Fluorescent Carbon Quantum Dots Research Articles

Yellow fluorescent carbon quantum dots for Ag+/GSH detection and differentiation between normal and cancer cells

In this paper, a novel multifunctional fluorescent carbon quantum dot (CDs) was prepared by the solvothermal method in which o-phenylenediamine (OPD) was used as the carbon source, p-aminobenzoic acid (PABA) was used as the nitrogen source and ethanol was used as the reaction solvent. The prepared CDs possessed fluorescence “off” response toward silver ions (Ag+) with a minimum detection limit of 75 nM. Meanwhile, glutathione (GSH) as an amino acid could selectively restore the fluorescence performance of CDs quenched by Ag+ ions and showed good detection sensitivity (detection limit of 10 nM). Owing to the low cell toxicity and high biocompatibility, the application of CDs in cell imaging demonstrated that they could be used as a distinguishing recognition between normal cells (EC) and cancer cells (MCF-7) because of their highly precise sensing ability for GSH. All of the above indicated that the prepared CDs would have great application prospects in biological diagnosis and sensing.

A multifunctional sensing of two carbon dots based on diaminonaphthalenes for detection of ofloxacin drug

Fluorescent carbon quantum dots (CQDs) have gained increased attention due to their diverse properties in the development of sensors and visualizing dynamic processes. This contribution demonstrates the synthesis of two carbon quantum dots, 2,3-CQDs and 1,8-CQDs from 2,3-Diaminonaphthalene and 1,8-Diaminonaphthalene, respectively by hydrothermal process. The results showed that the two CQDs had distinct optical properties with different sizes and therefore we observed different sensing performance and different dynamics interactions, which is dependent on the geometrical structure of precursors. Both CQDs exhibit bi-exponential decay curves with long and short-lived decay components, corresponding to recombination from the defect and intrinsic states, respectively. The sensing performance of 2,3-CQDs which possess high fluorescence quantum yield (0.2) demonstrates an ability to detect Ofloxacin based on fluorescence-enhanced turn off- on with a low detection limit of 0.46 μM and good linear range of 0–120 μM. Meanwhile the sensing of 1,8-CQDs with a quantum yield of 0.17 was performed for detection of Ofloxacin based on fluorescent turn-on–off due to energy transfer mechanism with wide linear response range of 0–120 μM and a satisfactory detection limit of 24 nM. These results indicate that we can adapt our systems to the intended applications by specifically and selectively altering carbon dots.

Fabrication of FRET based nano sensor from biomass-derived fluorescent carbon quantum dots and naphthalimide for ratiometric detection of nitric oxide: To examine nitrite levels in meat samples

Nitric oxide (NO) is a ubiquitous, gaseous, free radical signaling molecule which plays a key role in physiological and pathological processes. Literature reports revealed that the conventional methods such as colorimetry, electron paramagnetic resonance (EPR), electrochemical etc. to detect NO are costly, time consuming and lack resolution, particularly in aqueous or biological system. Thus, in this context, herein we have developed covalently linked biomass derived carbon quantum dots (CQDs) and naphthalimide based nano sensor system for FRET based ratiometric detection of nitric oxide (NO) in pure aqueous media. The CQDs derived from orange peels were characterized using UV–visible absorption, fluorescence spectroscopy, PXRD, TEM, FT-IR and zeta potential studies. Further, the obtained CQDs were functionalized with amine functionality, and subsequently linked with naphthalimide derivative (5) using terephthaldehyde through covalent bond formation. The conjugation of naphthalimide (5) and functionalized CQDs was studied using DLS, zeta potential, FT-IR and time resolved fluorescence spectroscopy. The excitation of developed nano sensor system at λex 360 nm results in fluorescence emission at λem 530 nm which establishes the FRET pair between the CQDs and naphthalimide unit. However, in the presence of NO, the observed FRET pair abolishes due to the cleavage of NO susceptible imine bond. The developed sensor demonstrates high selectivity towards NO with limit of detection (LOD) and limit of quantification (LOQ) of 15 nM and 50 nM respectively. Further, the developed sensor system was also utilized for indirect detection of nitrite (NO2−) in food samples for food safety and monitoring.

Sustainable synthesis and characterization of fluorescent nanoprobe based on unintentional heteroatom doped-carbon quantum dots for bioimaging of human neuroblastoma cancer cells and living organisms

This study demonstrated an economical, ecologically sustainable, and simple method for producing biocompatible fluorescent carbon quantum dots (CQDs) co-doped with N, K, and Ca from bathua (Chenopodium album), a popular medicinal herb leaf extract and nutritious vegetable. The nearly spherical shaped CQDs were discovered to be 3–5 nm in size in nature, with a quantum yield of around 48.12%, robust photo-stability, and excellent water solubility. Various morphological, compositional, physicochemical and optical characteristics were investigated. Additional factors affecting the photoluminescence of CQDs, such as hydrothermal process parameters, pH, and solvent sensitivity, were investigated further. Moreover, the newly synthesized N, K, Ca-doped CQDs were demonstrated to be a useful fluorescent nanoprobe for in vitro cellular imaging of SH-SY5Y human neuroblastoma cells, as well as other living organisms such as bacteria, fungal, and plant cells, as a cost-effective alternative to organic or synthetic fluorescent probes. Cell survival and cytotoxicity were found to be acceptable, with 95% of SH-SY5Y and HCT-116 cells surviving and other organisms able to withstand higher doses (10.9 mg/mL) for up to 4 days.

Natural Biowaste Derived Fluorescent Carbon Quantum Dots: Synthesis, Characterization and Biocompatibility Study.

In this present study, a straightforward and affordable method for the environmentally safe synthesis of carbon quantum dots (CQDs) by employing human hair as the carbon source without any need of chemicals was synthesized. CQDs obtained from human hair was further functionalized with Poly-L-Lysine to form PLLCQDs. The synthesized PLLCQDs was demonstrated numerous advantageous characteristics like strong fluorescence intensity, superior photostability, and outstanding water solubility. Various physicochemical characterization was employed to confirm successful formation of PLLCQDs including UV-vis Spectroscopy, Fluorescence Spectroscopy, Fourier Transform Infrared (FTIR) Spectroscopy, Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM). The size of synthesized PLLCQDs is 3 nm. The resultant PLLCQDs exhibited strong blue emission with a quantum yield of 28%. Under UV light, the synthesized PLLCQDs emit blue (at 365nm) fluorescence. The optimization of synthesis parameters including synthesis method, effect of reaction temperature, effect of reaction time and effect of reaction concentration have a significant impact on the quality and quantity of synthesized PLLCQDs, as well as their properties and applications. The effect of pH and UV radiation on synthesized PLLCQDs exhibited excellent photo and chemical stability. The cytotoxicity of bulk system (Hair precursor) and PLLCQDs was evaluated using fibroblast cell line (L929). The cell viabilities of 99.47% was obtained from L929 cells using MTT assay and it can applicably function as agents for cell labelling as a good bioimaging probe.

Fluorescent N-doped carbon quantum dots: A selective detection of Fe3+ and understanding its mechanism

Carbon quantum dots (CQDs) based sensor has been built many times. Optical properties, such as optical absorption, have been neglected for too long. Here, we have reported the luminescence of blue-emitting nitrogen-doped carbon quantum dots (N-CQDs) with average particle size 3–6 nm, synthesized via a simple hydrothermal method, which give intense blue emission under 340 nm excitation wavelengths. As the fluorescence of N-CQDs can be efficiently quenched by Fe3+, the N-CQDs can be constructed as a sensor system for Fe3+ with good sensitivity and selectivity. Effective detection and quantification of Fe3+ at as little as 0.07 µM and 0.22 µM is achieved.

One-step hydrothermal synthesis of near-infrared emission carbon quantum dots as fluorescence aptamer sensor for cortisol sensing and imaging

Fluorescence carbon quantum dots (CQDs) have been widely applied to sensing and bioimaging. In this paper, near-infrared carbon quantum dots (NIR-CQDs) were prepared through a simple one-step hydrothermal approach using reduced glutathione and formamide as raw materials. Based on NIR-CQDs, aptamer (Apt) and graphene oxide (GO) has been applied to fluorescence sensing cortisol. NIR-CQDs-Apt adsorbed to the surface of GO through π-π stacking and an inner filter effect (IFE) occurred between NIR-CQDs-Apt and GO leading to NIR-CQDs-Apt fluorescence “off”. The IFE process is disrupted in the presence of cortisol, allowing NIR-CQDs-Apt fluorescence “on”. This led us to construct a detection method with excellent selectivity over other cortisol sensors. The sensor can detect cortisol from 0.4 to 500 nM and has a detection limit as low as 0.13 nM. Importantly, this sensor can be used to detect intracellular cortisol with excellent biocompatibility and cellular imaging capabilities, which is promising for biosensing.

Carbon Quantum Dots with High Photothermal Conversion Efficiency and Their Application in Photothermal Modulated Reversible Deformation of Poly(N-isopropylacrylamide) Hydrogel.

The fluorescence of carbon quantum dots (CQDs) has been paid a lot of attention, but its photothermal performance attracts less attention since preparing CQDs with high photothermal conversion efficiency (PCE) is a big challenge. In this work, CQDs with an average size of 2.3 nm and a PCE of up to 59.4% under 650 nm laser irradiation were synthesized by a simple one-pot microwave-assisted solvothermal method using citric acid (CA) and urea (UR) as the precursors and N,N-dimethylformamide as the solvent under an optimized condition (CA/UR = 1/7, 150 °C, and 1 h). The as-prepared CQDs were demonstrated to have unique surface chemical states; i.e., abundant pyrrole, amide, carboxyl, and hydroxyl groups were found on the surfaces of CQDs, which ensure a high PCE. These CQDs were introduced into a thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) to form a CQDs@PNIPAM nanocomposite, and then, a bilayer hydrogel composed of CQDs@PNIPAM and polyacrylamide (PAM) was fabricated. The bilayer hydrogel can be reversibly deformed just by a light switching on/off operation. Based on the excellent photothermal performance, the developed CQDs are expected to be used in photothermal therapy, photoacoustic imaging, and other biomedical fields, and the CQDs@PNIPAM hydrogel nanocomposite is promising to be applied in intelligent device systems as a light-driven smart flexible material.

Multifunctional fluorescent carbon quantum dots for Zr4+ ion detection, pH response and cell imaging

Multifunctional fluorescent carbon quantum dots for Zr4+ ion detection, pH response and cell imaging

One-step green synthesis of in–situ functionalized carbon quantum dots from Tagetes patula flowers: Applications as a fluorescent probe for detecting Fe3+ ions and as an antifungal agent

In this research, for the first time, fluorescent carbon quantum dots (CQDs) synthesized by using a green, simple, and efficient one-step hydrothermal carbonization technique from Tagetes patula flowers as carbon precursors without using any toxic chemicals are reported. The as-prepared CQDs have been characterized by Transmission electron microscope (TEM), Field emission scanning electron microscopy with Energy dispersive X-ray spectroscopy (FESEM-EDX), UV–Visible spectroscopy, Raman spectroscopy, X-ray Diffraction (XRD), zeta potential analysis, Fourier-transform infrared spectroscopy (FTIR), fluorescence spectroscopy, and X-ray photoelectron spectroscopy (XPS). As analyzed by TEM and XRD analysis, it is observed that the as-synthesized CQDs are spherical having an average particle diameter of about 5.15 nm. The quantum yield (QY) of the CQDs was calculated and found to be 29.88%. The as-synthesized CQDs show an excellent fluorescence quenching behavior towards Fe3+ ions as compared to other metal ions. Therefore, CQDs were used as a sensing probe for detecting Fe3+ ions in a linear range of 0–4 μM and a limit of detection (LOD) of 0.32 μM. A comprehensive study has been conducted to show the effectiveness of the CQDs on the growth of rice plants (Oryza sativa) and the antifungal activities of CQDs on the mycelial growth of Magnaporthe oryzae (a plant pathogenic fungus).

Non-spherical gold nanoparticles enhanced fluorescence of carbon dots for norovirus-like particles detection

BackgroundNorovirus is a common pathogen that causes foodborne outbreaks every year and the increasing number of deaths caused by it has become a substantial concern in both developed and underdeveloped countries. To date, no vaccines or drugs are able to control the outbreak, highlighting the importance of finding specific, and sensitive detection tools for the viral pathogen. Current diagnostic tests are limited to public health laboratories and/or clinical laboratories and are time-consuming. Hence, a rapid and on-site monitoring strategy for this disease is urgently needed to control, prevent and raise awareness among the general public.ResultsThe present study focuses on a nanohybridization technique to build a higher sensitivity and faster detection response to norovirus-like particles (NLPs). Firstly, the wet chemical-based green synthesis of fluorescent carbon quantum dots and gold nanoparticles (Au NPs) has been reported. Then, a series of characterization studies were conducted on the synthesized carbon dots and Au NPs, for example, high-resolution transmission emission microscopy, fluorescence spectroscopy, fluorescence life-lime measurement, UV–visible spectroscopy, and X-ray diffraction (XRD). The fluorescence emission of the as-synthesized carbon dots and the absorption of Au NPs were located at 440 nm and 590 nm, respectively. Then, the plasmonic properties of Au NPs were utilized to enhance the fluorescence emission of carbon dots in the presence of NLPs in human serum. Here, the enhanced fluorescence response was linearly correlated up to 1 μg mL−1. A limit of detection (LOD) value was calculated to be 80.3 pg mL−1 demonstrating that the sensitivity of the proposed study is 10 times greater than that of the commercial diagnostic kits.ConclusionsThe proposed exciton-plasmon interaction-based NLPs-sensing strategy was highly sensitive, specific, and suitable for controlling upcoming outbreaks. Most importantly, the overall finding in the article will take the technology a step further to applicable point-of-care (POC) devices.

Metal-Enhanced Fluorescent Carbon Quantum Dots via One-Pot Solid State Synthesis for Cell Imaging

In this study, a facile one-pot solid-state synthesis method is developed to shed light on the metal-enhanced fluorescence (MEF) effect in carbon quantum dots (CQDs) and gold nanoparticles (AuNPs) hybrid materials. This is one of the few studies on the solid-state synthesis of N-doped CQDs/gold hybrid nanomaterials. We have conducted various sets of experiments to reveal the role of individual reagents during the nucleation and growth of nanoparticles. We have demonstrated that the addition of a small amount of gold salt illustrates a paramount effect (103-fold) in photoluminescence intensity. This effect is ascribed to MEF, which is caused due to interactions between the excited-state fluorophores and the free surface electrons of metal nanoparticles. It is interesting to note that a further increase of gold yields fluorescence quenching due to a large number of formed AuNPs causing fluorescence resonance energy transfer. By adjusting the volume ratio of gold salt and CD precursors, it is possible to obtain the CQDs-AuNPs hybrid with the highest fluorescence, which produces extensive visible light under 460 nm excitation. Synthesized materials have been successfully used for imaging human dermal fibroblasts and A549 lung epithelial cells. The dose-dependent cytotoxicity studies reveal that the hybrid structures do not have cytotoxicity.

The synthesis of fluorescent carbon quantum dots for tartrazine detection in food: a novel one-step microwave heating approach

Nowadays, carbon quantum dots (CDs) as semiconductor synthesized nanoparticles have become an attractive subject for lots of applications due to their remarkable features. In the current study, the highly fluorescent (FL) CDs with great characteristics were synthesized through a novel one-step microwave irradiation by citric acid monohydrate and urea as carbon precursors. The as-prepared CDs were quasi-spherical shape with an average diameter of 4.5 nm and emitted bright blue FL under ultraviolet light irradiation (UV). Furthermore, the synthesized CDs possessed different properties such as diverse functional groups, good sensitivity and selectivity, high water-solubility, low toxicity, and significant stability in various environmental conditions. The results indicated that the as-prepared CDs can be applied as a fluorescent probe for detection of different concentrations of tartrazine from 5 to 100 µM in food samples. In addition, the findings revealed that the good linear relationship was obtained between the FL intensity of CDs and different concentrations of tartrazine over the range of 5 to 100 µM with the detection limit of 2.58 µM.

Near-infrared carbon quantum dots from PEG-based deep eutectic solvents for high-accuracy quantitative analysis of naphthenic acids in wastewater

Naphthenic acids (NAs) are toxic components in refinery wastewater and in oil sands process water. The presence of NAs in aqueous environments would cause serious environmental problems. Development of a rapid method for screening and determination of trace NAs is urgent. In this work, a near-infrared fluorescence carbon quantum dots (CQDs) was successfully synthesized with p-phenylenediamine (PPD) and polyethylene glycol 400 (PEG 400) by the hydrothermal method. It showed a good fluorescence response to NAs with good detectability. The limit of detection was calculated to be 0.16 mmol‧L−1, with a linear range from 0.5 to 15 mmol‧L−1. The detection mechanism of NAs and CQDs was also proposed with in situ infrared spectrometer. This work provides new insights into the fluorescence detection of CQDs in the petrochemical industry, broadening the application of CQDs in the detection of environmental organic pollutants.

Synthesis of sulfur-chlorine-doped fluorescent carbon quantum dots from leachate membrane concentrate as a selective probe for Pd2+ detection

In this work, humic acid-based sulfur-chlorine-doped carbon quantum dots (L-CQDs) were synthesized by using a polyethylene glycol (PEG)-assisted hydrothermal technique using landfill leachate concentrate (LLC) as a carbon source. The prepared L-CQDs contain many oxygen-containing functional groups on the surface with a small average particle size of 4–6 nm, resulting in excellent hydrophilicity and dispensability. The three-dimensional fluorescence spectrum shows that the characteristic peak for humic acid for LLC is redshifted after adding PEG as an inactivator, indicating that L-CQDs are synthesized by PEG encapsulation and linkage. The optimum condition for preparing L-CQDs involves the addition of 0.5 g PEG (MW = 2000) into 20 mL LLC and reaction at 200 °C for 5 h, with the optimal L-CQD quantum yield reaching 5.32%. L-CQDs were used to prepare fluorescent nanoprobes for the detection of palladium ions (Pd2+). The obtained nanoprobe shows admirable performance in detecting Pd2+, with high selectivity, excellent water solubility and stability. The fluorescence intensity of the nanoprobe is selectively quenched through static quenching by Pd2+ in the concentration range of 5–40 μmol L−1. This work provides a simple, easy, and fast detection method for Pd2+ and opens up a way for the resource utilization of LLC.

Non-cytotoxic lanthanum and nitrogen co-doped lignin-based carbon dots for selective detection of ions in biological imaging

Owing to their versatility, fluorescent carbon quantum dots (CQDs) have attracted significant attention for applications in sensors, bioimaging, microfluidics, photodynamic therapy, drug delivery, light-emitting diode, etc. Herein, nitrogen and lanthanum co-doped multifunctional lignin-based carbon quantum dots ((N, La)-CQDs) were prepared from enzymatic hydrolysis lignin using a simple one-step hydrothermal method. The diameter of the CQDs obtained was about 2.2 nm with a good water solubility at the excitation wavelength of around 365 nm and emission wavelength of around 465 nm. This is the first discovery of (N, La)-CQDs to detect Sn2+. (N, La)-CQDs were successfully used to detect Fe3+, Sn2+, and ClO- ions in the range of 0–100 μM with the detection limits of 0.99 μM, 1.1 μM and 1.1 μM sequentially, and the linear fit R2 of 0.9997, 0.9943 and 0.9941 respectively. Non-cytotoxic (N, La)-CQDs can be used for labeling cells and detecting Sn2+ in zebrafish. These attractive features make these non-toxic, environmentally friendly CQDs material highly promising for applications in a wide range of areas, such as biomedicine, biosensing, disease diagnosis, and environmental monitoring.

Biomass-based carbon quantum dots for polycrystalline silicon solar cells with enhanced photovoltaic performance

Polycrystalline silicon solar cells modified using biomass resources are promising candidates to accomplish the goal of carbon neutrality. Developing a device with high power conversion efficiency (PCE) is important to resolve the ever-increasing energy shortage issues. Therefore, we develop a facile solution-casting approach to synthesise ethylene-vinyl acetate (EVA) films modified with ultra-high fluorescent carbon quantum dots (CQDs). The films were coated on the surface of polycrystalline silicon solar cells and the PCE increased from 13.19% to 13.65%. The ultra-high fluorescent CQDs were prepared from Ginkgo biloba via a hydrothermal process, and different parts of Ginkgo biloba-based CQDs were investigated in various conditions. The ultra-high fluorescent CQDs obtained at 180 °C, 8 h and a reaction concentration of 0.048 g/mL from Ginkgo wood resulted in high fluorescence of up to 976.74 a.u.. At an excitation wavelength of 365 nm. This work substantially expands the potential of EVA films containing ultra-high fluorescent CQDs for applications in the photovoltaic, environment and energy fields.

Preparation of molecularly imprinted ratiometric fluorescence sensor for visual detection of tetrabromobisphenol A in water samples.

A sensitive molecularly imprinted ratiometric fluorescence sensor was constructed for the first time to visually detect tetrabromobisphenol A (TBBPA). The blue fluorescent carbon quantum dots (CQDs) were coated with SiO2 through the reverse microemulsion method to obtain a stable internal reference signal CQDs@SiO2. The ratiometric fluorescence sensor was finally prepared using red fluorescent CdTe QDs as the response signal in the presence of CQDs@SiO2. When the molecularly imprinted polymers were combined with TBBPA, the fluorescence of CdTe QDs (Ex = 365nm, Em = 665nm) was rapidly quenched, while that of CQDs (Ex = 365nm, Em = 441nm) remained stable, resulting in a noticeable fluorescence color change. Moreover, the fluorescence intensity ratio (I665/I441)0/(I665/I441) of the sensor showed a linear response to TBBPA in the concentration range 0.1 to 10μM with a low detection limit of 3.8nM. The prepared sensor was successfully applied to detect TBBPA in water samples. The recoveries were in the range 98.2-103%, with relative standard deviations lower than 2.5%. Furthermore, a fluorescent test strip for visual monitoring of TBBPA was constructed to streamline the procedure. The excellent results demonstrate that the prepared test strip has a broad prospect for the offline detection of pollutants.

Tissue-Derived Primary Cell Type Dictates the Endocytic Uptake Route of Carbon Quantum Dots and In Vivo Uptake.

Carbon quantum dots (CQDs) require systemic biological delivery to advance their applications in drug delivery, biosensing, and bioimaging. We describe the endocytic pathways of green-emitting fluorescent carbon quantum dots (GCQDs) with sizes varying from 3 to 5 nm in mouse tissue-derived primary cells, tissues, and zebrafish embryos. The GCQDs demonstrated cellular internalization into mouse kidney and liver primary cells via a clathrin-mediated pathway. Using imaging, we were able to identify and reinforce the animal's body features in terms of different tissues exhibiting differential affinity for these CQDs, which will be extremely beneficial in the development of next-generation bioimaging and therapeutic scaffolds based on carbon-based quantum dots.

Cyan Fluorescent Carbon Quantum Dots with Amino Derivatives for the Visual Detection of Copper (II) Cations in Sea Water

Amino- and carboxyl-functionalized carbon quantum dots (Amino-CQDs) were synthesized through fast and simple microwave treatment of a citric acid, ethylenediamine and ethylenediaminetetraacetic acid (EDTA) mix. The reproducible and stable optical properties from newly synthesized CQD dispersion with a maximum absorbance spectra at 330 nm and the symmetric emission maximum at 470 nm made the Amino-CQDs a promising fluorescence material for analytical applications. The highly aminated and chelate moieties on the CQDs was appropriate for a copper (Cu2+) cation sensor in the linear range from 1 × 10-4 mg/mL to 10 mg/mL with a limit of detection at 0.00036 mg/mL by static fluorescence quenching effects. Furthermore, Amino-CQDs demonstrated stable fluorescence parameters for assays in diluted alkali metal solution (Na+ and K+) and sea water. Finally, a visual sensor, based on Amino-CQDs, was successfully created for the 0.01-100 mg/mL range to produce a colorimetric effect that can be registered by computer vision software (Open CV Python).