Fluorescent N-doped Carbon Dots Research Articles

Development of FRET-based optical sensors using N-doped carbon dots for detection of chromium (VI) and manganese (VII) in water for a sustainable future

Carbon dots (CDs) synthesis has received much attention due to their considerable application potential. Natural compounds are efficient CD carbon precursors, exhibiting significant physical and chemical characteristics. In the present work, the hydrothermal method has successfully derived blue fluorescent N-doped carbon dots (NCDs) from Alstonia scholaris leaves and ethylenediamine. The synthesized NCDs were characterized by Fourier transform infrared (FTIR), Transmission Electron Microscopy (TEM), fluorescence and UV–vis analysis. It exhibits better chemical and physical properties with a relatively good quantum yield of 21%. As-synthesized NCDs were applied for the FRET-based detection of Cr6+ and Mn7+ ions in water samples to investigate their suitability as fluorescent probes. The detection limit was 0.173 µM and 0.394 µM for Cr6+ and Mn7+, respectively. This study has illustrated an environmentally friendly approach for the facile synthesis of blue fluorescent NCDs with remarkable potential for further utilization in sensing devices.

The fabrication of fluorescent sensor for Fe3+ detection and configurable logic gate operation based on N-doped carbon dots

Herein, fluorescent N-doped carbon dots (N-CDs) were obtained using hydrothermal treatment of polyethyleneimine and melamine. The N-CDs exhibit nanoscale structure, good water solubility, photostability and excellent fluorescence property with a high fluorescence quantum yield of 26 %. The as-prepared N-CDs were selected for the detection of Fe3+ with a fluorescence “OFF-ON” strategy by the mechanism of internal filtration effect (IFE). A good linear relationship can be observed for the concentration of Fe3+ from 0 to 500 μM, and the calculated detection limit (LOD) for Fe3+ was 0.88 μM (3σ/slope). Meanwhile, the N-CDs based sensor can be utilized for tracing Fe3+ in real water samples. In addition, the quenched fluorescence can be recovered with the treatment of l-cysteine, and thus can be designed for quantitative determination of l-cysteine with a fluorescent “ON-OFF-ON” switch. Moreover, a set of resettable, multireadout logic gate operations including OR and AND have been realized for the N-CDs.

A study on the photophysical properties of strong green-fluorescent N-doped carbon dots and application for pH sensing

Color tuneable effective pH sensor in both acidic and alkaline medium is important for environment and bioanalytical purpose. In this report, natural biomass derived N-doped fluorescent carbon dots are utilized as pH sensor. The fast microwave irradiation method was employed for synthesis using natural sweet lime juice extract. Ethylenediamine (EDA) was used for nitrogen doping with different amounts. The prepared N-doped carbon dots are comprehensively studied by various characterization methods to analyse the effect of dopant concentrations on photophysical and luminescence properties. Improved thermal stability from 900 °C to 1000 °C with EDA content is observed. The fluorescence spectra of prepared N-doped carbon dots exhibited stable green emission with high quantum yield 83 % under ultraviolet and 440 nm irradiation wavelengths for an optimal concentration of EDA. The color of emission confirmed by CIE plot and about 3.47 ns decay time is found by PL decay curve. The anti-photo bleaching ability and good photostability for 10 days are found. The prepared N-doped carbon dots exhibit high ionic stability and bio compatibility. Further, pH dependent color tuneable (green to yellow) emission spectra of prepared N-doped carbon dots displayed high fluorescence in acidic medium at pH -5. Although, emission was quenched and red shifted in alkaline medium. The effective pH-sensitivity, and good reversibility of fluorescent N-doped carbon dots samples were tested with real water samples having different pH values. The reasonable mechanism is discussed. It depicts the prepared N-doped carbon dots have potential to serve as pH sensor for physiochemical and bioanalytical measurements.

High-throughput detection of mycophenolic acid in human plasma based on sensitive and rapid fluorescence nitrogen-doped carbon dots sensing platform

In this experiment, a water-soluble, nitrogen-doped yellow-green fluorescent N-doped carbon dots (N-CDs) were synthesized by one-step hydrothermal method using β-cyclodextrin as carbon source and L-phenylalanine as nitrogen source. The fluorescence quantum yield of the obtained N-CDs was as high as 9.96%, and the N-CDs exhibited photostability at different pH, ionic strength and temperature. The morphology of the N-CDs was approximately spherical with an average particle size of about 9.4 nm. Based on the fluorescence enhancement effect of mycophenolic acid (MPA) on N-CDs, a quantitative detection method of MPA was established. This method had good selectivity and high sensitivity for MPA. The fluorescence sensing system was applied to the detection of MPA in human plasma. The linear range of MPA were 0.06–3 μg·mL−1 and 3–27 μg·mL−1 with a detection limit of 0.016 μg·mL−1, and the recoveries were 97.03∼100.64 % with the RSDs of 0.13∼2.90 %. The interference experiment results showed that the interference of other coexisting substances, including Fe3+, can be ignored in the actual detection. Comparing the results measured by the established method with the EMIT method, it was found that the results obtained by the two methods were similar, and the relative error was within ± 5 %. This study provided a simple, rapid, sensitive, selective and effective method for the quantitative analysis of MPA, and was expected to be applied to clinical MPA blood concentration monitoring.

Cynodon dactylon derived fluorescent N-doped carbon dots: Implications of photocatalytic and biological applications

CQDs possess various appealing properties like excellent light harvesting capability, unique photo-induced electron transfer ability, low toxicity, and good biocompatibility. This work aims to demonstrate the potential of CQDs from natural waste resources in wastewater treatments and biomedical applications. Herein we report the eco-friendly approach for preparing nitrogen-doped carbon quantum dots (N-CQDs) using the Cynodon dactylon (grass) as a carbon precursor via a highly effective hydrothermal process. The structural aspects and chemical nature of N-CQDs were considered using FTIR, XRD, SEM & EDX, TEM, AFM, EPR, and XPS. In addition, UV–vis and fluorescence spectroscopy elucidated the optical performance of N-CQDs. N-CQDs possess stable fluorescent properties, good biocompatibility, and acceptable quantum yield (24.44%). In this study, five dyes, namely Toluidine Blue (TB), Amido Black (AB), Congo Red (CR), and Xylol Orange (XO), were chosen to investigate the photocatalytic performance of the nanomaterial under UV–vis light irradiation. The synthesized N-CQDs exhibited remarkable photocatalytic activity for various model dyes of varying concentrations (5, 10, 50, and 100 ppm), highlighting the pivotal role of N-CQDs in promoting the separation migration efficiency of photoexcited e−- h+ pairs. Moreover, the impact of pH, contact time, and amount of catalyst on the degradation of dyes were also examined. Additionally, we investigated the interaction of N-CQDs with lysozyme protein using fluorescence quenching. Thus, the developed nanomaterial efficiently treats wastewater and holds great promise in biosensing applications.

High Fluorescent N-Doped Carbon Dots Derived from Sanghuangporus Lonicericola for Detecting Tetracyclines in Aquaculture Water and Rat Serum Samples

High Fluorescent N-Doped Carbon Dots Derived from Sanghuangporus Lonicericola for Detecting Tetracyclines in Aquaculture Water and Rat Serum Samples

Nitrogen-doped carbon dots as a fluorescent probe for folic acid detection and live cell imaging

The folic acid (FA) level in human body can be used as an indicator for body's normal physiological activities and offer insight into the growth and reproduction of the body's cells. But the abnormal level of FA can cause some diseases. Herein, we designed a simple and convenient approach to prepare fluorescent N-doped carbon dots (N-CDs) for the FA detection. These N-CDs have excellent hydrophilicity, high photostability, and outstanding biocompatibility, as well as excitation-independent emission behavior with typical excitation/emission peaks at 295 nm/412 nm. Upon the existence of FA, the fluorescence emission spectrum of N-CDs was significantly quenched through the synergy of static quenching mechanism and internal filtering effect (IFE). Under optimal conditions, the limit of detection was 28.0 nM (S/N = 3) within the FA concentration range of 0–200.0 μM. In addition, N-CDs were successfully employed to detect FA in real samples such as urine and fetal bovine serum (FBS), with a recovery rate of 99.6%-100.7% for quantitative addition. Furthermore, cell experiments confirmed the low toxicity and the cell imaging performance of these N-CDs, indicating that the obtained N-CDs could be served as a credible quantitative probe for FA analysis in the field of biosensing.

A comparison of fluorescent N-doped carbon dots supported on the surface of hollow and solid carbon spheres, and solid silica spheres

Fluorescent carbon dots (Cdots) have attracted many researchers due to their strong optical photoluminescence (PL) properties; however, due to their small size they agglomerate in the solid state which makes it difficult to remove them from solution. To overcome these problems, Cdots can be deposited on a support, but to date, few systematic studies of Cdots-support systems have been reported, especially those on carbon supports. Herein, we report a systematic study of the effect of the use of N-Cdots (5, 10, 15 and 20%) supported on the surface of hollow carbon spheres (HCSs), solid carbon spheres (SCSs) and silica spheres (SSs). The morphology of the Cdots and their composites (Cdots/SSs, Cdots/HCSs and Cdots/SCSs) was studied by TEM, TGA, XRD, FTIR, UV–vis and PL techniques. The FTIR, XRD and TGA data suggest different interactions of the Cdots with the supports. The PL quantum yield for bare Cdots was 34% and this value was dependent on the supports, in the order Cdots/SSs > Cdots/HCSs > Cdots/SCSs due to different interactions between the Cdots and the support.

Facile and Green synthesis of fluorescent N-doped carbon dots from betel leaves for sensitive detection of Picric acid and Iron ion

In this present work, a facile, green, cost effective route has been applied for the synthesis of water soluble carbon dots from betel leaves by hydrothermal route. As obtained nitrogen doped carbon dots (N-CDs) show remarkable advantages such as water solubility, biocompatibility and excellent stability. It is analyzed by vital characterization techniques such as HR-TEM, AFM, PSA, XRD, XPS, FTIR, UV-–vis and fluorescence spectroscopy with lifetime analysis. It exhibits blue emission under UV lamp (wavelength 365 nm), excitation dependent emission behavior and independent of pH. The obtained N-CDs show excellent response to picric acid (PA) and Fe3+ ions which leads to fluorescence quenching. This phenomenon was applied to design a single probe fluorescence based system for dual detection with high selectivity and sensitivity. A good linear response was obtained between concentration of analyte and fluorescence intensity with limit of detection (LOD) 0.11μM in the range of 0.3−3.3μM for PA and 0.135μM in the range of 0.3−3.3μM for Fe3+. Finally, the obtained fluorescent probe could be a promising tool for sensitive detection of PA and Fe3+ in aqueous solution.

Fe3+ detection, bioimaging, and patterning based on bright blue-fluorescent N-doped carbon dots.

Bright blue fluorescent N-doped carbon dots (N-CDs) with satisfactory yield (54%) were successfully fabricated by one-step hydrothermal treatment of astragalus. The obtained N-CDs possessed superior stability, solubility and high resistance to photo bleaching, and can be used as label-free nanosensors for the determination of Fe3+. The quantitative analysis of Fe3+ showed a linear range of 50 to 250 μM with the detection limit as low as 42 nM. Moreover, the as-prepared N-CDs have been used in cellular imaging owing to their distinct merits of simplicity, convenience, fast response and good selectivity towards Fe3+. Besides, the N-CDs could also be further used as fluorescent inks for drawing luminescent patterns.

N-Doped carbon dots with pH-sensitive emission, and their application to simultaneous fluorometric determination of iron(III) and copper(II).

Simultaneous fluorometric determination of iron(III) and copper(II) without the use of any masking agent or additional treatment is achieved by using N-doped carbon dots (NCDs). The NCDs were hydrothermally prepared, have strongest excitation/emission peaks at 320/406nm and a 47% quantum yield. Excitation-tunable emission is found to depend on solution pH values. This supports the involvement of surface states in the origin of the excitation dependent nature. The NCDs were employed as a fluorescent probe for the simultaneous determination of Fe(III) with a linear response in the 3-60μM concentration range and a 0.31μM detection limit (LOD). The probe also responds linearly to Cu(II) in the 0.5-15μM concentration range and witha 56nM LOD. With the addition of Cu(II), the absorption spectra of NCDs presented a clear decrease in the intensity at 312nm followed by an increase at 360nm. This is not observed in the presence of Fe(III). The fluorescence lifetime of NCDs (5.8ns) is reduced by Fe(III) but not by Cu(II). Thus, the two metal ions can be simultaneously detected without the need for any reagents. The probe was employed to quantify Fe(III) and Cu(II) in spiked water, serum, and urine samples. Graphical abstract Schematic representation of hydrothermal synthesis of highly fluorescent N-doped carbon dots with novel pH dependent emission and their application for the simultaneous determination of Cu(II) and Fe(III) with individual ion discrimination.

Microwave Assisted Synthesis and Optical Properties of Highly Fluorescent N-Doped Carbon Dots

Herein, a rapid microwave assisted solid state method is reported for the synthesis of highly fluorescent N-doped carbon dots (NCDs) using citric acid as carbon source and guanidine hydrochloride as N-dopant. Synthetic parameters such as microwave power, irradiation time and reactants ratio were optimized to produce high quality N-doped carbon dots. The N-doped carbon dots were well characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), SEM-EDS, FTIR, UV-visible and fluorescence spectroscopies. N-Doped carbon dots exhibited bright emission with a quantum yield of 11 %. Detailed study of their optical properties revealed their excellent property of resistance to photo bleaching, high ionic strength and solution pH. Further they exhibited excitation dependent emission behaviour, high aqueous solubility and a long shelf life of 60 days. This strong fluorescence emission combined with high stability make N-doped carbon dots a promising fluorescent probe for wide range of applications.

Fluorescent N-doped carbon dots from bacterial cellulose for highly sensitive bacterial detection

Carbon dots have good dispersion capability, strong visible fluorescence, low toxicity, and photo-induced accepting and donating abilities. Carbon dots were obtained from biomass bacterial cellulose (BC) via one-step hydrothermal carbonization. Effects of hydrothermal time and temperature on the microstructure, fluorescence, and excitation wavelength dependent photoluminescence (PL) behavior were explored for the prepared carbon dots. The results showed that the carbon dots obtained directly from the BC (C dots) had small particle sizes (2.0 to 3.0 nm) and green luminescence behavior. Conversely, the N-doped carbon dots (N-C dots) exhibited more uniform and smaller particle sizes (approximately 1.0 nm), strong blue luminescence, acceptable fluorescence lifetime, and good stability in a wide range of pH values (2.0 to 10.0). Thus, carbon dots could serve as a fluorescent material used in high performance optical cellular imaging and highly sensitive bacterial detection.

Facile Synthesis of Nitrogen-Doped Carbon Dots from Lignocellulosic Waste.

The current research mainly focuses on transforming low-quality waste into value-added nanomaterials and investigating various ways of utilising them. The hydrothermal preparation of highly fluorescent N-doped carbon dots (N–CDs) was obtained from the carboxymethylcellulose (CMC) of oil palm empty fruit bunches and linear-structured polyethyleneimines (LPEI). Transmission electron microscopy (TEM) analysis showed that the obtained N–CDs had an average size of 3.4 nm. The N–CDs were monodispersed in aqueous solution and were strongly fluorescent under the irradiation of ultra-violet light. A detailed description of the morphology and shape was established using Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). It was shown that LPEI were successfully tuned the fluorescence (PL) properties of CDs in both the intrinsic and surface electronic structures, and enhanced the quantum yield (QY) up to 44%. The obtained N–CDs exhibited remarkable PL stability, long lifetime and pH-dependence behaviour, with the excitation/emission maxima of 350/465.5 nm. Impressively, PL enhancement and blue-shifted emission could be seen with the dilution of the original N–CDs solution. The obtained N–CDs were further applied as fluorescent probe for the identification of Cu2+ in aqueous media. The mechanism could be attributed to the particularly high thermodynamic affinity of Cu2+ for the N-chelate groups over the surface of N–CDs and the fast metal-to-ligand binding kinetics. The linear relationship between the relative quenching rate and the concentration of Cu2+ were applied between 1–30 µM, with a detection limit of 0.93 µM. The fluorescent probe was successfully applied for the detection of Cu2+ in real water. Moreover, a solid-state film of N–CDs was prepared in the presence of poly (vinyl alcohol) (PVA) polymer and found to be stable even after 72-h of continuous irradiation to UV-lamp. In contrast to the aqueous N–CDs, the composite film showed only an excitation independent property, with enhanced PL QY of around 47%. Due to the strong and stable emission nature of N–CDs in both aqueous and solid conditions, the obtained N–CDs are ideal for reducing the overall preparation costs and applying them for various biological and environmental applications in the future.

One-step hydrothermal-assisted synthesis of highly fluorescent N-doped carbon dots from gum tragacanth: Luminescent stability and sensitive probe for Au3+ ions

Water-soluble nitrogen-doped carbon dots (N-CDs) were fabricated by one-step hydrothermal treatment of mixture of gum tragacanth (GT) and ethylenediamine (EDA). The as-prepared N-CDs were highly fluorescent generator depending on the excitation wavelength and pH. The quantum yield (at 436 nm) was 66.74% at excitation 365 nm and pHs 2–4. The fluorescent intensity of N-CDs solution (5 μg/mL) irradiated at 365 nm for 60 min and stored at −4 °C. Also, the fluorescent intensity decreased slightly (~10%) after 20 weeks of storage. The as-prepared N-CDs showed good antioxidant activity, and the cytotoxicity test against human fibroblast cells using MTT assay indicated the cell survival rate of ~94% in <125 μg/mL concentration of N-CDs. The resulting N-CDs showed a remarkably sensitive and selective quenching effect of fluorescent emission toward Au3+ ions with the detection limit reached 2.69 μM and a linear range extended in the range of 0–100 μM.

N-doped carbon dots covalently functionalized with pillar[5]arenes for Fe3+ sensing.

Fluorescent N-doped carbon dots (CN-dots) covalently functionalized with carboxylatopillar[5]arene (CP[5]), namely CCDs, have been prepared the first time. Compared with CN-dots without pillarene units, the newly constructed fluorescent CCDs could recognize Fe3+ with high selectivity. Therefore, such CCDs can potentially serve as a promising chemical sensor for Fe3+ ions.

Food waste-driven N-doped carbon dots: Applications for Fe3+ sensing and cell imaging

We report highly fluorescent N-doped carbon dots (CDs) synthesized from food waste via one-step hydrothermal carbonization. To study the chemical transition of carbon dots from food wastes, the cat feed stocks driven from food waste were used as the waste model. In the model study, the core of the CDs was successfully self N-doped without extra pre- or post-treatments. The experimental results reveal that the nitrogen in the waste model played an important role in the formation of graphitic N and pyridinic N in the core and functional groups on the surface. Especially, high process temperature (≥180 °C) resulted in high quantum yield as 23% of the CDs from the waste model. To demonstrate the conversion of real food waste into CDs, the hamburger sandwich leftover was used as a precursor for CDs. The food waste driven CDs had similar chemical and fluorescent properties to that of the waste model, having quantum yield of 28%. This study exhibits the food waste driven carbon dots are excellent candidates for fluorescence probe to Fe3+ with high selectivity even under the interference of other metal, and for bio-imaging material with good cell viability over 80%.

Pyromellitic acid-derived highly fluorescent N-doped carbon dots for the sensitive and selective determination of 4-nitrophenol

Highly fluorescent N-doped carbon dots (NCDs) were fabricated using pyromellitic acid (PA) and ethylene diamine (EDA) as novel precursors. The NCDs exhibited excellent fluorescent properties with a quantum yield as high as 75% due to the enhancement effect of the N dopant on the surface of the NCDs. Moreover, owing to its strong cyan fluorescence, the newly synthesized NCDs were applied effectively as a fluorescence platform for the sensitive and selective determination of 4-nitrophenol (4-NP) without further chemical modification. The NCDs fabricated in this study exhibited a wide linear range, low detection limit, and excellent selectivity towards other organic compounds.

Highly fluorescent N-doped carbon dots with two-photon emission for ultrasensitive detection of tumor marker and visual monitor anticancer drug loading and delivery

Early diagnosis and therapy are practically important to effectively prevent cancer and improve patients’ life quality. Herein, a simple and sensitive two-photon imaging fluorescent nitrogen-doped carbon dots (N-CDs) platform was constructed to detect β-glucuronidase (βG, a tumor-invasive biomarker) based on inner filter effect (IFE), to visually monitor anticancer drug loading by fluorescence resonance energy transfer (FRET), and to effectively treat cancer by chemotherapy. To build this sensing platform, novel N-CDs with strong green emission (Ca. QY = 45%) were synthesized by one-pot pyrolysis reaction, and specifically, careful structure design of the excitation bands of N-CDs well covered the absorption bands of p-nitrophenol (PNP, βG catalytic product), making it ultra-sensitive towards the activity of βG and showing good linear relationship from 1 to 15 U/L and exciting detection limit of 0.3 U/L (S/N = 3). This sensing platform has been successfully employed for βG sensing in both human serum and intracellular detection. Moreover, we also demonstrated the first application of N-CDs as a novel visual detection sensor to monitor the loading process of doxorubicin, and as a nanocarrier for cancer therapy. More importantly, the N-CDs also exhibited high quality single- and two-photon fluorescence in high depth (18 μm), enabling the N-CDs to real-time monitor the endocytosis, intracellular distribution and release of drugs, indicating significant potential for biomedicine and bioimaging applications.

Facile green synthesis of fluorescent N-doped carbon dots from Actinidia deliciosa and their catalytic activity and cytotoxicity applications

Green synthesis of fluorescent nitrogen doped carbon dots (N-CDs) using Actinidia deliciosa (A. deliciosa) fruit extract as a carbon precursor and aqueous ammonia as a nitrogen dopant is reported here. The synthesized N-CDs were characterized by high resolution transmission electron microscopy (HR-TEM), energy dispersive spectroscopy (EDS), selected area electron diffraction (SAED), UV–Visible spectroscopy (UV–Vis), fluorescence spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The average size of the N-CDs was approximately 3.59 nm and the calculated inter layer distance was found to be 0.21 nm. Raman spectroscopy and SAED pattern revealed the graphitic nature of the synthesized N-CDs. The N-CDs were found to emit intense blue color at 405 nm under the excitation of 315 nm. The doping of nitrogen over the surface of the N-CDs was confirmed by EDS, FT-IR and XPS studies. The synthesized N-CDs were found to exhibit excellent catalytic activity in the reduction of Rhodamine-B using sodium borohydrate. The MTT assay was used to evaluate the cytotoxicity and biocompatibility of N-CDs towards L-929 and MCF-7 cells. From the results obtained, it was found that the N-CDs exhibit low cytotoxicity and superior biocompatibility on both L-929 and MCF-7 cells.