation of dendritic cells (DCs) via mannose receptor-mediated targeting delivery. Upon intratumoral injection, the as-prepared iCD@Gel induced ICD, and damage-associated molecular patterns (DAMPs) were released via photothermal ablation under 808 nm NIR irradiation. Subsequently, the iCD@Gel synergized with the DAMPs to significantly promote the maturation and antigen cross-presentation ability of DCs. This work provides a promising strategy to develop carbon dot-based therapeutic hydrogels for photothermal therapy and immune activation.

Carbon-Based Fluorescent Nano-Biosensors for the Detection of Cell-Free Circulating MicroRNAs

Currently, non-communicable diseases (NCDs) have emerged as potential risks for humans due to adopting a sedentary lifestyle and inaccurate diagnoses. The early detection of NCDs using point-of-care technologies significantly decreases the burden and will be poised to transform clinical intervention and healthcare provision. An imbalance in the levels of circulating cell-free microRNAs (ccf-miRNA) has manifested in NCDs, which are passively released into the bloodstream or actively produced from cells, improving the efficacy of disease screening and providing enormous sensing potential. The effective sensing of ccf-miRNA continues to be a significant technical challenge, even though sophisticated equipment is needed to analyze readouts and expression patterns. Nanomaterials have come to light as a potential solution as they provide significant advantages over other widely used diagnostic techniques to measure miRNAs. Particularly, CNDs-based fluorescence nano-biosensors are of great interest. Owing to the excellent fluorescence characteristics of CNDs, developing such sensors for ccf-microRNAs has been much more accessible. Here, we have critically examined recent advancements in fluorescence-based CNDs biosensors, including tools and techniques used for manufacturing these biosensors. Green synthesis methods for scaling up high-quality, fluorescent CNDs from a natural source are discussed. The various surface modifications that help attach biomolecules to CNDs utilizing covalent conjugation techniques for multiple applications, including self-assembly, sensing, and imaging, are analyzed. The current review will be of particular interest to researchers interested in fluorescence-based biosensors, materials chemistry, nanomedicine, and related fields, as we focus on CNDs-based nano-biosensors for ccf-miRNAs detection applications in the medical field.

Achieving High-Efficiency Large-Area Luminescent Solar Concentrators

Luminescent solar concentrators (LSCs) are semitransparent windows that are able to generate electricity from sunlight absorption. LSCs have shown huge promise for realizing building-integrated photovoltaics (BIPV). Unfortunately, to date, the power conversion efficiency (PCE) of LSCs is still very low which dramatically hampers their practical applications. In this Perspective, We summarize and review the latest developments of LSCs by looking at different structures. Among others, we focus more on the next developments in the field of LSCs, i.e., the possibility of high PCE, large area, mass production, and durability needed for future industrial development. We hope to promote the application of uniform testing standards and to draw attention to industrial development, toxicity, and durability. Then, we will provide a critical assessment of the field of LSCs. Finally, the challenge and solution will be discussed.

One-Pot Three Carbon Dots with Various Lifetimes Rooted in Different Decarboxylation Degrees for Matrix-Free, Anti-Oxygen, and Time-Resolved Information Encryption and Cellular Imaging

Activating long-lived room temperature phosphorescence (RTP) in the aqueous environment and thus realizing matrix-free, anti-oxygen, and time-resolved information encryption and cellular imaging remain a great challenge. Here, we fabricated three types of carbon dots (C-dots), i.e., fluorescent C-dots (F-C-dots) and two types of phosphorescent C-dots denoted as Pw-C-dots and Py-C-dots by a one-pot strategy. Their formation was attributed to the difference in the decarboxylation degree at high temperatures using trimesic acid (TMA) as a sole precursor. Unexpectedly, the yield reached as high as ∼92%, and the proportions were ∼27% for F-C-dots, ∼17% for Pw-C-dots, and ∼56% for Py-C-dots. These nanomaterials could help implement carbon peaking and carbon neutrality. Both green RTP of the two C-dots resulted from the small energy gap (ΔEST). These two RTP C-dots had a long lifetime of over 270 ms with a relatively high quantum yield (4.5 and 6.2%). They exhibited excellent photostability and anti-photobleaching performances. The dry and wet powders of the RTP C-dots were applied to high-level information encryption. The lifelike patterns were greatly different from those of the original ones and could last for several seconds to the naked eye, demonstrating that the RTP C-dots could be potentially employed as anti-oxygen and time-resolved contrast reagents. Most significantly, the cellular imaging experiments showed that the biofriendly PVP-coated Py-C-dots could localize at lysosomes and sustain hundreds of milliseconds. This approach not only pioneers a time-resolved lysosome localization model but also opens up a promising door for anti-oxygen and time-resolved RTP cytoimaging.

Fabrication of Carbon-Based Quantum Dots via a "Bottom-Up" Approach: Topology, Chirality, and Free Radical Processes in "Building Blocks"

The discovery of carbon-based quantum dots (CQDs) has allowed opportunities for fluorescence bioimaging, tumor diagnosis and treatment, and photo-/electro-catalysis. Nevertheless, in the existing reviews related to the "bottom-up" approaches, attention is mainly paid to the applications of CQDs but not the formation mechanism of CQDs, which mainly derived from the high complexities during the synthesis of CQDs. Among the various synthetic methods, using small molecules as "building blocks", the development of a "bottom-up" approach has promoted the structural design, modulation of the photoluminescence properties, and control of the interfacial properties of CQDs. On the other hand, many works have demonstrated the "building blocks"-dependent properties of CQDs. In this review, from one of the most important variables, the relationships among intrinsic properties of "building blocks" and photoluminescence properties of CQDs are summarized. The topology, chirality, and free radical process are selected as descriptors for the intrinsic properties of "building blocks". This review focuses on the induction and summary of recent research results from the "bottom-up" process. Moreover, several empirical rules pertaining thereto are also proposed.

Synthesis and upconversion emission studies of CaYF5:Ho3+/Yb3+ phosphor and its applications in optical thermometry, fingerprint detection, and security ink†

In this work, a CaYF₅:Ho³⁺/Yb³⁺ upconversion phosphor was synthesized and its structural, morphological, and optical properties were studied. The upconversion emission study was performed at an excitation pump power density of 5 W cm⁻² and emissions at 544 nm, 650 nm and 747 nm due to the ⁵F₄(⁵S₂) → ⁵I₈, ⁵F₅ → ⁵I₈ and ⁵F₄(⁵S₂) → ⁵I₇ transitions of the Ho³⁺ ion, respectively were observed. From temperature-dependent upconversion spectra temperature sensitivity was calculated and sensitivity is found to be 14 × 10⁻³ K⁻¹ for the synthesized upconversion phosphor. The photothermal conversion efficiency of the prepared sample in ethanol medium was tested. Moreover, the sample was used to develop latent fingerprints on various surfaces and good contrast in recorded images is observed. The invisible ink was prepared using the upconversion phosphor and then written words were recorded in upconversion emission mode.

In this work, a CaYF₅:Ho³⁺/Yb³⁺ upconversion phosphor was synthesized and its structural, morphological, and optical properties were studied. Apart from these studies, latent fingerprint detection and security ink applications were also demonstrated using this phosphor.

Carbon dot-based nanomaterials: a promising future nano-platform for targeting tumor-associated macrophages

The tumor microenvironment (TME) is the internal environment that tumors depend on for survival and development. Tumor-associated macrophages (TAMs), as an important part of the tumor microenvironment, which plays a crucial role in the occurrence, development, invasion and metastasis of various malignant tumors and has immunosuppressant ability. With the development of immunotherapy, eradicating cancer cells by activating the innate immune system has yielded encouraging results, however only a minority of patients show a lasting response. Therefore, in vivo imaging of dynamic TAMs is crucial in patient-tailored immunotherapy to identify patients who will benefit from immunotherapy, monitor efficacy after treatment, and identify alternative strategies for non-responders. Meanwhile, developing nanomedicines based on TAMs-related antitumor mechanisms to effectively inhibit tumor growth is expected to become a promising research field. Carbon dots (CDs), as an emerging member of the carbon material family, exhibit unexpected superiority in fluorescence imaging/sensing, such as near infrared imaging, photostability, biocompatibility and low toxicity. Their characteristics naturally integrate therapy and diagnosis, and when CDs are combined with targeted chemical/genetic/photodynamic/photothermal therapeutic moieties, they are good candidates for targeting TAMs. We concentrate our discussion on the current learn of TAMs and describe recent examples of macrophage modulation based on carbon dot-associated nanoparticles, emphasizing the advantages of their multifunctional platform and their potential for TAMs theranostics.

Solvent-Type Passivation Strategy Controls Solid-State Self-Quenching-Resistant Behavior in Sulfur Dots

Treatment of sulfur dots with polyethylene glycol (PEG) has been an efficient way to achieve a high luminescence quantum yield, and such a PEG-related quantum dot (QD)-synthesis strategy has been well documented. However, the polymeric insulating capping layer acting as the "thick shell" will significantly slow down the electron-transfer efficiency and severely hamper its practical application in an optoelectric field. Especially, the employment of synthetic polymers with long alkyl chains or large molecular weights may lead to structural complexity or even unexpected changes of physical characteristics for QDs. Therefore, in sulfur dot preparation, it is a breakthrough to use short-chain molecular species to replace PEG for better control and reproducibility. In this article, a solvent-type passivation (STP) strategy has been reported, and no PEG or any other capping agent is required. The main role of the solvent, ethanol, is to directly react with NaOH, and the generated sodium ethoxide passivates the surface defects. The afforded STP-enhanced emission sulfur dots (STPEE-SDs) possess not only the self-quenching-resistant feature in the solid state but also the extension of fluorescence band toward the wavelength as long as 645 nm. The realization of sulfur dot emission in the deep-red region with a decent yield (8.7%) has never been reported. Moreover, a super large Stokes shift (300 nm, λ_ex = 345 nm, λ_em = 645 nm) and a much longer decay lifetime (109 μs) have been found, and such values can facilitate to suppress the negative influence from background signals. Density functional theory demonstrates that the surface passivation via sodium ethoxide is dynamically favorable, and the spectroscopic insights into emission behavior could be derived from the passivation effect of the sulfur vacancy as well as the charge-transfer process dominated by the highly electronegative ethoxide layer.

Fabrication of manganese-coordinated polyphenol carbon dots for photothermal therapy and immune activation

Background

Nanoparticle-based photothermal therapy (PTT) is capable of inducing immunogenic cell death (ICD) and eradicating local tumor via hyperthermia. However, it can hardly prevent tumor recurrence and metastasis owing to inadequate immune activation.

Results

To this end, manganese-coordinated polyphenol carbon dots (MP-CDs) were synthesized by hydrothermal carbonization and metal–polyphenol coordination. This prepared MP-CDs had ultra-small particle size of 5 nm, excellent optical performance, good dispersibility in water and favorable biocompatibility. Under 808 nm near-infrared laser irradiation, the MP-CDs with high photothermal conversion efficiency could kill tumor cells and induce the release of damage-associated molecular patterns (DAMPs) from tumor cells. Notably, the MP-CDs can promote the maturation and antigen presentation ability of dendritic cells (DCs) via manganese-mediated immune activation.

Conclusion

The present work offers a versatile strategy to integrate functional metal into CDs via metal–polyphenol coordination for photothermal/immune therapy.

The Emerging Development of Multicolor Carbon Dots

As a relatively new type of fluorescent carbon-based nanomaterials, multicolor carbon dots (MCDs) have attracted much attention because of their excellent biocompatibility, tunable photoluminescence (PL), high quantum yield, and unique electronic and physicochemical properties. The multicolor emission characteristics of carbon dots (CDs) obviously depend on the carbon source precursor, reaction conditions, and reaction environment, which directly or indirectly determines the multicolor emission characteristics of CDs. Therefore, this review is the first systematic classification and summary of multiple regulation methods of synthetic MCDs and reviews the recent research progress in the synthesis of MCDs from a variety of precursor materials such as aromatic molecules, small organic molecules, and natural biomass, focusing on how different regulation methods produce corresponding MCDs. This review also introduces the innovative applications of MCDs in the fields of biological imaging, light-emitting diodes (LEDs), sensing, and anti-counterfeiting due to their excellent PL properties. It is hoped that by selecting appropriate adjustment methods, this review can inspire and guide the future research on the design of tailored MCDs, and provide corresponding help for the development of multifunctional MCDs.

Phase Behavior and Aggregate Transition Based on Co-assembly of Negatively Charged Carbon Dots and a pH-Responsive Tertiary Amine Cationic Surfactant

We studied the co-assembly of an oppositely changed binary mixture of selenium-doped carbon quantum dots (Se-CQDs) and N,N-dimethyl octylamide-propyl tertiary amine (DOAPA) through turbidity, ζ potential measurement, and cryogenic transmission electron microscopy (cryo-TEM) with the aim of fabricating supramolecular assemblies with multiple dimensions and novel morphologies. The Se-CQD/DOAPA binary mixture exhibited abundant phase behavior, in which an isotropic phase (I₁) was first observed, followed by turbidity (T), precipitation (P), and a second isotropic phase (I₂), as the DOAPA concentration increased. Then we focused on investigating the morphologies of samples. In cryo-TEM observations, spherical aggregates were observed in all phase sequences, whereas the aggregates have different ζ potentials and sizes. In the I₂ phase, interesting nanocapsule-like aggregates and spindle-like aggregates can be identified in addition to spherical aggregates. In combination with the rheological behaviors of the I₂ phase solution and the detailed structure of the aggregates from enlarged cryo-TEM images, it is possible that the Se-CQDs and DOAPA co-assemble with novel network-like building blocks. The turbid solutions were found to be responsive to pH in phase P, and spherical aggregates were obtained at pH 6.5 but turned into vesicles when the pH reached 5.0. On the basis of these findings, CQDs and surfactants can be good structural building blocks for supramolecular structures, and the diverse morphologies of aggregates offer the prospect of multiple applications in the future.

Self-assembly of carbon nanodots induced by liquid-liquid phase separation in a surface microdroplet

Evaporating a sessile drop of ternary solutions containing one hydrotrope (such as ethanol) and two immiscible fluids exhibiting fascinating phase separation behaviours, has opened up a new pathway for controlled nanomaterial assembly. In this work, we studied the influence of liquid-liquid phase separation (LLPS) on the assembly of carbon nanodots (C-dots), 2 nm fluorescent carbon-based nanomaterials with high water solubility. Through self-evaporation of a micro-sized droplet containing ethanol, C-dot-water solution and different oils on a hydrophobic surface, C-dots rearranged into film, porous and granular structures by controlling the properties of oil component in the tenary droplet. Vapour pressure, solubility, surface tension and compositions of the oil components were investigated systematically for their impacts on the evaporation process of C-dot-laden droplets. By using confocal microscopy, we clearly revealed that C-dot assembly was triggered by LLPS in these four oil-water-ethanol ternary systems. The corresponding evaporation and assembly processes were unravelled to be determined by how the ternary solutions pass through the liquid-liquid equilibrium curves in the phase diagrams during evaporation. Our findings deepen the understanding of phase-separation behaviours for nanomaterial assembly as well as provide a novel, simple, and well-controlled approach for depositing different C-dot based nanostructures onto surfaces, which will benefit a wide range of practical applications in the fields of energy, environment and health.

Synergistic Effect of Oxygen- and Nitrogen-Containing Groups in Graphene Quantum Dots: Red Emitted Dual-Mode Magnetic Resonance Imaging Contrast Agents with High Relaxivity

Contrast agents (CAs) in magnetic resonance imaging generally involve the dissociative Gd³⁺. Because of the limited ligancy of Gd³⁺, the balance between Gd³⁺ coordination stability (reducing the concentration of dissociative Gd³⁺) and increases in the number of coordination water molecules (enhancing the relaxivity) becomes crucial. Herein, the key factor of the synergistic effect between the O- and N-containing groups of graphene quantum dots for the structural design of CAs with both high relaxivity and low toxicity was obtained. The nitrogen-doped graphene quantum dots (NGQDs) with an O/N ratio of 0.4 were selected to construct high-relaxivity magnetic resonance imaging (MRI)-fluorescence dual-mode CAs. The coordination stability of Gd³⁺ can be increased through the synergetic coordination of O- and N-containing groups. The synergetic coordination of O- and N-containing groups can result in the short residency time of the water ligand and achieve high relaxivity. The resulting CAs (called NGQDs-Gd) exhibit a high relaxivity of 32.04 mM^-1 s^-1 at 114 μT. Meanwhile, the NGQDs-Gd also emit red fluorescence (614 nm), which can enable the MRI-fluorescence dual-mode imaging as the CAs. Moreover, the bio-toxicity and tumor-targeting behavior of NGQDs-Gd were also evaluated, and NGQDs-Gd show potential in MRI-fluorescence imaging in vivo.

State-of-the-art developments in carbon quantum dots (CQDs): Photo-catalysis, bio-imaging, and bio-sensing applications

Carbon quantum dots (CQDs), the intensifying nanostructured form of carbon material, have exhibited incredible impetus in several research fields such as bio-imaging, bio-sensing, drug delivery systems, optoelectronics, photovoltaics, and photocatalysis, thanks to their exceptional properties. The CQDs show extensive photonic and electronic properties, as well as their light-collecting, tunable photoluminescence, remarkable up-converted photoluminescence, and photo-induced transfer of electrons were widely studied. These properties have great advantages in a variety of visible-light-induced catalytic applications for the purpose of fully utilizing the energy from the solar spectrum. The major purpose of this review is to validate current improvements in the fabrication of CQDs, characteristics, and visible-light-induced catalytic applications, with a focus on CQDs multiple functions in photo-redox processes. We also examine the problems and future directions of CQD-based nanostructured materials in this growing research field, with an eye toward establishing a decisive role for CQDs in photocatalysis, bio-imaging, and bio-sensing applications that are enormously effective and stable over time. In the end, a look forward to future developments is presented, with a view to overcoming challenges and encouraging further research into this promising field.

Photoluminescence mechanisms of red-emissive carbon dots derived from non-conjugated molecules

Red-emissive carbon dots (R-CDs) have been widely studied because of their potential application in tissue imaging and optoelectronic devices. At present, most R-CDs are synthesized by using aromatic precursors, but the synthesis of R-CDs from non-aromatic precursors is challenging, and the emission mechanism remains unclear. Herein, different R-CDs were rationally synthesized using citric acid (CA), a prototype non-aromatic precursor, with the assistance of ammonia. Their structural evolution and optical mechanism were investigated. The addition of NH₃·H₂O played a key role in the synthesis of CA-based R-CDs, which shifted the emission wavelength of CA-based CDs from 423 to 667 nm. Mass spectrometry (MS) analysis indicated that the amino groups served as N dopants and promoted the formation of localized conjugated domains through an intermolecular amide ring, thereby inducing a significant emission redshift. The red-emissive mechanism of CDs was further confirmed by control experiments using other CA-like molecules (e.g., aconitic acid, tartaric acid, aspartic acid, malic acid, and maleic acid) as precursors. MS, nuclear magnetic resonance characterization, and computational modeling revealed that the main carbon chain length of CA-like precursors tailored the cyclization mode, leading to hexatomic, pentatomic, unstable three/four-membered ring systems or cyclization failure. Among these systems, the hexatomic ring led to the largest emission redshift (244 nm, known for CA-based CDs). This work determined the origin of red emission in CA-based CDs, which would guide research on the controlled synthesis of R-CDs from other non-aromatic precursors.

Carbon Dots in Hydroxy Fluorides: Achieving Multicolor Long-Wavelength Room-Temperature Phosphorescence and Excellent Stability via Crystal Confinement

Carbon dots (CDs) have aroused widespread interest in the construction of room-temperature phosphorescent (RTP) materials. However, it is a great challenge to obtain simultaneous multicolor long-wavelength RTP emission and excellent stability in CD-based RTP materials. Herein, a novel and universal "CDs-in-YOHF" strategy is proposed to generate multicolor and long-wavelength RTP by confining various CDs in the Y(OH)_xF_3-x (YOHF) matrix. The mechanism of the triplet emission of CDs is related to the space confinement, the formation of hydrogen bonds and C-F bonds, and the electron-withdrawing fluorine atoms. Remarkably, the RTP lifetime of orange-emissive CDs-o@YOHF is the longest among the reported single-CD-matrix composites for emission above 570 nm. Furthermore, CDs-o@YOHF exhibited higher RTP performance at long wavelength in comparison to CDs-o@matrix (matrix = PVA, PU, urea, silica). The resulting CDs@YOHF shows excellent photostability, thermostability, chemical stability, and temporal stability, which is rather favorable for information security, especially in a complex environment.

Carbon Quantum Dots-Based Nanozyme from Coffee Induces Cancer Cell Ferroptosis to Activate Antitumor Immunity

Carbon quantum dots (CQDs) offer huge potential due to their enzymatic properties as compared to natural enzymes. Thus, discovery of CQDs-based nanozymes with low toxicity from natural resources, especially daily food, implies a promising direction for exploring treatment strategies for human diseases. Here, we report a CQDs-based biocompatible nanozyme prepared from chlorogenic acid (ChA), a major bioactive natural product from coffee. We found that ChA CQDs exhibited obvious GSH oxidase-like activities and subsequently promoted cancer cell ferroptosis by perturbation of GPX4-catalyzed lipid repair systems. In vivo, ChA CQDs dramatically suppressed the tumor growth in HepG2-tumor-bearing mice with negligible side toxicity. Particularly, in hepatoma H22-bearing mice, ChA CQDs recruited massive tumor-infiltrating immune cells including T cells, NK cells, and macrophages, thereby converting "cold" to "hot" tumors for activating systemic antitumor immune responses. Taken together, our study suggests that natural product-derived CQDs from coffee can serve as biologically safe nanozymes for anticancer therapeutics and may aid the development of nanotechnology-based immunotherapeutic.

Enabling robust and hour-level organic long persistent luminescence from carbon dots by covalent fixation

The first carbon dot (CD)-based organic long persistent luminescence (OLPL) system exhibiting more than 1 h of duration was developed. In contrast to the established OLPL systems, herein, the reported CDs-based system (named m-CDs@CA) can be facilely and effectively fabricated using a household microwave oven, and more impressively, its LPL can be observed under ambient conditions and even in aqueous media. XRD and TEM characterizations, afterglow decay, time-resolved spectroscopy, and ESR analysis were performed, showing the successful composition of CDs and CA, the formation of exciplexes and long-lived charged-separated states. Further studies suggest that the production of covalent bonds between CA and CDs plays pivotal roles in activating LPL and preventing its quenching from oxygen and water. To the best of our knowledge, this is a very rare example of an OLPL system that exhibits hour-level afterglow under ambient conditions. Finally, applications of m-CDs@CA in glow-in-the-dark paints for emergency signs and multicolored luminous pearls were preliminarily demonstrated. This work may provide new insights for the development of rare-earth-free and robust OLPL materials.

Vibronic effect and influence of aggregation on the photophysics of graphene quantum dots

Graphene quantum dots, atomically precise nanopieces of graphene, are promising nano-objects with potential applications in various domains such as photovoltaics, quantum light emitters and bio-imaging. Despite their interesting prospects, precise reports on their photophysical properties remain scarce. Here, we report on a study of the photophysics of C₉₆H₂₄(C₁₂H₂₅) graphene quantum dots. A combination of optical studies down to the single molecule level with advanced molecular modelling demonstrates the importance of coupling to vibrations in the emission process. Optical fingerprints for H-like aggregates are identified. Our combined experimental-theoretical investigations provide a comprehensive description of the light absorption and emission properties of nanographenes, which not only represents an essential step towards precise control of sample production but also paves the way for new exciting physics focused on twisted graphenoids.

Anhydride-Terminated Solid-State Carbon Dots with Bright Orange Emission Induced by Weak Excitonic Electronic Coupling

In this work, fluorescent solid carbon dots (CDs) welcome a new member, namely anhydride-terminated CDs, which have a photoluminescence quantum yield (PLQY) of 28% for orange-emitted CDs at 580 nm in powder form. For the first time, we revealed that the electronic coupling of the functional groups should be a crucial factor affecting the optical properties of solid CDs. Due to the negligible hydrogen bonding interaction between the anhydride groups, the electronic coupling of excitons between neighboring anhydride groups is weak, leading to a high PLQY of 28% and an immobile emission peak at 580 nm in solid state. Anhydride-terminated CDs can be partly converted into carboxyl-terminated CDs after dispersion in ethanol. However, the strong electronic coupling of carboxyl groups at high concentration generates the stacking mode of J-aggregates, giving rise to a red-shifted emission from 450 to 515 nm as well as quenched fluorescence in solid state. In comparison, a useful blue emission for solid-state CDs occurs from low sp² hybridized carbon atoms, which possess weak electronic coupling and a stationary emission band at 450 nm in both solution and solid state. By adjusting the feed ratio of the reactants, the relevant intensities between the emission from low sp² hybridized carbon atoms at 450 nm and the emission from anhydride groups at 580 nm can be controlled. As a result, single-component anhydride-terminated CD powder with tunable emission color from orange to white light can be achieved. As-prepared anhydride-terminated CDs can be used for fabricating light-emitting diodes (LEDs), white LEDs, and luminescent solar concentrators (LSCs).

A multifunctional chemical toolbox to engineer carbon dots for biomedical and energy applications

Photoluminescent carbon nanoparticles, or carbon dots, are an emerging class of materials that has recently attracted considerable attention for biomedical and energy applications. They are defined by characteristic sizes of <10 nm, a carbon-based core and the possibility to add various functional groups at their surface for targeted applications. These nanomaterials possess many interesting physicochemical and optical properties, which include tunable light emission, dispersibility and low toxicity. In this Review, we categorize how chemical tools impact the properties of carbon dots. We look for pre- and postsynthetic approaches for the preparation of carbon dots and their derivatives or composites. We then showcase examples to correlate structure, composition and function and use them to discuss the future development of this class of nanomaterials.