Co-doped Carbon Nanodots Research Articles

One-step synthesis of nitrogen and chlorine co-doped fluorescent carbon nanodots for the sensitive detection of Ag+

Nitrogen and chlorine co-doped fluorescent carbon nanodots (CDs) were prepared using a facile and eco-friendly solvothermal process in which N-Chlorosuccinimide(NCS) was used as a carbon source. The resulting CDs were characterized by UV-visible absorption spectroscopy, fluorescence spectroscopy, high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared and X-ray photoelectron spectroscopy (XPS). It shows emission of blue light at 410 nm when excited at 340 nm. High quantum yield of 21.7% and good biocompatibility were also observed. Importantly, the fluorescence intensity of CDs was selectively quenched after addition of Ag+. Based upon the aforementioned phenomenon, a new fluorescent biosensor for the detection of Ag+ was proposed. The linear range and detection limit was 5-70 μM and 1.06 μM, respectively. Eventually, these superior properties demonstrated that the CDs have promising applications in the field of environmental and biomedicine research.

High Quality Nitrogen and Silicon Co-Doped Carbon Dots (N/Si-CDs) for Fe3+ Sensing.

Nitrogen and silicon co-doped carbon nanodots (N/Si-CDs) were synthesized by one-step hydrothermal carbonization of folic acid and 3-aminopropyl trimethoxy silane with the assistance of glycerol. The resultant N/Si-CDs present intense excitation-independent photoluminescence (PL) emission owing to their monodisperse sizes and specific surface states. In comparison to nitrogen single doped CDs (N-CDs), the co-doped N/Si-CDs possess better PL properties following different emission manner due to the synergistic effects of the nitrogen and silicon dopants. Besides, the functionalized surfaces of N/Si-CDs endow them with superior solubility and stability. The as-synthesized N/Si-CDs demonstrate selective and sensitive fluorescence response to Fe3+, which could be explained by the PL quenching effects of Fe3+ on N/Si-CDs. Based on this finding, the quantitative analysis of aqueous Fe3+ by N/Si-CDs was established, showing good linearity in a range of 10 nM~45 μM and good sensitivity with a detection limit of 3.8 nM, so did for the detection of Fe3+ in fetal bovine serum (FBS) spiked samples. Therefore, the N/Si-CDs as a novel fluorescence probe hold promising for monitoring environmental and clinical Fe3+.

Antioxidant Capacity of Nitrogen and Sulfur Codoped Carbon Nanodots.

Carbon nanodots (CNDs) have shown potential for antioxidative activity at the cellular level. Here we applied a facile hydrothermal method to prepare fluorescent nitrogen and sulfur (N,S-)codoped CNDs using α-lipoic acid, citric acid, and urea as precursor molecules. This work describes a comprehensive study for exploring their antioxidation activity using UV-vis absorption and electrochemistry measurements of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH•), as well as a lucigenin chemiluminescence (lucigenin-CL) assay. The lucigenin-CL assay detects superoxide anion radicals, i.e., reactive oxygen species (ROS) produced through the xanthine/xanthine oxidase (XO) reaction. The electrochemically derived relationship between the unreacted nitrogen-centered DPPH• and CND concentrations agrees with that obtained from UV-vis measurements. A reaction pathway for the ROS antioxidative reaction of N,S-codoped CNDs is proposed. These findings should aid in the development of N,S-codoped CNDs for practical use in biomedical applications.

Carbonization of Human Fingernails: Toward the Sustainable Production of Multifunctional Nitrogen and Sulfur Codoped Carbon Nanodots with Highly Luminescent Probing and Cell Proliferative/Migration Properties.

A simple yet effective method is employed to prepare multifunctional fluorescent carbon nanodots (CNDs) from human fingernails. The results demonstrate that the CNDs have excellent optical properties and a quantum yield of 81%, which is attributed to the intrinsic composition of the precursor material itself. The CNDs are used to develop an ultrasensitive fluorescent probe for the detection of hexavalent chromium (limit of detection: 0.3 nM) via a combined inner-filter and static mechanism. Moreover, the toxicity of the CNDs over four epithelial cell lines is assessed. A negligible toxicity is induced on the three of the cell lines, whereas an increase in HEK-293 cell viability is demonstrated, granting cell proliferation properties to the as-synthesized CNDs. According to cell cycle analysis, cell proliferation is achieved by enhancing the transition of cells from the S phase to the G2/M one. Interestingly, CNDs are found to significantly promote cell migration, maybe because of their free-radical scavenging ability, making the CNDs suitable for wound healing applications. In addition, relevant experiments have revealed the blood compatibility of the CNDs. Finally, the CNDs were found suitable for cell imaging applications, and all of the aforementioned merits make it possible for them to be used for extraordinary, more advanced biological applications.

Hydrothermal synthesis of N,S co-doped carbon nanodots for highly selective detection of living cancer cells.

This study presents a facile synthesis method for the preparation of positively charged N,S co-doped carbon nanodots with excellent optical properties, and it develops a selective method for fluorescent detection of living cancer cells. The specific recognition is due to the application of an aptamer sequence, which shows high affinity and specificity to target cells. The aptamer is firstly labeled with BHQ and wraps around the carbon nanodots, then it finally quenches the fluorescence emission of the carbon nanodots. For the sensitive and selective analysis of target cells, the cells are simply mixed with the carbon nanodot-aptamer nanoconjugates, which are then centrifuged at a low speed. The recognition reaction between aptamer and target cells releases the quencher from the surface of the carbon nanodots and the centrifugation process enables the recovery of fluorescence intensity of the suspension, which reflects the level of initial cancer cells. The developed method is simple, highly selective and cost-effective, thus, it may be further exploited in clinical applications in the future.

One-step synthesis of nitrogen, sulfur co-doped carbon nanodots and application for Fe3+ detection.

Carbon nanodots (CDs) are novel forms of zero-dimensional carbonaceous nanomaterials, which have attracted the attention of researchers. Long wavelength emission decreases the interference of auto-fluorescence of tissue and can also penetrate more deeply. However, it is still a challenge to develop red emissive CDs. In this work, nitrogen, sulfur co-doped CDs are synthesized with red light emission through one-step solvothermal treatment. The as-synthesized CDs exhibit excellent properties such as high chemical stability, good biocompatibility, excellent photoluminescence properties, good water solubility, and low toxicity, and also show high sensitivity and selectivity towards Fe3+ sensing. The detection limit is as low as 17.3 nM. In addition, the CDs are successfully utilized for monitoring Fe3+ in living cells, which demonstrates their promising applicability in bioimaging. Furthermore, a test paper based on the CQDs has been prepared. This developed nanosensor can detect Fe3+ visually and sensitively without any further steps which will make a great contribution to the development of ion sensors.

N,S,P Co-Doped Carbon Nanodot Fabricated from Waste Microorganism and Its Application for Label-Free Recognition of Manganese(VII) and l-Ascorbic Acid and AND Logic Gate Operation.

A novel fluorescent probe based on N,S,P codoped carbon nanodots (N,S,P-CNDSac) is very simple and quickly fabricated by a one-step hydrothermal pyrolysis of Saccharomyces cerevisiae and utilized for label-free and "on-off-on" sequential detection of manganese(VII) and l-ascorbic acid (l-AA). The fluorescence of N,S,P-CNDSac can be effectively quenched by Mn(VII) based on an inner filter effect (IFE) and recovered upon the addition of l-AA due to the easy conversion of Mn(VII) to reduced states (i.e., Mn(IV), Mn(II), and Mn(0)) by l-AA. This probe exhibited favorable selectivity and sensitivity toward Mn(VII) and l-AA with detection limits of 50 nmol/L and 1.2 μmol/L, respectively. Simultaneously, an "AND" logic gate based on the as-fabricated N,S,P-CNDSac has been constructed. Also, the as-proposed fluorescent probe was extended to detect Mn(VII) and l-AA in biosystems. Furthermore, the as-constructed fluorescent probe system was successfully applied to the analyses of Mn(VII) in tap water, Fenhe River water, and medicinal herb samples with satisfactory results. The proposed method is simple and easily accessible, demonstrating the great potential of N,S,P-CNDSac in biosensing, disease diagnosis, cellular labeling, and environmental monitoring.

Extraordinary sensitizing effect of co-doped carbon nanodots derived from mate herb: Application to enhanced photocatalytic degradation of chlorinated wastewater compounds under visible light

The present work investigates the role of two types of carbon nanodots (CNDs) as novel sensitizers of TiO2 to create a visible-light driven photo-catalyst that is not only efficient for solar-driven pollution abatement, but also inexpensive, durable and environmentally-friendly. Two widely available green organic precursors, the Argentinean herb Mate and the Stevia plant have been selected as the carbogenic source to thermally induce the formation of different types of CNDs with different levels of N and P doping and tunable photoluminescence response in the UV–vis-near infrared (NIR) ranges. These CNDs have been successfully assembled with TiO2 to form heterogeneous photocatalysts that are highly active in the visible-light and NIR- driven photodegradation of 2,4-dichlorophenol (2,4-DCP), a persistent chlorinated organic compound present in numerous pesticide formulations.

Onion derived carbon nanodots for live cell imaging and accelerated skin wound healing.

Nitrogen, sulfur, and phosphorous co-doped water-soluble carbon nanodots are synthesized from culinary waste onion peel powder (OPP) by a short microwave treatment. Onion Derived Carbon Nano Dots (OCND) that comprised hydrophilic group-decorated amorphous nano-dots exhibited bright, stable fluorescence at an excitation of 450 nm and emission wavelength at 520 nm along with a free radical scavenging property. The OCND exhibited excellent stability at different pH and UV exposure. Although extracted polyphenols degraded in the extract, interestingly it was shown to be cytocompatible and blood compatible as observed during cytotoxicity, fluorescence imaging of the cell and a hemolysis study. The present work not only focuses on the synthesis of OCND from the OPP extract but also provides an interesting fact that, even after the degradation of polyphenols in the extract, they are non-toxic to human cells (HFF & MG63) and RBCs. Moreover, OCND had no adverse effect on the migration rate of Human Foreskin-derived Fibroblasts (HFFs) as observed from a scratch assay. In addition to accelerating the migration rate of fibroblasts, the OCND altered intra- and extracellular reactive oxygen species (ROS) by enhancing the antioxidant mechanism of a fibroblast under oxidative stress. Further, OCND was observed to accelerate wound healing in a full thickness (FT) wound in a rat model for topical application, which can be attributed to its radical scavenging potential. In summary, this study leads to a new type of OCND synthesis route, which is inherently co-doped with phosphorous, sulfur and nitrogen and holds a great promise for a myriad of biological applications, including bio-imaging, free radical scavenging and wound healing.

Integrative Approach toward Uncovering the Origin of Photoluminescence in Dual Heteroatom-Doped Carbon Nanodots

The pursuit of exceptionally high photoluminescence (PL) and stability is critical in the development of novel fluorophores for use in challenging bioimaging and optoelectronic devices. Carbon nanodots (CDs) doped with heteroatoms provide a particularly attractive means of effectively tailoring their intrinsic properties and exploiting new phenomena. Here, we report a one-step, scalable synthesis of boron-and-nitrogen co-doped CD (BN-CD) with outstanding optical properties unlike those of nitrogen-doped CD (N-CD) in solid state as well as solution. The detailed mechanistic framework was explored using a series of spectroscopic analyses and ultrafast spectroscopy coupled with density functional theory calculations, which all conclusively confirmed that the presence of more graphitic structures in the core and well-distributed surface states are responsible for the enhanced PL in BN-CD. Furthermore, single-molecule spectroscopy analysis demonstrated that a single BN-CD shows higher PL intensity and enhanced...

Nitrogen and Phosphorus Co-Doped Carbon Nanodots as a Novel Fluorescent Probe for Highly Sensitive Detection of Fe3+ in Human Serum and Living Cells

Chemical doping with heteroatoms can effectively modulate physicochemical and photochemical properties of carbon dots (CDs). However, the development of multi heteroatoms codoped carbon nanodots is still in its early stage. In this work, a facile hydrothermal synthesis strategy was applied to synthesize multi heteroatoms (nitrogen and phosphorus) codoped carbon nanodots (N,P-CDs) using glucose as carbon source, and ammonia, phosphoric acid as dopant, respectively. Compared with CDs, the multi heteroatoms doped CDs resulted in dramatic improvement in the electronic characteristics and surface chemical activities. Therefore, the N,P-CDs prepared as described above exhibited a strong blue emission and a sensitive response to Fe(3+). The N,P-CDs based fluorescent sensor was then applied to sensitively determine Fe(3+) with a detection limit of 1.8 nM. Notably, the prepared N,P-CDs possessed negligible cytotoxicity, excellent biocompatibility, and high photostability. It was also applied for label-free detection of Fe(3+) in complex biological samples and the fluorescence imaging of intracellular Fe(3+), which indicated its potential applications in clinical diagnosis and other biologically related study.

A rapid microwave synthesis of nitrogen–sulfur co-doped carbon nanodots as highly sensitive and selective fluorescence probes for ascorbic acid

A ultrafast one-step microwave-assisted method was developed for the synthesis of nitrogen–sulfur co-doped carbon nanodots (N,S-CDs) by using ethylenediamine as the carbon source and sulfamic acid as the surface passivation reagent. The morphology and the properties of N,S-CDs were explored by a series of techniques, such as high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV–vis absorption and fluorescence spectroscopy. The prepared N,S-CDs exhibit bright blue photoluminescence with a high fluorescence quantum yield (FLQY) up to 28%, and high stability and excellent water solubility. A N,S-CDs-based fluorescent probe was developed for sensitive detection ascorbic acid (AA) in the presence of Cu2+, based on the mechanism that AA reduces Cu2+ to Cu+, then Cu+ quenches the fluorescence of N,S-CDs through electron or energy transfer due to the interaction between Cu+ and thiol ligand on the N,S-CDs surface. The observed linear response concentration range was from 0.057 to 4.0μM to AA with a detection limit as low as 18nM. The probe exhibited a highly selective response toward AA even in the presence of possible interfering substances, such as uric acid and citric acid. Moreover, these promising features made the sensing system used for the analysis of human serum and urine samples.

Facile synthesis of highly luminescent co-doped carbon nanodots for rapid, sensitive, and label-free detection of Hg2+

A simple, low-cost and straightforward hydrothermal method for synthesis of highly fluorescent nitrogen- and sulfur-co-doped carbon dots (N, S-CDs) has been developed via one-step pyrolysis of ethylenediaminetetraacetic acid salt (EDTA) and thiourea. The prepared N, S-CDs had an average size of 2.45±0.37nm and showed a strong emission at the wavelength of 450nm with an optimum excitation of 390nm. Comparing to the other metal ions, mercury ions (Hg2+) dramatically quenched the fluorescence of the N, S-CDs. Meanwhile, the fluorescence intensity displayed a good linear response with Hg2+ concentration in the range of 0–3.0×10−7M (R2=0.9997) and the detection limit was 1.37×10−9M. The cell viability results of Hela cells and the imaging experiments of Escherichia coli also certified that the N, S-CDs could be served as an effective fluorescent sensing probe for label-free sensitive and selective detection of Hg2+ in biological samples on account of their low toxicity and good biocompatibility.

Oxidative Synthesis of Highly Fluorescent Boron/Nitrogen Co-Doped Carbon Nanodots Enabling Detection of Photosensitizer and Carcinogenic Dye

Current research efforts have demonstrated the facile hydrothermal oxidative synthetic route to develop highly fluorescent boron/nitrogen co-doped carbon nanodots (CNDs). During this process, N-(4-hydroxyphenyl)glycine served as a source of N doping and a carbon precursor as well, while boric acid H3BO3 is used as an oxidizing agent in the N2 environment. Surface passivation through ultrasonic treatment of CNDs was performed to induce modifications by using various surface passivating agents. Polyethyleneimine (PEI) remarkably enhanced the fluorescence performance and monodispersity of polymerized carbon nanodots (P-CNDs) in aqueous phase with an enhanced quantum yield of 23.71%, along with an increase in size from ~3 nm to ~200 nm. For characterization of CNDs and P-CNDs, UV, infrared, photoluminescence, transmission electron microscopy, x-ray photoelectron spectra, and atomic force microscopy techniques were utilized. Application potentials of synthesized P-CNDs were developed via introduction of protoporphyrin (PPD, a photosensitizer) which has great doping affinity with polymer PEI to switch-off the fluorescence of P-CNDs, leading to the production of dye-doped nanoprobes. Fluorescence resonance energy transfer (FRET) was also observed during dye-doping, and PPD was detected with a limit of detection (LOD, 3σ) of 15 pM. The fluorescence recovery of this switched-off nanoprobe was made possible by using Sudan red III (carcinogenic dye), which was oxidized by PPD doped in P-CNDs. Sudan red III was detected in the concentration range of 9.9 pM-0.37 nM. Meanwhile, it was also confirmed that the dye-doped nanoprobe is highly selective and exceptionally sensitive to detect this carcinogenic agent in commercial products with a LOD (3σ) of 90 fM.