Boron and nitrogen co-doped carbon dots as a sensitive fluorescent probe for the detection of curcumin

Fluorescent Molybdenum Disulfide Quantum Dots for Sensitive Detecting Curcumin in Food Samples through FRET Mechanism

A selective and sensitive fluorometric assay was developed for specific determination of curcumin (Cur) based on fluorescence resonance energy transfer (FRET) between molybdenum disulfide quantum dots (MoS2 QDs) and Cur. The MoS2 QDs were prepared via a one-step hydrothermal protocol using sodium molybdate dihydrate, L-cysteine (Cys) as precursors, and sodium cholate (SC) as a modification agent. The as-prepared MoS2 QDs possessed maximum fluorescence emission at 460 nm with a 20% of fluorescence quantum yield (FQY). It was found that the fluorescence of MoS2 QDs could be quantitatively quenched by Cur through FRET mechanism. Therefore, Cur could be detected in the range of 0.1-20 µg mL- 1 with a detection limit of 5 ng mL- 1. Additionally, the developed MoS2 QDs based fluorescent assay has been successfully applied for real food sample analysis with satisfactory results.

CARBON DOTS: Bioimaging and Anticancer Drug Delivery

Cancer, responsible for approximately 10 million lives annually, urgently requires innovative treatments, as well as solutions to mitigate the limitations of traditional chemotherapy, such as long-term adverse side effects and multidrug resistance. This review focuses on Carbon Dots (CDs), an emergent class of nanoparticles (NPs) with remarkable physicochemical and biological properties, and their burgeoning applications in bioimaging and as nanocarriers in drug delivery systems for cancer treatment. The review initiates with an overview of NPs as nanocarriers, followed by an in-depth look into the biological barriers that could affect their distribution, from barriers to administration, to intracellular trafficking. It further explores CDs' synthesis, including both bottom-up and top-down approaches, and their notable biocompatibility, supported by a selection of in vitro, in vivo, and ex vivo studies. Special attention is given to CDs' role in bioimaging, highlighting their optical properties. The discussion extends to their emerging significance as drug carriers, particularly in the delivery of doxorubicin and other anticancer agents, underscoring recent advancements and challenges in this field. Finally, we showcase examples of other promising bioapplications of CDs, emergent owing to the NPs flexible design. As research on CDs evolves, we envisage key challenges, as well as the potential of CD-based systems in bioimaging and cancer therapy.

One-Pot, Optimized Microwave-Assisted Synthesis of Difunctionalized and B-N Co-Doped Carbon Dots: Structural Characterization

In this work, we employed a novel microwave-assisted synthesis method to produce nitrogen and boron co-doped carbon dots (B-N co-doped CDs). To achieve optimal synthesis, we conducted a comprehensive parameter modulation approach, combining various synthesis temperatures, times, and precursor concentrations, while keeping the power constant at 150 W and pH 5. Using maximum fluorescence emission as our response variable, the best conditions were identified as 120 °C, 3 min, and a precursor concentration of 1 mg/mL. Characterization using field emission scanning electron microscopy revealed these CDs to have a spherical morphology with an average size of 10.9 ± 3.38 nm. Further high-resolution transmission electron microscopy showed an interplanar distance of 0.23 nm, which is in line with prior findings of CDs that present a 0.21 nm distance corresponding to the (100) plane of graphite. Optical properties were ascertained through UV-vis absorption, identifying distinct π-π* and n-π* transitions. Fluorescence spectroscopy highlighted an emission peak at 375 nm when excited at 295 nm, achieving a quantum yield of 56.7%. Fourier-transform infrared spectroscopy and Raman spectroscopy analyses confirmed the boronic acid and amine groups' presence, underscoring the graphitic nature of the core and the co-doping of boron and nitrogen. These empirical observations were compared with theoretical investigations through simulated Raman spectra, proposing a potential structure for the CDs. X-ray photoelectron spectroscopy further endorsed the co-doping of nitrogen and boron, along with the detection of the specified functional groups. All these characteristics could lend this nanomaterial to different types of applications such as fluorescent probes for a broad range of analytes and for fluorescent cell imaging.

Curcumin: Overview of Extraction Methods, Health Benefits, and Encapsulation and Delivery Using Microemulsions and Nanoemulsions

Curcumin is the principal curcuminoid found in the rhizomes of turmeric. Due to its therapeutic action against cancer, depression, diabetes, some bacteria, and oxidative stress, it has been used widely in medicine since ancient times. Due to its low solubility, the human organism cannot completely absorb it. Advanced extraction technologies, followed by encapsulation in microemulsion and nanoemulsion systems, are currently being used to improve bioavailability. This review discusses the different methods available for curcumin extraction from plant material, methods for the identification of curcumin in the resulting extracts, its beneficial effects on human health, and the encapsulation techniques into small colloidal systems that have been used over the past decade to deliver this compound.

Turn on fluorescence detection of curcumin in food matrices by the novel fluorescence sensitizer

In this study, silane reagents were for the first time explored as the fluorescence sensitizer. They were demonstrated to have fluorescence sensitization effect on curcumin and 3-glycidoxypropyltrimethoxysilane (GPTMS) possessed the strongest effect. Thus, GPTMS was adopted as the novel fluorescence sensitizer to turn on the fluorescence of curcumin by more than two orders of magnitude for detection. In this way, curcumin could be determined with a linear range of 0.2-2000 ng/mL and an LOD of 0.067 ng/mL. The method was applicable to determine curcumin in several actual food samples, which had the good consistency with the high performance liquid chromatographic method, demonstrating the high accuracy of the proposed method. In addition, the curcumins sensitized by GPTMS could be cured under certain conditions and held the potential for solid fluorescence application. This study expanded the scope of fluorescence sensitizer to silane reagents, and provided the novel approach for fluorescence detection of curcumin and further to generate new solid fluorescence system.

A convenient fluorescence sensor of tetracycline based on B, N codoped carbon dots/polymer composite film

A convenient fluorescence sensor of tetracycline (TC) was constructed based on carbon dots (CDs) and polyvinyl alcohol (PVA) hydrogel film. The immobilization of CDs in PVA carrier can stabilize the fluorescence of CDs by inhibiting the fluorescence quench due to the aggregation of CDs with time. CDs were prepared by a hydrothermal method. CDs showed bright blue fluorescence with the quantum yield of 0.35. The fluorescence of CDs was quenched by TC owing to the inner filter effect. The linear range for TC detection was 0-350 µM and the limit of detection was 0.17 µM. To test conveniently, PVA film was employed to upload CDs. Therefore, a novel sensor for TC was constructed in a visual mode. By comparison with the most of previous works, the present method displayed higher sensitivity and better selectivity. The results suggest that the present sensor has potential applications in the real-time detection of TC in food analysis.

Synthesis of Doped/Hybrid Carbon Dots and Their Biomedical Application

Carbon dots (CDs) are a novel type of carbon-based nanomaterial that has gained considerable attention for their unique optical properties, including tunable fluorescence, stability against photobleaching and photoblinking, and strong fluorescence, which is attributed to a large number of organic functional groups (amino groups, hydroxyl, ketonic, ester, and carboxyl groups, etc.). In addition, they also demonstrate high stability and electron mobility. This article reviews the topic of doped CDs with organic and inorganic atoms and molecules. Such doping leads to their functionalization to obtain desired physical and chemical properties for biomedical applications. We have mainly highlighted modification techniques, including doping, polymer capping, surface functionalization, nanocomposite and core-shell structures, which are aimed at their applications to the biomedical field, such as bioimaging, bio-sensor applications, neuron tissue engineering, drug delivery and cancer therapy. Finally, we discuss the key challenges to be addressed, the future directions of research, and the possibilities of a complete hybrid format of CD-based materials.

Nanomaterials for fluorescent detection of curcumin

Owing to the attractive biological and pharmacological activities, sensitive and selective detection of curcumin is of great significance. Nanomaterials possessing unique optical properties exhibit potential applications in the fluorescent detection of curcumin. This review first discussed the detection strategies of fluorescent nanosensors. In the subsequent section, we highlighted the recent advances of different nanomaterials for fluorescent detection of curcumin, including semiconductor QDs, lanthanide upconversion nanoparticles, fluorescent metal nanoclusters, and carbon quantum dots. And we further provided the merits of fluorescent nanosensors for curcumin. Lastly, the challenges and further directions were presented.

Preparation of yellow emissive nitrogen-doped carbon dots from o-phenylenediamine and their application in curcumin sensing

In this work, o-phenylenediamine (o-PD) and ethanol are used as raw materials, and a simple solvothermal method is used to prepare yellow emissive nitrogen-doped CDs (YNCDs) (with yellow emission λex/λem = 410/555 nm).

Green-emissive water-dispersible silicon quantum dots for the fluorescent and colorimetric dual mode sensing of curcumin

Curcumin, an active ingredient in Curcuma longa, which possesses good biological and pharmacological activities, is effective in treating many diseases. Developing simple and sensitive methods for the detection of curcumin is of great significance. In this study, novel water-dispersible silicon quantum dots (SiQDs), which can sensitively respond to curcumin through fluorescent and colorimetric dual modes were synthesized via a one-step hydrothermal treatment of N-[3-(trimethoxysilyl) propyl]-ethylenediamine (DAMO) and p-phenylenediamine. The fluorescence of SiQDs could be remarkably quenched by curcumin via the inner filter effect (IFE) and static quenching effect (SQE). A good linear relationship was obtained in the range of 0.25-75 μM with a detection limit of 91 nM. More interestingly, curcumin could also be visually detected using SiQDs via an obvious color change of the solution from pale yellow to orange-red, which allows the establishment of a sensitive colorimetric method for curcumin detection in the linear range of 0.05-57.5 μM with a detection limit of 32 nM. The proposed method was successfully applied to detect curcumin in health care products and spices. Notably, to realize rapid and convenient visual detection of curcumin, a paper sensor was also fabricated.

Sulfur-doped carbon dots synthesis under microwave irradiation as turn-off fluorescent sensor for Cr(III)

This study synthesized a facile and high sensitive fluorescent probe based on sulfur-doped carbon dots (S-CDs) using a one-step microwave irradiation method. The probe exhibited a strong blue emission and a high quantum yield (QY) of 36.40%. In the detection, the presence of trivalent chromium (Cr(III)) strongly quenched the PL intensity of S-CDs by the inner filter effect (IFE) quenching mechanism of Cr(III) on the S-CDs. The S-CDs exhibited good sensitivity to turn-off Cr(III) detection with a linear range concentration of 0–45 μM and a detection limit of 0.17 μM. Furthermore, the proposed method has been successfully applied for Cr(III) detection in natural water samples with the 93.68–106.20% recoveries.

Hydrophilic silicon nanoparticles as a turn-off and colorimetric fluorescent probe for curcuminoids detection in food samples and cell imaging

Hydrophilic fluorescent silicon nanoparticles (SiNPs) with good pH stability, salt-tolerance and anti-photobleaching were for the first time prepared from hydrophobic 3-glycidoxypropyltrimethoxysilane. Employing SiNPs as the fluorescence probe, selective quantification of curcuminoids based on the quenching effect was realized with a linearity of 0.046-7.4 μg/mL and a limit of detection of 17.6 ng/mL. Moreover, in light of fluorescence redshift of SiNPs corresponding to the elevated concentration of curcuminoids, a fluorescence colorimetric method was established based on only one extra probe, i.e. herein SiNPs. Thus, semi-quantification of curcuminoids (0-14.7 μg/mL) was visualized from blue to yellow color. Both the developed quantitative and semi-quantitative probe were successfully applied to determine curcuminoids in various actual food samples. Furthermore, SiNPs possessed low cytotoxicity and succeeded in intracellular curcuminoids imaging. The proposed SiNPs could be a promising fluorescence probe for multiple applications.

Carbon dots for ratiometric fluorescence detection of morin

The B,N dual-doped carbon dots (B,N-CDs) for ratiometric fluorescence detection the morin were prepared from sodium tetraborate and polyethyleneimine through the single-step hydrothermal method. The B,N-CDs exhibited the optimum excitation and emission wavelength at 340 nm and 467 nm, respectively. Interestingly, the intensities of emission peak at 467 nm of B,N-CDs reduced meanwhile a new peak emerged at 560 nm with the continuous addition of morin, which revealed the ratio fluorescence characteristic between F_560nm/F_467nm and morin concentration with the linearity range and detection limit of 14.5-32.5 μmol/L and 0.3 μmol/L (S/N = 3), respectively. The interference of common antibiotics and remedies could be ignored when the concentration of morin was detected by the B,N-CDs, which demonstrating the outstanding selectivity. Furthermore, the proposed fluorescence method is used to detect morin in urine with recoveries are 99.8-104.5%. The results of this research indicate the feasibility and practicality of B,N-CDs as an effective fluorescent probe for the determination of morin.

Nitrogen-doped fluorescence carbon dots as multi-mechanism detection for iodide and curcumin in biological and food samples

Iodine ion is one of the most indispensable anions in living organisms, particularly being an important substance for the synthesis of thyroid hormones. Curcumin is a yellow-orange polyphenol compound derived from the rhizome of Curcuma longa L., which has been commonly used as a spice and natural coloring agent, food additives, cosmetics as well as Chinese medicine. However, excess curcumin may cause DNA inactivation, lead to a decrease in intracellular ATP levels, and trigger the tissue necrosis. Therefore, quantitative detection of iodine and curcumin is of great significance in the fields of food and life sciences. Herein, we develop nitrogen-doped fluorescent carbon dots (NCDs) as a multi-mechanism detection for iodide and curcumin in actual complex biological and food samples, which was prepared by a one-step solid-phase synthesis using tartaric acid and urea as precursors without adding any other reagents. An assembled NCDs-Hg2+ fluorescence-enhanced sensor for the quantitative detection of I- was established based on a fluorescence "turn-off-on" mechanism in a linear range of 0.3-15 μM with a detection limit of 69.4 nM and successfully quantified trace amounts of I- in water samples and urine sample. Meanwhile, the as-synthesized NCDs also can be used as a fluorescent quenched sensor for curcumin detection based on the synergistic internal filtration effect (IFE) and static quenching, achieving a good linear range of 0.1-20 μM with a satisfactory detection limit of 29.8 nM. These results indicate that carbon dots are potential sensing materials for iodine and curcumin detection for the good of our health.

One-step synthesis of red emission multifunctional carbon dots for label-free detection of berberine and curcumin and cell imaging

In this work, the red emission multifunctional carbon dots (R-CDs) were prepared via one-pot hydrothermal strategy of neutral red (NR) and ethylenediamine (EDA) for the label-free detection of berberine and curcumin, cell imaging, and fluorescent flexible film. The as-fabricated R-CDs not only possess good water dispersibility and excellent fluorescence stability, but also were successfully employed as a photoluminescent nanoprobe for label-free monitoring of berberine (BRH) and curcumin (Cur) based on dynamic quenching and internal filter effect (IFE), respectively. More importantly, as-proposed R-CDs displayed outstanding cellular permeability and lower cytotoxicity for cellular applications, which was consistent with the results of confocal fluorescence imaging and cell viability measurement of SMMC7721 cells. Thus, the multifunctional R-CDs may provide a rich tool library for biosensing and cellular imaging reagent applications. Interestingly, R-CDs were also used to manufacture R-CDs/PVA composites as fluorescent flexible films. To the best of our knowledge, this is the first demonstration of a label-free multifunctional fluorescent nanoprobe for berberine and curcumin based on red emission CDs.

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

As a fascinating class of fluorescent carbon dots (CDs), doped-CDs are now sparked intense research interest, particularly in the diverse fields of biomedical applications due to their unique advantages, including low toxicity, physicochemical, photostability, excellent biocompatibility, and so on. In this review, we have summarized the most recent developments in the literature regarding the employment of doped-CDs for pharmaceutical and medical applications, which are published over approximately the past five years. Accordingly, we discuss the toxicity and optical properties of these nanomaterials. Beyond the presentation of successful examples of the application of these multifunctional nanoparticles in photothermal therapy, photodynamic therapy, and antibacterial activity, we further highlight their application in the cellular labeling, dual imaging, and in vitro and in vivo bioimaging by use of fluorescent-, photoacoustic-, magnetic-, and computed tomography (CT)-imaging. The potency of doped-CDs was also described in the biosensing of ions, small molecules, and drugs in biological samples or inside the cells. Finally, the advantages, disadvantages, and common limitations of doped-CD technologies are reviewed, along with the future prospects in biomedical research. Therefore, this review provides a concise insight into the current developments and challenges in the field of doped-CDs, especially for biological and biomedical researchers.

Development of an ultrasensitive spectrophotometric method for carmine determination based on fluorescent carbon dots

A high-efficiency spectrophotometric method based on nitrogen-doped fluorescent carbon dots (N-FCDs) was developed for the ultrasensitive determination of carmine (CRM) in foodstuffs. The N-FCDs were fabricated via a one-pot hydrothermal method with m-phenylenediamine as the starting material. The detection principle was based on the fluorescence quenching effect of N-FCDs by CRM, where their interaction was due to the inner filter effect (IFE) and static quenching. A good linear relationship was established for CRM detection in a concentration range of 0.1-10.0 μM with a detection limit as low as 11.2 nM. The proposed method achieved satisfactory results for CRM determination in commercial food products with recoveries better than 98.6% and relative standard deviations (RSDs) less than 4.07%. The method established in this study was simple, ultrasensitive and reliable for rapid detecting CRM in a food matrix, which could be potentially used as a useful sensing agent for the analysis of additive food colourants.

Development of a highly sensitive fluorescence method for tartrazine determination in food matrices based on carbon dots

In this work, an ultrasensitive sensing system based on fluorescent carbon dots (CDs) was developed for the tartrazine (Tar) determination. The CDs were prepared via a simple one-pot hydrothermal method with m-phenylenediamine as the only precursor. The physical and chemical properties were in detail characterized by transmission electron microscopy (TEM), MALDI-TOF MS, UV-vis absorption and photoluminescence (PL) spectroscopy, elemental analysis, and Fourier transform infrared spectroscopy (FTIR). Upon exposure to Tar, the fluorescence of CDs was efficiently quenched via the dynamic interaction between CDs and Tar as well as the inner filter effect (IFE). With this information, the CDs were proposed as a fluorescence probe for Tar detection. It was found that CDs had high sensitivity and selectivity for Tar sensing, and the linear relationship was observed in the range of 0.01-25.0 μM with the corresponding detection limit (3σ/k) of 12.4 nM, which is much more sensitive than any of the existed CD-based sensing platform. The investigated sensing system was finally utilized for Tar sensing in various food matrices with a high degree of accuracy. The spiked recoveries were in a range of 96.4-105.2%, and the relative standard deviations (RSDs) were lower than 4.13%. This work highlights the great application prospects of CDs for Tar sensing in a rapid, simple, and sensitive way.

Carbon-based Nanomaterials and Curcumin: A Review of Biosensing Applications

Curcumin, the main active constituent of turmeric (Curcuma longa L.), is a naturally occurring phenolic compound with a wide variety of pharmacological activities. Although it has multiple pharmaceutical properties, its bioavailability and industrial usage are hindered due to rapid hydrolysis and low water solubility. Due to the growing market of curcumin, exact determination of curcumin in trade and human biological samples is important for monitoring therapeutic actions. Different nanomaterials have been suggested for sensing curcumin; and in this case, carbon-based nanomaterials (CNMs) are one of the most outstanding developments in nanomedicine, biosensing, and regenerative medicine. There are a considerable number of reports which have shown interesting potential of CNMs-based biosensors in the sensitive and selective detection of curcumin. Therefore, this review aims to increase understanding the interaction of curcumin with CNMs in the context of biosensing.

A sensitive spectrofluorimetry method based on S and N dual-doped carbon nanoparticles for ultra-trace detection of ferrocyanide ion in food salt samples

An ultra-sensitive spectrofluorimetry method was developed and validated for the rapid determination of ferrocyanide ions (hexacyanidoferrate(II), FeCN₆ ^4-, FCNs) by using sulphur (S) and nitrogen (N) dual-doped fluorescence carbon nanoparticles (S,N-FCNPs) as nanoprobe. The fluorescence of S,N-FCNPs was strongly reduced due to the dynamic interaction between S,N-FCNPs and FeCNs. The developed method proved to be highly sensitive and selective for FeCNs detection with linearity in three concentration ranges over four orders of magnitude, covering 0.01-200.0 μg/mL. A limit of detection (LOD) of 2.8 ng/mL was obtained. The method was successfully applied for the determination of FeCNs in a series of dietary food salt samples and gave satisfactory results; the spiked recoveries were 97.6‒104.6% with standard uncertainty less than 5.8%. The method proved to be applicable for ultra-trace detection of FeCNs in food salt samples, having advantages in great simplicity, rapid response, low cost, favourable selectivity, and high sensitivity.

Inactivation of HIV-1 Infection through Integrative Blocking with Amino Phenylboronic Acid Attributed Carbon Dots

Current antiretroviral HIV therapies continue to have problems related to procedural complications, toxicity, and uncontrolled side effects. In this study, amino phenylboronic acid-modified carbon dots (APBA-CDs) were introduced as a new nanoparticle-based on gp120 targeting that inhibits HIV-1 entry processes. Prolonged by simple pyrolysis for preparing carbon dots, this report further explores attributing amino phenylboronic acid on carbon dots, which prove the formation of graphene-like structures on carbon dots and boronic acid sites, thereby enabling the enhancement of positive optical properties through photoluminescent detection. Aside from performing well in terms of biocompatibility and low cytotoxicity (the CC₅₀ reach up to 11.2 mg/mL), APBA-CDs exhibited superior capabilities in terms of prohibiting HIV-1 entry onto targeted MOLT-4 cells recognized by the delimitations of syncitia formation and higher ATP signal rather than bare carbon dots. The modified carbon dots also promote dual-action on HIV-1 treatment by both intracellularly and extracellularly viral blocking by combining with the Duviral drug, along with compressing p24 antigen signals that are better than APBA-CDs and Duviral itself.

A critical review of analytical methods for determination of curcuminoids in turmeric

Turmeric (Curcuma longa) is one of the most important ingredients in Indian and Chinese cuisine. Curcuminoids and volatile oils present in turmeric are known for their functional and nutraceutical properties. Health benefits attributed to curcuminoids have resulted in their wide utilization in food and pharmaceutical formulations. Therefore, characterization and estimation of the curcuminoids in fresh/dry turmeric, food and nutraceutical products are essential for their quality control during processing and storage. To meet the demand for analytical methods of curcuminoids, several methods have been developed for their quantification in turmeric powder and food formulations. In the present review, various analytical methods (spectrophotometric, chromatographic, capillary electrophoresis and biosensor techniques) which are used for monitoring curcuminoids have been thoroughly summarized and discussed. The spectrophotometric method is not useful when individual components of curcuminoids are required. Mobile phase optimization, the broadness of spots, plate-to-plate variations are significant limitations for TLC and HPTLC methods. Many analysts believe that HPLC method is the best choice for curcuminoids determination because of its rapid analysis. Spectrofluorimetry and Electrochemical methods are the more advanced methods with high sensitivity as well as rapid analysis. However, the selection of analytical method for curcuminoids analysis depends on the type of sample matrix, purpose of the analysis and limit of detection and limit of quantitation of the method.

Electrochemiluminescence "turn-off" detection of curcumin via energy transfer using luminol-doped silica nanoparticles

A method is presented for electrochemiluminescent (ECL) detection of the food additive curcumin via an energy transfer strategy and by using luminol-doped silica nanoparticles (luminol-NPs). The ECL emission of the luminol-NPs (peaking at 425 nm) is reduced in the presence of curcumin due to spectral overlap. The assay can be performed within 1 min, response is linear in the 0.1 to 100 µM curcumin concentration range, and the limit of detection is 32 nM. The method is selective over many ions, adenosine triphosphate, ascorbic acid, cysteine and folic acid. It was successfully applied to the determination of curcumin in spiked human serum and urine. The average recoveries range from 99.0 to 102.6%. Graphical abstract Electrochemiluminescence (ECL) "turn-off" detection of curcumin at levels as low as 32 nM via energy transfer using luminol-doped silica nanoparticles. No hydrogen peroxide (H₂O₂) is used in ECL detection which makes the luminol-NPs ECL system more stable than the conventional luminol-H₂O₂ ECL system.

Fluorescent boron and nitrogen co-doped carbon dots with high quantum yield for the detection of nimesulide and fluorescence staining

In this work, we firstly developed a new rapid detection method of nimesulide (Nim) based on the boron and nitrogen co-doped carbon dots (B,N-CDs) as the fluorescence probe. The B,N-CDs were prepared by a facile hydrothermal treatment using ammonium citrate and bis(pinacolato)diboron as precursors. The as-prepared B,N-CDs were mono-dispersed with an average diameter of 3.3 nm, and exhibited good stability and strong fluorescence emission with a high quantum yield of 68.89%. The fluorescence of B,N-CDs was obviously quenched with the addition of Nim. A good linear relationship between ln (F₀/F) and the concentration of Nim was obtained in the range of 0-100 μM, and the limit of detection was 125 nM. Furthermore, the proposed analysis method was successfully applied for the detection of Nim in pharmaceutical samples and recoveries ranged from 94.60%-96.73%. More remarkably, it was further found that the as-prepared B,N-CDs displayed bright blue solid-state fluorescence, exhibiting potential application in invisible fluorescent ink for anti-counterfeiting and fluorescent dye.

Nitrogen and Sulfur Co-doped Fluorescent Carbon Dots for the Detection of Morin and Cell Imaging

Background:

Morin has many pharmacological functions including antioxidant, anticancer, anti-inflammatory, and antibacterial effects. It is commonly used in the treatment of antiviral infection, gastropathy, coronary heart disease and hepatitis B in clinic. However, researches have shown that morin is likely to show prooxidative effects on the cells when the amount of treatment is at high dose, leading to the decrease of intracellular ATP levels and the increase of necrosis process. Therefore, it is necessary to determine the concentration of morin in biologic samples.

Method:

Novel water-soluble and green nitrogen and sulfur co-doped carbon dots (NSCDs) were prepared by a microwave heating process with citric acid and L-cysteine. The fluorescence spectra were collected at an excitation wavelength of 350 nm when solutions of NSCDs were mixed with various concentrations of morin.

Results:

The as-prepared NSCDs were characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The fluorescence intensity of NSCDs decreased significantly with the increase of morin concentration. The fluorescence intensity of NSCDs displayed a linear response to morin in the concentration 0.10-30 μM with a low detection limit of 56 nM. The proposed fluorescent probe was applied to analysis of morin in human body fluids with recoveries of 98.0-102%.

Conclusion:

NSCDs were prepared by a microwave heating process. The present analytical method is sensitive to morin. The quenching process between NSCDs and morin is attributed to the static quenching. In addition, the cellular toxicity on HeLa cells indicated that the as-prepared NSCDs fluorescent probe does not show obvious cytotoxicity in cell imaging. Our proposed method possibly opens up a rapid and nontoxic way for preparing heteroatom doped carbon dots with a broad application prospect.

Ultrafast and Energy-saving Synthesis of Nitrogen and Chlorine Co-doped Carbon Nanodots via Neutralization Heat for Selective Detection of Cr(VI) in Aqueous Phase

In this work, it is presented for the first time that nitrogen and chlorine co-doped carbon nanodots (N,Cl-CDs) were synthesized by simply mixing glucose, concentrated hydrochloric acid (HCl), and 1,2-ethylenediamine (EDA). No external heat was employed; the neutralization reaction served as the heat source. The glucose served as the carbon source while EDA and HCl were the N and Cl dopants, respectively. The fluorescence of N,Cl-CDs was adequately quenched by hexavalent chromium Cr(VI) based on a combination of dynamic quenching and inner filter effect (IFE). Accordingly, an efficient N,Cl-CDs-based fluorescence probe was established for sensitive and selective detection of Cr(VI). The proposed fluorescence sensor provides a linear recognition range for Cr(VI) determination from 3 to 40 µM with a limit of detection (LOD) of 0.28 µM (14.6 µg/L). The proposed fluorescence method was successfully utilized to detect Cr(VI) in different water samples with satisfactory results. The spike recoveries vary from 97.01% to 103.89% with relative standard deviations (RSDs) of less than 0.82%. This work highlights the development of a simple, ultrafast, and energy-saving one-step synthetic route to fabricate N,Cl-CDs for highly selective and sensitive detection of Cr(VI) in real water samples. It is anticipated that the proposed fluorescence method could be further explored and widely used for Cr(VI) detection in the environmental industry.

Carbon dots doped with nitrogen and boron as ultrasensitive fluorescent probes for determination of α-glucosidase activity and its inhibitors in water samples and living cells

An ultrasensitive fluorometric assay is described for the determination of the activity of the enzyme α-glucosidase in waters and living cells. Carbon dots doped with nitrogen and boron (N,B-CDs) were prepared that have excitation/emission peaks at 400/510 nm and a fluorescence quantum yield of 47%. 4-Nitrophenylglucoside is added and then hydrolyzed by α-glucosidase to form yellow 4-nitrophenol which screens off fluorescence due to an inner filter effect. The method was applied to the determination of α-glucosidase activity and has a 3 mU mL^-1 detection limit. It was subsequently applied to the determination of the α-glucosidase inhibitor acarbose which can be determined in a concentration as low as 10 nM (at three times the standard deviation versus slope). The method was also applied to the determination of α-glucosidase activity and acarbose in living HeLa cells and MCF-7 cells. The method is simple, sensitive, and excellently selective. Graphical abstract N,B-CDs as ultrasensitive fluorescence probe for α-glucosidase activity and its inhibitor in waters and living cells based on IFE.

Nitrogen and phosphorus dual-doped carbon dots as a label-free sensor for Curcumin determination in real sample and cellular imaging

A nitrogen and phosphorus dual-doped carbon dots (NP-Cdots) was fastly synthesized with glucose as the carbon source, 1,2-ethylenediamine as N-dopant and concentrated phosphoric acid as P-dopant. The as-synthesized NP-Cdots was utilized as a label-free sensor for determination of Curcumin (Cur). The proposed NP-Cdots-based fluorescence sensor was applied for sensitive detection of Cur in aqueous solution, achieving a linear range of 0.5-20 µmol/L and a detection limit of 58 nmol/L (21.37 ng/mL). The common amino acids and other drugs do not interfere with the detection of Cur, providing good selectivity. The constructed sensor was successfully applied to the determination of Cur in drinking water and the food samples with satisfactory results and the RSDs and recoveries were 0.08-5.39% and 95.2-105.2%, respectively. More importantly, the as-prepared NP-Cdots was used as effective fluorescent agent for cellular imaging without noticeable cytotoxicity. The proposed sensor is simple and practical, illustrating that the potential application of NP-Cdots for biosensing, food monitoring and cellular labeling and imaging.