Fluorescent Carbon Quantum Dots Research Articles

Synthesis of Fluorescent Carbon Quantum Dots Doped Graphitic Carbon Nitride and Its Application as Fe3+ Sensors

Synthesis of Fluorescent Carbon Quantum Dots Doped Graphitic Carbon Nitride and Its Application as Fe3+ Sensors

Machine Learning System To Monitor Hg2+ and Sulfide Using a Polychromatic Fluorescence-Colorimetric Paper Sensor.

An optical monitoring device combining a smartphone with a polychromatic ratiometric fluorescence-colorimetric paper sensor was developed to detect Hg2+ and S2- in water and seafood. This monitoring included the detection of food deterioration and was made possible by processing the sensing data with a machine learning algorithm. The polychromatic fluorescence sensor was composed of blue fluorescent carbon quantum dots (CDs) (BU-CDs) and green and red fluorescent CdZnTe quantum dots (QDs) (named GN-QDs and RD-QDs, respectively). The experimental results and density functional theory (DFT) prove that the incorporation of Zn can improve the stability and quantum yield of CdZnTe QDs. According to the dynamic and static quenching mechanisms, GN-QDs and RD-QDs were quenched by Hg2+ and sulfide, respectively, but BU-CDs were not sensitive to them. The system colors change from green to red to blue as the concentration of the two detectors rises, and the limits of detection (LOD) were 0.002 and 1.488 μM, respectively. Meanwhile, the probe was combined with the hydrogel to construct a visual sensing intelligent test strip, which realized the monitoring of food freshness. In addition, a smartphone device assisted by multiple machine learning methods was used to text Hg2+ and sulfide in real samples. It can be concluded that the fabulous stability, sensitivity, and practicality exhibited by this sensing mechanism give it unlimited potential for assessing the contents of toxic and hazardous substances Hg2+ and sulfide.

High-Yield, Stable, and Ultrasensitive Carbon Dots for pH Sensing and Fe2+ Detection Are Synthesized at Room Temperature

Fluorescent carbon quantum dots (r-CDs) were synthesized safely and readily by stirring at room temperature with a yield of 76.5%. The synthesized r-CDs exhibit bright green emission with an absolute quantum yield of 12.0% under the excitation of ultraviolet light. Within the pH range of 3–12, the r-CDs exhibit excellent fluorescence stability. Interestingly, the fluorescence intensity of r-CDs faded promptly when the pH value diminished to 2 and then regained when the pH value returned to 3. This means that r-CDs can be used as “on–off–on” fluorescent probes for pH sensing. The mechanism of this sensitive pH response behavior was discussed in detail, and a possible mechanism of protonation–deprotonation–protonation processes was proposed. In addition, we have proposed a green preparation route for eco-friendly filter paper using anticounterfeiting. Interestingly, the presence of Fe2+ significantly quenched the fluorescence of r-CDs. Experimental results demonstrated the r-CDs can also be used to detect the content of Fe2+ in water, and the detection limit was 8.82 μM/L.

Hydrothermal synthesis of orange fluorescent carbon dots and their application in fabrication of warm WLEDs and fluorescent ink

Herein, we are reporting the synthesis of orange fluorescent carbon quantum dots (OFCDs) using o-phenylenediamine and semicarbazide by hydrothermal method and the synthesized OFCDs were applied for warm white light emitting diodes (WLEDs) and fluorescent ink applications. The fluorescence emission spectrum of OFCDs shows the emission maximum at 625 nm with an excitation wavelength of 540 nm. The quantum yield of OFCDs was calculated to be 23%. We have prepared warm WLED device by coating PVA-OFCDs polymer matrix on near UV LED light (λem: 420 nm). The OFCDs based warm WLED device exhibits chromaticity coordinate (0.42, 0.48), Colour Correlated Temperature (CCT) 2500 K and Color Rendering Index (CRI) value 82. We also prepared the highly stable fluorescent ink using the same PVA-OFCDs for security information encryption and anti-counterfeiting applications. This OFCDs and their WLEDs device would be an efficient one in optoelectronics and forensic fields.

Facile and Green Synthesis of Novel Fluorescent Carbon Quantum Dots and Their Silver Heterostructure: An In Vitro Anticancer Activity and Imaging on Colorectal Carcinoma.

Carbon dots (CQDs) have been widely investigated as prime candidates for developing a tumor theranostic platform due to their tunable fluorescence emission and excitation, high water solubility, good photostability, and biocompatibility. Among the CQDs, natural CQDs are an emerging class of nanomaterials in the carbon family. Herein, highly fluorescent carbon quantum dots (CQDs) were synthesized from orange juice using a one-step hydrothermal method and characterized by different techniques. After that, CQD/Ag heterostructures were synthesized by the reduction of silver salt, in particular silver nitrate (AgNO3) solution using sodium borohydride (NaBH4) in different ratios. The photostability and characterization of CQD/Ag heterostructures were investigated. At last, a comparative cellular toxicity measurement was done to select the superior CQD/Ag heterostructure in the human colorectal carcinoma (HCT 116) cell line along with the imaging property. The detailed cell death signaling was also observed in the HCT 116 cell line via the ROS-dependent mitochondrial-mediated pathway, where Akt (RAC-α serine/threonine-protein kinase) played a important role.

Rare-earth free solid-state fluorescent carbon-quantum dots: Multi-color emission and its application as optical dual-mode sensor

Proposing a straightforward technique for producing multi-color carbon quantum dots (CQDs) and investigating how luminescence can be tuned and improved is appealing and encouraging. The production of white light-emitting nanophosphors is crucial for the development of future display and lighting technologies, and their outstanding luminescent qualities provide considerable potential in sensing applications. The rare-earth ions have been used often as dopants to produce semiconducting nanophosphors, the restricted unavailability of rare-earth elements in our planet necessitates to look for more appropriate substitutes. Herein, we present the fabrication of CQDs co-doped with Cu and Mn (Cu/Mn:CQDs) transition metal ions that exhibit strong white light emission with the Commission Internationale de L′Eclairage (CIE) chromaticity coordinates (0.36, 0.30), which has a high color rendering index (CRI) value of 89. The as-produced Cu/Mn:CQDs have a quantum yield of 28.35 % and are employed as a fluorescent sensor for Fe3+ and ascorbic acid (AA) detection through "on-off-on" sequential mode. The fluorescence of Cu/Mn:CQDs can be greatly suppressed by Fe3+ ions via static quenching and then recovered by adding AA, as AA causes Fe3+ to be reduced to Fe2+. This sensor demonstrated high selectivity and sensitivity towards Fe3+ and AA with detection limits of 16 and 46 nM, respectively. Most importantly, the as-proposed fluorescence sensing system are successful for detecting Fe3+ and AA in real water samples with satisfactory results. Furthermore, an IMPLICATION logic gate is built based on the unique properties of Cu/Mn:CQDs nanohybrids, indicating new prospects for application in single and multiple biological sensing. This research could open the path for the development of low cost, high performance and environment-friendly multicolor phosphor for optoelectronic devices and sensing applications.

A ratiometric fluorescent sensor based on dual-emissive carbon dot for the selective detection of Cd2+

Cadmium (Cd2+), a heavy metal ion used in numerous industries, has toxic adverse effects on the environment; it is crucial to develop a quick and reliable method for Cd2+ determination. Fluorescent biomass-derived carbon quantum dots (CD) with rich carboxyl groups on the surface were synthesized using water amaranth leaves by hydrothermal method with a 12.1% quantum yield. The surface of CD was further modified with 1-pyrene carboxaldehyde (PC) to synthesize pyrene carboxaldehyde-carbon quantum dots (PC-CD). This study developed a fluorescent ratiometric nanosensor using a covalently functionalized CD with pyrene derivative and demonstrates highly selective identification capability towards Cd2+ over competing metal ions. The Nano sensor has significant selectivity towards Cd2+ in an excellent linear range of 0–70 µM with a detection limit as low as 15 nM and demonstrates excellent water solubility and biocompatibility. Transmission electron spectroscopy (TEM), Fourier Transform infrared spectroscopy (FT-IR), and X-ray photon spectroscopy (XPS) were used to identify the surface functionalization of PC-CD. Finally, the developed ratiometric sensor was used for detecting Cd2+ metal ions from various water effluents.

Picomolar Detection of Lead Ions (Pb2+) by Functionally Modified Fluorescent Carbon Quantum Dots from Watermelon Juice and Their Imaging in Cancer Cells.

Water contamination due to the presence of lead is one of the leading causes of environmental and health hazards because of poor soil and groundwater waste management. Herein we report the synthesis of functionally modified luminescent carbon quantum dots (CQDs) obtained from watermelon juice as potential nanomaterials for the detection of toxic Pb2+ ions in polluted water and cancer cells. By introducing surface passivating ligands such as ethanolamine (EA) and ethylenediamine (ED) in watermelon juice, watermelon-ethanolamine (WMEA)-CQDs and watermelon-ethylenediamine (WMED)-CQDs exhibited a remarkable ~10-fold and ~6-fold increase in fluorescence intensity with respect to non-doped WM-CQDs. The relative fluorescence quantum yields of WMEA-CQDs and WMED-CQDs were found to be 8% and 7%, respectively, in an aqueous medium. Among various functionally-modified CQDs, only WMED-CQDs showed high selectivity towards Pb2+ ions with a remarkably good limit of detection (LoD) of 190 pM, which is less than that of the permissible limit (72 nM) in drinking water. The functionally altered WMED-CQDs detected Pb2+ metal ions in polluted water and in a human cervical cancer cell line (HeLa), thus advocating new vistas for eco-friendly nanomaterials for their use as diagnostic tools in the environment and biomedical research areas.

Cucurbit[7]uril-based carbon dots for recognizing histamine.

Fluorescent carbon quantum dots (CQDs) were synthesized from cucurbit[7]uril (Q[7]) and 2,2-bis(hydroxymethyl)propionic (DMPA) by a hydrothermal method. The Q[7]-DMPA complex was confirmed by X-ray crystallography. The CQDs showed blue fluorescence, photostability, and ionic strength stability. They were used to detect histamine with a low limit of 2.33 × 10-6 M.

Dual-mode luminescence anti-counterfeiting and white light emission of NaGdF4:Ce,Eu,Tb/carbon dot hydrophilic nanocomposite ink.

NaGdF4:Ce,Eu,Tb nanocrystals were successfully prepared by a one-step hydrothermal method with Ce3+ ions as sensitizers, Eu3+ and Tb3+ ions as activators, and polyethylenimine (PEI) as surfactants. Color-adjustable fluorescence emission was achieved by the energy transfer effect between rare earth ions. Blue fluorescent carbon quantum dots (CDs) with a double UV response under 254 nm and 365 nm excitation were synthesized by a one-step hydrothermal method. A hydrophilic NaGdF4:Ce,Eu,Tb/CD composite ink was prepared by an easy physical mixing method. Because of the electrostatic self-assembly effect, the color adjustable luminescence was achieved in a few seconds, and the white light emission with color coordinates of (0.32, 0.32) was obtained. A dual-mode luminescence anti-counterfeiting pattern was designed and achieved by excitation with ultraviolet light at 254 nm and 365 nm.

Facile synthesis of surface-functionalized fluorescent carbon quantum dots for the selective detection of ferric ions

Biomass-derived carbon quantum dots are gaining a lot of attention from contemporary world because of their fascinating physical, chemical and electronic properties which bestowed them excellent water solubility, low cytotoxicity, good biocompatibility and high photostability.

Design and preparation of a near-infrared-emissive nanosensor for the quantification and imaging of alpha-fetoprotein in vitro and in vivo

Alpha fetoprotein (AFP) is an embryonic glycoprotein that is produced by hepatocytes and soft yellow sacs, which is closely related to liver cell proliferation, as well as the development of cirrhosis, chronic hepatitis and other diseases. Thus, AFP has been widely used as an important tumor marker in the basic research and clinical diagnosis of diseases such as early-stage liver cancer, endodermal sinus tumors and germ cell tumors. In this study, we developed a near-infrared (NIR) fluorescent carbon quantum dots by microwave synthesis, and constructed a turn-on fluorescent nanosensor by unique modifications. This nanosensor not only has specific response to AFP, but also good biocompatibility and high photostability. The results show that the proposed NIR nanosensor has very high sensitivity, and its detection limit is 3.0 pg/mL for AFP. Thus, it was used for the accurate quantification of AFP in human serum and the imaging of AFP in vitro and in vivo. Therefore, the diagnosis of early-stage liver cancer can be achieved by using proposed method.

Incorporation of Fluorescent Carbon Quantum Dots into Metal–Organic Frameworks with Peroxidase-Mimicking Activity for High-Performance Ratiometric Fluorescent Biosensing

Incorporation of Fluorescent Carbon Quantum Dots into Metal–Organic Frameworks with Peroxidase-Mimicking Activity for High-Performance Ratiometric Fluorescent Biosensing

Sustainable synthesis of nitrogen-doped fluorescent carbon quantum dots derived from Cissus quadrangularis for biomarker applications

This study demonstrated an environmentally friendly, cost-effective, and easy method for manufacturing biocompatible fluorescent carbon quantum dots (CQDs) from the leaf extract of the medicinal herb Cissus quadrangularis. As-synthesized nitrogen doped-CQDs had fluorescence quantum yields of up to 5%. The presence of pyrrolic/pyridinic-N, quaternary-N (N–C3), and OC–N, as verified by X-ray photoelectron spectroscopy, reveals that nitrogen atoms were efficiently doped in CQDs. The size distribution of as-synthesized CQDs was found to be within 4–9 nm using a high-resolution transmission electron microscope. Meanwhile, nuclear magnetic resonance studies showed the presence of a significant proportion of sp2 and sp3 carbon groups. The zeta potential of as-synthesized CQDs was −7.8 mV, demonstrating the presence of a negatively charged surface with good stability in aqueous solution. Furthermore, the development of easy, affordable, and non-destructive fluorescence-based staining agents as an alternative to organic or synthetic dyes is widely sought. In this regard, as-synthesized N-doped CQDs shown remarkable fluorescent staining capabilities in this study and might be employed as a useful probe for optical and bio-imaging of bacteria, fungal, and plant cells. On the other hand, the cytotoxicity and cell viability of pine leaf, mushrooms, algae, fungus, and bacteria have also been examined. Even at higher doses (10.9 mg/ml), cell survival was demonstrated to be rather excellent and cytotoxicity was minimal for up to 4 days.

Enhancement of short-wavelength range responsibility for PIN silicon photodetectors using additional fluorescent carbon quantum dots nanoparticles

We demonstrate a hybrid Si photodetector structure by employing an additional layer of fluorescent carbon quantum dot (CQD) nanoparticles constructed on the surface of a Si positive-intrinsic-negative (PIN) photodetector. The experimental studies reveal that the optimized hybrid device can efficiently enhance short-wavelength range responsibility between 300 nm to 600 nm without inducing any deteriorated photodetection performance beyond the short-wavelength region, and thereby achieve broadband sensitivity across the UV–vis-NIR spectra region. The measured photoresponsivity of the optimized device can achieve ∼0.088 A W−1 (@500 nm), which was ∼25% higher than that of a commercial blank PIN Si photodetector.

Effect of synthesized carbon quantum dots on the photocatalytic properties of ZnO

ABSTRACT. In this work, synthesized carbon quantum dots (CQDs) and zinc oxide nanoparticles (ZnO NPs) are used to form ZnO/CQDs nanocomposite. The characterization of this nanocomposite using X-ray diffraction (XRD) indicates that ZnO NPs and ZnO/CQDs nanocomposite have the same profile, suggesting that the presence of CQDs does not impinge the crystal structure of ZnO in ZnO/CQDs nanocomposite. Besides, an analysis performed with scanning electron microscopy (SEM) displays plate-like nanostructure with an average thickness of about 22 nm and 25 nm for ZnO NPs and ZnO/CQDs, respectively. Furthermore, the reflectance study in the visible range shows a reduction of sunlight reflection intensity of ZnO/CQDs compared with the reflection intensity of ZnO NPs. In addition, the photocatalytic studies indicate that the rate of photocatalytic degradation of methylene blue (MB) of ZnO/CQDs nanocomposites is higher than that of ZnO NPs. Indeed, in optimized conditions, the photocatalytic activity can reach 100% within 45 min of sunlight exposure for the degradation of 7.5 mg/L MB using ZnO/CQDs while it takes 90 min using ZnO NPs under the same conditions. These fascinating results is attributed to the reduction of the reflective properties of ZnO/CQDs.
 
 KEY WORDS: Fluorescent carbon quantum dots (CQDs), Photocatalytic degradation of methylene blue, Sunlight reflectance property, Synthesis of ZnO nanoparticles
 Bull. Chem. Soc. Ethiop. 2023, 37(2), 463-476. 
 DOI: https://dx.doi.org/10.4314/bcse.v37i2.15

A Design-assisted Spectrofluorometric Method Utilizing a One-pot Fluorescent Probe for the Quantitation of some Calcium Channel Blockers

Based on their reaction with highly fluorescent carbon quantum dots (CQDts), a precise and reliable spectrofluorometric approach was developed for the determination of three calcium channel blockers. The studied drugs are: lercanidipine, nimodipine and nifedipine. (CQDts) were produced using a one-step hydrothermal method with ascorbic acid as the carbon source. The produced CQDts were capped by alcohol to create yellow emitters displaying a high fluorescence emission at 524 nm when excited at 325 nm. The fluorescence intensity of CQDts was noticeably quenched by each of the three calcium channel blockers. The relation between their concentrations and fluorescence quenching is linear over the concentration range of 0.5–20 µg/mL for each of the three drugs. A full factorial design was used to optimize the effect of variable factors. Therefore, under optimum experimental design conditions, the detection limits for lercanidipine, nimodipine, and nifedipine were 0.11 ± 1.09, 0.10 ± 0.25 and 0.12 ± 0.71 µg/mL, respectively. The LOQ was 0.33, 0.30, and 0.37 µg/mL respectively. The quenching of fluorescent CQDts occurred through the inner filter effect (IFE) for nimodipine, while it was mixed with dynamic quenching for lercanidipine and nifedipine. The proposed method was effectively used to determine the cited drugs in their pharmaceutical products and had an acceptable level of precision. The selectivity of the CQDts system towards the studied drugs was examined indicating no interference from interfering species.

Turning Agroforestry Waste into Value-Added Fluorescent Carbon Quantum Dots for Effective Detection of Fe3+ in an Aqueous Environment

In the context of the circular economy, the high quantity of agroforestry waste should be transformed into sustainable and high-value materials to abate pollution, CO2 emissions, and expensive waste disposal. Herein, the agroforestry waste of apple leaves was initially used as a precursor to extract the value-added nanomaterial carbon quantum dots (CQDs) by way of an easy hydrothermal strategy without complicated purification processes, as extracted CQDs doped with N and P possess a typical graphite-like structure, a fine particle size of 2.0 nm, and excitation-dependent photoluminescence (PL) behavior. The doping of N and P endows CQDs with a much higher quantum yield (18.1%), good water solubility, high fluorescence stability, and specific recognition ability for the detection of Fe3+. The fluorescence of CQDs could be quickly quenched by Fe3+ within 1 min and recovered with the addition of ascorbic acid, suggesting the recyclability of the prepared CQD-based fluorescent probe. Systematic analyses support that a synergistic mechanism of static fluorescence quenching and inner filter effect was involved in the detection of Fe3+ by CQDs, showing a linear range between 0 and 160 μM and a limit of detection (LOD) of 4.0 μM. Furthermore, the feasibility of detecting Fe3+ by CQDs in practice was verified by tap water/lake water samples. The present work evinces that apple leaves are useful in producing green and low-cost CQDs as a promising fluorescent probe for sensitive, rapid, and selective detection of Fe3+ in an aqueous environment.

Temperature Sensing Performance of Fluorescent Carbon Quantum Dots Prepared from Loblolly Pine Processing Waste

Temperature Sensing Performance of Fluorescent Carbon Quantum Dots Prepared from Loblolly Pine Processing Waste

Eco-friendly Synthesis of Carbon Quantum Dots as an Effective Adsorbent

Fluorescent carbon quantum dots (CQDs) were prepared by an economical, green, and single-step procedure with the assistance of microwave heating of urea with bagasse (SCB), cellulose (C), or carboxymethyl cellulose (CMC). The prepared CQDs were characterized using a series of spectroscopic techniques, and they had petite size, intense absorption in the UV, and excitation wavelength-dependent fluorescence. The prepared CQDs were used for Pb(II) adsorption from an aqueous solution. The removal efficiency percentages (R %) were 99.16, 96.36, and 98.48% for QCMC, QC, and QSCB, respectively. The findings validated the efficiency of CQDs synthesized from CMC, cellulose, and SCB as excellent materials for further utilization in the environmental fields of wastewater pollution detection, adsorption, and chemical sensing applications. The kinetics and isotherms studied found that all CQDs isotherms fit well with the Langmuir model than Freundlich and Temkin models. According to R2, the pseudo-second-order fits the adsorption of QCMC, while the first-order one fits with QC and QSCB.