A functional preservation strategy for the production of highly photoluminescent emerald carbon dots for lysosome targeting and lysosomal pH imaging

Intense Circularly Polarized Fluorescence and Room-Temperature Phosphorescence in Carbon Dots/Chiral Helical Polymer Composite Films

Chiral carbon dots (C-dots) with a circularly polarized fluorescence (CPF) property have attracted tremendous attention due to their significant applications in chiral optoelectronics and theranostics. However, constructing circularly polarized room-temperature phosphorescent (CPRTP) C-dots remains a great challenge. Herein, a strategy is established to achieve efficient CPF and CPRTP emissions in C-dots/chiral helical polymer bilayer composite film. Taking advantage of the chiral filter effect of chiral helical polymer, intense CPF and CPRTP emissions with large dissymmetric factors up to 1.4 × 10^-1 and 1.2 × 10^-2 are respectively obtained, even though there is only a simple interface contact between the C-dots layer and the chiral helical polymer layer. More importantly, white-color CPF emission and multiple information display and encryption are further realized based on the prepared chiral luminescent composite films.

Boron Dopants in Red-Emitting B and N Co-Doped Carbon Quantum Dots Enable Targeted Imaging of Lysosomes

Lysosomes are of great significance to cell growth, metabolism, and survival, as they independently maintain acidity and regulate various balances in cells. Therefore, it is essential to develop advanced probes for lysosome visualization and live tracking. Herein, a type of lysosome-targeting probe based on boron (B) and nitrogen (N) co-doped carbon quantum dots (B/N-CQDs) is presented, which exhibits red emission at 618 nm, high quantum yield (28%), and excellent fluorescence stability (97% at 1 h). These B/N-CQDs are prepared by a novel and green solid-state reaction and purified using a simple extraction process without additional chemical modifications. It is found that the boron dopants in the structure play a crucial role in the resultant lysosome-specific targeting property through borate esterification between boronic acid groups in the sample and diol structures in glycoproteins. This can be applied as a powerful tool for cell apoptosis, necrosis, and endosomal escape tracking. This work not only offers a new concept for targeted subcellular probe designs via chemical doping but also demonstrates the feasibility of these tools for analyzing complex cellular physiological activities.

Effective and selective measurement of 2,4-dinitroaniline utilizing constructed fluorescent carbon dots sensor derived from vitamin B1

2,4-Dinitroaniline is a multifunctional product and has been applicated in various fields. It has absorbed much concerns due to its large consumption and occurrence in many environmental matrices. It is urgent to explore reliable and sensitive measurement technology. Present study described an outstanding fluorescence sensor constructed with carbon dots (CDs) derived from vitamin B₁. The CDs were fabricated by dealing with a facile hydrothermal process, and exhibited good water solubility, fluorescence stability and highly fluorescence quenching characteristics in presence of 2,4-dinitroaniline. The excitation and emission wavelengths of the obtained CDs were 305 and 378 nm, respectively. The sensor displayed good selectivity and sensitivity for 2,4-dinitroaniline. Good linearity can be achieved in two-stage of 0.2-3 μmol L^-1 and 3-20 μmol L^-1. The sensor earned low detection limit for 2,4-dinitroaniline down to 0.05 μmol L^-1. The sensor has been commendably employed for analysis of 2,4-dinitroaniline in real aqueous samples with spiked recoveries in the range of 95.0-99.6%. The proposed sensor provided a promising alternative for analysis of environmental pollutants or other meaningful employment.

Lysosome Imaging Based on Fluorescent Carbon Dots

Lysosomes play key roles in different cellular processes such as autophagy, phagocytosis, and apoptosis. Lysosomal dysfunction is related to many diseases. Fluorescence lysosome staining strategy is valuable for the researches on the lysosome involvement in different pathological diagnosis. Here we describe fluorescence lysosome staining methods with carbon dots for the identification of lysosomes in living and fixed cells.

High-quality full-color carbon quantum dots synthesized under an unprecedentedly mild condition

Carbon quantum dots (CQDs) are highly promising to be applied in light-emitting, chemosensing, and other cutting-edge domains. Herein, we successfully fabricate high-quality full-color CQDs under unprecedentedly low temperature and pressure (85°C, 1.88 bar). Stable and narrow fluorescent emissions ranging from blue to green and red light were realized by simple amine engineering, which were further mixed into white-light CQDs with the absolute photoluminescent quantum yield reaching 19.2%. The average mass yield of the CQDs reached 69.0%. The optical performances demonstrated that the CQDs possessed uniform luminescent centers and dominant radiative decay channels. Component analysis further suggested that dehydrated condensation between carboxyl and amine groups directed the growth of the CQDs. By utilizing the CQDs, full-color light-emitting diodes and logic gate sensors were developed. This study paves an important step for promoting the application of CQDs by providing an energy-efficient, safe, and productive synthetic strategy.

An insight into the potentials of carbon dots for in vitro live-cell imaging: recent progress, challenges, and prospects

Carbon dots (CDs) are a strong alternative to conventional fluorescent probes for cell imaging due to their brightness, photostability, tunable fluorescence emission, low toxicity, inexpensive preparation, and chemical diversity. Improving the targeting efficiency by modulation of the surface functional groups and understanding the mechanisms of targeted imaging are the most challenging issues in cell imaging by CDs. Firstly, we briefly discuss important features of fluorescent CDs for live-cell imaging application in this review. Then, the newest modulated CDs for targeted live-cell imaging of whole-cell, cell organelles, pH, ions, small molecules, and proteins are elaborately discussed, and their challenges in these fields are explained.

Lighting up Individual Organelles With Fluorescent Carbon Dots

Cell organelles play crucial roles in the normal functioning of an organism, therefore the disruption of their operation is associated with diseases and in some cases death. Thus, the detection and monitoring of the activities within these organelles are of great importance. Several probes based on graphene oxide, small molecules, and other nanomaterials have been developed for targeting specific organelles. Among these materials, organelle-targeted fluorescent probes based on carbon dots have attracted substantial attention in recent years owing to their superior characteristics, which include facile synthesis, good photostability, low cytotoxicity, and high selectivity. The ability of these probes to target specific organelles enables researchers to obtain valuable information for understanding the processes involved in their functions and/or malfunctions and may also aid in effective targeted drug delivery. This review highlights recently reported organelle-specific fluorescent probes based on carbon dots. The precursors of these carbon dots are also discussed because studies have shown that many of the intrinsic properties of these probes originate from the precursor used. An overview of the functions of the discussed organelles, the types of probes used, and their advantages and limitations are also provided. Organelles such as the mitochondria, nucleus, lysosomes, and endoplasmic reticulum have been the central focus of research to date, whereas the Golgi body, centrosome, vesicles, and others have received comparatively little attention. It is therefore the hope of the authors that further studies will be conducted in an effort to design probes with the ability to localize within these less studied organelles so as to fully elucidate the mechanisms underlying their function.

Self-Targeting Carbon Quantum Dots for Peroxynitrite Detection and Imaging in Live Cells

Peroxynitrite (ONOO^-), a highly reactive nitrogen species (RNS) generated mainly in mitochondria, has been identified to be associated with numerous pathophysiological processes, and thus accurate ONOO^- imaging with superior sensitivity and selectivity is highly desirable. Herein, we prepared a new type of carbon quantum dots (CQDs) with mitochondria-targeting function without the aid of any targeting molecules via a simple one-step hydrothermal route. The as-prepared CQDs not only displayed relatively uniform size distribution, few surface defects, high photostability, and excellent biocompatibility but also exhibited good selective fluorescence turn-off response toward ONOO^-, owing to the oxidation of amino groups on the surface of carbon dots. A great linear correlation between the quenching efficiency and ONOO^- concentration in the range from 0.15 to 1.0 μM with a detection limit of 38.9 nM is shown. Moreover, the as-prepared CQDs acting as a functional optical probe through a self-targeting mechanism were successfully applied for in situ visualization of endogenous ONOO^- generated in the mitochondria of live cells, providing great promise for elucidating the complex biological roles of ONOO^- in related pathological processes.

Research Progress in the Synthesis of Targeting Organelle Carbon Dots and Their Applications in Cancer Diagnosis and Treatment

With increasing knowledge about diseases at the histological, cytological to sub-organelle level, targeting organelle therapy has gradually been envisioned as an approach to overcome the shortcomings of poor specificity and multiple toxic side effects on tissues and cell-level treatments using the currently available therapy. Organelle carbon dots (CDs) are a class of functionalized CDs that can target organelles. CDs can be prepared by a "synchronous in situ synthesis method" and "asynchronous modification method." The superior optical properties and good biocompatibility of CDs can be preserved, and they can be used as targeting particles to carry drugs into cells while reducing leakage during transport. Given the excellent organelle fluorescence imaging properties, targeting organelle CDs can be used to monitor the physiological metabolism of organelles and progression of human diseases, which will provide advanced understanding and accurate diagnosis and targeted treatment of cancers. This study reviews the methods used for preparation of targeting organelle CDs, mechanisms of accurate diagnosis and targeted treatment of cancer, as well as their application in the area of cancer diagnosis and treatment research. Finally, the current difficulties and prospects for targeting organelle CDs are prospected.

Tunable Organelle Imaging by Rational Design of Carbon Dots and Utilization of Uptake Pathways

Employing one-step hydrothermal treatment of o-phenylenediamine and lysine to exploit their self- and copolymerization, four kinds of CDs (ECDs, NCDs, GCDs, and LCDs) are synthesized, possessing different surface groups (CH₃, C-O-C, NH₂, and COOH) and lipophilicity which endow them with various uptake pathways to achieve tunable organelle imaging. Specifically, highly lipophilic ECDs with CH₃ group and NCDs with C-O-C group select passive manner to target to endoplasmic reticulum and nucleus, respectively. Amphiphilic GCDs with CH₃, C-O-C and NH₂ groups prefer caveolin-mediated endocytosis to locate at Golgi apparatus. Highly hydrophilic LCDs with CH₃, NH₂ and COOH groups are involved in clathrin-mediated endocytosis to localize in lysosomes. Besides, imaging results of cell division, three-dimensional reconstruction and living zebrafish demonstrate that the obtained CDs are promising potential candidates for specific organelle-targeting imaging.

Lysosome targeting, Cr(vi) and l-AA sensing, and cell imaging based on N-doped blue-fluorescence carbon dots

N-doped blue-fluorescence carbon dots (N-CDs) were fabricated via a one-pot hydrothermal method using folic acid and p-phenylenediamine. The obtained N-CDs exhibited strong fluorescence (FL) with a considerable quantum yield (QY) of 21.8% and exceptional optical stability under different conditions. Upon introducing Cr(vi), blue FL of N-CDs was distinctly quenched. On subsequent addition of l-AA, the FL of N-CDs could be partially recovered. The fluorescence changes of N-CDs have been utilized to detect Cr(vi) and l-AA in aqueous solutions with linear ranges of 0.10-150 μM and 0.75-2.25 mM, respectively, as well as limit of detection values of 9.4 nM and 25 μM, respectively. Furthermore, as-obtained N-CDs can be extended to monitor the fluctuation of intracellular Cr(vi) and l-AA. More intriguingly, N-CDs can target lysosomes with a satisfactory Pearson correction coefficient of 0.87, which indicates a promising application prospect in the biomedical field.

Carbon Nanomaterials: Synthesis, Functionalization and Sensing Applications

Recent advances in nanomaterial design and synthesis has resulted in robust sensing systems that display superior analytical performance. The use of nanomaterials within sensors has accelerated new routes and opportunities for the detection of analytes or target molecules. Among others, carbon-based sensors have reported biocompatibility, better sensitivity, better selectivity and lower limits of detection to reveal a wide range of organic and inorganic molecules. Carbon nanomaterials are among the most extensively studied materials because of their unique properties spanning from the high specific surface area, high carrier mobility, high electrical conductivity, flexibility, and optical transparency fostering their use in sensing applications. In this paper, a comprehensive review has been made to cover recent developments in the field of carbon-based nanomaterials for sensing applications. The review describes nanomaterials like fullerenes, carbon onions, carbon quantum dots, nanodiamonds, carbon nanotubes, and graphene. Synthesis of these nanostructures has been discussed along with their functionalization methods. The recent application of all these nanomaterials in sensing applications has been highlighted for the principal applicative field and the future prospects and possibilities have been outlined.

Fluorescent Carbon Dots: Fantastic Electroluminescent Materials for Light-Emitting Diodes

Fluorescent carbon dots (CDs) have emerged as fantastic luminescent nanomaterials with significant potentials on account of their unique photoluminescence properties, high stability, and low toxicity. The application of CDs in electroluminescent light-emitting diodes (LEDs) have aroused much interest in recent years. Herein, the state-of-the-art advances of CD-based electroluminescent LEDs are summarized, in which CDs act as active emission layer and interface transport layer materials is discussed and highlighted. Besides, the device structure of CD-based LEDs and preparation methods of CDs are also introduced. Furthermore, the opportunities and challenges for achieving high performance CD-based electroluminescent LED devices are presented. This review article is expected to stimulate more unprecedented achievements derived from CDs and CD-based electroluminescent LEDs, thus further promoting their practical applications in future solid-state lighting and flat-panel displays.

Quantitatively Switchable pH-Sensitive Photoluminescence of Carbon Nanodots

pH sensing plays a key role in the life sciences as well as the environmental, industrial, and agricultural fields. Carbon nanodots (C-dots) with small size, low toxicity, and excellent stability hold great potential in pH sensing as nanoprobes due to their intrinsic pH-sensitive photoluminescence (PL). Nonetheless, the undesirable sensitivity and response range of C-dot PL toward pH cannot meet the requirements of practical applications, and the unclear pH-sensitive PL mechanism makes it difficult to control their pH sensitivity. Herein, the quantitative correlation of pH-sensitive PL with specific surface structures of C-dots is uncovered for the first time, to our best knowledge. The association of carboxylate and H⁺ increases the ratio of nonradiation to radiation decay of C-dots through excited-state proton transfer, resulting in the decrease of PL intensity. Meanwhile, the dissociation of α-H in β-dicarbonyl forming enolate increases the extent of delocalization of the C-dots conjugated system, which induces the PL broadening to the red region and a decreasing intensity. Based on the understanding of the pH-sensitive PL mechanism, the pH-sensitive PL of C-dots can be switched by quantitative modulation of carboxyl and β-dicarbonyl groups to achieve a desirable pH response range with high sensitivity. This work contributes to a better understanding of the pH-sensitive PL of C-dots and therefore presents an effective strategy for controllably tuning their pH sensitivity, facilitating the rational design of C-dot-based pH sensors.

Biocompatibility nanoprobe of MXene N-Ti3C2 quantum dot/Fe3+ for detection and fluorescence imaging of glutathione in living cells

MXene quantum dots have attracted much attention due to their great optical performance and excellent water solubility. Glutathione (GSH) plays a key role in living cells. In this study, a biocompatibility nanoprobe was prepared for detecting intracellular GSH based on MXene N-Ti₃C₂ quantum dots (N-Ti₃C₂ QDs). The N-Ti₃C₂ QDs act as the fluorescence reporters and the ferric iron (Fe³⁺) as the quenchers based on nonradiative electron-hole annihilation. When Fe³⁺ encounters the amino group of N-Ti₃C₂ QDs, the electrons of N-Ti₃C₂ QDs in the excited state will transfer to the half-filled 3d orbitals of Fe³⁺, leading to the fluorescence quenching of N-Ti₃C₂ QDs. When the N-Ti₃C₂ QDs/Fe³⁺ nanoprobe acts on the cancer cell MCF-7, the abundant GSH in the cancer cells can reduce Fe³⁺ to Fe²⁺, which will restore the fluorescence of N-Ti₃C₂ QDs. The N-Ti₃C₂ QDs/Fe³⁺ nanoprobe displays a high sensitivity for GSH with a detection limit of 0.17 μM in range of 0.5-100 μM. It becomes a promising probe for detecting and showing cellular imaging of GSH in MCF-7 cells. The N-Ti₃C₂ QDs/Fe³⁺ nanoprobe might provide a new way for imaging-guided precision cancer diagnosis.

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.

A Mini Review on pH-Sensitive Photoluminescence in Carbon Nanodots

Carbon nanodots (C-dots) with sp2/sp3 framework and diameter of <10 nm contain abundant functional groups or polymers on their surface. C-dots have attracted immense attention because of their unique optical properties, excellent biocompatibility, facile preparation, and low cost. With these merits, C-dots have been used in a wide range of applications including sensing, bioimaging, catalysis, and light-emitting devices. C-dots exhibit good optical properties, such as tunable emission wavelength, good photostability, nonblinking, up-conversion emission, etc. Of note, C-dots show intrinsic pH-sensitive photoluminescence (PL), indicating their great potential for pH sensing, especially in biotic pH sensing. In this review, we systematically summarize the pH-sensitive PL properties and the pH-sensitive PL mechanism, as well as recent research progress of C-dots in pH sensing. The current challenges of pH-sensitive C-dots and their future research focus are also proposed here. We anticipate this review might be of great significance for understanding the characteristics of pH-sensitive C-dots and the development of photoluminescent nanomaterials with pH-sensitive properties.

The Rapid and Large-Scale Production of Carbon Quantum Dots and their Integration with Polymers

Carbon quantum dots (CDs) have inspired vast interest because of their excellent photoluminescence (PL) performances and their promising applications in optoelectronic, biomedical, and sensing fields. The development of effective approaches for the large-scale production of CDs may greatly promote the further advancement of their practical applications. In this Minireview, the newly emerging methods for the large-scale production of CDs are summarized, such as microwave, ultrasonic, plasma, magnetic hyperthermia, and microfluidic techniques. The use of the available strategies for constructing CD/polymer composites with intriguing solid-state PL is then described. Particularly, the multiple roles of CDs are emphasized, including as fillers, monomers, and initiators. Moreover, typical applications of CD/polymer composites in light-emitting diodes, fluorescent printing, and biomedicine are outlined. Finally, we discuss current problems and speculate on their future development.

Fe3+ and intracellular pH determination based on orange fluorescence carbon dots co-doped with boron, nitrogen and sulfur

The fluorescent boron, nitrogen and sulfur co-doped carbon dots (BNSCDs) were prepared by simple hydrothermal reaction of 4-carboxyphenylboronic acid and 2,5-diaminobenzenesulfonic acid at 200 °C for 8 h. The fluorescence of the BNSCDs could be quenched by Fe³⁺ based on the electron transfer between Fe³⁺ and BNSCDs, so a label-free, good selectivity and high sensitivity method for Fe³⁺determination was established with linear range and LOD of 1.5-692 μmol/L and 87 nmol/L, respectively. And then the fluorescent probe was employed for detection of Fe³⁺ in tap water, coal gangue, fly ash and food samples successfully. Moreover, the as-prepared BNSCDs could serve as a novel pH fluorescent probe in the range of pH 1.60-7.00, which could be attributed to the proton transfer of carboxyl groups on the surface of BNSCDs. More importantly, the pH fluorescent probe possesses fast, real-time and low toxicity, applying for intracellular pH fluorescence imaging in HIC, HIEC, LO2 and SMMC7721 cells. In view of its simplicity, timely response and outstanding compatibility, the as-fabricated BNSCDs show the potential applications in water quality and solid waste monitoring, food detection, real-time measuring of intracellular pH change in vitro.

Rational Design of Far-Red to Near-Infrared Emitting Carbon Dots for Ultrafast Lysosomal Polarity Imaging

Carbon dots (CDs) have been widely studied for their excellent properties. However, most of the prepared CDs only show strong emission in the blue to green region, which greatly limits the application of CDs in the biomedical field. In this report, a new design strategy of long-wavelength CDs was reported. The orange phenyl-CDs with good optical properties and biocompatibility were successfully prepared by changing the substituted group of the o-phenylenediamine and the main emission band of phenyl-CDs was in the far-red region. With the increase of polarity, the wavelength of phenyl-CDs red-shifts and the fluorescence intensity decreases, demonstrating their sensitive polarity response function. In addition, phenyl-CDs can achieve ultrafast target imaging of lysosome within 40 s through clathrin-mediated endocytosis. Finally, phenyl-CDs were successfully applied for monitoring lysosomal polarity induced by drugs, which is helpful in getting a better understanding of the physiological and pathological processes of lysosomes. This report provides an important theoretical basis for the rational design and precise synthesis of long-wavelength fluorescent CDs.

A ratiometric fluorescent probe for pH detection based on Ag2S quantum dots-carbon dots nanohybrids

In this study, a novel ratiometric fluorescent nanoprobe for pH monitoring has been developed by synthesizing red fluorescent Ag₂S quantum dots (Ag₂S QDs) and green fluorescent carbon dots (CDs) nanohybrids (Ag₂S CDs) in one pot using CDs as templates. The nanoprobe exhibits dual-emission peaks at 500 and 670 nm under a single-excitation wavelength of 450 nm. The red fluorescence can be selectively quenched by increasing pH, while the green fluorescence is an internal reference. Therefore, the change of the relative fluorescence intensity (I₅₀₀/I₆₇₀) in the ratiometric Ag₂S CDs probes can be used for pH sensing. The results revealed that I₅₀₀/I₆₇₀ of Ag₂S CDs probes was linearly related to pH variation between pH 5.4 and 6.8. Meanwhile, the Ag₂S CDs probes possessed a good reversibility along with pH changing between 5.0 and 7.0 without any interruption from common metal ions, proteins and other interferences.

N-doped carbon dots triggered the induction of ROS-mediated cytoprotective autophagy in Hepa1-6 cells

Carbon dots (CDs) are an emerging fluorescent nano-imaging probe due to their unique characteristics, such as good conductivity, carbon-based chemical composition, and photochemical stability, which sets up the potential of outperforming the classic metal-based quantum dots (QDs). It is a timely effort to proactively investigate the biocompatibility feature of CDs with a view to safely utilize this emerging nanomaterial in biological systems. In this study, we assessed the safety profile of an in-house synthesized CDs in hepatocyte-like Hepa 1-6 cells, which represents an important target organ for CDs exposure through either particle uptake and/or accumulation and elimination from primary exposure sites post particle administration. We not only demonstrated a dose- and time-dependent compromised cell viability, but also observed the induction of autophagy at high concentration (i.e. 400 μg mL-1), authenticated by the conversion of microtubule-associated protein light chain 3 (LC3)-I to LC3-II. We attributed these changes as the protective mechanism by which the cells used to compensate for CDs-induced apoptosis and cytotoxicity. The involvement of autophagy was further confirmed because the cytotoxicity profile can be increased or reduced by the use of 3-MA (autophagy inhibitor) and NAC (ROS inhibitor), respectively. Collectively, our findings revealed dose-dependent moderate cytotoxicity in Hepa 1-6 cells. Mechanistic understanding of autophagy during the cellular process revealed the homeostasis when liver cells deal with CDs as an external insult.

Carbon dots for lysosome targeting and imaging of lysosomal pH and Cys/Hcy in living cells

The abnormal concentrations of both biothiols and pH in lysosomes are seriously related to many major diseases, such as Parkinson's and Alzheimer's diseases. Up to now, there are few reports that clearly illustrate the relationship between lysosomal pH and biothiols via fluorescence assay. Herein, novel carbon dots (Scy-CDs) are prepared with good water dispersibility and excellent photostability, and a large Stokes shift of 106 nm is exhibited under an excitation wavelength of 450 nm. The remarkable pH-dependent behavior of Scy-CDs is presented with the fluorescence quenching based on the donor-excited photoinduced electron transfer (d-PET) process. The pKa value is 5.30, which is in good agreement with the range of the normal and abnormal lysosomal pH. Upon the addition of cysteine (Cys) or homocysteine (Hcy), the d-PET process is effectively inhibited with fluorescence recovery totally. The significant co-localization of Scy-CDs with Lyso-Tracker Deep Red in HEp-2 cells and the Pearson correlation coefficient 0.88 strongly suggest that the Scy-CDs can target lysosomal pH and Cys/Hcy in living cells.

Fluorescent Carbon Dots for Selective Labeling of Subcellular Organelles

With the recent advancement in understanding and control of the structure and optical properties of fluorescent carbon dots (CDs), they have been shown to be valuable in biolabeling of bacteria, tumor cells, tissues, and organelles. Their extremely small size and tunable functional properties coupled with ultrastable fluorescence enable CDs to be used for easy and effective labeling of various organelles. In addition, CDs with advantages of easy preparation and functionalization with recognition elements and/or drugs have emerged as nanocarriers for organelle-targeted drug delivery. In this review, we mainly discuss the applications of fluorescent CDs for the labeling of organelles, including lysosome, nucleoli, nucleus, endoplasmic reticulum, and mitochondria. We highlight the importance of the surface properties (functional groups, hydrophobicity/hydrophilicity, charges, zwitterions) and the size of CDs for labeling. Several interesting examples are provided to highlight the potential and disadvantages of CDs for labeling organelles. Strategies for the preparation of CDs for specific labeling of organelles are suggested. With the edge in preparation of diverse CDs, their potential in labeling and drug delivery is highly expected.

Self-Enhanced Carbonized Polymer Dots for Selective Visualization of Lysosomes and Real-Time Apoptosis Monitoring

Protons are highly related to cell viability during physiological and pathological processes. Developing new probes to monitor the pH variation could be extremely helpful to understand the viability of cells and the cell death study. Carbonized polymer dots (CPDs) are superior biocompatible and have been widely applied in bioimaging field. Herein, a new type of extreme-pH suitable CPDs was prepared from citric acid and o-phenylenediamine (CA/oPD-CPDs). Due to the co-existence of hydrophilic and hydrophobic groups, CA/oPD-CPDs tend to aggregate in neutral condition with a dramatic decrease of fluorescence, but disperse well in both acidic and alkaline conditions with brighter emission. This specialty enables them to selectively illuminate lysosomes in cells. Moreover, CA/oPD-CPDs in the cytoplasm could serve as a sustained probe to record intracellular pH variation during apoptosis. Furthermore, CA/oPD-CPDs present a continuous fluorescence increase upon 2-h laser irradiation in living cells, underscoring this imaging system for long-term biological recording.

Hg2+ detection, pH sensing and cell imaging based on bright blue-fluorescent N-doped carbon dots

A multifunctional sensing platform based on bright blue-fluorescent nitrogen-doped carbon dots (N-CDs) has been ingeniously designed for the sensitive determination of Hg²⁺ and pH.

Intrinsic lysosomal targeting fluorescent carbon dots with ultrastability for long-term lysosome imaging

Intrinsic lysosomal targeting carbon dots were synthesized with ultrastability for long-term lysosome imaging of living cells and drug-induced apoptotic cells.

Lifetime-tunable room-temperature phosphorescence of polyaniline carbon dots in adjustable polymer matrices

Despite the excellent room-temperature phosphorescence (RTP) property of carbon dot (CD)-based RTP composites, the development of these emerging materials with finely tunable afterglow lifetimes still remains a challenge. Herein, for the first time, we report a series of pure organic RTP composite materials based on adjustable polyaniline carbon dots (PACDs) and polymer matrices (polyacrylic acid, polyacrylamide, and polyvinyl alcohol) with tunable RTP lifetimes. By using different polymer matrices and adjusting the functional groups of PACDs, the strength of hydrogen bonding between each polymer matrix and PACDs was regulated, and green RTP emissions with a tunable average lifetime ranging from 184 ms to 652 ms were also realized. In addition, taking advantage of their different persistent afterglow lifetimes, naked-eye-observable and time-resolved anti-counterfeit and data encryption patterns were prepared using these PACDs/polymer composites, demonstrating the potential application of these materials.

High Amplification of the Antiviral Activity of Curcumin through Transformation into Carbon Quantum Dots

It is demonstrated that carbon quantum dots derived from curcumin (Cur-CQDs) through one-step dry heating are effective antiviral agents against enterovirus 71 (EV71). The surface properties of Cur-CQDs, as well as their antiviral activity, are highly dependent on the heating temperature during synthesis. The one-step heating of curcumin at 180 °C preserves many of the moieties of polymeric curcumin on the surfaces of the as-synthesized Cur-CQDs, resulting in superior antiviral characteristics. It is proposed that curcumin undergoes a series of structural changes through dehydration, polymerization, and carbonization to form core-shell CQDs whose surfaces remain a pyrolytic curcumin-like polymer, boosting the antiviral activity. The results reveal that curcumin possesses insignificant inhibitory activity against EV71 infection in RD cells [half-maximal effective concentration (EC₅₀ ) >200 µg mL^-1 ] but exhibits high cytotoxicity toward RD cells (half-maximal cytotoxic concentration (CC₅₀ ) <13 µg mL^-1 ). The EC₅₀ (0.2 µg mL^-1 ) and CC₅₀ (452.2 µg mL^-1 ) of Cur-CQDs are >1000-fold lower and >34-fold higher, respectively, than those of curcumin, demonstrating their far superior antiviral capabilities and high biocompatibility. In vivo, intraperitoneal administration of Cur-CQDs significantly decreases mortality and provides protection against virus-induced hind-limb paralysis in new-born mice challenged with a lethal dose of EV71.

Water-soluble organic probe for pH sensing and imaging

pH value is one of the most important parameters, which show significant application in environmental monitoring, chemistry and biology. Abnormal pH values always associate with some serious diseases, including cancer and Alzheimer's disease. Thus, development of highly sensitive and selective method for pH sensing and imaging is of great importance. In this paper, we synthesized a water-soluble organic probe for pH sensing either through its absorption or through its fluorescent signals. The probe was synthesized from the intermediate containing a phenol group, and the reaction was carried out in concentrated H₂SO₄ at 90 °C. In this way, the probe can introduce a sulfonic acid group into its structure, and thus improve its water solubility. The synthesized probe is pH-responsive, and the response process is reversible, because that the phenol group in the probe can transfer to deprotonation state with increasing the pH values to improve the intramolecular charge transfer. Meanwhile, the synthesized probe also showed high specificity and excellent biocompatibility, which is suitable for cell imaging applications.

Lysosome-targeted carbon dots for ratiometric imaging of formaldehyde in living cells

Formaldehyde (FA) is involved in many biological processes and is closely connected with many diseases including Alzheimer's disease and cancer. Therefore, methods for sensitive and selective detection of FA in living cells are highly demanded. As a new class of carbon nanomaterials, carbon dots (CDs) have attracted great attention owing to their robust photostability, good biocompatibility and environmental friendliness. In this manuscript, the first lysosome-targeted CDs for ratiometric fluorescence detection of FA were efficiently prepared from dexamethasone and 1,2,4,5-tetraaminobenzene through the microwave-assisted hydrothermal method. These CDs show highly selective and sensitive sensing ability towards FA with fast response and great changes of ratio values. The CDs exhibit robust photostability and good biocompatibility and were successfully employed in ratiometric fluorescence bioimaging of FA fluctuations in lysosomes of living cells, which demonstrates their great practicability in FA-related bioanalysis and biological studies.

A ratiometric fluorescent nanoprobe based on naphthalimide derivative-functionalized carbon dots for imaging lysosomal formaldehyde in HeLa cells

Endogenous formaldehyde (FA) exists in many living cells and in inhomogeneous distribution in organelles. In particular, lysosomes play significant roles in FA generation and the biofunction of living cells. Herein, we developed a new ratiometric fluorescent nanoprobe, based on naphthalimide derivative (ND)-functionalized carbon dots (CDs), for monitoring endogenous FA in lysosomes. The fluorescence intensity (F535) of green-emitting ND at 535 nm serves as the response signal and the fluorescence intensity (F414) of blue-emitting CDs at 414 nm acts as the reference signal. The fluorescence intensity ratio (F535/F414) of the CD-ND probe is linearly correlated with FA concentration within the range of 1-40 μM in aqueous solution, and the detection limit (3σ/slope) is estimated to be 0.34 μM. As for practical application, this nanoprobe is utilized for the ratiometric fluorescence imaging of FA in live cells. Remarkably, this nanoprobe can specifically target and stain the lysosomes and detect exogenous and endogenous FA in HeLa cells. The new FA probe shows a superior lysosomal targeting ability with a Pearson's coefficient of 0.93, which is attributed to the macromolecular size and basic amine group functionalized surface of CD-ND.

Near-white photoluminescence in paramagnetic Gd6O5F8 nanoparticles

White light emission has been achieved by near full band excitation from 10.7 nm sized pure Gd₆O₅F₈ nanoparticles.

Synthesis of highly stable red-emissive carbon polymer dots by modulated polymerization: from the mechanism to application in intracellular pH imaging

Great efforts have been made to develop facile and efficient methods to prepare carbonaceous nanostructures with long-wavelength emission. Herein, we report a low-temperature aqueous strategy to synthesize red-emissive carbon polymer dots (R-CPDs) through the regulation of oxidative polymerization of p-phenylenediamine at 80 °C. The morphology, chemical composition and photophysical properties of the R-CPDs are characterized and analyzed in detail, thereby elucidating their photoluminescence origins from the surface state and crosslink enhanced emission effect. The resulting R-CPDs possess unique features including high pH-sensitivity within pH 4-6 and a wide-range tunable solvent-color effect (λ_em 528-600 nm). Moreover, the R-CPDs show high stability in physiological media with high salinity, and good resistance to photobleaching. In addition to their favorable biocompatibility, the R-CPDs are applied for monitoring the pH fluctuation in HeLa cells. This study not only provides a unique red emissive carbonaceous nanomaterial for cellular imaging and multicolor applications, but also presents a novel perspective for the construction of long-wavelength emission carbon-based nanomaterials by simple and controllable strategies.