Doped-carbon dots: Recent advances in their biosensing, bioimaging and therapy applications

Metal-doped carbon dots for biomedical applications: From design to implementation

Carbon dots (CDs), as a new kind of fluorescent nanomaterials, show great potential for application in several fields due to their unique nano-size effect, easy surface functionalization, controllable photoluminescence, and excellent biocompatibility. Conventional preparation methods for CDs typically involve top-down and bottom-up approaches. Doping is a major step forward in CDs design methodology. Chemical doping includes both non-metal and metal doping, in which non-metal doping is an effective strategy for modulating the fluorescence properties of CDs and improving photocatalytic performance in several areas. In recent years, Metal-doped CDs have aroused the interest of academics as a promising nano-doping technique. This approach has led to improvements in the physicochemical and optical properties of CDs by altering their electron density distribution and bandgap capacity. Additionally, the issues of metal toxicity and utilization have been addressed to a large extent. In this review, we categorize metals into two major groups: transition group metals and rare-earth group metals, and an overview of recent advances in biomedical applications of these two categories, respectively. Meanwhile, the prospects and the challenges of metal-doped CDs for biomedical applications are reviewed and concluded. The aim of this paper is to break through the existing deficiencies of metal-doped CDs and fully exploit their potential. I believe that this review will broaden the insight into the synthesis and biomedical applications of metal-doped CDs.

In-Brain Multiphoton Imaging of Vaterite Cargoes Loaded with Carbon Dots

Biocompatible fluorescent agents are key contributors to the theranostic paradigm by enabling real-time in vivo imaging. This study explores the optical properties of phenylenediamine carbon dots (CDs) and demonstrates their potential for fluorescence imaging in cells and brain blood vessels. The nonlinear absorption cross-section of the CDs was measured and achieved values near 50 Goeppert-Mayer (GM) units with efficient excitation in the 775-895 nm spectral range. Mesoporous vaterite nanoparticles were loaded with CDs to examine the possibility of a biocompatible imaging platform. Efficient one- and two-photon imaging of the CD-vaterite composites uptaken by diverse cells was demonstrated. For an in vivo scenario, CD-vaterite composites were injected into the bloodstream of a mouse, and their flow was monitored within the blood vessels of the brain through a cranial window. These results show the potential of the platform for high-brightness biocompatible imaging with the potential for both sensing and simultaneous drug delivery.

Rapid environmentally benign label free detection of heparin using highly fluorescent N,S-CDs sensing probe through a turn-on mechanism

Heparin (HEP) is one of the oldest anticoagulant drugs that currently still in widespread clinical use. It lacks chromophore and not easily derivatized due to its hydrophilic nature. In this work we developed a green, selective, and sensitive fluorescence sensor for detection of HEP in its injection dosage forms. The sensor is composed of nitrogen and sulfur co-doped carbon quantum dots (N,S-CDs) semi quenched by Fe3+. The N,S-CDs were prepared using microwave assisted pyrolysis in 3.5 min and exhibited high emission at 425 nm after excitation at 350 nm with high quantum yield of 96%. Owing to the anionic nature of HEP, it could compete with N,S-CDs for Fe3+ complexation resulting in turning-on the quenched fluorescence. This fluorescence enhancement was linear over a concentration range between 6 and 20 μg/mL (R2 = 0.99) with a limit of detection of 1.41 µg/ml. The accuracy and precision of the proposed sensor were indicated by percentage recovery values between 98% -102% and %RSD less than 2, respectively. Furthermore, the proposed sensor was successfully applied for determination of HEP in injection dosage form. The developed sensor showed excellent greenness on analytical eco-scale (score 93%) and GAPI scale.

High Quantum Yield Amino Acid Carbon Quantum Dots with Unparalleled Refractive Index

Carbon quantum dots (CQDs) are one of the most promising types of fluorescent nanomaterials due to their exceptional water solubility, excellent optical properties, biocompatibility, chemical inertness, excellent refractive index, and photostability. Nitrogen-containing CQDs, which include amino acid based CQDs, are especially attractive due to their high quantum yield, thermal stability, and potential biomedical applications. Recent studies have attempted to improve the preparation of amino acid based CQDs. However, the highest quantum yield obtained for these dots was only 44%. Furthermore, the refractive indices of amino acid derived CQDs were not determined. Here, we systematically explored the performance of CQDs prepared from all 20 coded amino acids using modified hydrothermal techniques allowing more passivation layers on the surface of the dots to optimize their performance. Intriguingly, we obtained the highest refractive indices ever reported for any CQDs. The values differed among the amino acids, with the highest refractive indices found for positively charged amino acids including arginine-CQDs (∼2.1), histidine-CQDs (∼2.0), and lysine-CQDs (∼1.8). Furthermore, the arginine-CQDs reported here showed a nearly 2-fold increase in the quantum yield (∼86%) and a longer decay time (∼8.0 ns) compared to previous reports. In addition, we also demonstrated that all amino acid based CQD materials displayed excitation-dependent emission profiles (from UV to visible) and were photostable, water-soluble, noncytotoxic, and excellent for high contrast live cell imaging or bioimaging. These results indicate that amino acid based CQD materials are high-refractive-index materials applicable for optoelectronic devices, bioimaging, biosensing, and studying cellular organelles in vivo. This extraordinary RI may be highly useful for exploring cellular elements with different densities.

Functionalized heteroatom-doped carbon dots for biomedical applications: A review

Carbon nanoparticles (CDs) have recently drawn a great attention in (bio)chemical analysis, sensing and bioimaging owing to their photostability, water stability, minimal toxicity, biocompatibility and ease of surface functionalization. While the vast majority of CDs applications rely on exploiting their fluorescent properties, doping such nanomaterials with various elements has recently received increasing attention as an effective approach to modify their optoelectronic characteristics, introducing novel improved optical features such as phosphorescence, upconversion luminescence or multimodal imaging capabilities. This review article focuses in the recent advances on the synthesis of heteroatom-doped CDs, exhibiting distinctive features of high value for sensing and imaging, as well as various functionalization schemes developed for guided analyte labeling. Relevant applications in chemical sensing, bioimaging and disease therapy are here presented. A final section intends to provide an overview towards future developments of such emerging light-emitting nanomaterials in the design of future devices and strategies for (bio)analytical chemistry.

Pharmaceutical pollution fingerprinting and waterbodies remediation using waste-derived carbon dots as sustainable advanced nanomaterials

The conversion of biomass waste into high-value nanomaterials such as carbon dots might represent a great advancement towards a circular economy system. Biomass wastes are an excellent choice as carbon precursors because of their wide availability, abundance, chemical composition, and eco-friendly nature. Moreover, their use as a raw material might decrease the total cost of the synthesis processes and reduce the environmental impacts. In addition, the complex composition of biomass leads to carbon dots with abundant functional groups, which in turn enhances water dispersibility and photoluminescence properties. In this manner, the effective transformation of biomass wastes into carbon dots reduces environmental pollution through the inadequate management of waste while producing carbon dots with enhanced performances. Therefore, this review describes biomass wastes as potential candidates for the synthesis of carbon dots through different synthesis methods. In addition, we have analyzed the great potential of biomass-derived carbon dots (CDs) for the degradation and detection of emerging pharmaceutical pollutants by promoting a circular economy approach. Finally, we identified current challenges to propose possible research directions for the large-scale and sustainable synthesis of high-quality biomass-derived CDs.

Silicon-Carbon Dots-Loaded Mesoporous Silica Nanocomposites (mSiO2@SiCDs): An Efficient Dual Inhibitor of Cu2+-Mediated Oxidative Stress and Aβ Aggregation for Alzheimer's Disease

The redox-active metal ions, especially Cu2+, are highly correlated to Alzheimer's disease (AD) by causing metal ion-mediated oxidative stress and toxic metal-bound β-amyloid (Aβ) aggregates. Numerous pieces of evidence have revealed that the regulation of metal homeostasis could be an effective therapeutic strategy for AD. Herein, in virtue of the interaction of both amino-containing silane and ethylenediaminetetraacetic acid disodium salt for Cu2+, the silicon-carbon dots (SiCDs) are deliberately prepared using these two raw materials as the cocarbon source; meanwhile, to realize the local enrichment of SiCDs and further maximize the chelating ability to Cu2+, the SiCDs are feasibly loaded to the biocompatible mesoporous silica nanoparticles (mSiO2) with the interaction between residual silane groups on SiCDs and silanol groups of mSiO2. Thus-obtained nanocomposites (i.e., mSiO2@SiCDs) could serve as an efficient Cu2+ chelator with satisfactory metal selectivity and further modulate the enzymic activity of free Cu2+ and the Aβ42-Cu2+ complex to alleviate the pathological oxidative stress with an anti-inflammatory effect. Besides, mSiO2@SiCDs show an inspiring inhibitory effect on Cu2+-mediated Aβ aggregation and further protect the neural cells against the toxic Aβ42-Cu2+ complex. Moreover, the transgenic Caenorhabditis elegans CL2120 assay demonstrates the protective efficacy of mSiO2@SiCDs on Cu2+-mediated Aβ toxicity in vivo, indicating its potential for AD treatment.

Carbon dots and composite materials with excellent performances in cancer-targeted bioimaging and killing: a review

Carbon dots (CDs) are nanomaterials with excellent properties, including good biocompatibility, small size, ideal photoluminescence and surface modification, and are becoming one of the most attractive nanomaterials for the imaging, detection and treatment of tumors. Based on these advantages, CDs can be combined other materials to obtain composite particles with improved, even new, performance, mainly in photothermal and photodynamic therapies. This paper reviews the research progress of CDs and their composites in targeted tumor imaging, detection, diagnosis, drug delivery and tumor killing. It also discusses and proposes the challenges and perspectives of their future applications in these fields. This review provides ideas for future applications of novel CD-based materials in the diagnosis and treatment of cancer.

The Green Synthesis of Carbon Quantum Dots through One-step Hydrothermal Approach by Orange Juice for Rapid, and Accurate Detection of Dopamine

In the current study, the fluorescent Carbon quantum dots (CDs) were synthesized through one-step hydrothermal approach by orange juice without any additional agents. The as-prepared green-CDs (GCDs) were quasi-spherical shape ranged from 2 to 8 nm with an average diameter of 5 nm, and emitted bright blue fluorescent (FL) under ultraviolet light irradiation (Uv). Different detailed analyses proved that the as-prepared GCDs had good morphologies, various functional groups, high water solubility, great optical features, and excellent stability towards diverse environmental conditions. The results indicated that the as-prepared GCDs can detect different concentrations of dopamine from 1 to 100 µM based on the quenching of their native fluorescent. Furthermore, the good linear relationship was obtained for dopamine in the broad range of concentrations from 1 to 100 µM with the limit of detection (LOD) of 0.81 µM. In addition, the as-prepared GCDs can be applied as a fluorescent probe for detection of dopamine in the different real samples.

Green synthesis of gardenia seeds-based carbon dots for bacterial imaging and antioxidant activity in aqueous and oil samples

In this work, luminescent carbon dots with gardenia seeds as carbon precursors (GCDs) were synthesized using a one-step mild pyrolysis process and were then used as probes for imaging of bacterial (Escherichia coli). The GCDs showed a strong emission at 430 nm when excited at 370 nm. The relative fluorescence quantum yield of GCDs was found to be 1.13% in an aqueous medium. Rapid internalization of the GCDs by bacteria was confirmed by three colors (blue, green, and yellow) images that were obtained using confocal fluorescence microscopy. In addition, GCDs were noted to exhibit potent scavenging activities against DPPH˙, ˙OH, and ˙O2- free radicals. GCDs were also assayed as antioxidants in an oil sample by volumetric determination of the peroxide value. Thus, GCDs exhibited good antioxidant properties both in aqueous and oil media. In addition, a free fatty acid quantification kit in the presence of GCDs showed enhanced fluorescence detection of palmitic acid with a remarkably good limit of detection of 0.08 μM, which is lower than that in the absence of GCDs (0.76 μM). The proposed fluorescence method was then successfully used to determine the concentration of palmitic acid spiked in milk powder samples, with spiked recoveries of 82.6-109.6% and relative standard deviations of 0.9-4.6%.

Physiological Functions of Carbon Dots and Their Applications in Agriculture: A Review

Carbon dots are carbon-based nanoparticles, which have the characteristics of a simple preparation process, photoluminescence, biocompatibility, an adjustable surface function, water solubility, and low-level toxicity. They are widely used in biological applications, such as imaging, biosensing, photocatalysis, and molecular transfer. They have also aroused great interest among researchers in agriculture, and there has been significant progress in improving crop growth and production. This review presents the physiological functions of carbon dots for crop growth and development, photosynthesis, water and nutrient absorption, and abiotic stress resistance and their applications in improving the ecological environment and agriculture as biosensors, and future application prospects and research directions of carbon dots in agriculture.

π-Conjugated Polymer Nanoparticles from Design, Synthesis to Biomedical Applications: Sensing, Imaging, and Therapy

In the past decade, π-conjugated polymer nanoparticles (CPNs) have been considered as promising nanomaterials for biomedical applications, and are widely used as probe materials for bioimaging and drug delivery. Due to their distinctive photophysical and physicochemical characteristics, good compatibility, and ease of functionalization, CPNs are gaining popularity and being used in more and more cutting-edge biomedical sectors. Common synthetic techniques can be used to synthesize CPNs with adjustable particle size and dispersion. More importantly, the recent development of CPNs for sensing and imaging applications has rendered them as a promising device for use in healthcare. This review provides a synopsis of the preparation and functionalization of CPNs and summarizes the recent advancements of CPNs for biomedical applications. In particular, we discuss their major role in bioimaging, therapeutics, fluorescence, and electrochemical sensing. As a conclusion, we highlight the challenges and future perspectives of biomedical applications of CPNs.

Green synthetic natural carbon dots derived from Fuligo Plantae with inhibitory effect against alcoholic gastric ulcer

Introduction: Fuligo Plantae (FP), the ash that sticks to the bottom of pots or chimneys after weeds burn, has long been used for its hemostatic effects and treatment of gastrointestinal bleeding. Nevertheless, the active ingredient of FP still needs to be further explored. Methods: The microstructure, optical and chemical properties of FP-CDs were characterized. An alcohol-induced gastric ulcer model was utilized to evaluate whether pre-administration of FP-CDs alleviated gastric bleeding symptoms and ameliorated gastric mucosal barrier disruption. In addition, the feces of each group of rats were extracted for 16S rDNA genome sequencing of intestinal flora. Results: FP-CDs with a diameter ranging from 1.4-3.2 nm had abundant chemical groups, which may be beneficial to the exertion of inherent activity. FP-CDs alleviated alcohol-induced gastric ulcer, as demonstrated by activating the extrinsic coagulation pathway, alleviating inflammation, and suppressing oxidative stress levels. More interestingly, FP-CDs can improve the diversity and dysbiosis of intestinal flora in rats with alcohol-induced gastric ulcer. Conclusion: These comes about illustrate the momentous inhibitory effects of FP-CDs on alcoholic gastric ulcer in rats, which give a modern methodology for investigating the effective ingredient of FP, and lay an experimental basis for the application of FP-CDs in the clinical treatment of alcoholic gastric ulcer.

A facile approach for sulphur and nitrogen co-doped carbon nanodots to improve photothermal eradication of drug-resistant bacteria

In this study, we produced S, N co-doped CNDs (SN@CNDs) by using dimethyl sulfoxide (DMSO) and formamide (FA) as single sources of S and N, respectively. We varied the S/N ratios by adjusting the volume ratios of DMSO and FA and investigated their effect on the red-shift of the CNDs' absorption peak. Our findings demonstrate that SN@CNDs synthesized using a volume ratio of 5:6 between DMSO and FA exhibit the most significant absorption peak redshift and enhanced near-infrared absorption performance. Based on comparative analysis of the particle size, surface charge, and fluorescence spectrum of the S@CNDs, N@CNDs, and SN@CNDs, we propose a possible mechanism to explain the change of optical properties of CNDs due to S, N doping. Co-doping creates a more uniform and smaller band gap, resulting in a shift of the Fermi level and a change in energy dissipation from radioactive to non-radiative decay. Importantly, the as-prepared SN@CNDs exhibited a photothermal conversion efficiency of 51.36% at 808 nm and demonstrated exceptional photokilling effects against drug-resistant bacteria in both in vitro and in vivo experiments. Our facile method for synthesizing S and N co-doped CNDs can be extended to the preparation of other S and N co-doped nanomaterials, potentially improving their performance.

Carbon Dots for the Treatment of Inflammatory Diseases: An Appraisal of In Vitro and In Vivo Studies

In recent decades, several studies demonstrating various applications of carbon dots (C-dots), including metal sensing, bioimaging, pH sensing, and antimicrobial activities, have been published. Recent developments have shifted this trend toward biomedical applications that target various biomarkers relevant to chronic diseases. However, relevant developments and research results regarding the anti-inflammatory properties of C-dots against inflammation-associated diseases have not been systematically reviewed. Hence, this review discusses the anti-inflammatory effects of C-dots in in vivo and in vitro models of LPS-induced inflammation, gout, cartilage tissue engineering, drug-induced inflammation, spinal cord injury, wound healing, liver diseases, stomach cancer, gastric ulcers, acute kidney and lung injury, psoriasis, fever or hypothermia, and bone tissue regeneration. The compiled studies demonstrate the promising potential of C-dots as anti-inflammatory agents for the development of new drugs.

Glycyrrhizic acid modified Poria cocos polyscaccharide carbon dots dissolving microneedles for methotrexate delivery to treat rheumatoid arthritis

Introduction: Rheumatoid arthritis is an autoimmune disease characterized by chronic joint inflammation. Methotrexate is one of the most effective drugs for rheumatoid arthritis, but the adverse reactions caused by oral methotrexate greatly limit its clinical application. Transdermal drug delivery system is an ideal alternative to oral methotrexate by absorbing drugs into the human body through the skin. However, methotrexate in the existing methotrexate microneedles is mostly used alone, and there are few reports of combined use with other anti-inflammatory drugs. Methods: In this study, glycyrrhizic acid was first modified onto carbon dots, and then methotrexate was loaded to construct a nano-drug delivery system with fluorescence and dual anti-inflammatory effects. Then hyaluronic acid was combined with nano-drug delivery system to prepare biodegradable soluble microneedles for transdermal drug delivery of rheumatoid arthritis. The prepared nano-drug delivery system was characterized by transmission electron microscopy, fluorescence spectroscopy, laser nanoparticle size analyzer, ultraviolet-visible absorption spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimeter and nuclear magnetic resonance spectrometer. The results showed that glycyrrhizic acid and methotrexate were successfully loaded on carbon dots, and the drug loading of methotrexate was 49.09%. The inflammatory cell model was constructed by lipopolysaccharide-induced RAW264.7 cells. In vitro cell experiments were used to explore the inhibitory effect of the constructed nano-drug delivery system on the secretion of inflammatory factors by macrophages and the cell imaging ability. The drug loading, skin penetration ability, in vitro transdermal delivery and in vivo dissolution characteristics of the prepared microneedles were investigated. The rat model of rheumatoid arthritis was induced by Freund's complete adjuvant. Results: The results of in vivo animal experiments showed that the soluble microneedles of the nano drug delivery system designed and prepared in this study could significantly inhibit the secretion of pro-inflammatory cytokines and had a significant therapeutic effect on arthritis. Discussion: The prepared glycyrrhizic acid-carbon dots-methotrexate soluble microneedle provides a feasible solution for the treatment of Rheumatoid arthritis.

High luminescent N,S,P co-doped carbon dots for the fluorescence sensing of extreme acidity and folic acid

Carbon dots are popular luminescent materials because of their excellent fluorescence properties, but the low quantum yield limits their application. Heteroatom doping is a more convenient and popular approach to increase the quantum yield of carbon dots. Here, novel N,S,P heteroatom co-doped carbon dots (N,S,P-CDs) were synthesized by a simple one-step hydrothermal method using m-phenylenediamine, L-cysteine and phosphoric acid as raw materials. The as-prepared N,S,P-CDs showed excellent photoluminescence properties with a fluorescence quantum yield of up to 41%, which greatly encourages their application in fluorescence sensing. The N,S,P-CDs exhibited good fluorescence stability under salt solution, xenon lamp irradiation and ultraviolet lamp irradiation except for a high sensitivity to extreme acidity. The fluorescence intensity of the N,S,P-CDs can be decreased by as much as 85% when the pH of the solution changes from 2.50 to 4.75, that is, a small fluctuation in pH can cause an intense response of the fluorescence of the N,S,P-CDs. Therefore, an excellent fluorescence sensing platform for accurately monitoring the pH of extreme acidity has been constructed. In addition, the N,S,P-CDs can be applied for quantitative detection of folic acid based on the strong quenching effect of folic acid on the fluorescence of the N,S,P-CDs. Good linearity was obtained in the concentration range of 4.85-82.45 μM, with a detection limit of 0.148 μM. The constructed sensing platform was used for the determination of folic acid in actual samples of orange juice, oatmeal and tablets with satisfactory results.

Fluorescence turn off-on detection of Co2+ and enrofloxacin by N, Cl-carbon dots prepared in deep eutectic solvent and study of their photocatalytic antibacterial activity

Nitrogen, chloride doped carbon dots (N, Cl-CDs) were synthesized in deep eutectic solvent. TEM, XRD, FT-IR, XPS, EDAX, UV-Vis and fluorescence were used for characterization. Quantum yield and average size of N, Cl-CDs were 38.75 % and 2-3 nm, respectively. N, Cl-CDs fluorescence was turn off by cobalt ion and then turn on gradually after addition of enrofloxacin. Linear dynamic range and detection limit (DL) for Co²⁺ and enrofloxacin were (0.1-70 µM and 30 nM) and (0.05-50 µM and 25 nM), respectively. Enrofloxacin was detected in blood serum and water samples with the recovery of 96-103 %. Finally, Antibacterial activity of the carbon dots was also investigated.

Nitrogen and copper-doped saffron-based carbon dots: Synthesis, characterization, and cytotoxic effects on human colorectal cancer cells

AIM

Doped carbon dots (CDs) have attracted tremendous attention in cancer therapy. We aimed to synthesize copper, nitrogen-doped carbon dots (Cu, N-CDs) from saffron and investigated their effects on HCT-116 and HT-29 colorectal cancer (CRC) cells.

MAIN METHODS

CDs were synthesized by hydrothermal method and characterized by transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV-Vis) absorption spectroscopy, and fluorescence spectroscopy. HCT-116 and HT-29 cells were incubated with saffron, N-CDs, and Cu, N-CDs for 24 and 48 h for cell viability. Cellular uptake and intracellular reactive oxygen species (ROS) were evaluated by immunofluorescence microscopy. Oil Red O staining was used to monitor lipid accumulation. Apoptosis was evaluated using acridine orange/propidium iodide (AO/PI) staining and quantitative real-time polymerase chain reaction (Q-PCR) assay. The expression of miRNA-182 and miRNA-21 was measured by Q-PCR, while the generation of nitric oxide (NO) and lysyl oxidase (LOX) activity was calculated by colorimetric methods.

KEY FINDINGS

CDs were successfully prepared and characterized. Cell viability decreased in the treated cells dose- and time-dependently. HCT-116 and HT-29 cells uptook Cu, N-CDs with a high level of ROS generation. The Oil Red O staining showed lipid accumulation. Concomitant with an up-regulation of apoptotic genes (p < 0.05), AO/PI staining showed increased apoptosis in the treated cells. In comparison to control cells, NO generation, and miRNA-182 and miRNA-21 expression significantly changed in the Cu, N-CDs treated cells (p < 0.05).

SIGNIFICANCE

The results indicated that Cu, N-CDs could inhibit CRC cells through the induction of ROS generation and apoptosis.

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

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

One-Step Colloidal Synthesis of Non-Toxic Electroactive Carbon Dots with a Better Threshold Cytotoxicity and Cytocompatibility

Carbon dots (CDs), because of their characteristic size (<10 nm) and highly fluorescent nature, can be internalized in biological cells or can be tagged to the key components of a living system. While these attributes can be potentially exploited for biomedical applications, the toxicity of CDs remains an important issue to be addressed. Both the synthesis approach and morphological attributes critically determine the dose-dependent toxicity and cytocompatibility of CDs. Against this perspective, we report herein a one-step colloidal synthesis of CDs using different reaction solvents that lead to the formation of three types of CDs (type I, type II, and type III CDs). The cytocompatibility and cellular uptake of CDs in human mesenchymal stem cells (hMSCs) are dependent on the nature of functionalization and concomitantly on the type of precursors. In particular, type I CDs are synthesized using citric acid, hexadecylamine, and octadecene that are immiscible in culture media. The type II CDs synthesized using citric acid and octadecene emit green fluorescence at a 488 nm excitation and were found to be agglomerated when internalized in hMSCs, whereas the type III CDs, synthesized using citric acid and deionized water, exhibit an agglomeration-free behavior. Further, type III CDs show a wide particle distribution, wide emission bandwidth range of 280-700 nm, threshold toxicity of 1 mg/mL, and good cytocompatibility with hMSCs, much better than those in the published reports. When benchmarked against commercial graphene quantum dots, the as-synthesized type III CDs have better electrical conductivity and cytocompatibility at a given dosage. Thus, the electroactive nature of synthesized type III CDs along with their inherent fluorescent property and less cytotoxicity would enable their potential applications in bio-imaging, directional lineage commitment, and cell-based therapy.

Nitrogen-Doped Carbon Quantum Dots for Biosensing Applications: The Effect of the Thermal Treatments on Electrochemical and Optical Properties

The knowledge of the ways in which post-synthesis treatments may influence the properties of carbon quantum dots (CDs) is of paramount importance for their employment in biosensors. It enables the definition of the mechanism of sensing, which is essential for the application of the suited design strategy of the device. In the present work, we studied the ways in which post-synthesis thermal treatments influence the optical and electrochemical properties of Nitrogen-doped CDs (N-CDs). Blue-emitting, N-CDs for application in biosensors were synthesized through the hydrothermal route, starting from citric acid and urea as bio-synthesizable and low-cost precursors. The CDs samples were thermally post-treated and then characterized through a combination of spectroscopic, structural, and electrochemical techniques. We observed that the post-synthesis thermal treatments show an oxidative effect on CDs graphitic N-atoms. They cause their partially oxidation with the formation of mixed valence state systems, [CDs]⁰⁺, which could be further oxidized into the graphitic N-oxide forms. We also observed that thermal treatments cause the decomposition of the CDs external ammonium ions into ammonia and protons, which protonate their pyridinic N-atoms. Photoluminescence (PL) emission is quenched.

Facile Synthesis of Carbon Dots from Amido Black 10b for Sensing in Real Samples

Herein, a one-step hydrothermal synthesis method was adopted to fabricate carbon dots (CDs) from amido black 10b in a sodium hydroxide solution. The morphology and composition of the CDs were investigated by XRD, FTIR TEM, XPS, UV-vis, and fluorescence spectroscopy. The obtained CDs (AB-CDs) with an average diameter of 19.4 nm displayed a well-dispersed characteristic in aqueous solutions. The as-prepared CDs showed bright blue fluorescence and good photostability, with a high quantum yield of 24.1%. AB-CDs displayed a selective and noticeable turn-off response to Fe³⁺. Accordingly, the quantitative detection of Fe³⁺ was achieved in the range of 5-200 μmol L^-1 with a detection limit of 1.84 μmol L^-1. The fluorescence response mechanism of Fe³⁺ to AB-CDs was ascribed to static quenching due to the emergence of the ground-state complex. Moreover, ascorbic acid could restore the fluorescence of AB-CDs quenched by Fe³⁺ by reducing Fe³⁺ to Fe²⁺. The developed nanoprobe was used to detect ascorbic acid with a limit of detection of 7.26 μmol L^-1 in the range of 20-300 μmol L^-1. Furthermore, the developed sensing system was successfully applied for an Fe³⁺ assay in a lake water sample and ascorbic acid detection in a human urine sample. The AB-CD-based analytical system showed its latent practical value in the chemical analysis and bioanalytical fields.

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.

Excitation-independent deep-blue emitting carbon dots with 62% emission quantum efficiency and monoexponential decay profile for high-resolution fingerprint identification

Reaching emissive nanomaterials at short wavelengths with a high quantum efficiency (QE) is an attractive task for researchers. This is more demanding in carbon dots (CDs) with diverse applications that usually emit photons at wavelengths around 450-620 nm. In this study, deep blue-emissive doped-CDs (d-CDs) with high photoluminescence (PL) QE up to 62% and excitation-independent properties were prepared via a short-time microwave irradiation method. The prepared CDs showed simultaneous amorphous and crystalline features, with average sizes of 4.75 nm and bright emission color located at 422 nm. It was found that the presence of sulfur-related dopant levels plays a key role in emission properties in such a way that the PL signal drops significantly in the absence of N-acetyl-l-cysteine (NAC) as a dopant source. On the other hand, the trisodium citrate dihydrate (TSC) was selected as a carbon source to form the main carbon skeleton without it no emission was recorded. Monoexponential-fitted recombination trend with an average lifetime of about 10 ns also confirmed excellent PL emission properties with uniform energy levels and minimized defect-contributing recombinations. The practical use of the as-prepared N, S-doped CDs was assessed in fingerprint detection indicating a bright and clear scheme for both core and termination regions of the fingerprint. Simplicity, cost-effectiveness, high-product yield, low toxicity, along with high/stable PL quantum efficiency in deep-blue wavelengths, and demonstrated ability for fingerprint purposes, support the prospective application of these dual doped-CDs for sensing and bioimaging applications.

Sulfur quantum dots as a novel platform to design a sensitive chemiluminescence probe and its application for Pb2+ detection

The monitoring of Pb as a hazardous heavy metal element for the environment and human health is of high importance. In this study, a simple and sensitive chemiluminescence (CL) probe based on sulfur quantum dots (SQDs) was designed for the determination of Pb²⁺ . To the best of our knowledge, this is the first report about the analytical application of the CL method based on SQDs. For this purpose, SQDs were synthesized by a simple hydrothermal method and characterized by TEM, FT-IR, XPS and X-ray diffraction. Then, the direct chemiluminescence (CL) of SQDs elicited by common oxidants was investigated. The highest CL intensity was observed for the SQDs-KMnO₄ reaction, and its CL mechanism was studied. We indicated that the CL intensity of introduced system can be diminished as a result of interaction between Pb²⁺ and SQDs, and exploited this fact for designing a CL-based probe for the determination of Pb²⁺ . The CL intensity of SQDs-KMnO₄ reaction was linearly quenched by Pb²⁺ at the range of 50 to 2000 nM with a limit of detection as 16 nM (S/N=3). The probe was employed for the determination of Pb²⁺ in different water samples and the recovery results (95.2 to 102.8%) indicated the good analytical performance of the developed method.

Carbon dots-based nanomaterials for fluorescent sensing of toxic elements in environmental samples: Strategies for enhanced performance

Rapid industrialization and manufacturing expansion have caused heavy metal pollution, which is a critical environmental issue faced by global population. In addition, the disadvantages presented by conventional detection methods such as the requirement of sophisticated instruments and qualified personnel have led to the development of novel nanosensors. Recently, carbon dots (CDs) have been presented as a multifunctional nanomaterial alternative for the accurate detection of heavy metal ions in water systems. The capacity of CDs to detect contaminants in wastewater -including heavy metals- can be found in the literature; however, to the best of our knowledge, none of them discusses the most recent strategies to enhance their performance. Therefore, in this review, beyond presenting successful examples of the use of CDs for the detection of metal ions, we further discuss the strategies to enhance their photoluminescence properties and their performance for environmental monitoring. In this manner, strategies such as heteroatom-doping and surface passivation are reviewed in detail, as well as describing the mechanisms and the effect of precursors and synthesis methods. Finally, the current challenges are described in detail to propose some recommendations for further research.

The Application of Carbon Nanomaterials in Sensing, Imaging, Drug Delivery and Therapy for Gynecologic Cancers: An Overview

Gynecologic cancers are one of the main health concerns of women throughout the world, and the early diagnosis and effective therapy of gynecologic cancers will be particularly important for the survival of female patients. As a current hotspot, carbon nanomaterials have attracted tremendous interest in tumor theranostics, and their application in gynecologic cancers has also been developed rapidly with great achievements in recent years. This Overview Article summarizes the latest progress in the application of diverse carbon nanomaterials (e.g., graphenes, carbon nanotubes, mesoporous carbon, carbon dots, etc.) and their derivatives in the sensing, imaging, drug delivery, and therapy of different gynecologic cancers. Important research contributions are highlighted in terms of the relationships among the fabrication strategies, architectural features, and action mechanisms for the diagnosis and therapy of gynecologic cancers. The current challenges and future strategies are discussed from the viewpoint of the real clinical application of carbon-based nanomedicines in gynecologic cancers. It is anticipated that this review will attract more attention toward the development and application of carbon nanomaterials for the theranostics of gynecologic cancers.

Photoluminescent carbon dots (PCDs) from sour apple: a biocompatible nanomaterial for preventing UHMWPE wear-particle induced osteolysis via modulating Chemerin/ChemR23 and SIRT1 signaling pathway and its bioimaging application

Photoluminescent nanomaterials have been widely employed in several biological applications both in vitro and in vivo. For the first time, we report a novel application of sour apple-derived photoluminescent carbon dots (PCDs) for reducing ultra-high molecular weight polyethylene (UHMWPE) wear particle-induced osteolysis using mouse calvarial model. Generally, aseptic prosthetic loosening seems to be a significant postoperative problem for artificial joints replacement, which is mainly contributed by UHMWPE-induced osteolysis. Hence, inhibiting osteoclastic bone-resorption could minimize UHMWPE-induced osteolysis for implant loosening. Prior to osteolysis studies, the prepared sour apple-derived PCDs were employed for bioimaging application. As expected, the prepared PCDs effectively inhibited the UHMWPE particle-induced osteoclastogenesis in vitro. The PCDs treatment effectively inhibited the UHMWPE-induced osteoclast differentiation, F-actin ring pattern, and bone resorption in vitro. Also, the PCDs reduced the UHMWPE-induced ROS stress as well as the expression level of pro-inflammatory cytokines, including TNF-α, IL-1, IL-6, and IL-8. Further, the qPCR and western blot results hypothesized that PCDs inhibited the UHMWPE wear particle-induced osteolysis through suppressing chemerin/ChemR23 signaling and NFATc1 pathway, along with upregulation of SIRT1 expression. Overall, these findings suggest that the synthesized PCDs could be a potential therapeutic material for minimizing UHMWPE particle-induced periprosthetic osteolysis to avoid postoperative complications.

Highly Photostable Carbon Dots from Citric Acid for Bioimaging

Bioimaging supported by nanoparticles requires low cost, highly emissive and photostable systems with low cytotoxicity. Carbon dots (C-dots) offer a possible solution, even if controlling their properties is not always straightforward, not to mention their potentially simple synthesis and the fact that they do not exhibit long-term photostability in general. In the present work, we synthesized two C-dots starting from citric acid and tris (hydroxymethyl)-aminomethane (tris) or arginine methyl ester dihydrochloride. Cellular uptake and bioimaging were tested in vitro using murine neuroblastoma and ovine fibroblast cells. The C-dots are highly biocompatible, and after 24 h of incubation with the cells, 100% viability was still observed. Furthermore, the C-dots synthesized using tris have an average dimension of 2 nm, a quantum yield of 37%, high photostability and a zeta potential (ζ) around −12 mV. These properties favor cellular uptake without damaging cells and allow for very effective bioimaging.

Tuning the photoluminescence by engineering surface states/size of S, N co-doped carbon dots for cellular imaging applications

In this research, we have synthesized carbon dots (CDs) co-doped with nitrogen and sulfur by facile hydrothermal method, using citric acid and cysteine as carbon source. The effect of solid-state thermic treatment (STT) at 303-453 K on the size, surface, fluorescence and cellular cytotoxicity of the CDs were systematically investigated. Through a simple STT, it was possible to tune surface states and the average size of the CDs, causing a permanent red shift. Initially, CDs showed a decrease in cell viability with increasing concentration. However, after STT, its viability remained constant with an increase in concentration. Here, we show the possibility to label the cells cytoplasm according to the CDs fluorescence emission before (blue emission) and after STT (red emission). The CDs studied in this paper show selective luminescence properties, which are fundamental for any cell imaging application.

One-step high-yield preparation of nitrogen- and sulfur-codoped carbon dots with applications in chromium(vi) and ascorbic acid detection

In this research, a nitrogen- (N) and sulfur- (S) codoped carbon dot (CDs-IPM)-based sensor was synthesized using a single-step hydrothermal method. Specifically, microcrystalline cellulose (MCC) was the main raw material, which was extracted from banana pseudo-stem-based waste, while autonomous sulfonic acid-functionalized ionic liquid (SO₃H-IL) and polyethylene glycol 400 (PEG 400) acted as the N, S dopant, and surface modifier, respectively. Comprehensive spectroscopic characterization of the synthesized CDs-IPM revealed the introduction of S, N atoms in the matrix with existence of surface oxygenic functional groups. The CDs-IPM possessed enhanced photoluminescence (PL) intensity, synthetic yield, and PL quantum yield (PLQY). Additionally, electron transfer between the CDs-IPM, hexavalent chromium (Cr(vi)), and subsequent ascorbic acid (AA) succeeded in turning the fluorescence on and off. The detection limit was 17 nM for Cr(vi), while it was 103 nM for AA. Our study data can simplify the process of synthesis of CDs utilizing biodegradable starting materials. The probe reported in this study may serve as a valuable addition to the field of environment monitoring by virtue of its enhanced detection sensitivity, high selectivity, and stability.

A novel bio-based nitrogen- and sulfur-codoped carbon dot with enhanced synthetic yield and photoluminescence quantum yield for reversible detection of chromium (Cr)(vi) and ascorbic acid was fabricated by a one-pot hydrothermal method.

Bismuth- and gadolinium-codoped carbon quantum dots with red/green dual emission for fluorescence/CT/T1-MRI mode imaging

The synthesized novel Bi,Gd-CQDs exhibit red and green fluorescence, enabling CT and MR imaging, and providing an approach for multifunctional biological imaging.

Acidic Groups Functionalized Carbon Dots Capping Channels of a Proton Conductive Metal-Organic Framework by Coordination Bonds to Improve the Water-Retention Capacity and Boost Proton Conduction

Crystalline porous materials, such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), have been demonstrated to be versatile material platforms for the development of solid proton conductors. However, most crystalline porous proton conductors suffer from decreasing proton conductivity with increasing temperature due to releasing water molecules, and this disadvantage severely restricts their practical application in electrochemical devices. In this work, for the first time, hydrophilic carbon dots (CDs) were utilized to hybridize with high proton conductivity MOF-802, which is a model of MOF proton conductors, aiming to improve its water-retention capacity and thus enhance proton conduction. The resultant CDs@MOF-802 exhibits impregnable proton conduction with increasing temperature, and the proton conductivity reaches 10^-1 S cm^-1, much superior to that of MOF-802, making CDs@MOF-802 one of the most efficient MOF proton conductors reported so far. This study provides a new strategy to improve the water-retention capacity of porous proton conductors and further realize excellent proton conduction.

A turn off-on fluorometric and paper based colorimetric dual-mode sensor for isoniazid detection

In the present study, Cobalt oxyhydroxide (CoOOH) nanosheets were applied for establishing a dual fluorometric and smartphone-paper-based colorimetric method to detect isoniazid. CoOOH nanosheets quenched the fluorescence emission of sulfur and nitrogen co-doped carbon dots (S,N-CDs) due to inner filter effect (IFE). The quenched fluorescence intensity of S,N-CDs restored in the presence of isoniazid due to destroying CoOOH nanosheets by this drug. Moreover, with adding isoniazid the solution color of CoOOH nanosheets altered from brownish yellow to pale yellow. We exploited these facts to design a turn off-on fluorometric and paper based colorimetric sensor for isoniazid measurement at the range of 0.5-10 and 5-100 μM with detection limits of 0.28 μM and 4.0 μM, respectively. The introduced dual sensor was used for pharmaceutical, environmental and biological analysis of isoniazid with satisfactory results. The paper based colorimetric sensor can be applied for isoniazid portable monitoring by smartphone as a detector and even nocked eyes.

Herbal medicine derived carbon dots: synthesis and applications in therapeutics, bioimaging and sensing

Since the number of raw material selections for the synthesis of carbon dots (CDs) has grown extensively, herbal medicine as a precursor receives an increasing amount of attention. Compared with other biomass precursors, CDs derived from herbal medicine (HM-CDs) have become the most recent incomer in the family of CDs. In recent ten years, a great many studies have revealed that HM-CDs tend to be good at theranostics without drug loading. However, the relevant development and research results are not systematically reviewed. Herein, the origin and history of HM-CDs are outlined, especially their functional performances in medical diagnosis and treatment. Besides, we sort out the herbal medicine precursors, and analyze the primary synthetic methods and the key characteristics. In terms of the applications of HM-CDs, medical therapeutics, ion and molecular detection, bioimaging, as well as pH sensing are summarized. Finally, we discuss the crucial challenges and future prospects.