Green Fluorescent Carbon Dots Research Articles

A Ratiometric Fluorescent Detection Platform Using G‐CDs@[Ru(bpy)3]2+ for the Specific Detection of Hypochlorite and Live Cell Imaging

AbstractHypochlorite (ClO−), an essential reactive oxygen species (ROS) in physiological processes, is identified to be closely connected with oxidative stress and related diseases. Meanwhile, ClO− is a commonly‐used disinfector for water treatment, and in public places, under acidic conditions, it's easily decomposed into hypertoxic chlorine gas. Since the strong oxidizing property of ClO−, many oxidizing agents may disturb the ClO− detection. Specific and accurate detection of ClO− with superior sensitivity is a challenge. In this work, a sensing platform for rapid, sensitive, and specific ClO− detection is constructed using green fluorescent carbon dots (G‐CDs), with a linear detection range of 0.5–11 µm and a detection limit of 0.233 µm. Moreover, introducing a red fluorescent tripyridinium ruthenium ([Ru(bpy)3]2+) as a reference, a ratiometric fluorescence nanoprobe G‐CDs@[Ru(bpy)3]2+ is prepared and shows favorable intracellular imaging of exogenous and endogenous ClO−. With G‐CDs@[Ru(bpy)3]2+‐based test paper microarrays and a color recognition APP, a smartphone‐based sensing system for point‐of‐care testing of ClO− is also fabricated. In summary, this work proposed a versatile and economical smartphone‐based sensing system that featured reliability and simplicity, and suggested its potential applications in environmental water quality monitoring and live cell imaging.

Green Synthesis of Baby Pumpkin Derived Fluorescent Carbon Dots – A Potent Label‐Free Probe for Cd2+ Determination

AbstractThis study demonstrates a facile solvothermal approach to synthesizing green fluorescent carbon dots (G‐CDs) using baby pumpkin as a natural precursor. The G‐CDs exhibit strong fluorescence emission at 547 nm under excitation at 467 nm, and the highest quantum yield reaching 17.5 % in acetone, making them suitable for a range of applications including sensing, bioimaging, catalysis, and drug delivery. The G‐CDs demonstrate excellent stability under various conditions, such as prolonged light exposure, high salt concentration, extended periods, and elevated temperatures. Furthermore, the G‐CDs show a good linear relationship with Cd2+ within the concentration range of 0 to 16.5 μmol/L, with a linear correlation coefficient of 0.9920. The detection limit (LOD) was calculated to be 0.68 μmol/L. The recovery rate ranges between 85.66% to 97.43%, indicating their potential for use in environmental metal ion detection. This study provides a convenient and economical method for the synthesis of G‐CDs using baby pumpkin as a precursor, offering a sustainable alternative for various applications in sensing, imaging, catalysis, and drug delivery.

One-pot Synthesis of High-performance Green-emitting Carbon Dots for Cd2+ Sensing and Anti-counterfeiting Applications.

This study presents a facile one-pot solvothermal synthesis of high-performance green fluorescent carbon dots (G-CDs) using o-phenylenediamine and ethylenediamine as precursors. The G-CDs show excellent optical, temporal, and chemical stability. Notably, they exhibit the highest quantum yield of 24.2% in ethanol and a strong green emission peaking at 546nm under 440-490nm excitation. In addition, G-CDs have outstanding salt resistance and multi-solvent compatibility. Due to its bright photoluminescence, G-CDs can be used as a secure ink for anti-counterfeiting. More remarkably, Cd2+ ions can efficiently quench the fluorescence of G-CDs with a detection limit of 0.152 µmol/L, enabling accurate quantification of Cd2+ in water systems. The simple synthesis of high-performance G-CDs expands their applicability in sensing and bioimaging.

Efficient electrochemical synthesis of green fluorescent carbon dots for curcumin detection in common foods

Curcumin (Cur) is commonly employed as a food additive in the pharmaceutical and food industries. However, improper use of curcumin can lead to adverse effects on human health. In this research, we developed an electrochemical approach for the synthesis of green fluorescence nitrogen and sulfur co-doped carbon dots (G-CDs) specifically designed for curcumin detection. The prepared G-CDs displayed strong fluorescent emissions at 540 nm, along with notable attributes such as excellent fluorescence stability against photobleaching, and resilience to changes in ionic strength. The G-CDs demonstrated selective recognition of curcumin, resulting in fluorescence quenching in a linear range of 0–140 μmol/L, with an impressive detection limit of 46.4nmol/L. Five distinct food samples were effectively detected for curcumin using the developed G-CDs nanoprobe, yielding satisfactory outcomes. This newly proposed approach offers simplicity, outstanding sensitivity, and selectivity, showcasing its promising capabilities as an alternative method for Cur detection without the need for specialized instruments.

Application of Multicolor Fluorescent Carbon Dots Based on Tea Polyphenols in a White Light-Emitting Diode and Room-Temperature Phosphorescence.

Carbon dots (CDs) are new carbon nanomaterials, among which those prepared from biomass are popular due to their excellent optical properties and environmental friendliness. As representative natural phenolic compounds, tea polyphenols are ideal precursors with fluorescent aromatic rings and phenolic hydroxyl structures. Usually, polyphenolic precursors can only be used to produce blue or green fluorescent CDs, and fluorescence in long wavelength domains, such as orange or red, cannot be achieved. Herein, the high reactivity of the phenolic hydroxyl groups in tea polyphenols with o-phthalaldehyde was exploited to modulate the pH during the carbonation process, which led to redshifts of the fluorescence wavelengths. Different pH values during the reaction caused the precursors to take different reaction paths and form fluorescent groups exhibiting different conjugated structures, resulting in carbon dots providing different fluorescent colors. Finally, by utilizing the in situ hydrolysis of ethyl orthosilicate, the tea polyphenol-based carbon dots were embedded into a silica matrix, inducing phosphorescence of the carbon dots. This study provides a new approach for green preparation and application of natural polyphenolic CDs.

Fe-doping green fluorescent carbon dots via co-electrolysis of chrysoidine G and potassium ferrocyanide for sensitive Cr(VI) detection

In this study, we aimed to synthesis of Fe-doping green fluorescent carbon dots (G-CDs) through the co-electrolysis of chrysoidine G and potassium ferrocyanide for Cr(VI) detection. The use of potassium ferrocyanide improves the quantum yield and sensing performance of G-CDs toward Cr(VI). The G-CDs have a maximum excitation wavelength of 308 nm and an emission wavelength of 510 nm. Comprehensive analyses including Raman, FT-IR, and XPS provided insights into the chemical structure and composition of the G-CDs. Under optimal conditions, G-CDs demonstrated concentration-dependent quenching upon interaction with Cr(VI). A linear relationship within the range of 0.25–100 µM was established with a calibration equation of ΔF/F0 = 0.005 + 0.015CCr(VI), yielding an R2 value of 0.996 and a limit of detection of 0.15 μM. The applicability of the G-CDs method was demonstrated by successful Cr(VI) detection in water samples with recovery rates ranging from 98.8 % to 100.1 % and relative standard deviation within 3.0 %. The fluorescence lifetime and Zeta potential measurements confirmed that the mechanism was via a static quenching process, while redox reaction, nanoparticle aggregation, and surface charge variation also played significant roles.

Nitrogen- and Sulfur-Codoped Strong Green Fluorescent Carbon Dots for the Highly Specific Quantification of Quercetin in Food Samples.

Carbon dots (CDs) doped with heteroatoms have garnered significant interest due to their chemically modifiable luminescence properties. Herein, nitrogen- and sulfur-codoped carbon dots (NS-CDs) were successfully prepared using p-phenylenediamine and thioacetamide via a facile process. The as-developed NS-CDs had high photostability against photobleaching, good water dispersibility, and excitation-independent spectral emission properties due to the abundant amino and sulfur functional groups on their surface. The wine-red-colored NS-CDs exhibited strong green emission with a large Stokes shift of up to 125 nm upon the excitation wavelength of 375 nm, with a high quantum yield (QY) of 28%. The novel NS-CDs revealed excellent sensitivity for quercetin (QT) detection via the fluorescence quenching effect, with a low detection limit of 17.3 nM within the linear range of 0-29.7 μM. The fluorescence was quenched only when QT was brought near the NS-CDs. This QT-induced quenching occurred through the strong inner filter effect (IFE) and the complex bound state formed between the ground-state QT and excited-state NS-CDs. The quenching-based detection strategies also demonstrated good specificity for QT over various interferents (phenols, biomolecules, amino acids, metal ions, and flavonoids). Moreover, this approach could be effectively applied to the quantitative detection of QT (with good sensing recovery) in real food samples such as red wine and onion samples. The present work, consequently, suggests that NS-CDs may open the door to the sensitive and specific detection of QT in food samples in a cost-effective and straightforward manner.

Green fluorescent carbon dots for sensing of quercetin and pH and cell imaging

AbstractGreen fluorescent carbon dots (G‐CDs) were fabricated from Coptis chinensis directly via one‐step hydrothermal treatment for the determination of quercetin (QCT) and pH sensing. The obtained G‐CDs have low cytotoxicity, good photostability and excellent water solubility. The optimal excitation wavelength and emission wavelength were 480 and 530 nm. A remarkable emission reduction displayed when QCT was added to the G‐CDs and the linear detection range is 0–200 μM, the limit of detection is 4.41 nM. The proposed method was applied to the determination of QCT in Haerbin beer products with satisfactory successful recovery. Furthermore, the G‐CDs exhibited sensitive changes to pH and two fluorescent pH sensors in the linear ranges of 2.0–6.0 and 6.0–11.0 were constructed based on this. They also provide a feasible method to measure the pH value of real water samples. Importantly, the fluorescent sensor has been extended to detect QCT in yeast cell, demonstrating the G‐CDs present potential biosensing application prospect.

PH-responsive green fluorescent nitrogen-doped carbon dots for visualization of intracellular pH with intuitive color changes

Designing pH-sensitive nanoprobes for visualization of intracellular pH with intuitive color change is of high significance for better understanding the pathogenesis of diseases. However, most of the reported intracellular pH imaging strategies are the single intensity-based strategies, which are susceptible to interferences from background effects. In this work, pH-responsive green fluorescent nitrogen-doped carbon dots were synthesized for visualization of intracellular pH with intuitive color change. The as-prepared green fluorescent N-CDs exhibited obvious red fluorescence when the pH value was less than 7, while only the green fluorescence intensity changed under neutral or alkaline conditions, which can be visually observed by the naked eye. In addition, the mechanism of the green fluorescence of the N-CDs was systematically investigated by density-functional theory (DFT) theoretical calculation together with X-ray photoelectron spectroscopy (XPS) and Fourier transform-infrared spectrophotometer (FT-IR), as well as the mechanism of the response of N-CDs to pH was systematically investigated by absorption spectrum and transmission electron microscope (TEM). Furthermore, the as-prepared green fluorescent N-CDs were used to visualize intracellular pH with intuitive color changes, demonstrating its promising potential in visual bio-imaging.

Synthesis of multicolor fluorescent carbon dots from zanthoxylum bungeanum and their application in fluorescent anti-counterfeiting ink

Multicolor fluorescent carbon dots (CDs) have wide application prospects in many fields. Presented herein reported a synthesis of multicolor fluorescent CDs using zanthoxylum bungeanum as a carbon precursor. By changing the nitrogen sources, blue, green, and red fluorescent carbon dots (B-CDs, G-CDs, and R-CDs) with stable optical properties and high quantum yields (QY) were synthesized. Their emission wavelengths are 492 nm, 523 nm, and 601 nm respectively and their QYs were measured to be 13.1%, 11.2%, and 9.8%, respectively. These CDs exhibit good salt resistance, photobleaching resistance, and chemical stability. These characteristics make them suitable for various applications, particularly in the field of anti-counterfeiting fluorescent ink. This study provides an economic and efficient strategy for synthesizing multicolor fluorescent CDs derived from natural products, highlighting the potential for producing multicolor CDs and enhancing their application value.

Carbon dots-based fluorescence enhanced probe for the determination of glucose

In this work, a novel “turn-on” fluorescence sensor for the detection of H2O2 and glucose was developed based on green fluorescent carbon dots (CDs). The CDs was newly prepared by a facile one-pot hydrothermal method with Eosin Y and branched polyethylenimine as precursors. Interestingly, in the presence of H2O2 and HRP, the fluorescence of the CDs enhanced significantly with a red-shift emission due to their “aggregation”. Meanwhile, the oxidation of glucose catalyzed by glucose oxidase could generate H2O2. Thus, a simple sensing system based on the CDs as fluorescent probes was constructed for H2O2 and glucose determination, avoiding the fluorescence quenching and subsequent recovery process in conventional turn-on strategy. The method showed good selectivity and sensitivity for glucose sensing with the detection limit of 0.12 μM. The method was further applied to glucose detection in real samples. The obtained results demonstrated the simplicity, selectivity and practicality of the method. This work expands the carbon nanomaterials with fluorescence emission enhancement properties. It provides a new and direct “turn-on” strategy for H2O2 and glucose detection, which could be a simple and effective tool for screening biological substances involved in H2O2-generation reaction.

Molecular‐fusion Synthesis of Bright Green Fluorescent Carbon Dots for Cell Imaging

AbstractFluorescent carbon dots (CDs) with advantages including excellent biocompatibility, low cost, and easy modification make them highly promising for applications in biological imaging. Here, we successfully synthesized dark green fluorescent CDs (g‐CDs) using trinitropyrene as a carbon source and 2,4‐diaminobenzenesulfonic acid as the reactant in one‐pot synthesis. The results revealed that the g‐CDs had an average uniform particle size of 4.93 nm, with a structure similar to graphite. The g‐CDs imparted excellent water‐solubility due to the presence of hydrophilic groups. The g‐CDs exhibited an optimal fluorescence emission wavelength of 512 nm in acetone solvent, with a maximum quantum yield of 38.4%. When transferred into a normal saline solution, the g‐CDs retained their green fluorescence, with the optimal fluorescence emission wavelength shifting to 505 nm. Notably, we observed a significant increase in fluorescence intensity and maximum quantum yield of up to 79.4% when the g‐CDs were dissolved in a polar solvent. Furthermore, in vitro fluorescence imaging experiments demonstrated rapid cell entry, excellent fluorescence performance, high biocompatibility, and universality of the g‐CDs. These findings underscore the high hydrophobicity and biocompatibility of our newly designed g‐CDs, thus highlighting their immense potential as fluorescent probes in bioimaging and disease tracing applications.

Electrochemically synthesized green fluorescent carbon dots for quantitation of hypochlorite and carbendazim.

Green emission carbon dots (CDs) electrochemically prepared from 2,6-pyridinedicarboxylic acid and o-phenyl-enediamine were applied separately for the quantitation of hypochlorite and carbendazim. The characteristic and optical properties of the CDs were studied through fluorescence, UV-vis absorption, X-ray photoelectron spectroscopy, and transmission electron microscopy. The synthesized CDs were mainly 0.8-2.2 nm in size, with an average size of 1.5 nm. The CDs exhibited green luminescence centered at 520 nm when excited by 420 nm light. The green emission of the CDs is quenched after the addition of hypochlorite, mainly through the redox reaction between hypochlorite and hydroxyl groups on the CDs surface. Furthermore, the hypochlorite-induced fluorescence quenched can be prevented in the presence of carbendazim. The sensing approaches exhibit good linear ranges of 1-50 μM and 0.05-5 μM for hypochlorite and carbendazim, respectively, with low detection limits of 0.096 and 0.005 μM, respectively. Practicalities of the luminescent probes were separately validated by the quantitation of the two analytes in real sample matrix with recoveries ranging from 96.3 to 108.9% and the relative standard deviation values below 5.51%. Our results show the potential of the sensitive, selective, and simple CD probe for water and food quality control.

Bright, green fluorescent carbon dots for sensitive and selective detection of ferrous ions

Iron is critical to living organisms; excess or lack of iron could lead to a series of diseases. In this work, fluorescent carbon dots were developed as an efficient probe for sensitive and selective detection of ferrous ions (Fe2+). We reported on simple and one-pot synthesis of uniform, bright, and green fluorescent carbon dots with aqueous stability in a wide pH range. The formation of green fluorescence is attributed to the doping of nitrogen into carbon materials. The as-synthesized carbon dots demonstrated wavelength-independent emission properties. Fluorescence of carbon dots was quenched efficiently, sensitively and selectively by ferrous ions over a series of other common metal ions and anions, with a detection limit of 16 µM, and a wide detection range of 0.033 -1.044 mM. Efficient quenching of carbon dots could be explained by the efficient binding of ferrous ions on carbon dots surface. Aggregation caused quenching was later proposed and verified as the quenching mechanism of carbon dots toward ferrous ions. The developed carbon dots show great promise in the development of efficient sensors and adsorbents for ferrous ions.

Waste to value transformation: Converting Carica papaya seeds into green fluorescent carbon dots for simultaneous selective detection and degradation of tetracycline hydrochloride in water

Rampant use of antibiotics has resulted in their seepage into groundwater and ultimately ending up in the food chain, causing antimicrobial resistance. To address this issue, it is imperative to not only quantitatively detect but eliminate them from water. An eco-friendly, one-step microwave-induced pyrolysis of waste papaya seeds (PS) with ethylenediamine (EDA) for just 5min gave green fluorescent nitrogen-doped carbon dots (PS-CDs), which are capable of detecting and photocatalytically degrading TC. The fluorescence properties of PS-CDs displayed that it has high sensitivity and selectivity towards sensing of TC with a detection limit as low as 120 nM. Also, the method gave satisfactory recovery results when extrapolated to determine TC in spiked milk, orange juice, tap water, and honey samples. On the other hand, PS-CDs alone potentially function as an efficient photocatalyst for the degradation of TC. PS-CDs' dual functionality provides an effectual method for the simultaneous detection and degradation of TC by a single nanoprobe.

Ratiometric and visual determination of copper ions with fluorescent nanohybrids of semiconducting polymer nanoparticles and carbon dots

Developing nanohybrid composition based fluorescent carbon dots (CDs) for ratiometric detection of copper ions is highly appealing. Herein, a ratiometric sensing platform (GCDs@RSPN) for copper ions detection has been developed by loaded green fluorescence carbon dots (GCDs) on the surface of red emission semiconducting polymer nanoparticles (RSPN) through electrostatic adsorption. The GCDs, featuring abundant amino groups, can selectively bind copper ions to induce the photoinduced electron transfer, leading to fluorescence quenching. A good linearity within the range of 0–100 μM is obtained, and the limit of detection (LOD) is 0.577 μM by using obtained GCDs@RSPN as ratiometric probe to detect copper ion. Moreover, the paper-based sensor derived from GCDs@RSPN was successfully applied for the visual detection of Cu2+.

Solvothermal synthesis of green fluorescent carbon dots from palm kernel shells

Carbon dots (CDs) enriched with functionalities are of great interest in biological and electrochemical applications. Herein, CDs of an average diameter of 2.5 nm were synthesized from palm kernel shells (PKS) using the solvothermal method with N-N dimethylformamide as the solvent. These CDs were shown to have fluorescence emission at 520 nm due to the presence of rich functional groups decorating the surfaces of the CDs. The developed CDs exhibited excellent photo, thermal and ionic stability. Further, these CDs were utilized as fluorescent ink, which was invisible in daylight and exhibited bright green fluorescence under UV irradiation of 365 nm. The use of DMF as the solvent in this study opens up the possibilities for the developed CDs to be used in wide applications such as optoelectronics, charge storage systems and electrospinning, without any further protocols.

Hydrogen bonds and space restriction promoting long-lived room-temperature phosphorescence and its application for white light-emitting diodes

Achieving the long-lived and strong room-temperature phosphorescence (RTP) is challengeable but desirable, especially for the enhanced phosphorescence and metal-free nanomaterials. Herein, we initially synthesized the green-fluorescence carbon dots (pm-CDs), and further obtained the composite of pm-CDs@DCDA with a long RTP lifetime of 1.01 s through embedding pm-CDs in dicyandiamide (DCDA). And the bright and long-lived afterglow of pm-CDs@DCDA with 365 nm of UV light excitation was observed by the naked eyes for more than 17 s either emerging as the dry solid or in water. Importantly, the phosphorescence intensity and lifetime of pm-CDs@DCDA were remarkably promoted owing to the intermolecular hydrogen bonds and the rigid environment, hence facilitating the intersystem crossing (ISC) process and restricting the non-radiative transition of triplet excitons. Taking advantage of the superior solid-state luminescence of pm-CDs@DCDA, we further innovatively prepared the white light-emitting diodes (WLEDs) with the tunable color temperatures by regulating the mass of pm-CDs@DCDA coated on the chips. This proposed study originally employed DCDA as a matrix to separate and immobilize pm-CDs, which built up a new avenue to improve the RTP property and offered a promising application in WLEDs.

Ganoderma lucidum bran-derived blue-emissive and green-emissive carbon dots for detection of copper ions.

Ganoderma lucidum bran (GB) has a broad application prospect in the preparation of activated carbon, livestock feed, and biogas, but the preparation of carbon dots (CDs) from GB has never been reported. In this work, GB was applied as a carbon source and nitrogen source to prepare both blue fluorescent CDs (BCDs) and green fluorescent CDs (GCDs). The former were prepared at 160 °C for 4 h by a hydrothermal approach, while the latter were acquired at 25 °C for 24 h by chemical oxidation. Two kinds of as-synthesized CDs exhibited unique excitation-dependent fluorescence behavior and high fluorescent chemical stability. Based on the fantastic optical behavior of the CDs, they were utilized as probes for fluorescent determination of copper ions (Cu2+). In the range of 1-10 μmol L-1, the fluorescent intensity of BCDs and GCDs decreased linearly with the increase of Cu2+ concentration; the linear correlation coefficient reached 0.9951 and 0.9982, and the limit of detection (LOD) was 0.74 and 1.08 μmol L-1, respectively. In addition, these CDs remained stable in 0.001-0.1 mmol L-1 salt solutions; BCDs were more stable in the neutral pH range, but GCDs were more stable in neutral to alkaline conditions. The CDs prepared from GB are not only simple and low-cost, but also can realize the comprehensive utilization of biomass.

Highly efficient carbon dots for quantitatively visualizing pH fluctuations in cells, zebrafish, mice and tumors.

In vivo pH is closely related to complicated physiological and pathological processes. Quantitatively probing pH and visualizing pH variation via fluorescence (FL) imaging technique in living cells and organisms is crucial but difficult to accomplish. Herein, green fluorescent carbon dots (CDs) were synthesized, and their distinct advantages of extraordinarily high fluorescence quantum yield (FQY, 71.4%), unique photostability, high selectivity, sterling biocompatibility, appropriate pKa for biosensing, enable CDs to serve as pH-activatable probes for real time quantitative detection of continuous pH fluctuation in living cells, zebrafish, mice and tumors. We believe CDs are presently among the best-of-breed pH probes for comprehensive biomedical applications.