Nitrogen, phosphorus and sulfur tri-doped carbon dots are specific and sensitive fluorescent probes for determination of chromium(VI) in water samples and in living cells

Multifunctional In-MOF and Its S-Scheme Heterojunction toward Pollutant Decontamination via Fluorescence Detection, Physical Adsorption, and Photocatalytic REDOX

A novel doubly interpenetrated indium-organic framework of 1 has been assembled by In3+ ions and highly conjugated biquinoline carboxylate-based bitopic connectors (H2L). The isolated 1 exhibits an anionic framework possessing channel-type apertures repleted with exposed quinoline N atoms and carboxyl O atoms. Owing to the unique architecture, 1 displays a durable photoluminescence effect and fluorescence quenching sensing toward CrO42-, Cr2O72-, and Cu2+ ions with reliable selectivity and anti-interference properties, fairly high detection sensitivity, and rather low detection limits. Ligand-to-ligand charge transition (LLCT) was identified as the essential cause of luminescence by modeling the ground state and excited states of 1 using DFT and TD-DFT. In addition, the negatively charged framework has the ability to rapidly capture single cationic MB, BR14, or BY24 and their mixture, including the talent to trap MB from the (MB + MO) system with high selectivity. Moreover, intrinsic light absorption capacity and band structure feature endow 1 with effective photocatalytic decomposition ability toward reactive dyes RR2 and RB13 under ultraviolet light. Notably, after further polishing the band structure state of 1 by constructing the S-scheme heterojunction of In2S3/1, highly efficient photocatalytic detoxification of Cr(VI) and degradation of reactive dyes have been fully achieved under visible light. This finding may open a new avenue for designing novel multifunctional MOF-based platforms to address some intractable environmental issues, i.e., detection of heavy metal ions, physical capture of pony-sized dyes, and photochemical decontamination of ultrastubborn reactive dyes and highly toxic Cr(VI) ions from water.

Rational design of nitrogen (N), boron (B), and phosphorous (P) tri-doped carbon nano-spheres as advanced anode materials for sodium-ion batteries with an ultra-long lifespan

Developing improved anode materials is critical to the performance enhancement and the lifespan prolonging of sodium-ion batteries (SIBs). In this context, carbon-based nanostructures have emerged as a promising candidate. In this work, we have synthesized N, B, and P tri-doped carbon (NBPC) spheres using a one-step carbonization method. The as-prepared NBPC exhibits exceptional properties, including an expanded layer space, sufficient structural defects, and enhanced electrical conductivity. These characteristics synergistically contribute to the remarkable rate capability and ultra-long lifespan when NBPC is employed as an anode material for SIBs. The as-prepared NBPC demonstrates a reversible capacity of 290.6 mAh/g at 0.05 A/g, with a capacity retention of 98.4% after 800 cycles. Furthermore, NBPC exhibits an impressively ultra-long cycle life of 2400 cycles at 1.0 A/g with a reversible capacity of 140.2 mAh/g. First principle calculations confirm that the introduction of N, B, and P heteroatoms in carbon enhances the binding strength of sodium ions within NBPC. This work presents a novel approach for fabricating advanced anode materials, enabling the development of long-life SIBs for practical applications.

A Novel Non-Metallic Photocatalyst: Phosphorus-Doped Sulfur Quantum Dots

In this paper, a novel phosphorus-doped sulfur quantum dots (P-SQDs) material was prepared using a simple hydrothermal method. P-SQDs have a narrow particle size distribution as well as an excellent electron transfer rate and optical properties. Compositing P-SQDs with graphitic carbon nitride (g-C₃N₄) can be used for photocatalytic degradation of organic dyes under visible light. More active sites, a narrower band gap, and stronger photocurrent are obtained after introducing P-SQDs into g-C₃N₄, thus promoting its photocatalytic efficiency by as much as 3.9 times. The excellent photocatalytic activity and reusability of P-SQDs/g-C₃N₄ are prospective signs of its photocatalytic application under visible light.

Effect of Doping Heteroatoms on the Optical Behaviors and Radical Scavenging Properties of Carbon Nanodots

Heteroatom doping is regarded as a promising method for controlling the optoelectronic properties of carbon nanodots (CNDs), notably their fluorescence and antioxidation activities. In this study, phosphorous (P) and boron (B) are doped at different quantities in the CNDs' structures to investigate their effects on the optical and antioxidation properties. Both the dopants can enhance light absorption and fluorescence, yet via different approaches. After doping, the UV-vis absorption of high P%-CNDs demonstrated a slight blue shift (348-345 nm), while the high B%-CNDs showed a minor red shift (348-351 nm), respectively. The fluorescence emission wavelength of doped CNDs changes marginally while the intensity increases significantly. Structural and composition characterizations show elevated levels of C=O on the surface of high P%-CND compared to low P%-CNDs. In B-doped CNDs, more NO₃ ^- functional groups and O-C=O bonds and fewer C-C bonds form at the surface of high B%-CNDs compared to the low B%-CNDs. A radical scavenging study using 2,2-diphenyl-1-picrylhydrazyl (DPPH) was carried out for all CNDs. It was found that the high B%-CNDs exhibited the highest scavenging capacity. The effects of the atomic properties of dopants and the resulting structures of CNDs, including atomic radius, electronegativity, and bond lengths with carbon, on the optoelectronic property and antioxidative reactions of CNDs are comprehensively discussed. It suggests that the effect of P-doping has a major impact on the carbogenic core structure of the CNDs, while the B-doping mainly impacts the surface functionalities.

Inner-filter Effect Induced Fluorescence Quenching of Carbon Dots for Cr(VI) Detection with High Sensitivity

Carbon dots (CDs) were used to develop a sensitive sensing technique for detecting Cr(VI). CDs were made using a hydrothermal technique from citric acid and glutamic acid. These prepared CDs emitted blue fluorescence under excitation of 350 nm (λ_em = 420 nm), and the fluorescence quantum yield was 48.41%. Transmission electron microscope was used to examine the morphology of the CDs, which had an average size of 2.21 ± 0.39 nm. The elementary composition and bonding structure of the CDs were conducted by XPS and FT-IR spectrum. Cr(VI) quenched the fluorescence of CDs through a static quenching effect and an inner filter effect, allowing Cr(VI) to be detected quantitatively. This approach was used to detect Cr(VI) in two samples of water, with the findings demonstrating that it is reliable and accurate. The fluorescence intensity change was linearly related to the concentration of Cr(VI) in the range from 0.5 to 400 μM, with the detection limit being 0.10 μM. This approach has the virtues of wide detection range, low cost and fast response. The strategy has a great application prospect for detecting Cr(VI) in practical samples.

Synthesis of intrinsic dual-emission type N,S-doped carbon dots for ratiometric fluorescence detection of Cr (VI) and application in cellular imaging

In this paper, intrinsic dual-emission fluorescent carbon dots (CDs) doped with N and S atoms have been firstly fabricated. The characterization results show that CDs are successfully synthesized with two separate fluorescence emissions at 468 nm and 628 nm, respectively. The strong and selective interaction of Cr (VI) ions with CDs lead to obvious fluorescence decrease of CDs at 468 nm, which is caused by a mixed quenching mechanism. At the same time, the fluorescence at 628 nm increase. Interestingly, the CDs solution show obvious color change under the daylight and UV light, so visualization detection of Cr (VI) can be realized in water samples. Based on the data of the emission intensity ratios of F₄₆₈/F₆₂₈, Cr (VI) can be detected from 3.8 to 38.9 μM combined with the linear correlation coefficient of 0.998, and the lowest detection concentration is 47.2 nM. The platform is satisfactorily applied to the detection of Cr (VI) ions in water samples. In addition, the CDs could be applied as fluorescent probes for cell imaging with dual fluorescent emission.

Ultrasensitive ratiometric fluorescent probes for Hg(ii) and trypsin activity based on carbon dots and metalloporphyrin via a target recycling amplification strategy

A ultrasensitive ratiometric fluorescent probe was developed for Hg(ii) and trypsin based on CDs and TPPS via a target recycling amplification strategy. The detection limits of Hg2+ and trypsin were 0.086 nM and 0.013 ng mL−1.

Fluorescent nitrogen-doped carbon dots for high selective detecting p-nitrophenol through FRET mechanism

A facile, friendly and one-step hydrothermal protocol was used to synthesize nitrogen-doped carbon dots (N-CDs) by utilizing hexamethylenetetramine and ethanediamine as the carbon and nitrogen sources. It demonstrated good water solubility and fluorescence properties were stable, whether in acidic or alkaline. Quantum yield (QY) of N-CDs was 8.3% at an excitation wavelength of 325 nm with maximum emission at 425 nm. The fluorescence of N-CDs achieved very high fluorescence quenching of 60% in the detection of p-nitrophenol (p-NP) in aqueous medium via fluorescence resonance energy transfer (FRET) mechanisms. Under optimum conditions, fluorescence probs of N-CDs had strong selectivity to p-NP, and the fluorescence intensity was linearly proportional to p-NP concentration from 0.5 to 70.0 μM with a detection limit of 0.201 μM. The corresponding cell experiments were also performed, indicating that the prepared N-CDs possessed low cytotoxicity and good biocompatibility. Meanwhile, the N-CDs can be used for the determination of p-NP in river water and industrial wastewater.

Green preparation of carbon dots from Momordica charantia L. for rapid and effective sensing of p-aminoazobenzene in environmental samples

p-Aminoazobenzene (pAAB) is a hazardous azo dye that causes considerable harm to human health and the environment. The development of novel and sensitive sensors for the rapid detection of pAAB is in high demand. In this study, a simple fluorescent sensor for pAAB detection is designed based on carbon dots (CDs) which are prepared using green carbon source of Momordica charantia L. via a facile hydrothermal approach. The fluorescence spectra of CDs exhibit considerable overlap with the absorption band of pAAB, and the fluorescence is specifically suppressed in the presence of pAAB ascribed to the inner filter effect. Good and wide linearity is observed in the pAAB concentration range of 0.01-12.5 μg mL^-1 with a lower detection limit of 3.9 ng mL^-1. The established method achieves good results with a rapid analysis of pAAB in different practical water and soil samples. The as-constructed fluorescent sensor provides a simple, rapid, economical and eco-friendly platform and possesses prospective applications for the effective, selective and sensitive detection of pAAB in the environmental field.

Carbon dots derived from Poria cocos polysaccharide as an effective “on-off” fluorescence sensor for chromium (VI) detection

Chromium is a harmful contaminant showing mutagenicity and carcinogenicity. Therefore, detection of chromium requires the development of low-cost and high-sensitivity sensors. Herein, blue-fluorescent carbon quantum dots were synthesized by one-step hydrothermal method from alkali-soluble Poria cocos polysaccharide, which is green source, cheap and easy to obtain, and has no pharmacological activity due to low water solubility. These carbon quantum dots exhibit good fluorescence stability, water solubility, anti-interference and low cytotoxicity, and can be specifically combined with the detection of Cr(VI) to form a non-fluorescent complex that causes fluorescence quenching, so they can be used as a label-free nanosensor. High-sensitivity detection of Cr(VI) was achieved through internal filtering and static quenching effects. The fluorescence quenching degree of carbon dots fluorescent probe showed a good linear relationship with Cr(VI) concentration in the range of 1–100 μM. The linear equation was F₀/F = 0.9942 + 0.01472 [Cr(VI)] (R² = 0.9922), and the detection limit can be as low as 0.25 μM (S/N = 3), which has been successfully applied to Cr(VI) detection in actual water samples herein.

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Carbon dots was synthesized from alkaloid-soluble Poria cocos polysaccharide, which used for Cr (VI) detection.

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High sensitivity and selectivity detection of Cr(VI) based on internal filtering effect and static quenching mechanism.

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The method analysis speed is quick, sensitive, raw materials for convenient, inexpensive.

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The method has been applied to the determination of Cr(VI) in actual samples with satisfactory recovery.

Hydrothermal synthesis of N-doped carbon quantum dots and their application in ion-detection and cell-imaging

Carbon quantum dots (CQDs), owing to their characteristic luminescent properties, have become a new favorite in the field of luminescence. They have been widely used in light emitting diode, ion detection, cell-imaging, ect. Herein a facile synthesis method of nitrogen-doped carbon quantum dots (N-CQDs) has been developedviaa one-step hydrothermal of glucose and m-phenylenediamine. The chemical composition, surface functional groups, and crystal structure of so prepared N-CQDs were systematically characterized. The characterizations indicate that nitrogen has been chemically doped in the CQDs and the N-CQDs crystallize in a graphene structure. Photoluminescence (PL) measurements show that the N-CQDs emit strong blue emission under the irradiation of ultraviolet. The emission is excitation-dependent, is resistant to photo bleaching and high ionic strength, and slightly decreases with the increase of temperature. The quantum yield of them is about 17.5%. The PL intensity of N-CQDs quenches linearly with the increase of the concentrations of Fe³⁺(0.5-1.0 mM) and CrO₄^2-(0.3-0.6 mM), which are a kind of excellent fluorescent probe for the detection of Fe³⁺ and CrO₄^2-. The quenching mechanism of Fe³⁺ and CrO₄^2-is verified to be a static quenching mechanism based on inner filter effect. The N-CQDs are also found to be a good cell-imaging reagent of Hela cells.

You Don't Learn That in School: An Updated Practical Guide to Carbon Quantum Dots

Carbon quantum dots (CQDs) have started to emerge as candidates for application in cell imaging, biosensing, and targeted drug delivery, amongst other research fields, due to their unique properties. Those applications are possible as the CQDs exhibit tunable fluorescence, biocompatibility, and a versatile surface. This review aims to summarize the recent development in the field of CQDs research, namely the latest synthesis progress concerning materials/methods, surface modifications, characterization methods, and purification techniques. Furthermore, this work will systematically explore the several applications CQDs have been subjected to, such as bioimaging, fluorescence sensing, and cancer/gene therapy. Finally, we will briefly discuss in the concluding section the present and future challenges, as well as future perspectives and views regarding the emerging paradigm that is the CQDs research field.

Carbon dots as naked eye sensors

Optical sensors are always fascinating for chemists due to their selectivity, sensitivity, robustness and cost-effective nature.

An efficient fluorescent nano-sensor of N-doped carbon dots for the determination of 2,4,6-trinitrophenol and other applications

N-Doped carbon dots (CDs) had been simply produced by a one-pot synthesis process using amygdalic acid and threonine. The resulting product was water-soluble and exhibited strong luminescence emission with a fluorescence quantum yield of 19.25%. The emission of CDs was obviously and selectively decreased upon adding 2,4,6-trinitrophenol (TNP). It was proved that the fluorescence resonance energy transfer was the main mechanism for quenching. An efficient fluorescence probe with satisfied sensitivity for TNP determination was found. The range of the linear response for TNP detection was 0.5-40.0 μmol L^-1, and the limit of detection was 20 nmol L^-1. The content of trace TNP in water samples was successfully detected with this method. The CDs were also applied in HepG2 cell imaging and the fabrication of fluorescent films by dispersing the solid freeze-drying CD (SCD) powder into PMMA, which exhibited some application value in biology and photovoltaics.

Bright Mn-doped carbon dots for the determination of permanganate and L-ascorbic acid by a fluorescence on-off-on strategy

A one-pot hydrothermal synthesis of manganese-doped carbon dots (Mn-CDs) is reported for fluorescent "on-off-on" determination of Mn(VII) and L-ascorbic acid (L-AA) in aqueous solution and living cells. Mn-CDs were prepared by using sulfanilic acid, tetrakis(hydroxymethyl)phosphonium chloride, and Mn(II) chloride as precursors. Mn-CDs were characterized by several spectroscopic methods and microscopic techniques. Mn-CDs show distinctly long fluorescence lifetime (12.39 ± 0.07 ns) and high absolute fluorescence quantum yield (around 37%) with excitation and emission wavelengths of 362 and 500 nm, respectively. Mn-CDs exhibit no significant cytotoxicity to human cervical carcinoma HeLa cells and human embryonic kidney HEK-293T cells at 200 μg mL^-1 level after 48 h incubation. The fluorescence of Mn-CDs at 500 nm (excited at 362 nm) is quenched efficiently by Mn(VII) and can be further recovered after the addition of L-AA, resulting in a fluorescent "on-off-on" assay for the determination of Mn(VII) and L-AA. Under optimal experimental conditions, the linear response covers the 3 to 150 μM Mn(VII) concentration range and the 3 to 140 μM L-AA concentration range. This method offers relatively low detection limits of 0.66 μM for Mn(VII) and 0.90 μM for L-AA. This strategy was applied to visual determination of Mn(VII) and L-AA in living HeLa cells with satisfying results. Graphical abstract Schematic presentation of bright Mn-CD-based fluorescence "on-off-on" assay for both Mn(VII) and L-AA. This fluorescent assay possessed low detection limit of 0.66 μM for Mn(VII) and 0.90 μM for L-AA. This strategy was applied for visual determination of Mn(VII) and L-AA in living HeLa cells with satisfying results.

Nitrogen-Doped Carbon Quantum Dots from Poly(ethyleneimine) for Optical Dual-Mode Determination of Cu2+ and l-Cysteine and Their Logic Gate Operation

In this work, nitrogen-doped carbon quantum dots from poly(ethyleneimine) (PQDs) were synthesized by a low-cost and facile one-step hydrothermal method without other reagents. A quantum yield (QY) of up to 23.2% with maximum emission at 460 nm under an excitation wavelength of 340 nm was ascribed to the high nitrogen doping (20.59%). The PQDs selectively form a blue complex with Cu²⁺ accompanied by strong quenching of the fluorescence emission. Meanwhile, the PQD-Cu²⁺ complex exhibited selective fluorescence recovery and color disappearance on exposure to l-cysteine (Cys). The electron transfer from amino or oxygen groups on the PQDs to Cu²⁺ leads to fluorescence quenching, and a chromogenic reaction of the cuprammonium complex results in a color change. The strong affinity between Cys and Cu²⁺ causes the detachment of Cu²⁺ from the surface of PQDs, so the color of the solution disappears and the fluorescence of PQDs recovers. Under the optimized condition, the proposed sensor was applied to detect Cu²⁺ in the linear range of 0-280 μM. A detection limit of 4.75 μM is achieved using fluorescence spectroscopy and 4.74 μM by monitoring the absorbance variation at 272 nm. For Cys detection, the linear range of 0-800 μM with detection limits of 28.11 μM (fluorescence determination) and 19.74 μM (peak shift determination at 272 nm) was obtained. Meanwhile, the PQD-Cu²⁺ system exhibits distinguishable responses to other biothiols such as l-glutathione (GSH) and dl-homocysteine (Hcy). Based on the multimode signals, an "AND" logic gate was constructed successfully. Interestingly, besides Cu²⁺, Fe³⁺ can also quench the fluorescence of PQDs and the PQD-Fe³⁺ system exhibits superior selectivity for Cys detection. Most importantly, the proposed assay is not only simple, cheap, and stable but also suitable for detecting Cu²⁺ and Cys in some real samples.

Ultraviolet Carbon Nanodots Providing a Dual-Mode Spectral Matching Platform for Synergistic Enhancement of the Fluorescent Sensing

The sensing of chromium(VI) (Cr(VI)) is highly desired, due to its toxic and carcinogenic effects upon human health. Fluorescent probes, especially carbon nanodots (CNDs), have been widely used for Cr(VI) sensing via the inner filter effect (IFE). However, improving the sensitivity of these probes remains a difficult issue. In this work, CNDs derived from β-Lactoglobulin were applied as an ultrasensitive fluorescent probe for Cr(VI). With 260 nm excitation, the CNDs showed multi-band emission, including an ultraviolet 360 nm peak. The spectral matching of the CNDs with Cr(VI) led to synergistic suppression of both the excitation and emission light in the fluorescent sensing. As a consequence, the CNDs showed high sensitivity toward Cr(VI), the detection limit reaching as low as 20 nM. Moreover, taking advantage of the multi-emissive property of the CNDs, the synergistic effect was proven in an IFE-based sensing system, which might be extended to the design of other kinds of fluorescent probes.

Fluorescent Carbon Quantum Dots-Synthesis,Functionalization and Sensing Application in FoodAnalysis

Carbon quantum dots (CQDs) with stable physicochemical properties are one of theemerging carbon nanomaterials that have been studied in recent years. In addition to the excellentoptical properties such as photoluminescence, photobleaching resistance and light stability, thismaterial also has favorable advantages of good biocompatibility and easy functionalization, whichmake it an ideal raw material for constructing sensing equipment. In addition, CQDs can combinedwith other kinds of materials to form the nanostructured composites with unique properties, whichprovides new insights and ideas for the research of many fields. In the field of food analysis,emerging CQDs have been deeply studied in food composition analysis, detection and monitoringtrace harmful substances and made remarkable research progress. This article introduces andcompares the various methods for CQDs preparation and reviews its related sensing applicationsas a new material in food components analysis and food safety inspection in recent years. It isexpected to provide a significant guidance for the further study of CQDs in the field of foodanalysis and detection. CQDs; synthesis; fluorescent sensing; food analysis.

Polyethylenimine-stabilized silver nanoclusters act as an oxidoreductase mimic for colorimetric determination of chromium(VI)

A new and efficient assay is proposed for the photometric determination of Cr⁶⁺ by employing polyethylenimine-stabilized Ag nanoclusters (PEI-AgNCs) as an oxidoreductase mimic. Cr⁶⁺ with certain oxidicability is able to specifically react with 3,3',5,5'-tetramethylbenzidine (TMB), giving a color change from colorless to blue indicating the presence of Cr⁶⁺. However, the redox kinetics is so slow that the sensitivity obtained for Cr⁶⁺ determination is very poor. It is interestingly found that PEI-AgNCs can act as an oxidoreductase-like nanozyme to significantly promote the sluggish reaction, making it possible to rapidly detect toxic Cr⁶⁺ with remarkably enhanced performance. With the use of PEI-AgNCs, fast and convenient determination of Cr⁶⁺ was realized, with a limit of detection as low as 1.1 μM. Additionally, the proposed assay exhibited excellent selectivity; other ions, including Cr³⁺, hardly affected the determination of Cr⁶⁺. Graphical abstract Polyethylenimine-stabilized silver nanoclusters (PEI-AgNCs) act as an oxidoreductase mimic to catalyze the redox reaction of Cr⁶⁺ and 3,3',5,5'-tetramethylbenzidine (TMB), enabling the high-performance colorimetric determination of toxic Cr⁶⁺.

Convenient synthesis of carbon nanodots for detecting Cr(vi) and ascorbic acid by fluorimetry

Carbon nanodots (CDs) were simply synthesized from Sophora flavescens Ait. “On–off–on” fluorescent probes for the sensitive and selective detections of Cr(iv) and ascorbic acid (AA) were founded and well applied in real samples.