A Review of Carbon Dots Produced from Biomass Wastes

A "turn-on" fluorescence sensor for hydroquinone detection based on BSA doped carbon dots (BSA@CDs) from crawfish shells

By using crawfish shells as the precursor and hydrothermal synthesis, Bovine serum albumin doped carbon dots (BSA@CDs) were prepared without excessive chemical reagents. The relationship between the fluorescence properties of different BSA@CDs and BSA amount was investigated by variouscharacterization techniques. When the amount of BSA added was 30 %, the prepared BSA@CDs' quantum yield (QY) reached 25.01 %, which was the highest. Inner Filter Effect (IFE) suggested that Cr (VI) can selectively quench the fluorescence of BSA@CDs. Cr (VI) can be reduced to Cr (III) by Hydroquinone (HQ), thus recovering the fluorescence. Accordingly, using BSA@CDs as a probe, a "turn-on" fluorescence sensor applied in HQ determination was constructed. The linear range was 10-200 µmol/L and limit of detection (LOD) was 0.18 µmol/L. Further, it has been employed to the determination of HQ in both crawfish tail meat and aquaculture water with good performance.

Pineapple stem starch-based films incorporated with pineapple leaf carbon dots as functional filler for active food packaging applications

Pineapple leaf waste, a byproduct of agricultural processes, was used as a novel raw material to synthesize carbon dots (CDs) through a simple hydrothermal method. The CDs were subsequently incorporated into pineapple stem starch (PSS)-based active food packaging films. The characterization of the CDs and PSS-CDs films was conducted using various techniques, including UV-light spectroscopy, fluorescence spectroscopy, and transmission electron microscopy. The results revealed that the CDs measured 2.36 ± 0.33 nm and exhibited antioxidant and antibacterial activities. The addition of the CDs led to notable enhancements in both mechanical strength and UV-barrier properties. Thus, PSS-CDs packaging film was successfully prepared, with the incorporation of CDs enhancing the antioxidant and antimicrobial properties of the film, thereby extending the shelf-life of fresh pork.

Solid-State Fluorescent Carbon Dots with Hydrophobic Modification Induced Red Emission for White Light-Emitting Diodes

Herein, we developed red solid-state fluorescent carbon dots (SSF-CDs) through a one-step solvothermal method, utilizing acetone as the carbonization solvent. Optical and structural characterization revealed that the sp2 domains in the core of the R-CDs were consistently interrupted and that the oxygen-containing groups on the surface were replaced by alkyl groups. This substitution mitigates excessive π-π interactions, thereby preventing quenching of fluorescence in the solid state. Adjusting the molar ratio of citric acid (CA) and urea yielded solid fluorescent carbon dots (CDs) with panchromatic luminescence, indicating enhanced π-π interactions and more pronounced red shifts in the emission peaks. Furthermore, we found that this strategy is applicable to other carbon sources, including phenylenediamine, salicylic acid, and lignin. This research presents an innovative strategy for the fabrication of solid-state luminescent CDs.

POE-Mediated Tunable Quantum Yield of Carbon Dots-Derived From Agapanthus Africanus (L.) Hoffmann Leaves

The green synthesis of carbon dots (CDs) from natural sources is a challenging goal. Herein CDs are produced from Agapanthus africanus (L.) Hoffmann leaves by carbonization at 200/300 °C for 2/3 h. Samples are named CZ-X-Y, where Z, X, and Y represent carbonization, temperature, and time, respectively. CZ-200-3, CZ-300-2, and CZ-300-3 CDs have average sizes of 3.7 ± 0.7, 5.3 ± 1.2, and 5.1 ± 1.6 nm, respectively. Their surface, devoid of chlorophyll, contains ─OH, ─C═O, and ─C(═O)OH groups and sylvite. Isolated CZ-300-3 emits at 400 nm (excited at 260 nm) and exhibits an emission quantum yield (QY) value of 2 ± 1%. Embedding in the d-U(600)/d-(900) di-ureasil matrices resulted in transparent films with emission intensity maxima at 420/450 nm (360 nm), and QY values of 7 ± 1/16 ± 2% (400 nm). The enhancement of the QY value of the bare CDs agrees with an efficient passivation provided by the hybrid host. The hydrophilic CZ-300-3 CDs also exerted a marked surface modifying role, changing the surface roughness and the wettability of the hybrid films.

Advances in the study of the biological activity of polysaccharide-based carbon dots: A review

Carbon dots have attracted worldwide interest due to their customizable nature, luminescent properties, and exceptional biocompatibility. In particular, biomass-derived carbon dots have attracted attention for their environmentally friendly and cost-effective synthesis. Recent research looks into how polysaccharides can be used to make carbon dots. Using them as starting materials for nanomaterials has benefits in terms of structure, morphology, and doping elements. Although research has extensively examined the optical properties of carbon dots, their potential biological applications have not been thoroughly investigated. This review mainly summarises the cytotoxicity and biological functions of polysaccharide-based carbon dots (e.g. agar, alginate, cellulose, carrageenan, chitosan, chitosan, starch, gelatin, etc.), such as antioxidant, antibacterial and anti-tumor functions, highlighting the different scenarios of the methods of preparation of carbon dots. The applications of carbon dots in food, biomedical sciences, soil fertilization, and power generation are highlighted by reviewing the low toxicity of carbon dots with safety and biocompatibility in human contact. Finally, the importance and challenges of polysaccharide-based carbon dots and the prospects and research directions of polysaccharide-based carbon dots are explained by comparing them with other nanomaterials.

Highly sensitive detection of kojic acid in food samples using fluorescent carbon dots derived from pomegranate peel

Kojic acid (KA) has gained significant attention due to its widespread use in the food and cosmetics industries. However, concerns about its potential carcinogenic effects have heightened the need for sensitive detection methods. This study introduces a fluorescence-based optical sensor for the quantification of KA in food samples, utilizing fluorescent carbon dots (CDs) synthesized from pomegranate peel via a hydrothermal method. The Stern-Volmer plot demonstrated a linear response for KA in the range of 120 to 1200 µM, with a Pearson correlation coefficient (r) of 0.9999 and. The sensor exhibited a detection limit of 30 ± 0.04 µM and a limit of quantification (LOQ) of 90 ± 0.14 µM. Application of the developed method to soy sauce and vinegar samples yielded accurate KA determinations, with recoveries of 103.11 ± 0.96% and 104.45 ± 2.15%, respectively. These findings highlight the potential of the proposed sensor for practical applications in food quality and safety assessment, offering valuable insights into the presence of KA in food products.

Edible coating using carbon quantum dots for fresh produce preservation: A review of safety perspectives

Fresh produce deteriorates and spoils after harvest due to its perishable nature. Deterioration in quality over time has become a major problem for the food industry, placing an undue burden on the economy and agriculture. Food scientists have developed various methods and technologies to prevent spoilage of fruits and vegetables during storage and logistics. Utilizing carbon quantum dots (CQDs) in the form of active packaging and coatings has been a popular strategy recently. CQDs have recently attracted attention as sustainable and functional nanomaterials. CQDs are popular among food scientists due to their easy and economical synthesis, sustainability, non-toxicity, biocompatibility, edibility, UV protection, and antibacterial and antioxidant activities. Although many studies have been conducted and reviewed on the utilization of CQDs in the manufacture of flexible active packaging materials, relatively few studies have investigated the use of CQDs in edible coating formulations for fresh produce. The main reasons for this are concerns about the potential toxicity and edibility of CQDs if they are coated directly on fresh produce. Therefore, this review aims to address these issues by investigating the dose-dependent non-toxicity and biocompatibility of sustainable CQDs along with other important properties from a food packaging perspective. Additionally, this review focuses on the studies performed so far on the direct coating of CQD-based formulations on fresh and fresh-cut fruits and vegetables and discusses the important impact of CQDs on the quality of coated agricultural products. This review is intended to provide food packaging researchers with confidence and prospects for utilizing sustainable CQDs in direct coating formulations for food.

Photo-activated Carbon dots (CDs) as Catalysts in the Knoevenagel Condensation: A Mechanistic Study by Dual-Mode Monitoring via ESI-MS

Carbon dots (CDs) obtained from 5-(hydroxymethyl)furfural (5-HMF) were activated by a 365 nm-UV irradiation source and employed in the Knoevenagel condensation to investigate their photocatalytic mechanism. To this end, electrospray ionization mass spectrometry (ESI-MS) was used to monitor the time progress of the condensation and follow the formation of the final product in positive and negative ion modes at once. The intervention of the superoxide radical anion in the photocatalytic mechanism of CDs was highlighted.

Synthesis of Carbon Dots via Microwave-Assisted Process: Specific Sensing of Fe(III) and Antibacterial Activity

Carbon dots synthesized from a renewable and sustainable source of biomass have greater attention in the nanomaterial research field. In the present study, we adopted a facile and green synthesis of carbon dots from bio waste of pumpkin seeds using a one-pot microwave-assisted carbonization method. The synthesized carbon dots exhibit excellent photoluminescence properties with a bright blue emission peak at 399 nm and fluorescence quantum yield was about 9.5%. The optical properties and structure of carbon dots were examined using various spectroscopy techniques and the synthesized carbon practical size was about 4.37 nm and possessed good solubility in water. Carbon dots were used for the detection of Ferric ions in the water bodies and the interaction between Fe3+ ions and carbon dots was evaluated by fluorescence spectroscopy techniques. This method is a simple and selective detection of Fe3+ in the aqueous medium. Interestingly carbon dots also show good antibacterial activity at a very low concentration (1 mg/L) for effective control of E. coli 93% and Pseudomonas aeruginosa (81%), within 12 h.

Exploring the potential of eco-friendly carbon dots in monitoring and remediation of environmental pollutants

Photoluminescent carbon dots (CDs) have garnered significant interest owing to their distinctive optical and electronic properties. In contrast to semiconductor quantum dots, which incorporated toxic elements in their composition, CDs have emerged as a promising alternative, rendering them suitable for both environmental and biological applications. CDs exhibit astonishing features, including photoluminescence, charge transfer, quantum confinement effect, and biocompatibility. Recently, CDs derived from green sources have drawn a lot of attention due to their strong photostability, reduced toxicity, better biocompatibility, enhanced fluorescence, and simplicity. These attributes have shown great promise in the areas of LED technology, bioimaging, photocatalysis, drug delivery, biosensing, and antibacterial activity. In contrast, this review offers a comprehensive overview of various green sources utilized to produce CDs and methodologies, along with their merits and demerits, with a notable emphasis on physiochemical properties. Additionally, the paper provides insight into the bibliometric analysis and recent advancements of CDs in sensing, photocatalysis, and antibacterial activity. In this field, extensive research is underway, and a total of 7,438 articles have been identified. Among these, 4242 articles are dedicated to sensing applications, while 1518 and 1678 focus on adsorption and degradation. Carbon dots demonstrate exceptional sensing capabilities within the nanomolar range with a selectivity of up to 95% for pollutants. They exhibit excellent degradation efficiency exceeding 90% within 10-130 min and possess an adsorption capacity from 100 to 800 mg/g. These fascinating qualities render them suitable for diverse applications.

Green synthesis of biomass-derived carbon quantum dots for photocatalytic degradation of methylene blue

Water pollution, significantly influenced by the discharge of synthetic dyes from industries, such as textiles, poses a persistent global threat to human health. Among these dyes, methylene blue, particularly prevalent in the textile sector, exacerbates this issue. This study introduces an innovative approach to mitigate water pollution through the synthesis of nanomaterials using biomass-derived carbon quantum dots (CQDs) from grape pomace and watermelon peel. Utilizing the hydrothermal method at temperatures between 80 and 160 °C over periods ranging from 1 to 24 h, CQDs were successfully synthesized. A comprehensive characterization of the CQDs was performed using UV-visible spectroscopy, Fourier-transform infrared spectroscopy, dynamic light scattering, Raman spectroscopy, and luminescence spectroscopy, confirming their high quality. The photocatalytic activity of the CQDs in degrading methylene blue was evaluated under both sunlight and incandescent light irradiation, with measurements taken at 20 min intervals over a 2 h period. The CQDs, with sizes ranging from 1-10 nm, demonstrated notable optical properties, including upconversion and down-conversion luminescence. The results revealed effective photocatalytic degradation of methylene blue under sunlight, highlighting the potential for scalable production of these cost-effective catalytic nanomaterials for synthetic dye degradation.

Luminescent Silicon Nanocrystals as Metal Ion Sensors

At relatively low concentrations in aqueous solution, Fe3+, Fe2+, Cu2+, and Ni2+ quench the photoluminescence (PL) of the undecenoic acid-capped silicon (Si) nanocrystals. The PL could be restored by adding a chelating agent, such as ethylenediaminetetraacetic acid (EDTA), to remove the ions. Fe3+ and Cu2+ also significantly increase the PL lifetime. Other metal ions, including Cd2+, Mn2+, Pb2+, Zn2+, In3+, K+, and Ca2+, had no effect on the Si nanocrystal PL. The limits of detection (LODs) for Fe3+ and Cu2+ of 370 and 150 nM, respectively, are low enough for metal ion sensing applications.

Biomass-derived carbon dots as emerging visual platforms for fluorescent sensing

Biomass-derived carbon dots (CDs) are non-toxic and fluorescently stable, making them suitable for extensive application in fluorescence sensing. The use of cheap and renewable materials not only improves the utilization rate of waste resources, but it is also drawing increasing attention to and interest in the production of biomass-derived CDs. Visual fluorescence detection based on CDs is the focus of current research. This method offers high sensitivity and accuracy and can be used for rapid and accurate determination under complex conditions. This paper describes the biomass precursors of CDs, including plants, animal remains and microorganisms. The factors affecting the use of CDs as fluorescent probes are also discussed, and a brief overview of enhancements made to the preparation process of CDs is provided. In addition, the application prospects and challenges related to biomass-derived CDs are demonstrated.

Heteroatom-doped carbon dots from medicinal plants as novel biomaterials for as-use biomedical applications in comparison with synthetic drug, zaltoprofen

FN-doped carbon dots were synthesized using powdered leaves of Moringa oleifera L./Chromolaena odorata L./Tridax procumbens L./Tinospora cordifolia L./ and Lantana camara L., along with a precursor called 4,5-difluoro-1,2-benzenediamine (DFBD) and compared against the drug zaltoprofen derived carbon dots. They were assessed for their optical and structural characteristics using photoluminescence (optimal emission λ of 600 nm), vibrational (FTIR) spectroscopy (characteristic wave numbers of 1156 and 1269 cm-1 for C-F), as well as X-ray diffraction (XRD) (highest intensity at 27.56°) and high-resolution transmission electron microscopy (HR-TEM) (particles in the size range of 15-20 nm). Further, field emission scanning electron microscopy (FESEM) / energy dispersive spectroscopy (EDX) indicated FN doping of oval/oblong carbon dots. Membrane protection in percent is found to be 55.3 and 80.4 for FN-CDs and Z-FN-CDs respectively. The DPPH-free radical scavenging activity by FN-CDs was 69.4%, while with Z-FN-CDs, it was 54.2%. When tested on six bacterial strains (three each for gram-positive and gram-negative), the FN-CDs displayed a halo (ZOI) between 9 and 19 mm, whereas the Z-FN-CDs displayed a clearance zone between 9 and 17 mm. The FN-CDs showed significant emission-red-shift effects and demonstrated concentration-dependent biocompatibility and viability in neuroblastoma and beta-TC6-cell lines.

Heteroatoms-doped carbon dots as dual probes for heavy metal detection

The utilization of l-cysteine in hydrothermal synthesis allows for the manufacture of carbon dots (CDs) that are doped with heteroatoms including oxygen, nitrogen, and sulfur (N, S, O-doped CDs). CDs have a particle size ranging from 1 to 3 nm, with an average particle size of 2.5 nm. N, S, and O-doped CDs display a blue fluorescence emission at a wavelength of 425 nm. It shows a reliance on the specific excitation wavelength between 320 and 500 nm. It has a selective quenching effect specifically with copper (Cu2+) ions when exposed to interactions with heavy metal ions, as compared to other metal ions. The assay has a limit of detection (LOD) of 2 μM and exhibits a linear correlation within the concentration range of 10-33.3 μM. The fluorescence mechanism was elucidated by employing various analytical techniques, such as transmission electron microscopy (TEM), high-resolution TEM , UV-Vis spectroscopy, zeta potential analysis, and conductometry. An analysis of the data reveals that Cu2+ ions exhibit a strong attraction to the external surface of N, S, and O-doped CDs, leading to the formation of aggregates. N, S, and O-doped CDs can be also used as probes for electrochemical investigations utilizing cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) to produce Nyquist and Bode plots. The electrochemical results offer substantiation for the interaction between Cu2+ ions and N, S, and O-doped CDs. Zero-dimensional carbon nanomaterials, i.e. CDs, can improve the detection of heavy metals using optical and electrochemical methods.

Green-synthesized chitosan‑carbon dot nanocomposite as turn-on aptasensor for detection and quantification of Leishmania infantum parasite

Leishmania is one of the most common diseases between human and animals, caused by Leishmania infantum parasite. Here, we have developed an ultra-selective turn-on fluorescent probe based on an aptamer and Chitosan-CD nanocomposite. The CD used in this study were synthesized using Quercus cap extract and a microwave-assisted approach. The Chitosan-CD nanocomposite was optimized using several microscopic and spectroscopic techniques to possess a bright fluorescence emission before adding aptamer and totally quenched fluorescence after addition of aptamer. The designed probe was proficient in the detection and quantification Leishmania infantum parasite by selective targeting of poly(A) binding protein (PABP) on the surface of the parasite. The designed fluorescent biosensor with high sensitivity, excellent selectivity, and a limit of detection (LOD) of 94 cells/mL of the Leishmania infantum parasite as well as a linear response in the ranges of 188-750 cells/mL and 3000-6000 cells/mL (R2 ≥ 0.98 for both linear ranges). Additionally, the selectivity of the designed probe was evaluated in the presence of different pathogenic species such as Trypanosoma brucei parasite and Staphylococcus aureus bacteria, as well as LiIF2α and LiP2a and BSA proteins as interference substances. The results of this study shows that using Chitosan-CD nanocomposite is a great strategy for developing selective turn-on probes with extraordinary accuracy and sensitivity in identifying Leishmania infantum parasite, especially in the early stages of the disease, and it is promising for the future clinical applications.

Biomass-derived carbon dots as significant biological tools in the medicinal field: A review

Early disease detection is crucial since it raises the likelihood of treatment and considerably lowers the cost of therapy. Therefore, the improvement of human life and health depends on the development of quick, efficient, and credible biosensing methods. For improving the quality of biosensors, distinct nanostructures have been investigated; among these, carbon dots have gained much interest because of their great performance. Carbon dots, the essential component of fluorescence nanoparticles, having outstanding chemical characteristics, superb biocompatibility, chemical inertness, low toxicity and potential optical characteristics have attracted the researchers from every corner of the globe. Several carbon dots applications have been thoroughly investigated in recent decade, from optoelectronics to biomedical investigations. This review study primarily emphasizes the recent advancements in the field of biomass-derived carbon dots-based drug delivery, gene delivery and bioimaging, and highlights achievements in two major areas: in vivo applications that involve carbon dots absorption in zebrafish and mice, tumour therapeutics, and imaging-guided drug delivery. Additionally, the possible advantages, difficulties, and future possibilities of using carbon dots for biological applications are also explored.

Carbon Dots Derived from Non-Biomass Waste: Methods, Applications, and Future Perspectives

Carbon dots (CDs) are luminescent carbon nanoparticles with significant potential in analytical sensing, biomedicine, and energy regeneration due to their remarkable optical, physical, biological, and catalytic properties. In light of the enduring ecological impact of non-biomass waste that persists in the environment, efforts have been made toward converting non-biomass waste, such as ash, waste plastics, textiles, and papers into CDs. This review introduces non-biomass waste carbon sources and classifies them in accordance with the 2022 Australian National Waste Report. The synthesis approaches, including pre-treatment methods, and the properties of the CDs derived from non-biomass waste are comprehensively discussed. Subsequently, we summarize the diverse applications of CDs from non-biomass waste in sensing, information encryption, LEDs, solar cells, and plant growth promotion. In the final section, we delve into the future challenges and perspectives of CDs derived from non-biomass waste, shedding light on the exciting possibilities in this emerging area of research.

Understanding Antibiotic Detection with Fluorescence Quantum Dots: A Review

The utilization of fluorescent quantum dots (FL QDs) has gained significant traction in the realm of antibiotic detection, owing to their exceptional FL properties and versatility. Various types of QDs have been tailored to exhibit superior FL characteristics, employing diverse capping agents such as metals, surfactants, polymers, and biomass to protect and stabilize their surfaces. In their evolution, FL QDs have demonstrated both "turn-off" and "turn-on" mechanisms in response to the presence of analytes, offering promising avenues for biosensing applications. This review article provides a comprehensive overview of the recent advancements in antibiotic detection utilizing FL QDs as biosensors. It encompasses an extensive examination of different types of FL QDs, including carbon, metal, and core-shell QDs, deployed for the detection of antibiotics. Furthermore, the synthesis methods employed for the fabrication of various FL QDs are elucidated, shedding light on the diverse approaches adopted in their preparation. Moreover, this review delves into the intricate sensing mechanisms underlying FL QDs-based antibiotic detection. Various mechanisms, such as photoinduced electron transfer, electron transfer, charge transfer, Forster resonance energy transfer, static quenching, dynamic quenching, inner filter effect, hydrogen bonding, and aggregation-induced emission, are discussed in detail. These mechanisms provide a robust scientific rationale for the detection of antibiotics using FL QDs, showcasing their potential for sensitive and selective sensing applications. Finally, the review addresses current challenges and offers perspectives on the future improvement of FL QDs in sensing applications. Insights into overcoming existing limitations and harnessing emerging technologies are provided, charting a course for the continued advancement of FL QDs-based biosensing platforms in the field of antibiotic detection.

Microwave synthesized novel biomass carbon dots applied in the fluorescent detection of crystal violet

To establish a new method for detecting crystal violet (CV), a harmful dye, herein, a genre of novel biomass carbon dots (CDs) was synthesized via a microwave method and employed as a fluorescent probe, in which water spinach and polyethylene glycol (PEG) performed as raw materials. Based on the inner filter effect (IFE) between the luminescent CDs and CV, the blue emission of this probe at 430 nm could be quenched by CV. Hence, a new strategy was proposed to selectively determine CV in aquaculture ambient. Moreover, under the optimal experiment conditions, this method showed a good linearity between the concentration of CV (c) and fluorescence quenching rate (ΔF/F0) in the concentration range of 4-200 μmol/L with the corresponding correlation coefficient (r) and the detection limit of 0.997 and 710 nmol/L, respectively. With advantages of environmental protectivity, sensitivity, affordability, and user-friendliness, the facilely fabricated CDs could be successfully applied in detecting CV in aquaculture samples, providing a technical foundation for monitoring the pollution of CV and ensuring the quality and safety of aquatic products.

Facile and green synthesis of chlorophyll-derived multi-color fluorescent carbonized polymer dots and their use for sensitive detection of hemin

Due to the very important role in physiological process, a simple and sensitive hemin detection method is necessarily required. Biomass-based carbonized polymer dots (CPDs) have been widely studied especially as fluorescence probe owing to the advantages of low toxicity and the variety of fluorescence color, yet there are still challenges in developing their multi-color emission property from the same raw materials. In this work, red, white and blue emissive CPDs derived from chlorophyll have been synthesized via hydrothermal method. Then white-emitted CPDs (white-CPDs) with the Commission International d'Eclairage (CIE) coordinates at (0.34, 0.32) were used to develop a fluorescence quenched sensing system for hemin determination. There is a good linear relationship between (F0-F)/F0 and concentration of hemin in the range of 0.1-0.95 μM with a detection limit of 0.043 μM, and the quenching mechanism was considered to be caused by inner filter effect (IFE). Moreover, it has been successfully used for hemin detection in serum and also for visual determination, which indicating great potential in applications of disease diagnoses and trace identification.

Determination of carbohydrate content in kenaf degumming wastewater and converting them to carbon dots

The traditional textile degumming process produces abundant wastewater, which contains a lot of monosaccharides and oligosaccharides. It is of great economic and environmental significance to utilize these carbohydrates in high value. In this study, high performance liquid chromatography (HPLC) was used to analyze the carbohydrate components in kenaf degumming wastewater, and then the production of C-dots using the wastewater was explored. The results showed that the types and content in the degumming wastewater were monosaccharides (glucose, xylose and arabinose) and oligosaccharides (dextran, xylan and araban). The carbohydrate (mainly glucan and xylan) content in wastewater accounted for 91.16 % of the total carbohydrates weight loss in kenaf degumming process. By using hydrolysis and hydrothermal reaction on kenaf degumming wastewater, blue-green carbon dots (C-dots) with good performance were prepared and successfully applied to anti-counterfeiting printing. In particular, the as-prepared C-dots prepared from kenaf degumming wastewater with urea added (WUC-dots) showed an excitation-dependent photoluminescence (PL) spectrum and quantum yield (QY) of 2.4 % in aqueous solution. The fluorescent code exhibited a clear outline, excitation-tunable color and good stability, showing a great potential for anti-counterfeiting system.

Bio-functionalized carbon dots for signaling immuno-reaction of carcinoembryonic antigen in an electrochemical biosensor for cancer biomarker detection

Early diagnosis of cancer demands sensitive and accurate detection of cancer biomarkers in blood. Carbon dots (CDs) bio-functionalization with antibodies, peptides or aptamers have played significant role in cancer diagnosis and targeted cancer therapy. Herein, a biosensor for detection of cancer biomarker carcinoembryonic antigen (CEA) in blood serum has been designed using CDs bio-functionalized with HRP-conjugated CEA antibody (CUCDs@CEAAb2) as detection probe. CDs were synthesized by upscaling of cow urine, a nitrogen rich biomass waste, by hydrothermal method. Detection probe based on CDs resulted in 3.5 times higher sensitivity as compared to conventional electrochemical sandwich immunoassay. To further improve the sensor performance, hyper-branched polyethylenimine grafted poly amino aniline (PEI-g-PAANI) was used as the sensing interface, which enabled immobilization of higher amount of capture antibody. Detection of CEA in human blood serum coupled with wide linear range (0.5-50 ng/ml), good specificity, stability, reproducibility and low detection limit (10 pg/ml) signified the excellence of CUCDs based CEA immunosensor. CUCDs exhibited excitation wavelength dependent fluorescence property and showed strong blue emission under UV irradiation. MTT assay indicated that the material is not toxic towards human dental pulp stem cells (hDPSCs) and MG63 osteosarcoma cells (cell viability > 90%). The present study demonstrates a methodology for valorization of animal waste to a cost-effective carbon based functional nanomaterial for clinical detection of cancer biomarkers.

Route-dependent tailoring of carbon dot release in alginate hydrogel beads (HB-Alg@WTR-CDs): A versatile platform for biomedical applications

The present investigation explores the different pathways for development of waste tea residue carbon dots (WTR-CDs) loading into hydrogel matrix for WTR-CDs releasing probe. Fluorescent WTR-CDs incorporated into hydrogel matrix were synthesized by valorisation of kitchen waste tea by simple carbonization method (λem = 450 nm, ΦWTR-CDs =18.45 %). Biopolymeric alginate-based hydrogel beads (HB-Alg) were prepared by simple extrusion method. Three routes (ex-situ/in-situ) were employed for loading of WTR-CDs into hydrogel matrix. Successful synthesis of WTR-CDs and its loading into hydrogel matrix was confirmed via various characterization techniques. Developed protocol was employed for stimuli-responsive cumulative release of WTR-CDs study (pH = 3.0, 7.4, 9.0) was monitored over 7 days. Results suggests that, the HB-Alg@WTR-CDs-A system with in-situ loaded WTR-CDs have sustained release due to ionic interaction of WTR-CDs with crosslinked polymer network, whereas in HB-Alg@WTR-CDs-B, WTR-CDs loaded in wet-beads having burst release in which loosely bound WTR-CDs into hydrogel cavities releases rapidly. While, in case of HB-Alg@WTR-CDs-C, lowest release was observed due to weakly surface bound WTR-CDs, low loading and shrinkage of pores into dry-beads. Radical scavenging activity was studied and shown antioxidant properties of WTR-Powder, WTR-CDs and HB-Alg@WTR-CDs-A,B,C. Cytotoxicity of all systems was checked via CAM assay and significant growth in blood vascularization with no loss of chick embryo confirming the released WTR-CDs are biocompatible. Successful investigation and summarization of results ensure that, waste-valorisation, simple, sustainable, and smart hydrogel systems with different routes of WTR-CDs loading have opened a window to understand the mechanistic pathways in release behaviour. This robust approach for improvement of smarter and biocompatible materials can be fruitfully applicable in advanced, controlled and stimuli responsive delivery probes.

A comprehensive exploration of tartrazine detection in food products: Leveraging fluorescence nanomaterials and electrochemical sensors: Recent progress and future trends

Azo dyes are widely used as food coloring agents because of their affordability and stability. Examples include brilliant blue, carmoisine, sunset yellow, allura red, and tartrazine (Tar), etc. Notably, Tar is often utilized in hazardous food goods. They are frequently flavoured and combined with food items, raising the likelihood and danger of exposure. Therefore, detecting Tar in food is crucial to prevent health risks. Fluorescence nanomaterials and electrochemical sensors, known for their high sensitivity, affordability, simplicity, and speed, have been widely adopted by researchers for Tar detection. This comprehensive paper delves into the detection of Tar in food products. It extensively covers the utilization of advanced carbon-based nanomaterials, including CDs, doped CDs, and functionalized CDs, for sensitive Tar detection. Additionally, the paper explores the application of electrochemical sensors. The paper concludes by addressing current challenges and prospects, emphasizing efforts to enhance sensitivity, and selectivity for improved food safety.

Selective and reliable fluorometric quantitation of anti-cancer drug in real plasma samples using nitrogen-doped carbon dots after MMIPs solid phase microextraction: Monitoring methotrexate plasma level

A novel selective and reliable ratiometric fluorescence probe has been successfully synthesized for precise, sensitive, and simple quantitation of methotrexate (MTX). Hydrothermal method was employed to fabricate nitrogen-doped carbon dots using Annona squamosa seeds (AS-CDs) as a starting material, and their characteristics were confirmed using transmission electron microscopy (TEM), UV-Vis spectroscopy, fluorescence spectroscopy, X-ray diffractometry (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). The ratiometric fluorometric assay, which is based on measuring the ratio of emissions (F355/F430), has a wide detection range of 5-2000 ng /mL and a limit of detection (LOD, S/N = 3) of 1.5 ng /mL. The developed sensing method was successfully applied to the quantification of MTX in rabbit plasma samples and parenteral formulations, achieving satisfactory recoveries %. Magnetic molecularly imprinted solid-phase microextraction was used for selective extraction of MTX from plasma samples. The pharmacokinetic parameters were successfully determined in real rabbit plasma samples after intravenous administration of MTX. The as-designed probe does not only improve the sensitivity, but also enhances the precision and accuracy of the proposed method. Overall, this study presents a promising approach for the detection of MTX in genuine samples with acceptable degree of selectivity and sensitivity.

WO3 nanosheets with peroxidase-like activity and carbon dots based ratiometric fluorescent strategy for xanthine oxidase activity sensing and inhibitor screening

The abnormal level of xanthine oxidase (XOD) often causes pathological changes, which are related to a series of diseases. Herein, a novel and sensitive ratiometric fluorescent sensing platform based on WO3 nanosheets and carbon dots (CDs) was constructed to detect XOD activity for the first time. Under the catalytic oxidation of xanthine by XOD, hydrogen peroxide (H2O2) was generated. In the presence of H2O2, WO3 nanosheets were able to catalyze the oxidation of o-phenylenediamine to generate 2,3-diaminophenazine (DAP) with a yellow fluorescence signal at 570 nm due to its great peroxidase-like activity. The oxidation product DAP was capable of quenching the fluorescence of CDs at 430 nm through the inner filter effect. Therefore, the fluorescence intensity ratio F570/F430 can be used for quantitative analysis of XOD activity. This assay displayed good linear relationships in the range of 0.005-0.05 U/L and 0.5-40 U/L with a detection limit of 0.002 U/L. In addition, this ratiometric fluorescent sensing platform was successfully applied to the determination of XOD in human serum samples and XOD inhibitor screening, demonstrating significant potential in disease diagnosis and drug-screening applications.

Green, facial zinc doped hydrothermal synthesis of cinnamon derived fluorescent carbon dots (Zn-Cn-CDs) for highly selective and sensitive Cr6+ and Mn7+ metal ion sensing application

Carbon dots have demonstrated a great potential as luminescent nanoparticles in energy, drug delivery, sensors, and various biomedical applications as well as environmental pollutants and water analysis. Although, such nanoparticles appear to exhibit low toxicity compared to other semiconductor and metal based luminescent nanomaterials. Today, we know that toxicity of carbon dots (CDs) strongly depends on the protocol of fabrication. The various dopants or heteroatoms have been used to enhance the optical and physicochemical properties. In this work, zinc doped aqueous fluorescent Zn-Cn-CDs have been synthesized from cinnamon by hydrothermal synthesis method. The synthesized Zn-Cn-CDs were confirmed for their physicochemical properties by using various characterization techniques viz. UV-Vis. and spectrofluorometer for optical properties, Fourier transform infrared spectroscopy (FTIR) and XRD, as well as TEM and XPS, was done for morphological and chemical analysis. The successfully synthesized Zn-Cn-CDs showed outstanding optical performance for metal ion sensing applications. The developed heteroatom doped Zn-Cn-CDs as a fluorescent probe exhibited higher selectivity and sensitivity for Cr6+ and Mn7+ metal ions. The obtained results showed a better linear range with excellent limit of detection (LOD) 3.97 µg/mL and 2.05 µg/mL for Cr6+ and Mn7+ metal ions respectively. The low cost, simple and highly fluorescent probe can be effectively applicable for development of environmental pollutants sensing purposes.

Valorization of food industrial waste: Green synthesis of carbon quantum dots and novel applications

Food analysis is a key element in monitoring food quality for risk assessment concerning public health. Instead of using chemically prepared carbon sources for food analysis, eco-friendly and green technology based CQDs are in great demand due to their least toxicity. Carbon quantum dots (CQDs) represent an innovative group of fluorescent nanomaterials, possessing characteristics like photoluminescence, minimal toxicity, high water solubility, and a strong affinity for biocompatibility. Their versatility extends to various applications in fields like sensor technology, biomedicine, and photocatalysis, among other areas. This paper reviews the current challenges related to the use of food by-products as a source of carbon not only enhances the value of waste but also facilitates food safety detection. The integration of CQDs into food technology for food safety analysis shows a great impact on the economy and environment. Furthermore, the details of synthesis, toxicity, application, and characterization of CQDs were also described along with a brief conceptual overview. Particularly, the detection of food additives, food-borne pathogens, heavy metal ions, and pesticide residues was also elaborated. Furthermore, the advantages and the drawbacks are also discussed, with an emphasis on their future prospects in this emerging research field. This review concluded that the use of food residual components has been associated with several toxic effects and accumulation of these residues leads to many disorders like cancer, neurological disorder, reproductive disease, cardiovascular and arthritis. Moreover, the carbon source produced from food waste interacted with other functional groups like oxygen, hydrogen, and nitrogen through π- π* and n- π* interactions. Overall, understanding the mechanism of fluorescence quenching of residual components is of great interest in the field of food detection, as it can provide insights into the design of cost-effective fluorescence probes with low toxicity.

Photoluminescence of Argan-Waste-Derived Carbon Nanodots Embedded in Polymer Matrices

In this work, photoluminescent (PL) carbon nano dots (CNDs) prepared from argan waste were embedded in highly optical transparent poly(styrene-co-acrylonitrile) (PSA) and cyclo-olefin copolymer (COC) matrices, which were further processed into thin films. In the first step, the luminescent CNDs were prepared through thermal processing of fine-groundargan waste, followed, in the second step, by direct dispersion in the polymer solutions, obtained by solving PSA and COC in selected solvents. These two polymer matrices were selected due to their high optical transparency, resilience to various environmental factors, and ability to be processed as quality thin films. The structural configuration of the CNDs was investigated through EDX, XPS, and FTIR, while DLS, HR-SEM, and STEM were used for their morphology investigation. The luminescence of the prepared CNDs and resulted polymer nanocomposites was thoroughly investigated through steady-state, absolute PLQY, and lifetime fluorescence. The quality of the resulted CND-polymer nanocomposite thin films was evaluated through AFM. The prepared highly luminescent thin films with a PL conversion efficiency of 30% are intended to be applied as outer photonic conversion layers on solar PV cells for increasing their conversion efficiency through valorization of the UV component of the solar radiation.

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.

An overview on animal/human biomass-derived carbon dots for optical sensing and bioimaging applications

Over the past decade, carbon dots (CDs) have emerged as some of the extremely popular carbon nanostructures for diverse applications. The advantages of sustainable CDs, characterized by their exceptional photoluminescence (PL), high water solubility/dispersibility, non-toxicity, and biocompatibility, substantiate their potential for a wide range of applications in sensing and biology. Moreover, nature offers plant- and animal-derived precursors for the sustainable synthesis of CDs and their doped variants. These sources are not only readily accessible, inexpensive, and renewable but are also environmentally benign green biomass. This review article presents in detail the production of sustainable CDs from various animal and human biomass through bottom-up synthetic methods, including hydrothermal, microwave, microwave-hydrothermal, and pyrolysis methods. The resulting CDs exhibit a uniform size distribution, possibility of heteroatom doping, surface passivation, and remarkable excitation wavelength-dependent/independent emission and up-conversion PL characteristics. Consequently, these CDs have been successfully utilized in multiple applications, such as bioimaging and the detection of various analytes, including heavy metal ions. Finally, a comprehensive assessment is presented, highlighting the prospects and challenges associated with animal/human biomass-derived CDs for multifaceted applications.

Spectrofluorometric quantitative analysis of aripiprazole based on quenching of natural derived carbon quantum dots in spiked human plasma

Autism spectrum disorder is a significant concern worldwide, particularly in Middle Eastern countries. Aripiprazole, a psychiatric medicine that works as a partial agonist at D2 receptors, is often used for autism-related behavior issues in children. Monitoring the therapy of aripiprazole could enhance the safety and effectiveness of treatment for autistic individuals. The purpose of this study was to develop a highly sensitive and environmentally friendly method for analysis of aripiprazole in plasma matrix. To achieve this, water-soluble N-carbon quantum dots were produced from a natural green precursor, guava fruit, and used in fluorescence quenching spectroscopy to determine the presence of aripiprazole. The synthesized dots were analyzed and characterized using transmission electron microscopy and Fourier transform infrared spectroscopy, and they showed a strong fluorescence emission peak at 475 nm. The proposed method was validated according to ICH M10 guidelines and was shown to be highly sensitive, allowing for nanoscale determination of aripiprazole in plasma matrix. Additionally, the method was compared to a previously reported spectrophotometric method, and it was found to be more sensitive and consistent with the principles of green analytical chemistry.

A recent update on development, synthesis methods, properties and application of natural products derived carbon dots

Natural resources are practically infinitely abundant in nature, which stimulates scientists to create new materials with inventive uses and minimal environmental impact. Due to the various benefits of natural carbon dots (NCDs) from them has received a lot of attention recently. Natural products-derived carbon dots have recently emerged as a highly promising class of nanomaterials, showcasing exceptional properties and eco-friendly nature, which make them appealing for diverse applications in various fields such as biomedical, environmental sensing and monitoring, energy storage and conversion, optoelectronics and photonics, agriculture, quantum computing, nanomedicine and cancer therapy. Characterization techniques such as Photoinduced electron transfer, Aggregation-Induced-Emission (AIE), Absorbance, Fluorescence in UV-Vis and NIR Regions play crucial roles in understanding the structural and optical properties of Carbon dots (CDs). The exceptional photoluminescence properties exhibited by CDs derived from natural products have paved the way for applications in tissue engineering, cancer treatment, bioimaging, sensing, drug delivery, photocatalysis, and promising remarkable advancements in these fields. In this review, we summarized the various synthesis methods, physical and optical properties, applications, challenges, future prospects of natural products-derived carbon dots etc. In this expanding sector, the difficulties and prospects for NCD-based materials research will also be explored.

Potential Efficacy of Herbal Medicine-Derived Carbon Dots in the Treatment of Diseases: From Mechanism to Clinic

Carbon dots (CDs), a crucial component of nanomaterials, are zero-dimensional nanomaterials with carbon as the backbone structure and smaller than 10 nm. Due to their beneficial characteristics, they are widely used in biomedical fields such as biosensors, drug delivery, bio-imaging, and interactions with DNA. Interestingly, a novel type of carbon dot, generated by using herbal medicines as synthetic raw materials, has emerged as the most recent incomer in the family of CDs with the extensive growth in the number of materials selected for carbon dots synthesis. Herbal medicine-derived carbon dots (HM-CDs) have been employed in the biomedical industry, and are rapidly emerging as "modern nanomaterials" due to their unique structures and exceptional capabilities. Emerging trends suggest that their specific properties can be used in bleeding disorders, gastrointestinal disorders, inflammation-related diseases, and other common intractable diseases including cancer, menopausal syndrome, central nervous system disorders, and pain of various forms and causes. In addition, HM-CDs have been found to have organ-protective and antioxidant properties, as evidenced by extensive studies. This research provides a more comprehensive understanding of the biomedical applications of HM-CDs for the aforementioned disorders and investigates the intrinsic pharmacological activities and mechanisms of these HM-CDs to further advance their clinical applications.

Carbon dots from alcohol molecules: principles and the reaction mechanism

Carbon dots (CDs) have attracted significant attention in the energy, environment, and biology fields due to their exceptional physicochemical properties. However, owing to the multifarious precursors and complex reaction mechanisms, the production of carbon dots from organic molecules is still a mysterious process. Inspired by the color change of sodium hydroxide ethanol solution after standing for some time, in this work, we thoroughly investigated the reaction mechanism from alcohol molecules to carbon dots through a lot of experiments and theoretical calculations, and it was found that the rate-controlling reaction is the formation of aldehydes, and it is also confirmed that there is a self-catalysis reaction, which can accelerate the conversion from alcohol to aldehyde, further facilitating the final formation of CDs. After the rate-controlling reaction of alcohol to aldehyde, under strongly alkaline conditions, an aldol reaction occurs to form unsaturated aldehydes, followed by further condensation and polymerization reactions to form long carbon chains, which are cross-linked and dehydrated to form carbon dots with a carbon core and surface functional groups. Additionally, it is found that the reaction can be largely accelerated with the assistance of electricity, which indicates the great prospect of industrial production. Furthermore, the obtained CDs with rich functional groups can be utilized as electrolyte additives to optimize the deposition behavior of Na metal, manifesting great potential towards safe and stable Na metal batteries.

Comprehensive advances in the synthesis, fluorescence mechanism and multifunctional applications of red-emitting carbon nanomaterials

Red emitting fluorescent carbon nanomaterials have drawn significant scientific interest in recent years due to their high quantum yield, water-dispersibility, photostability, biocompatibility, ease of surface functionalization, low cost and eco-friendliness. The red emissive characteristics of fluorescent carbon nanomaterials generally depend on the carbon source, reaction time, synthetic approach/methodology, surface functional groups, average size, and other reaction environments, which directly or indirectly help to achieve red emission. The importance of several factors to achieve red fluorescent carbon nanomaterials is highlighted in this review. Numerous plausible theories have been explained in detail to understand the origin of red fluorescence and tunable emission in these carbon-based nanostructures. The above advantages and fluorescence in the red region make them a potential candidate for multifunctional applications in various current fields. Therefore, this review focused on the recent advances in the synthesis approach, mechanism of fluorescence, and electronic and optical properties of red-emitting fluorescent carbon nanomaterials. This review also explains the several innovative applications of red-emitting fluorescent carbon nanomaterials such as biomedicine, light-emitting devices, sensing, photocatalysis, energy, anticounterfeiting, fluorescent silk, artificial photosynthesis, etc. It is hoped that by choosing appropriate methods, the present review can inspire and guide future research on the design of red emissive fluorescent carbon nanomaterials for potential advancements in multifunctional applications.

Assessment of biomass-derived carbon dots as highly sensitive and selective templates for the sensing of hazardous ions

Access to safe drinking water and a hygienic living environment are the basic necessities that encourage healthy living. However, the presence of various pollutants (especially toxic heavy metal ions) at high concentrations in water renders water unfit for drinking and domestic use. The presence of high concentrations of heavy-metal ions (e.g., Pb2+, Hg2+, Cr6+, Cd2+, or Cu2+) greater than their permissible limits adversely affects human health, and increases the risk of cancer of the kidneys, liver, skin, and central nervous system. Therefore, their detection in water is crucial. Due to the various benefits of "green"-synthesized carbon-dots (C-dots) over other materials, these materials are potential candidates for sensing of toxic heavy-metal ions in water sources. C-dots are very small carbon-based nanomaterials that show chemical stability, magnificent biocompatibility, excitation wavelength-dependent photoluminescence (PL), water solubility, simple preparation strategies, photoinduced electron transfer, and the opportunity for functionalization. A new family of C-dots called "carbon quantum dots" (CQDs) are fluorescent zero-dimensional carbon nanoparticles of size < 10 nm. The green synthesis of C-dots has numerous advantages over conventional chemical routes, such as utilization of inexpensive and non-poisonous materials, straightforward operations, rapid reactions, and renewable precursors. Natural sources, such as biomass and biomass wastes, are broadly accepted as green precursors for fabricating C-dots because these sources are economical, ecological, and readily/extensively accessible. Two main methods are available for C-dots production: top-down and bottom-up. Herein, this review article discusses the recent advancements in the green fabrication of C-dots: photostability; surface structure and functionalization; potential applications for the sensing of hazardous anions and toxic heavy-metal ions; binding of toxic ions with C-dots; probable mechanistic routes of PL-based sensing of toxic heavy-metal ions. The green production of C-dots and their promising applications in the sensing of hazardous ions discussed herein provides deep insights into the safety of human health and the environment. Nonetheless, this review article provides a resource for the conversion of low-value biomass and biomass waste into valuable materials (i.e., C-dots) for promising sensing applications.

Green one-step synthesis of mushroom-derived carbon dots as fluorescent sensors for Fe3+ detection

Blue photoluminescent carbon dots were synthesized from Lentinus polychrous Lèv. via a simple hydrothermal process without additional chemical reagents or functionalization. The carbon dots (hereafter referred to as LCDs) were quasi-spherical with an average diameter of 6.0 nm. The strong fluorescence emissions of LCDs were utilized as the basis of efficient turn-off probes for Fe3+. The quenching phenomenon could be used to rapidly determine Fe3+ concentrations in the range of 0.0-2.0 mM in aqueous solution, with a limit of detection (LOD) of 16 μM. In the presence of interference, LCDs demonstrated good sensitivity and selectivity towards Fe3+ in both solution-based and paper-based systems. The LCDs also exhibited excellent photostability and an eco-friendly nature, making them an ideal choice for environmental monitoring with significant potential for diagnostic applications.

Scaling-up of carbon dots hydrothermal synthesis from sugars in a continuous flow microreactor system for biomedical application as in vitro antimicrobial drug nanocarrier

Carbon dots (CDs) are a new class of nanomaterials exhibiting high biocompatibility, water solubility, functionality, and tunable fluorescence (FL) property. Due to the limitations of batch hydrothermal synthesis in terms of low CDs yield and long synthesis duration, this work aimed to increase its production capacity through a continuous flow reactor system. The influence of temperature and time was first studied in a batch reactor for glucose, xylose, sucrose and table sugar precursors. CDs synthesized from sucrose precursor exhibited the highest quantum yield (QY) (175.48%) and the average diameter less than 10 nm (~6.8 ± 1.1 nm) when synthesized at 220°C for 9 h. For a flow reactor system, the best condition for CDs production from sucrose was 1 mL min-1 flow rate at 280°C, and 0.2 MPa pressure yielding 53.03% QY and ~ 6.5 ± 0.6 nm average diameter (6.6 mg min-1 of CDs productivity). CDs were successfully used as ciprofloxacin (CP) nanocarrier for antimicrobial activity study. The cytotoxicity study showed that no effect of CDs on viability of L-929 fibroblast cells was detected until 1000 µg mL-1 CDs concentration. This finding demonstrates that CDs synthesized via a flow reactor system have a high zeta potential and suitable surface properties for nano-theranostic applications.

Size-dependent activity of carbon dots for photocatalytic H2 generation in combination with a molecular Ni cocatalyst

Carbon dots (CDs) are low-cost light-absorbers in photocatalytic multicomponent systems, but their wide size distribution has hampered rational design and the identification of the factors that lead to their best performance. To address this challenge, we report herein the use of gel filtration size exclusion chromatography to separate amorphous, graphitic, and graphitic N-doped CDs depending on their lateral size to study the effect of their size on photocatalytic H2 evolution with a DuBois-type Ni cocatalyst. Transmission electron microscopy and dynamic light scattering confirm the size-dependent separation of the CDs, whereas UV-vis and fluorescence spectroscopy of the more monodisperse fractions show a distinct response which computational modelling attributes to a complex interplay between CD size and optical properties. A size-dependent effect on the photocatalytic H2 evolution performance of the CDs in combination with a molecular Ni cocatalyst is demonstrated with a maximum activity at approximately 2-3 nm CD diameter. Overall, size separation leads to a two-fold increase in the specific photocatalytic activity for H2 evolution using the monodisperse CDs compared to the as synthesized polydisperse samples, highlighting the size-dependent effect on photocatalytic performance.

One-Pot Synthesis of Nitrogen-Doped Graphene Quantum Dots and Their Applications in Bioimaging and Detecting Copper Ions in Living Cells

Two natural carbon sources, glutamic acid and tyrosine, were used to fabricate strong green emission nitrogen-doped graphene quantum dots (N-GQDs) with the one-pot pyrolysis method. The morphology of the prepared GQDs has been characterized by high-resolution transmission electron microscopy, showing a well-displayed crystalline structure with a lattice spacing of 0.262 nm. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were used to analyze the surface functional groups and elemental composition, suggesting that the N-GQDs have active carboxylic and amino functional groups. Meanwhile, photoluminescence and ultraviolet-visible (UV-vis) spectroscopy were used to evaluate the optical properties of GQDs; the prepared N-GQDs show an excitation-dependent fluorescence behavior with a maximum excitation/emission wavelength at 460/522 nm, respectively. N-GQDs showed good photostability and the fluorescence intensity quenched about 10% after irradiating 2800 s in the experiment of time kinetic analysis. The MTT assay was utilized to assess the viability of N-GQDs; good biocompatibility with a relatively high quantum yield of 12% demonstrated the potential for serving as bioimaging agents. Besides, the selectivity study on metal ions indicates that the N-GQDs could be used in Cu2+ detection. The linear range is from 0.1 to 10 μM with a limit of detection of 0.06 μM. Overall, these proposed N-GQDs with one-pot synthesis showed their promising potential in cell imaging and Cu2+ monitoring applications involved in the biological environment.

An ultrasensitive ratiometric aptasensor based on the dual-potential electrochemiluminescence of Ru(bpy)32+ in a novel ternary system for detection of Patulin in fruit products

To sensitively monitor trace-level of toxic patulin (PAT), an ultrasensitive PAT ratiometric aptasensor based on the dual-potential electrochemiluminescence (ECL) of Ru(bpy)₃²⁺ was first proposed. Noteworthily, Ru(bpy)₃²⁺-doped trimetallic nanocube (Ru@Tri) innovatively integrated the luminophore and cathode coreaction accelerator (CCA), which could generate strong cathodic ECL in the existence of low concentration of K₂S₂O₈. Simultaneously, anthocyanin-derived carbon quantum dots (anth-CQDs) prepared from purple potato skins was first served as a green anodic coreactant. And SiO₂-coated anth-CQDs (anth-CQDs@SiO₂) exhibited excellent performance for enhancing anodic ECL of Ru@Tri. Based on this, a novel ternary ECL system was established. In the presence of PAT, the ECL intensity ratio of anode to cathode (I_ECL-A/I_ECL-C) was significantly increased, and a low detection limit of 0.05 pg mL^-1 was obtained. Moreover, when proposed method and high performance liquid chromatography (HPLC) were simultaneously applied to series of fruit products, the obtained results were completely consistent, reflecting its practicability.

Ionic liquid-enhanced lemon biomass carbon dots with sustainable use in bionic antibody microspheres for urea capture and ethyl carbamate inhibition

Herein, we reported the room-temperature fabrication of ionic liquid-modified carbon dots encapsulated in bionic antibodies (IL-modified CDs@BAs) by one-pot green synthesis. In order to enhance the fluorescence intensity of CDs, imidazole ILs and lemon rich in heteroatoms were selected as CDs modifiers and sources. The resulting IL-modified CDs@BAs showed good selectivity and capture toward urea and obviously induced fluorescence quenching by template-binding. The inhibition rate ofIL-modified CDs@BAs on the urea pathway of ethyl carbamate was about 29.07% in the simulated Huangjiu system, indicating a good inhibitory effect. The IL-modified CDs@BAs system was also reproducible after five consecutive uses, thus reducing the economic cost. This research would expand the application fields of BAs-based optical sensing system from the perspectives of energy conservation, environmental protection and resource recovery, focusing on their application in the field of food safety control.

Fiberglass cloth coated by coffee ground waste-derived carbon quantum dots/titanium dioxide composite for removal of caffeine and other pharmaceuticals from water

Coffee ground waste from the coffee beverage preparation is mainly discarded and consequently ends up in landfill, which cause the contamination of caffeine in various environmental compartments. This study focuses on the upcycling of coffee-ground waste to carbon quantum dots (CQDs) for use as a modifying material to improve the visible light activity of titanium dioxide (TiO₂). The CQD solution was synthesized by hydrothermal method, which has an average size of 2.80 ± 0.63 nm. The CQDs/TiO₂ photocatalysts were prepared by combining CQD solutions at various amounts with sol-gel TiO₂ and then coated on the fiberglass cloths (FGCs). The photocatalytic application mainly focuses on the removal of caffeine from the water. The photocatalytic experiment was preliminary run in a simple batch reactor under visible light. The 5CQDs/TiO₂ coated FGC (5 mL of CQD solution/g of Ti-based on sol-gel) showed the best performance, and it was selected for the removal of caffeine and other pharmaceuticals (i.e., carbamazepine and ibuprofen) in the recirculating reactor. The removals of caffeine, carbamazepine, and ibuprofen after irradiation for 9 h were 82%, 88%, and 84%, respectively. The residual concentrations were significantly lower than the reported toxicity levels based on specific species. The changes in total organic carbon were observed, indicating the mineralization of pharmaceuticals in water. The 5CQDs/TiO₂ coated FGC showed good flexible performance. No obvious loss of activity was observed for five runs. The actual wastewater from the coffee pot cleaning process was also tested. The removal was 80% for caffeine and 86% for color in the unit of the American Dye Manufacturers Institute (ADMI).

Guava-fruit based synthesis of carbon quantum dots for spectrofluorometric quantitative analysis of risperidone in spiked human plasma and pharmaceutical dosage forms

Autism is one of the most pressing issues facing the international community in recent years, particularly in Middle Eastern countries. Risperidone is a selective serotonin type 2 and dopamine type 2 receptor antagonist. It is the most administered antipsychotic medication in children with autism-related behavioral disorders. Therapeutic monitoring of risperidone may improve safety and efficacy in autistic individuals. The main objective of this work was to develop a highly sensitive green fitted method for the determination of risperidone in the plasma matrix and pharmaceutical dosage forms. Novel water-soluble N-carbon quantum dots were synthesized from guava fruit, a natural green precursor, and used for determination of risperidone based on quenching fluorescence spectroscopy phenomena. The synthesized dots were characterized by transmission electron microscopy and Fourier transform infrared spectroscopy. The synthesized N-carbon quantum dots exhibited aquantum yield of 26.12% and showed a strong emission fluorescence peak at 475 nm when excited at 380 nm. The fluorescence intensity of the N-carbon quantum dots decreased with increasing risperidone concentration, indicating that the fluorescence quenching was concentration dependent. The presented method was carefully optimized and validated according to the guidelines of ICH, and it demonstrated good linearity in a concentration range of 5-150 ng mL-1. With a LOD of 1.379 ng mL-1 and a LOQ of 4.108 ng mL-1, the technique was extremely sensitive. Due to the high sensitivity of the proposed method, it could be effectively used for the determination of risperidone in the plasma matrix. The proposed method was compared with the previously reported HPLC method in terms of sensitivity and green chemistry metrics. The proposed method proved to be more sensitive and compatible with the principles of green analytical chemistry.

Functional Carbon from Nature: Biomass-Derived Carbon Materials and the Recent Progress of Their Applications

Biomass is considered as a promising source to fabricate functional carbon materials for its sustainability, low cost, and high carbon content. Biomass-derived-carbon materials (BCMs) have been a thriving research field. Novel structures, diverse synthesis methods, and versatile applications of BCMs have been reported. However, there has been no recent review of the numerous studies of different aspects of BCMs-related research. Therefore, this paper presents a comprehensive review that summarizes the progress of BCMs related research. Herein, typical types of biomass used to prepare BCMs are introduced. Variable structures of BCMs are summarized as the performance and properties of BCMs are closely related to their structures. Representative synthesis strategies, including both their merits and drawbacks are reviewed comprehensively. Moreover, the influence of synthetic conditions on the structure of as-prepared carbon products is discussed, providing important information for the rational design of the fabrication process of BCMs. Recent progress in versatile applications of BCMs based on their morphologies and physicochemical properties is reported. Finally, the remaining challenges of BCMs, are highlighted. Overall, this review provides a valuable overview of current knowledge and recent progress of BCMs, and it outlines directions for future research development of BCMs.

Green synthesis of multi-functional carbon dots from medicinal plant leaves for antimicrobial, antioxidant, and bioimaging applications

In this research work, carbon dots (CDs) were synthesized from the renewable leaves of an indigenous medicinal plant by the one-pot sand bath method, Azadirachta indica. The synthesized CDs were characterized for its optical properties using UV-Vis, Fluorescence and Fourier transform infrared (FT-IR) spectrophotometry and for structural properties using dynamic light scattering (DLS), X-ray Diffraction (XRD) and high resolution Transmission electron microscopy (HR-TEM). The synthesized CDs exhibited concentration dependent biocompatibility when tested in mouse fibroblast L929 cell line. The EC50 values of biomedical studies, free radical scavenging activity (13.87 μgmL-1), and total antioxidant capacity (38 μgmL-1) proved CDs were exceptionally good. These CDs showed an appreciable zone of inhibition when examined on four bacterial (two gram-positive and gram-negative) and two fungal strains at minimum concentrations. Cellular internalisation studies performed on human breast cancer cells (MCF 7- bioimaging) revealed the applicability of CDs in bioimaging, wherein the inherent fluorescence of CDs were utilised. Thus, the CDs developed are potential as bioimaging, antioxidants and antimicrobial agents.

Detection of organic pollutants, food additives and antibiotics using sustainable carbon dots

The ecosystem across the globe has been adversely affected due to the adoption of unsustainable growth strategies. Overuse of organic pollutants such as dyes, pesticides, disinfectants, food additives and antibiotics, along with their release into the environment without proper treatment has severely affected the food chain and water bodies, hence ultimately the human race. As the organic contaminants, being non-biodegradable, persist in the environment for a long duration, a sustainable method for the detection of these harmful organic pollutants is essential. For food safety and restoration of ecological balance, simple, non-toxic, cost-effective and environmentally friendly green precursor derived carbon dots (CDs) are favorable as compared to inorganic nanoparticles (CdTe, CdS etc.) and chemically derived CDs. This review covers the summary of the studies devoted to the optical detection of organic pollutants, food additives and antibiotics through green precursor derived CDs, reported during the last few years. The upcoming studies of optical sensing systems with sustainable CDs provide powerful insight towards pollutant detection, as well as act as a future monitoring tool.

Multifunctional role of carbon dot-based polymer nanocomposites in biomedical applications: a review

Carbon-based 0D materials have shown tremendous potential in the development of biomedical applications of the next generation. The astounding results are primarily motivated by their distinctive nanoarchitecture and unique properties. Integrating these properties of 0D carbon nanomaterials into various polymer systems has orchestrated exceptional potential for their use in the development of sustainable and cutting-edge biomedical applications such as biosensors, bioimaging, biomimetic implants and many more. Specifically, carbon dots (CDs) have gained much attention in the development of biomedical devices due to their optoelectronic properties and scope of band manipulation upon surface revamping. The role of CDs in reinforcing various polymeric systems has been reviewed along with discussing unifying concepts of their mechanistic aspects. The study also discussed CDs optical properties via the quantum confinement effect and band gap transition which is further useful in various biomedical application studies.