Fluorescent carbon dots and their sensing applications

Design of novel dual-emitting ratiometric fluorescence system based on FMT-CDs and MnO2 NS for sensitive isoniazid detection in urine sample

In this work, a simple and sensitive ratiometric fluorescence probe to detect isoniazid (INH) was developed on the basis of carbon dots and MnO2 nanosheets (MnO2 NS). Nitrogen-doped carbon dots (FMT-CDs) were synthesized by microwave method using formononetin (FMT) in ammonia water. The oxidase-like activity of MnO2 NS was utilized to oxidize non-fluorescent o-phenylenediamine (OPD) to 2, 3-diaminophenazine (DAP) with orange fluorescence. It was demonstrated that DAP could effectively quench the fluorescence of FMT-CDs through the inner filtering effect (IFE). Due to the reducing nature of INH, MnO2 NS was decomposed and thus lost its oxidase-like activity after the addition of INH. Therefore, the production of DAP was reduced, and the fluorescence intensity was decreased, while IFE on FMT-CDs was weakened and the fluorescence of FMT-CDs was recovered. Based on the above principle, a sensitive method for the detection of INH was established based on the fluorescence intensity ratio of the two fluorescent substances, FMT-CDs and DAP, and was successfully applied to the detection of INH in human urine samples. The limit of detection (LOD) could reach to 0.16 μM in human urine samples.

Isolation, structural characterization of (1 → 4), (1 → 6)-α-D-glucan from Dioscorea Alata and synthesis and catalytic activity studies of (1 → 4), (1 → 6)-α-D-glucan derived carbon dots

Herein, a straightforward, productive protocol was adopted for the synthesis of carbon dots (CDs) by a simple microwave-assisted technique from (1 → 4), (1 → 6)-α-D-glucan polysaccharide (DAPS). The isolation and structural characterization of (1 → 4), (1 → 6)-α-D-glucan from the aqueous extracting of the Diascorea Alata was described here. The photo-physical and morphological studies of the prepared high quantum yield (27.70 %) CDs were systematically characterized using different analytical techniques: TEM, DLS, XPS, XRD, FT-IR, TCSPC, EDX, Fluorescence and UV-vis spectroscopy. In our study the carbon dots (CDs) obtained are non-toxic, highly water-soluble, spherical-shaped negatively charged particles with an average diameter of 3.28 nm. The photo-catalytic activity of carbon dots (CDs) was tested under the sunlight for photo-degradation of crystal violet (CV), a pollutant organic dye. Carbon dots (CDs) showed outstanding results regarding the photo degradation of CV (achieving 99.9 % degradation within 8 min) under sunlight.

Synthesis and application of optically stable red fluorescent carbon dots for sensitive and selective detection of ceftazidime

This study reports the successful synthesis of optically stable red-emitting carbon dots (R-CDs) through a solvothermal method, using glycine as the carbon source and o-phenylenediamine as the nitrogen-doping agent. The R-CDs exhibit long-wavelength emission characteristics with optimal excitation and emission wavelengths of 533 nm and 600 nm, respectively, and a quantum yield of 26.7 %. The results demonstrate that R-CDs possess excellent salt resistance and photostability. The R-CDs display bright fluorescence emission and show a sensitive response to ceftazidime (CF). Leveraging these properties, a fluorescent probe based on R-CDs was developed for the sensitive determination of CF. The fluorescence quenching intensity of this system exhibits a good linear relationship with CF concentration in the range of 0-0.7 mmol/L. The linear equation is (F0-F)/F0=0.9564CCF(mmol/L)+0.0089, with a linear correlation coefficient (R2) of 0.9945. The detection limit is 4.9 μmol/L, with recovery rates ranging from 94.2 % to 100.5 % and relative standard deviations between 2.2 % and 3.2 %. This work provides a theoretical basis for the detection of CF using red-emitting carbon dots and demonstrates promising potential for practical applications.

Carbon dots: synthesis, sensing mechanisms, and potential applications as promising materials for glucose sensors

The disruption of glucose (Glu) metabolism in the human body can lead to conditions such as diabetes and hyperglycemia. Therefore, accurately determining Glu levels is crucial for clinical diagnosis and other applications. Carbon dots (CDs) are a novel category of carbon nanomaterials that exhibit outstanding optical properties, excellent biocompatibility, high water solubility, low production costs, and straightforward synthesis. Recently, researchers have developed various carbon dot sensors for fast and real-time Glu monitoring. In this context, we provide a comprehensive introduction to Glu and CDs for the first time. We categorize the synthetic methods for CDs and the sensing mechanisms, further classifying the applications of carbon dot probes into single-probe sensing, ratiometric sensing, and visual detection. Finally, we discuss the future development needs for CD-based Glu sensors. This review aims to offer insights into advancing Glu sensors and modern medical treatments.

Ratiometric fluorescence and smartphone-assisted sensing platform based on dual-emission carbon dots for brilliant blue detection

In this study, an innovative ratiometric fluorescence and smartphone-assisted visual sensing platform based on blue-yellow dual-emission carbon dots (BY-CDs) was constructed for the first time to determine brilliant blue. The BY-CDs was synthesized via a facile one-step hydrothermal process involving propyl gallate and o-phenylenediamine. The synthesized BY-CDs exhibit favorable water solubility and exceptional fluorescence stability. Under excitation at 370 nm, BY-CDs show two distinguishable fluorescence emission bands (458 and 558 nm). Upon addition of brilliant blue, the fluorescence intensity at 558 nm exhibited a significant quenching effect attributed to fluorescence resonance energy transfer (FRET), while the fluorescence intensity at 458 nm was basically unchanged. The prepared BY-CDs can effectively serve as a ratiometric nanosensor for determining brilliant blue with the ratio of fluorescence intensities at 458 and 558 nm (F458/F558) as response signal. In addition, the developed ratiometric fluorescence sensor exhibits a noticeable alteration in color from yellow to green under UV light with a wavelength of 365 nm upon addition of varying concentrations of brilliant blue, which provides the possibility of visual detection of brilliant blue by a smartphone application. Finally, the BY-CDs based dual-mode sensing platform successfully detected brilliant blue in actual food samples and achieved a desirable recovery rate. This study highlights the merits of fast, convenient, economical, real-time, visual, high accuracy, excellent precision, good selectivity and high sensitivity for brilliant blue detection, and paves new paths for the monitoring of brilliant blue in real samples.

A responsive nanoprobe for ratiometric florescence detection of hydroxyl radicals in macrophage polarization

Quantification of hydroxyl radicals (˙OH), one form of reactive oxygen species (ROS), plays critical roles in early diagnosis and treatment monitoring of various diseases. In this work, we report the development of a responsive nanoprobe for ratiometric fluorescence detection and imaging of ˙OH in macrophage polarization. The nanoprobe, BSA-CCA@LDH-SRB, was designed and prepared using coumarin 3-carboxylic acid (CCA) as the sensing unit for ˙OH, and sulforhodamine B (SRB) loaded on layered double hydroxide (LDH) served as the fluorescent reference component. The coupling of CCA to bovine serum albumin (BSA) and the loading of BSA-CCA on the surface of LDH enabled the nanoprobe for fluorescence detection of ˙OH with high sensitivity and minimal interference from other biomolecules, ions, and ROS. The emission of the prepared BSA-CCA@LDH-SRB at 444 nm emerged and the intensity was increased according to the concentration of ˙OH, while the emission at 580 nm was maintained, allowing the nanoprobe for ratiometric fluorescence (F444/580) detection of ˙OH. Loading of the BSA protein on the LDH surface and the biocompatibility and colloidal stability of the LDH-based fluorescent nanoprobe were further improved, facilitating the detection of ˙OH generation in macrophage polarization stimulated by both biomolecules and physical ultrasound irradiation. This study thus offers a new nanoprobe as the tool for investigating ˙OH evolutions, advancing the biomedical investigations of macrophage polarization associated inflammation.

Neurological effects of carbon quantum dots on zebrafish: A review

Fluorescent carbon dots have emerged as promising nanomaterials for various applications, including bioimaging, food safety detection and drug delivery. However, their potential impact on neurological systems, especially in-vivo models, remains a critical area of investigation. This review focuses on the neurological effects of carbon dots and carbon quantum dots on zebrafish, an established vertebrate model with a conserved central nervous system. Recent studies have demonstrated the efficient uptake and distribution of carbon dots in zebrafish tissues, with a particular affinity for neural tissues. The intricate neural architecture of zebrafish allows for the precise examination of behavioral changes and neurodevelopmental alterations induced by fluorescent carbon dots. Neurotoxicity assessments reveal both short-term and long-term effects, ranging from immediate behavioral alterations to subtle changes in neuronal morphology. The review discusses potential mechanisms underlying these effects highlights the need for standardized methodologies in assessing neurological outcomes and emphasizes the importance of ethical considerations in nanomaterial research. As the field of nanotechnology continues to advance, a comprehensive understanding of the impact of fluorescent carbon dots on neurological function in zebrafish is crucial for informing safe and sustainable applications in medicine and beyond.

Fruit waste-derived carbon dots with rhodamine B for the ratiometric detection of Fe3+ and Cu2

A green and eco-friendly solvothermal approach is proposed for the synthesis of carbon quantum dots (CQDs) from watermelon rind. The as-prepared CQDs exhibited superior teal fluorescence in aqueous solutions, with a quantum yield of 13.9%. The CQDs and rhodamine B (RhB) were demonstrated to selectively react with Fe3+ and Cu2+, leading to a fluorescence (FL) quenching effect, which was successfully used for constructing "double-response-off" type ratiometric FL probes. A comparative study was conducted to assess the sensitivity and accuracy of ratiometric fluorescent probes, specifically those based on CQDs alone and in combination with RhB, for the selective detection of Fe3+ and Cu2+. By plotting the ratio of the differential fluorescence (ΔF) signals of CQDs to that of RhB against the practical application analyte concentration, the detection limits for Fe3+ (1.75 μM) and Cu2+ (0.43 μM) were markedly improved. The quenching mechanism was further explored, and the detection of Fe3+ and Cu2+ in surface water was demonstrated, showcasing the potential of efficient and effective nanosensors based on a static quenching effect. Futhermore, the addition of ascorbic acid can restore the fluorescence quenched by Fe3+. Therefore, in the presence of copper and iron, the ratiometric probe can demonstrate the ability to identify two different metals.

Influence of Carbon-Nitride Dot-Emitting Species and Evolution on Fluorescence-Based Sensing and Differentiation

Carbon dots have attracted widespread interest for sensing applications based on their low cost, ease of synthesis, and robust optical properties. We investigate structure-function evolution on multiemitter fluorescence patterns for model carbon-nitride dots (CNDs) and their implications on trace-level sensing. Hydrothermally synthesized CNDs with different reaction times were used to determine how specific functionalities and their corresponding fluorescence signatures respond upon the addition of trace-level analytes. Archetype explosives molecules were chosen as a testbed due to similarities in substituent groups or inductive properties (i.e., electron withdrawing), and solution-based assays were performed using ratiometric fluorescence excitation-emission mapping (EEM). Analyte-specific quenching and enhancement responses were observed in EEM landscapes that varied with the CND reaction time. We then used self-organizing map models to examine EEM feature clustering with specific analytes. The results reveal that interactions between carbon-nitride frameworks and molecular-like species dictate response characteristics that may be harnessed to tailor sensor development for specific applications.

One-Pot Synthesis of Sustainable Fluorescent Nanomaterials via Microwave Irradiation as a Probe for the Determination of Metformin in Pure and Pharmaceutical Dosage Forms: Greenness and Whiteness Metrics

A rapid, green and sensitive technique for the determination of metformin determination was developed based on the direct fluorescence enhancement of carbon dots (CDs) induced by the cited drug. The water-soluble CDs were prepared via a one-pot synthesis from avocado peels using domestic microwave. The prepared CDs exhibited strong fluorescence at 405 nm after excitation at 320 nm with a quantum yield of 51%. The fluorescence of CDs was enhanced linearly by increasing the concentration of metformin within the range 0.5-25 μg/mL with limit of detection 0.087 μg/mL and limit of quantification 0.263 μg/mL. The designed probe was proved to be selective toward metformin in the presence of other drugs such as vildagliptin and alogliptin and also in the presence of excipients in the pharmaceutical dosage form. The suggested and reported methods were compared with the help of the whiteness and greenness tools, specifically the white analytical chemistry and analytical greenness metric tools, for assessing hazardous solvents and reagents used.

Green Synthesis of Carbon Nanodots (CNDs) Moderated by Flavonoid Extracts from Moringa oleifera Leaves and Co-Doped Sulfur/Nitrogen (NS - CNDs - Fla) and Their Potential for Heavy Metals Sensing Application

Carbon nano dots (CNDs) has received a lot of attention in recent years due to their potential use in various kinds of applications. Many conventional chemical methods have been used to synthesis CNDs, but these processes have several drawbacks, such as hazardous by products, harsh chemicals, and high costs. To overcome these issues, green chemistry has an importance in the development of CNDs. Thus, it is essential to explore green synthesis approaches for production the CNDs. In this context, a novel precursor using flavonoid extraction from Moringa oleifera leaves is proposed. Moringa oleifera is the "magic tree" which contains many bioactive compounds such as flavonoids, especially in its leaves. Natural flavonoids and glycosides with specific components of structure can bind to metal ions. The content of bioactive compounds such as total flavonoids found in Moringa oleifera leaves is 172.10 mg/g. In addition, carbon (47.34%), nitrogen (51.67%), and sulfur (0.99%) are also the main composition. Then, the carbon nanodots (CNDs) synthesized in this research were moderated by flavonoid extract from Moringa oleifera using the hydrothermal method. The technique is easy, ecologically friendly, and requires neither specialized device or reagents. In practice, the CNDs produced are almost circular, with an average diameter of 3.49 nm. Furthermore, we enhanced synthesis CNDs - Fla with heteroatoms of nitrogen (N) and sulfur (S). They display a broad excitation-emission spectrum, excitation-dependent emission, and extraordinary fluorescence. Therefore, the synthesis of CNDs using flavonoids from Moringa oleifera as precursors would be a great potential candidate for the development of novel types of heavy metals sensing.

β-Cyclodextrin/carbon dots-grafted cellulose nanofibrils hydrogel for enhanced adsorption and fluorescence detection of levofloxacin

In this study, a novel hydrogel, β-cyclodextrin/carbon dots-grafted cellulose nanofibrils hydrogel (βCCH), was fabricated for removal and fluorescence determination of levofloxacin (LEV). A comprehensive analysis was performed to characterize its physicochemical properties. Batch adsorption experiments were conducted, revealing that βCCH reached a maximum adsorption capacity of 1376.9 mg/g, consistent with both Langmuir and pseudo-second-order models, suggesting that the adsorption process of LEV on βCCH was primarily driven by chemical adsorption. The removal efficiency of βCCH was 99.2 % under the fixed conditions (pH: 6, initial concentration: 20 mg/L, contact time: 300 min, temperature: 25 °C). The removal efficiency of βCCH for LEV still achieved 97.3 % after five adsorption-desorption cycles. By using βCCH as a fluorescent probe for LEV, a fast and sensitive method was established with linear ranges of 1-120 mg/L and 0.2-1.0 μg/L and a limit of detection (LOD) as low as 0.09 μg/L. The viability of βCCH was estimated based on the economic analysis of the synthesis process and the removal of LEV, demonstrating that βCCH was more cost-effective than commercial activated carbon. This study provides a novel approach for preparing a promising antibiotic detection and adsorption material with the advantages of stability, and cost-effectiveness.

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.

Carbon dots-based fluorescent probe for detection of foodborne pathogens and its potential with microfluidics

Concern about food safety triggers demand on rapid, accurate and on-site detection of foodborne pathogens. Among various fluorescent probes for detection, carbon dots (CDs) prepared by carbonization of carbon-rich raw materials show extraordinary performance for their excellent and tailorable photoluminescence property, as well as their facilely gained specificity by surface customization and modification. CDs-based fluorescent probes play a crucial role in many pathogenic bacteria sensing systems. In addition, microfluidic technology with characteristics of portability and functional integration is expected to combine with CDs-based fluorescent probes for point-of-care testing (POCT), which can further enhance the detection property of CDs-based fluorescent probes. Here, this paper reviews CDs-based bacterial detection methods and systems, including the structural modulation of fluorescent probes and pathogenic bacteria detection mechanisms, and describes the potential of combining CDs with microfluidic technology, providing reference for the development of novel rapid detection technology for pathogenic bacteria in food.

Application of fluorescent carbon quantum dots functional modified carboxymethyl cellulose film in toluene gas specific detection

With the increasing consumption of organic solvents in chemical and pharmaceutical industries, the environment pollution of volatile organic compounds (VOCs) has become an urgent problem. Therefore, the rapid-visual detection method is of great significance in the analysis of VOCs. Based on the fluorescence quenching/enhancement mechanism of carbon quantum dots (CQDs), with the help of carboxymethyl cellulose membrane with porous and large specific surface area structure, a series of green CQDs@carboxymethyl cellulose composite film (CQDs@CMC composite film) was prepared in this study. In the typical-targeted pollutants (toluene) detection application, a fluorescence spectroscopy method was established which could achieve the high sensitivity and strong specificity detection. The mainly conclusions were as follows: The fluorescence spectrometric detection method for toluene: A kind of hydrophobic Lmi/Bet CQDs@CMC composite film was prepared and characterized with imidazole/betaine CQDs and porous carboxymethyl cellulose composite film as raw materials. The toluene detection performance was studied, and the recognition mechanism was explored. The results showed that toluene enhanced the fluorescence of Lmi/Bet CQDs@CMC composite film. The fluorescence intensity of composite films was proportional to toluene concentration when the toluene concentration ranged from 200 to 2200 mg/L. The detection limit of toluene was 1.169 mg/L, which provides a theoretical basis for the detection of toluene by fluorescence spectrometry.

A review on green synthesis, biological applications of carbon dots in the field of drug delivery, biosensors, and bioimaging

Since the beginning of nanoscience and nanotechnology, carbon dots (CDs) have been the foundational idea and have dominated the growth of the nano-field. CDs are an intriguing platform for utilization in biology, technology, catalysis, and other fields thanks to their numerous distinctive structural, physicochemical, and photochemical characteristics. Since several carbon dots have already been created, they have been assessed based on their synthesis process, and luminescence characteristics. Due to their biocompatibility, less toxic effects, and most significantly their fluorescent features in contrast to other carbon nanostructures, CDs have several benefits. This review focuses on the most recent advancements in the characterization, applications, and synthesis techniques used for CDs made from natural sources. It will also direct scientists in the creation of a synthesis technique for adjustable carbon dots that is more practical, effective, and environmentally benign. With low toxicity and low cost, CDs are meeting the new era's requirements for more selectivity and sensitivity in the detection and sensing of various things, such as biomaterial sensing, enzymes, chemical contamination, and temperature sensing. Its variety of properties, such as optical properties, chemiluminescence, and morphological analysis, make it a good option to use in bioimaging, drug delivery, biosensors, and cancer diagnosis.

High-efficient nickel-doped lignin carbon dots as a fluorescent and smartphone-assisted sensing platform for sequential detection of Cr(VI) and ascorbic acid

Using lignin as a raw material to prepare fluorescent nanomaterials represents a significant pathway toward the high-value utilization of waste biomass. In this study, Ni-doped lignin carbon dots (Ni-LCDs) were rapidly synthesized with a yield of 63.22 % and a quantum yield of 8.25 % using a green and simple hydrothermal method. Exploiting the inner filter effect (IFE), Cr(VI) effectively quenched the fluorescence of the Ni-LCDs, while the potent reducing agent ascorbic acid (AA) restored the quenched fluorescence, thus establishing a highly sensitive fluorescence switch sensor platform for the sequential detection of Cr(VI) and AA. Importantly, the integration of a smartphone facilitated the portability of Cr(VI) and AA detection, enabling on-site, in-situ, and real-time monitoring. Ultimately, the developed fluorescence and smartphone-assisted sensing platform was successfully applied to detect Cr(VI) in actual water samples and AA in various fruits. This study not only presents an efficient method for the conversion and utilization of waste lignin but also broadens the application scope of the CDs in the field of smart sensors.

Detection and adsorption of florfenicol in milk using bifunctional carbon dot-doped molecularly imprinted polymers

Detection of florfenicol (FF) residues in animal-derived foods, as one of the most widely used antibiotics, is critically important to food safety. The fluorescent molecularly imprinted polymer (MIP) was synthesized by surface-initiated atom transfer radical polymerization technique with poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) microspheres, 4-vinylpyridine, ethylene glycol dimethacrylate, and FF as the matrix, functional monomer, crosslinker, and template molecule, respectively. Meanwhile, N-S co-doped carbon dot (CD) was synthesized with triammonium citrate and thiourea as precursors under microwave irradiation at 400 W for 2.5 min and then integrated into FF-MIP to obtain CD@FF-MIP. For comparison, non-imprinted polymer (NIP) without FF was also prepared. The adsorption capacity of CD@FF-MIP to FF reached 53.1 mg g-1, which was higher than that of FF-MIP (34.7 mg g-1), whereas the adsorption capacity of NIP was only 17.3 mg g-1. The adsorption equilibrium of three materials was reached within 50 min. Particularly, CD@FF-MIP exhibited an excellent fluorescence quenching response to FF in the concentration range of 3-50 µmol L-1. As a result, CD@FF-MIP was successfully utilized to extract FF in milk samples, which were analyzed by high-performance liquid chromatography. The standard recoveries were 95.8%-98.2%, and the relative standard deviation was 1.6%-4.2%. The method showed the advantages of simple operation, high sensitivity, excellent selectivity, and low cost, and also demonstrated a great application prospect in food detection.

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.

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.

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.

Blending polydopamine-derived imprinted polymers with rice straw-based fluorescent carbon dots for selective detection and adsorptive removal of ibuprofen

Dual-functioning probes capable of detecting and removing hazardous substances have recently received increased attention compared to exclusive sensory probes. Herein, a new composite is synthesized by blending polydopamine imprinted polymers with fluorescent carbon dots (PIP-FCDs) for the selective recognition and adsorption of Ibuprofen (IBF). IBF is a nonsteroidal anti-inflammatory drug and is excessively released in the pharmaceutical wastes. The PIP-FCDs consist of confined pockets for encasing IBF and quenches fluorescence signal when contact with the molecule. PIP-FCDs show high sensitivity (limit of detection = 1.58 × 10-5 μM) and selectivity towards IBF in the presence of other pharmaceutical drugs i.e., aspirin, ketoprofen, norfloxacin, and levofloxacin. The adsorption studies show an adsorption capacity of 209.8 mg g-1 with an extraction efficiency of around 99.9 %. Furthermore, PIP-FCDs are utilized to determine IBF levels in various aqueous pharmaceutical samples. This development provides a simple and dual-functioning probe for the detection and adsorption of IBF from various matrices.

Tris-assisted one-step fabrication of functional carbon dots for specific folate receptor positive-expressed cancer cell imaging

Specific staining of cancer cells is momentous for cancer research. Nanoprobe with multivalent recognition is emerging as powerful tools for bioimaging, but the nonspecific cell uptake and complex functional modification procedures are still obstacles for specific detection and convenient synthesis. Carbon dots (CDs) with an intrinsic targeting ability, excellent optical properties and biocompatibility acquired from an efficient one-step fabrication procedure were urgently desired in specific cancer cells visualization. Herein, inspired by the interrelationships between interface and biomolecular mechanisms, we suggested that it was possible to construct CDs with the desired characteristics for folate receptor (FR) positive-expressed cancer cell imaging via rich hydroxyl groups Tris-assisted one-step hydrothermal treatment of folate acid (FA) and l-Arginine (L-Arg) precursors. The prepared small-sized F-CDs were equipped with abundant hydroxyl, pterin and negative charge surface, and possessed environmental friendliness, outstanding photostability and biocompatibility. Moreover, F-CDs had an intrinsic FR positive-expressed cancer cell targeting ability without any post-modification of the ligands. Rich hydroxyl groups play a vital role in endowing the optical properties and biological effects of F-CDs. F-CDs could be used as a promising candidate for FR-expressed cancer cell labeling and tracking. In addition, the caveolae-mediated endocytosis pathway of F-CDs was ascertained. More importantly, experimental results confirmed that the combination of physicochemical properties may provide an efficient strategy to overcome non-specific cell uptake interactions for cell labeling. Our strategy put forward a promising alternative to design fluorescent CDs for extensive chemical and biomedical applications.

Comparison of Synthetic Pathways for Obtaining Fluorescent Nanomaterials Based on Halloysite and Carbon Dots for Potential Biological Sensing

Recently, fluorescent sensors have gained considerable attention due to their high sensitivity, low cost and noninvasiveness. Among the different materials that can be used for this purpose, carbon dots (CDs) represent valuable candidates for applications in sensing. These, indeed, are easily synthesized, show high quantum yield and are highly biocompatible. However, it was pointed out that the photoluminescence properties of these nanomaterials are strictly dependent on the synthetic and purification methods adopted. The presence of halloysite nanotubes (HNTs), a natural, low cost and biocompatible clay mineral, has been found to be efficient in obtaining small and highly monodispersed CDs without long and tedious purification techniques. Herein, we report the comparison of synthetic pathways for obtaining halloysite-N-doped CDs (HNTs-NCDs) that could be used in biological sensing. One was based on the synthesis of N-doped CDs by a bottom-up approach on HNTs' surface by a MW pyrolysis process; the other one was based on the post-modification of pristine N-doped CDs with halloysite derivatives. The evaluation of the best synthetic route was performed by different physico-chemical techniques. It was found that the bottom-up approach led to the formation of N-doped CDs with different functional groups onto the HNTs' surface. This evidence was also translated in the different fluorescence quantum yields and the existence of several functional groups in the obtained materials was investigated by potentiometric titrations. Furthermore, the ability of the synthesized nanomaterials as sensors for Fe3+ ions detection was assessed by spectroscopic measurements, and the cellular uptake was verified by confocal/fluorescence microscopies as well.

Recent Progress in Folic Acid Detection Based on Fluorescent Carbon Dots as Sensors: A Review

Folic acid (FA) is a water-soluble vitamin found in diverse natural sources and is crucial for preserving human health. The risk of health issues due to FA deficiency underscores the need for a straightforward and sensitive FA detection methodology. Carbon dots (CDs) have gained significant attention owing to their exceptional fluorescence performance, biocompatibility, and easy accessibility. Consequently, numerous research studies have concentrated on developing advanced CD fluorescent probes to enable swift and precise FA detection. Despite these efforts, there is still a requirement for a thorough overview of the efficient synthesis of CDs and their practical applications in FA detection to further promote the widespread use of CDs. This review paper focuses on the practical applications of CD sensors for FA detection. It begins with an in-depth introduction to FA and CDs. Following that, based on various synthetic approaches, the prepared CDs are classified into diverse detection methods, such as single sensing, visual detection, and electrochemical methods. Furthermore, persistent challenges and potential avenues are highlighted for future research to provide valuable insights into crafting effective CDs and detecting FA.

Nanobody mediated dual-mode immunoassay for detection of peanut allergen Ara h 3

To improve the performance of peanut allergen Ara h 3 detection, depending on boron and nitrogen carbon dots (B/N-CDs), a nanobody (Nb) mediated dual-mode immunoassay was established, which combines the dominance of colorimetry with ratiometric fluorescence techniques. With the catalysis of Horseradish peroxidase (HRP), the oxidization of o-phenylenediamine (o-PD) in the presence of H2O2, leading to the production of yellow 2,3-diaminophenolazine (DAP) with an absorption peak at 431 nm. Owing to inner filter effect (IFE), DAP quenched the fluorescence of B/N-CDs at 426 nm, and it emerged a new emission peak at 549 nm. The fluorescence intensity ratio and absorption intensity can be utilized for quantitative analysis of Ara h 3 concentration. Under optimal conditions, the detection limits were 6.61 and 9.79 ng·mL-1, respectively. The dual-mode immunoassay was assessed containing specificity, stability, reproducibility, and practicability. This method paved the way for sensitive detection of Ara h 3 without background Interference.

Carbon Dots and Their Polymeric Nanocomposites: Insight into Their Synthesis, Photoluminescence Mechanisms, and Recent Trends in Sensing Applications

Carbon dots (CDs), a novel class of carbon-based nanoparticles, have received a lot of interest recently due to their exceptional mechanical, chemical, and fluorescent properties, as well as their excellent photostability and biocompatibility. CDs' emission properties have already found a variety of potential applications, in which bioimaging and sensing are major highlights. It is widely acknowledged that CDs' fluorescence and surface conditions are closely linked. However, due to the structural complexity of CDs, the specific underlying process of their fluorescence is uncertain and yet to be explained. Because of their low toxicity, robust and wide optical absorption, high chemical stability, rapid transfer characteristics, and ease of modification, CDs have been recognized as promising carbon nanomaterials for a variety of sensing applications. Thus, following such outstanding properties of CDs, they have been mixed and imprinted onto different polymeric components to achieve a highly efficient nanocomposite with improved functional groups and properties. Here, in this review, various approaches and techniques for the preparation of polymer/CDs nanocomposites have been elaborated along with the individual characteristics of CDs. CDs/polymer nanocomposites recently have been highly demanded for sensor applications. The insights from this review are detailed sensor applications of polymer/CDs nanocomposites especially for detection of different chemical and biological analytes such as metal ions, small organic molecules, and several contaminants.

Green synthesis of carbon quantum dots from teak leaves biomass for in situ precipitation and regenerative-removal of methylene blue-dye

The objective of this study was to completely eliminate environmentally harmful cationic organic dye from aqueous solutions using the one-step ultrasonication method, renowned for its energy efficiency, user-friendliness, and minimal requirement for chemical resources, making it particularly suitable for large-scale applications. To achieve effective environmental remediation, we employed carbon dots derived from teak leaf biomass (TBCDs) layered with graphene oxide. We conducted a thorough characterization of the TBCDs using UV-vis spectroscopy (with absorption peaks at λmax = 208 and 276 nm), FTIR spectroscopy (confirming the presence of various functional groups including -OH, -CH, C = O, COO-, C-O-C, and = C-H), Raman spectroscopy (with bands at 1369 cm-1 (D-Band) and 1550 cm-1 (G-Band), and an intensity ratio (ID/IG) = 0.88, indicating structural defects correlated with the sp3 hybridization sites on the TBCDs), XRD analysis (indicating an amorphous nature of particles), HRTEM imaging (showing homogeneous dispersal of TBCDs with typical sizes ranging from 2 to 10 nm), FESEM analysis (showing a flat surface and minuscule particles), and Zeta potential analysis (revealing a surface charge peak at -51.0 mV). Our adsorption experiments yielded significant results, with a substantial 50.1 % removal rate and an impressive adsorption capacity of 735.2 mg g-1. Theoretical adsorption parameters were rigorously analyzed to understand the adsorption behavior, surface interactions, and mechanisms. Among these models, the Langmuir isotherm in conjunction with pseudo-second-order kinetics provided an exceptional fit (with R2 values closer to 1) for our system. The Gibbs free energy (ΔG) was found to be negative at all temperatures, indicating the spontaneity of the reaction. Regarding mechanism, electrostatic attraction ((+ve) MB dye + (- ve) TBCDs), π-π stacking adsorption facilitated by the graphitic structure, formation of multiple hydrogen bonds due to polar functional groups, and a pore-filling mechanism wherein the cationic MB dye fills the pores of TBCDs with graphene oxide layers, forming an adduct were identified. Furthermore, we demonstrated the regenerative capacity of our system by effectively extracting and recovering the MB dye (with a regeneration rate of 77.1%), utilizing ethyl alcohol as the solvent. These findings not only provide valuable insights into the adsorption capabilities of TBCDs but also highlight the potential of our approach in the recovery of expensive cationic organic dye compounds from polluted environments.

The Guidelines for the Design and Synthesis of Transition Metal Atom Doped Carbon Dots

Atoms doping is a practical approach to modulate the physicochemical properties of carbon dots (CDs) and thus has garnered increasing attention in recent years. Compared to non-metal atoms, transition metal atoms (TMAs) possess more unoccupied orbitals and larger atomic radii. TMAs doping can significantly alter the electronic structure of CDs and bestow them with new intrinsic characteristics. TMAs-doped CDs have exhibited widespread application potential as a new class of single-atom-based nanomaterials. However, challenges remain for the successful preparation and precise design of TMAs-doped CDs. The key to successfully preparing TMA-doped CDs lies in anchoring TMAs to the carbon precursors before the reaction. Herein, taking the formation mechanism of TMAs-doped CDs as a starting point, we systematically summarized the ligands employed for synthesizing TMAs-doped CDs and proposed the synthetic strategy involving multiple ligands. Additionally, we summarize the functional properties imparted to CDs by different TMA dopants to guide the design of TMA-doped CDs with different functional characteristics. Finally, we describe the bottlenecks TMAs-doped CDs face and provide an outlook on their future development.

Colloidal Quantum Dots for Explosive Detection: Trends and Perspectives

Sensitive, accurate, and reliable detection of explosives has become one of the major needs for international security and environmental protection. Colloidal quantum dots, because of their unique chemical, optical, and electrical properties, as well as easy synthesis route and functionalization, have demonstrated high potential to meet the requirements for the development of suitable sensors, boosting the research in the field of explosive detection. Here, we critically review the most relevant research works, highlighting three different mechanisms for explosive detection based on colloidal quantum dots, namely photoluminescence, electrochemical, and chemoresistive sensing. We provide a comprehensive overview and an extensive discussion and comparison in terms of the most relevant sensor parameters. We highlight advantages, limitations, and challenges of quantum dot-based explosive sensors and outline future research directions for the advancement of knowledge in this surging research field.

Turn-off/turn-on biosensing of tetracycline and ciprofloxacin antibiotics using fluorescent iron oxide quantum dots

A fluorescence probe based on iron oxide quantum dots (IO-QDs) was synthesized using the hydrothermal method for the determination of tetracycline (TCy) and ciprofloxacin (CPx) in aqueous solution. The IO-QDs were characterized using high-resolution transmission electron microscopy (HR-TEM), powder X-ray diffraction (P-XRD), vibrating sample magnetometry (VSM), and Fourier-transform infrared spectroscopy (FTIR). The as-prepared IO-QDs are fluorescent, stable, and with a fluorescence quantum yield (QY) of 9.8 ± 0.12%. The fluorescence of IO-QDs was observed to be quenched and enhanced in the presence of TCy and CPx, respectively. The fluorescence intensity ratio shows linearity at concentrations from 1-100 μM and 5-100 μM for TCy and CPx, respectively; the detection limit for TCy and CPx was estimated to be 0.71 μM and 1.56 μM, respectively. The proposed method was also successfully utilized in the spiked samples of drinking water and honey with good recoveries. The method offered convenience, rapid detection, high sensitivity, selectivity, and cost-efficient alternative options for the determination of TCy and CPx in real samples.

A highly sensitive fluorescence nanosensor for determination of amikacin antibiotics using composites of carbon quantum dots and gold nanoparticles

Amikacin is an aminoglycoside antibiotic widely used to treat various bacterial infections in humans. However, elevated concentrations of amikacin can damage the cochlear nerve. Thus, accurate and rapid amikacin detection is crucial. In this study, we developed an "on-off" fluorescence nanosensor for highly sensitive amikacin determination based on a composite of carbon quantum dots (CQDs) and gold nanoparticles (AuNPs). The method quenches CQD fluorescence (turn-off) when they bind to AuNPs but restores it (turn-on) when amikacin binds and releases the CQDs. Adding Cu2+ enhances sensitivity by cross-linking amikacin-coated AuNPs. Under optimal conditions (pH 4, 1 mM Na2SO4, 1 mM CuSO4), the method achieved a low detection limit of 3.5 × 10-11 M (0.02 ppb), a wide linear range (10-10 to 10-8 M), high precision (RSD < 5 %), and a rapid 2-minute response time. Exceptional selectivity was observed over other antibiotics. The CQDs/AuNPs-based sensor successfully detected amikacin in pharmaceutical and surface water samples. This approach offers a fast on-site analytical method for amikacin detection, with potential applications in clinical and environmental settings.

Facile preparation of low temperature carbon dots with long-wavelength emission and their sensing applications for crystal violet

Crystal violet (CV) is one of the main components of common fungicides in daily life, which has inhibitory effect on gram-positive bacteria. However, CV remains in the environment for a long time and have potential risk of disease. Therefore, it is necessary to develop effective methods for detecting CV. Low-temperature carbon dots (LT-CDs) are studied to provide a new idea for the development of CDs green preparation technology from the perspective of low energy consumption. In this experiment, LT-CDs with long-wavelength emission were prepared based on the oxidation, cross-linking polymerization and Schiff base reaction using o-phenylenediamine and hydroquinone as carbon source at low temperature, and were characterized by various techniques. It was found that LT-CDs could be used as a fluorescent probe for quantitative detection of CV based on the inner filter effect, and the practicability of the method was verified by real samples.

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.

Carbon Dots: From Synthesis to Unraveling the Fluorescence Mechanism

Carbon dots (CDs) being a new type of carbon-based nanomaterial have attracted intensive interest from researchers owing to their excellent biophysical properties. CDs are a class of fluorescent carbon nanomaterials that have emerged as a promising alternative to traditional quantum dots and organic dyes in applications including bioimaging, sensing, and optoelectronics. CDs possess unique optical properties, such as tunable emission, facile synthesis, and low toxicity, making them attractive for many applications in biology, medicine, and environmental areas. The synthesis of CDs is achievable by a variety of methods, including bottom-up and top-down approaches, involving the use of different carbon sources and surface functionalization strategies. However, understanding the fluorescence mechanism of CDs remains a challenge. Various mechanistic models have been proposed to explain their origin of luminescence. This review summarizes the recent developments in the synthesis and functionalization of CDs and provides an overview of the current understanding of the fluorescence mechanism.

Fabrication and characterization of microwave-assisted synthesis of carbon dots crosslinked sodium alginate hydrogel films

In this study, potassium-incorporated carbon dots (K-CDs) and nitrogen-incorporated carbon dots (N-CDs) were composted using the microwave-assisted method, in which the carbon source is citric acid. Subsequently, the prepared CDs were added into sodium alginate (NaAlg)/CaCO3 to form a hydrogel film. The Ca2+ in the system is tend to be released in the presence of acidic CDs to promote the cross-linking of NaAlg. This study presents a NaAlg hydrogel film preparation process that requires no additional acid and is natural and environmentally friendly. Moreover, it gives the NaAlg hydrogel film excellent antioxidant and antimicrobial properties and also improves its mechanical properties and gel strength. The release behaviors of the CDs in the hydrogel films were also explored. The prepared CD-incorporated NaAlg hydrogel films have potential applications in medical, biological engineering, food preservation, and other fields owing to their functional properties.

A Review of Dual-Emission Carbon Dots and Their Applications

Carbon dots (CDs), as a rising star among fluorescent nanomaterials with excellent optical properties and fascinating dual-emission characteristics, have attracted increasing attention in sensing, bio-imaging, drug delivery, and so on. The synthesis of dual-emission CDs (DE-CDs) and the establishment of ratiometric fluorescence sensors can effectively diminish background interference and provide more accurate results than single-emission CDs. Although DE-CDs have generated increased attention in many fields, the review articles about DE-CDs are still insufficient. Therefore, we summarized the latest results and prepared this review. This review first provides an overview of the primary synthesis route and commonly used precursors in DE-CDs synthesis. Then, the photoluminescence mechanism behind the dual-emission phenomenon was discussed. Thirdly, the application of DE-CDs in metal cation detection, food safety analysis, biosensing, cell imaging, and optoelectronic devices has been extensively discussed. Finally, the main challenges and prospects for further development are presented. This review presents the latest research progress of DE-CDs synthesis and its application in ratiometric sensing; hopefully, it can help and encourage researchers to overcome existing challenges and broaden the area of DE-CDs research.

Carbon-dot-triggered aggregation/dispersion of gold nanoparticles for colorimetric detection of nucleic acids and its application in visualization of loop-mediated isothermal amplification

In this study, cationic carbon dots (CDs) were prepared from p-phenylenediamine (pPDA) via a one-step hydrothermal method and used to trigger the aggregation and dispersion of gold nanoparticles (AuNPs) for the colorimetric detection of nucleic acids. Physicochemical characterization results revealed that the CDs are enriched with positively charged surface functional groups with an average size of ∼11 nm. The interaction between the CDs and AuNPs was confirmed via fluorescence and absorption studies. Absorption spectroscopic results revealed that the primary surface plasmon resonance (SPR) band of the AuNPs decreased upon introduction of CDs, and a new band emerged at ∼600 nm, indicating the aggregated assembly of AuNPs. Upon the introduction of double-stranded deoxyribonucleic acid (DNA), the band corresponding to the aggregated AuNPs showed a continuous decrease, accompanied by a simultaneous increase in the primary SPR band, leading to a noticeable purple-to-red color transformation. Based on this phenomenon, a colorimetric assay for DNA was developed, which relies on the interaction between negatively charged DNA and cationic CDs, leaving the AuNPs dispersed. The assay exhibited a linear response within a DNA concentration range of 0.7-14 nM with a detection limit of 1.70 nM. Selectivity results showed that colorimetric assays are specific for both DNA and single-stranded DNA (ssDNA). Smartphone-assisted detection was developed by monitoring the colorimetric response of a AuNPs/CDs probe. As a proof-of-concept experiment, the AuNPs/CDs probe was used to visualize the loop-mediated isothermal amplification (LAMP) of Escherichia coli (E. coli), a robust indicator of sewage contamination in water.

Turning food waste into value-added carbon dots for sustainable food packaging application: A review

Carbon dots (CDs) are a recent addition to the nanocarbon family, encompassing both crystalline and amorphous phases. They have sparked significant research interest due to their unique electrical and optical properties, remarkable biocompatibility, outstanding mechanical characteristics, customizable surface chemistry, and negligible cytotoxicity. Their current applications are mainly limited to flexible photonic and biomedical devices, but they have also garnered attention for their potential use in intelligent packaging. The conversion of food waste into CDs further contributes to the concept of the circular economy. It provides a comprehensive overview of emerging green technologies, energy-saving reactions, and cost-effective starting materials involved in the synthesis of CDs. It also highlights the unique properties of biomass-derived CDs, focusing on their structural performance, cellular toxicity, and functional characteristics. The application of CDs in the food industry, including food packaging, is summarized in a concise manner. This paper sheds light on the current challenges and prospects of utilizing CDs in the packaging industry. It aims to provide researchers with a roadmap to tailor the properties of CDs to suit specific applications in the food industry, particularly in food packaging.

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.

Green nanoarchitectonics of carbon quantum dots from Cinchona Pubescens Vahl as targeted and controlled drug cancer nanocarrier

Carbon quantum dots (CQDs) are a new carbon-based nanomaterial that has attracted tremendous attention due to their excellent fluorescent properties, chemical stability, water solubility, and biocompatibility features. Here, fluorescent CQDs synthesized by a green nanoarchitectonic method using Cinchona Pubescens Vahl extract were evaluated as drug nanocarriers for carboplatin (CBP) delivery. The characterization methods showed CQDs with semispherical shapes and sizes around 5 nm, temperature- and pH-dependent functional groups that interact with the CBP molecule adding specificity to the drug-delivery system. Based on the load efficiency results, it seems that the CQDs can carry almost 100 μg of carboplatin for every 1 mg of CQDs. This is possible due to the self-assembly process that takes place through the interaction between the protonation/deprotonation functional groups of CQDs and the hydrolyzed CBP molecule. Through this process, it is created spherical nanoparticles with an average size of 77.44 nm. The CQDs-CBP nanoparticles release the drug through a diffusion-controlled release mechanism where the acidic media is preferred, and the EPR effect also plays a helpful role. Besides, the viability test shows that the CQDs have almost null cytotoxicity suggesting that they could be used as a promising cancer treatment, improving the efficiency of cell internalization and significantly increasing their drug delivery.

Multicolor Photoluminescent Carbon Dots à La Carte for Biomedical Applications

Dual-emission fluorescence probes that provide high sensitivity are key for biomedical diagnostic applications. Nontoxic carbon dots (CDs) are an emerging alternative to traditional fluorescent probes; however, robust and reproducible synthetic strategies are still needed to access materials with controlled emission profiles and improved fluorescence quantum yields (FQYs). Herein, we report a practical and general synthetic strategy to access dual-emission CDs with FQYs as high as 0.67 and green/blue, yellow/blue, or red/blue excitation-dependent emission profiles using common starting materials such as citric acid, cysteine, and co-dopants to bias the synthetic pathway. Structural and physicochemical analysis using nuclear magnetic resonance, absorbance and fluorescence spectroscopy, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy in addition to transmission electron and atomic force microscopy (TEM and AFM) is used to elucidate the material's composition which is responsible for the unique observed photoluminescence properties. Moreover, the utility of the probes is demonstrated in the clinical setting by the synthesis of green/blue emitting antibody-CD conjugates which are used for the immunohistochemical staining of human brain tissues of glioblastoma patients, showing detection under two different emission channels.

Zero-Dimensional Carbon Nanomaterials for Fluorescent Sensing and Imaging

Advances in nanotechnology and nanomaterials have attracted considerable interest and play key roles in scientific innovations in diverse fields. In particular, increased attention has been focused on carbon-based nanomaterials exhibiting diverse extended structures and unique properties. Among these materials, zero-dimensional structures, including fullerenes, carbon nano-onions, carbon nanodiamonds, and carbon dots, possess excellent bioaffinities and superior fluorescence properties that make these structures suitable for application to environmental and biological sensing, imaging, and therapeutics. This review provides a systematic overview of the classification and structural properties, design principles and preparation methods, and optical properties and sensing applications of zero-dimensional carbon nanomaterials. Recent interesting breakthroughs in the sensitive and selective sensing and imaging of heavy metal pollutants, hazardous substances, and bioactive molecules as well as applications in information encryption, super-resolution and photoacoustic imaging, and phototherapy and nanomedicine delivery are the main focus of this review. Finally, future challenges and prospects of these materials are highlighted and envisaged. This review presents a comprehensive basis and directions for designing, developing, and applying fascinating fluorescent sensors fabricated based on zero-dimensional carbon nanomaterials for specific requirements in numerous research fields.

Green and Low-temperature Synthesis of Carbon Dots for Simple Detection of Kaempferol

As a common flavonols, kaempferol (Kae) has a broad market as health food and medicine for its anti-inflammatory, anti-oxidation, and anti-cancer properties. In this study, a novel convenient and simple fluorescent sensor based on carbon dots (CDs) for the detection of Kae was developed. The fluorescent CDs, with excellent photo-luminescence (PL) and up-conversion luminescence (UCPL) properties, were successfully prepared by low-temperature oil bath reaction based on ascorbic acid as carbon source at 90 °C in one pot. Under the optimal conditions, the fluorescence (FL) intensity of CDs was gradually quenched by the increasing addition of Kae with a linear relationship between F0/F and Kae concentration in a wide range from 5 µM to 100 µM with a detection limit of 0.38 µM. And this designed sensor was favourably applied for the detection of Kae in actual sample (xin-da-kang tablets). Moreover, the proposed CDs has great application prospects as a drug-sensor for detecting Kae due to its simple operation, economical and green materials, low equipment requirement, and rapid detection.

Recent advances and perspectives of functionalized carbon dots in bacteria sensing

Bacterial infectious diseases are severe threats to human health and increase substantial financial burdens. Nanomaterials have shown great potential in timely and accurate bacterial identification, detection, and monitoring to improve the cure rate and reduce mortality. Recently, carbon dots have been evidenced to be ideal candidates for bacterial identification and detection due to their superior physicochemical properties and biocompatibility. This review outlines the detailed recognition elements and recognition strategies with functionalized carbon dots (FCDs) for bacterial identification and detection. The advantages and limitations of different kinds of FCDs-based sensors will be critically discussed. Meanwhile, the ongoing challenges and perspectives of FCDs-based sensors for bacteria sensing are put forward.

Boron-Doped Carbon Nanodots as a Theranostic Agent for Colon Cancer Stem Cells

Carbon nanodots have drawn a great deal of attention due to their green and expedient opportunities in biological and chemical sciences. Their high fluorescence capabilities and low toxicity for living cells and tissues make them excellent imaging agents. In addition, they have a fluorimetric response against inorganic and organic species. Boron-doped carbon nanodots (B-CDs) with high fluorescence yield were produced from phenylboronic acid and glutamine as boron and carbon sources, respectively, by a hydrothermal method. First, the effects of the temperature on their fluorescence yield and the structural characteristics of B-CDs were investigated. Second, their cytotoxicity and cell death and proliferation behaviors were examined. The cytotoxicity was evaluated by the MTT assay. The cellular properties were evaluated with the distribution of caspase 3, Ki67, lamin B1, P16, and cytochrome c after the indirect immunoperoxidase technique. After the MTT assay, 1:1 dilution of all applicants for 24 h was used in the study. After immunohistochemical analyses, the application of B-CDs synthesized at 230 °C did not change control cell (Vero) proliferation, and also apoptosis was not triggered. Colo 320 CD133+ and CD133- cell-triggered apoptosis and cellular senescence were found to be synthesis temperature dependent. In addition, Colo 320 CD133- cells were affected relatively more than CD133+ cells from B-CDs. While B-CDs did not affect the control cells, the colon cancer stem cells (Colo 320 CD133+) were affected in a time-dependent manner. Therefore, the use of the synthesized B-CD product may be an alternative method for controlling or eliminating cancer stem cells in the tumor tissue.

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.