As-synthesized Carbon Quantum Dots Research Articles

Amine Group Surface-Functionalized Carbon Quantum Dots Exhibit Anti-amyloidogenic Effects Towards Hen Egg White Lysozyme by Inducing Formation of Nontoxic Spherical Aggregates.

The tendency of polypeptide chains to deviate from their conventional protein folding pathway and instead get trapped as off-pathway intermediates, has been a matter of great concern. These off-pathway intermediates eventually lead to the formation of insoluble, ordered fibrillar aggregates called amyloids, which are responsible for a host of neurodegenerative diseases like Alzheimer's disease, Parkinson's disease and Type II diabetes. In spite of extensive research, development of an effective therapeutic strategy against amyloidosis still remains elusive. In recent times, carbon quantum dots (CQD) have grabbed the attention of researchers against amyloidogenesis due to their ease of preparation, aqueous soluble nature, unique optical properties, high surface to volume ratio, physio-chemical properties, semi-conducting nature and mainly biocompatible. In the current study, we have reported an easy-to-prepare procedure for synthesis of amine group surface functionalized CQDs from commonly available kitchen spices with anti-oxidant properties. The as-synthesized CQDs were evaluated for their anti-amyloidogenic properties towards Hen Egg White Lysozyme (HEWL). Our results clearly show that the surfaced functionalized CQDs were able to interact with HEWL, thereby forming a stable complex, which was resistant towards amyloid formation and instead lead to the formation of non-toxic globular aggregates.

Synergistic Degradation of 2,4,4′-Trihydroxybenzophenone Using Carbon Quantum Dots, Ferrate, and Visible Light Irradiation: Insights into Electron Generation/Consumption Mechanism

In this study, we reported a unique single-step synthesis of photocatalytic carbon quantum dots (CQDs) with high electron density, efficient aggregation-induced emission, and improved surface chemistry properties. As-synthesized CQDs were applied with ferrate (a reactive and green oxidant) to synergistically degrade 2,4,4′-trihydroxybenzophenone (2,4,4′-HBP). The restriction of molecular rotation, vibration in the crystal structure, modification of the surface chemistry, and the aggregation/quenching of CQDs were highlighted by comprehensive characterization. Newly synthesized CQDs’ generated electrons were consumed by ferrate, and this mechanism was highlighted by photoluminescence analyses. It was found that the photoluminescence intensity of CQDs was reduced by more than 96% when ferrate was introduced into the CQDs reaction system. The reaction kinetics of 2,4,4′-HBP degradation was inspected at different pH values (7.0, 8.0 and 9.0) using ferrate in a single dose and multiple-dose (sequential) additions. The CQDs + ferrate + visible light (Vis) was proven to be the best reaction system with a 99.9% degradation efficiency, as compared to CQDs alone (63%) and ferrate single dose (85%) and multiple-dose (96%) methods. In addition, 10 reaction intermediates were identified, implying that C–C cleavage, hydroxylation, self, cross, and end linkage were involved in the potential reaction mechanism. Besides, hydroxyl radicals were found to be the primary reactive species in electron paramagnetic resonance (EPR) analyses. The computational analyses including density functional theory and molecular orbital distribution elucidated the reaction sites of CQDs and 2,4,4′-HBP. These findings have important implications in understanding electron generation and consumption mechanisms with the synergetic contribution of CQDs and ferrate to degrade organic pollutants such as 2,4,4′-HBP.

Efficient Continuous Hydrothermal Flow Synthesis of Carbon Quantum Dots from a Targeted Biomass Precursor for On–Off Metal Ions Nanosensing

Glucose, a readily available biomass precursor is used for the production of carbon quantum dots (CQDs) via a fast, efficient, and environmentally benign continuous hydrothermal flow synthesis (CHFS) process using supercritical water, an approach that can readily be scaled up for industrialization, producing materials with enhanced properties. The water-soluble CQDs exhibit an average particle size of 2.3 ± 0.5 nm, with an optimum emission intensity at 446 nm on excitation at 360 nm. The as-synthesized CQDs with no extra modification show promising sensitivity and good selectivity for the highly toxic, carcinogenic, and mutagenic chromium(VI) ion (limit of detection of 1.83 ppm) and for the essential bioactive transition metal, iron(II) ion (limit of detection of 6.09 ppm). The life-cycle assessment confirms that in comparison to the conventional batch synthetic method, the continuous hydrothermal flow synthesis process is significantly a more efficient and greener route for the synthesis of carbon quantum dots from the glucose biomass precursor.

One-pot hydrothermal synthesis and characterization of carbon quantum dots (CQDs)

Carbon quantum dots (CQDs) have emerged as the promising class of fluorescent nanomaterials with size ranging from 2 to 10 nm. The CQDs possess amazing properties such as good solubility, photoluminescence, high quantum yield, functional groups on surface, photostability, biocompatibility and low toxicity. CQDs are a trending topic of intense research as they are being used for a wide range of applications such as biological imaging, sensing, drug delivery and catalysis. Nowadays, the focus of researchers has shifted towards the green synthesis of CQDs from natural and environment friendly sources. The present work reports the synthesis of fluorescent CQDs from cabbage as the natural carbon source by hydrothermal method. The as-synthesized CQDs were characterized using various analytical techniques to obtain information regarding their absorption/emission spectra, chemical functionality and morphology. Further, the synthesized CQDs were explored for optical sensing of various heavy metal ions in aqueous medium. The study provides a simple and economical method of utilizing CQDs for environmental sensing applications.

Functionalized Carbon-based Quantum Dots: Optical Characterization and Potential Application as Bio-fluorophore

Carbon quantum dots (CQDs), in comparison to heavy metal-based quantum dots offer renewable, non-toxic, low cost and easy synthesis production route while having excellent physicochemical properties for biomedical or environmental use. This paper discusses development and application of functionalized carbon quantum dots from glycerol as primary carbon source and tetraethylene pentamine as functionalizing agent. As-synthesized CQDs were characterized by Fourier Transform Infrared Spectrometer (FTIR), UV-Vis Spectrophotometer and Spectrofluorometer. FTIR spectra confirmed functionalization of resulting CQDs with emission wavelength peaks at 314.18 nm and 381.15 nm and observed strong blue luminescence under UV lamp. The performance of produced CQDs as bio-fluorophore for Gram-stained bacterial models was validated. Results indicated that CQDs can effect fluoresced images but a more distinct image can be observed on S. aureus compared to E. coli. An attachment mechanism of carbon quantum dots to the bacteria surfaces was also proposed here.

High density sulfonated magnetic carbon quantum dots as a photo enhanced, photo-induced proton generation, and photo switchable solid acid catalyst for room temperature one-pot reaction

The preparation of photo enhanced and switchable (on/off mode) sulfonated magnetic carbon quantum dots was investigated in the present work. First, the as-synthesized carbon quantum dots (CQDs) were easily separated using a magnet (instead of using a dialysis method), then CQDs decorated with high density (9.6 mmol/g) acid groups (sulfonic + carboxylic) using chlorosulfonic acid. The photo-switchable activity of the catalyst related to the photoexitation of charge separation which in turn leads to electron withdrawing property in sulfonic groups. On the other hand, it was shown that sulfonated magnetic carbon quantum dot (S-M-CQDs) is more efficient than magnetic carbon quantum dot (M-CQDs). The as-prepared catalyst was characterized using SEM, TEM, EDX, XRD, IR, VSM and TGA. The catalytic activity of the as-prepared catalyst was evaluated at room temperature in one-pot reaction (synthesis of hexahydroquinoline derivatives). The as-synthesized catalyst easily retrieved using a magnet (than ultracentrifugation) and used in the next cycles.

Waste carbon paper derivatized Carbon Quantum Dots/(3-Aminopropyl)triethoxysilane based fluorescent probe for trinitrotoluene detection

Present work reports the green synthesis of highly stable, non-toxic, environmental friendly, fluorescent carbon quantum dots (CQD) via simple synthetic route using the waste carbon paper as their precursor. The as-synthesized CQD were post-synthetically modified with (3-Aminopropyl)triethoxysilane (APTES) as a nitrogen source for amine functionalized CQD (NCQD) formation. When excited at wavelength λex = 350 nm, the maximum emission intensity of NCQD was observed at wavelength λem = 450 nm. The QDs show blue colored luminescence with significant photoluminescence quantum yield (∼5.1%). Transmission electron microscopy and Energy-dispersive x-ray spectroscopy data show their size about 4.8 nm and the presence of nitrogen in elemental composition respectively. XRD and selected area electron diffraction patterns reveal their amorphous nature. This NCQD based sensing probe selectivity displays the high sensitivity for trinitrotoluene (TNT) in 4.4 nM to the 26.4 μM range. The probe delivers a 7.4ppb detection limit at 1.3% relative standard deviation.

Visible light assisted photocatalytic reduction of CO2 to ethane using CQDs/Cu2O nanocomposite photocatalyst

CO2 reduction through photocatalysis is considered a promising way to mitigate the abundance of this greenhouse gas in the earth's atmosphere. In this work, blue-fluorescent carbon quantum dots (CQDs) were synthesized via a facile top-down hydrothermal method using biochar as the carbon source. The as-synthesized CQDs were incorporated together with commercial copper (I) oxide (Cu2O) nanoparticles to form CQDs/Cu2O nanocomposite. The CQDs, Cu2O and CQDs/Cu2O nanocomposite were then applied for gas phase photocatalytic reduction of CO2. The experiments were performed under visible light irradiation in a self-designated photoreactor which was connected to an online Gas Chromatography (GC). High resolution transmission electron microscopy (HRTEM) confirmed the uniform deposition of CQDs with size ranging from 2.5 to 6.0 nm on the surface of Cu2O nanoparticles. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy further revealed the presence of CQDs on the surface of Cu2O. The CQDs/Cu2O nanocomposite photocatalyst showed a considerable improvement in the CO2 photoreduction with an enhancement of 54% compared to the pure Cu2O. In addition, the band alignment of CQDs/Cu2O, charge carriers transfer and separation as well as possible reaction pathways for CO2 photoreduction was proposed. Finally, the photostability test revealed the CQDs/Cu2O nanocomposite was able to retain its photostability of up to ~90% under five cycles of photoreaction.

A novel and facile synthesis of carbon quantum dots via salep hydrothermal treatment as the silver nanoparticles support: Application to electroanalytical determination of H2O2 in fetal bovine serum

A simple, low-cost, and green process was used for the synthesis of carbon quantum dots (CQDs) through the hydrothermal treatment of salep as a novel bio-polymeric carbon source in presence of only pure water. The silver nanoparticles (AgNPs) were embedded on the surface of CQDs by ultra-violate (UV) irradiation to the CQDs and silver nitrate mixture solution. The as-synthesized CQDs and AgNPs decorated CQDs nanohybrid (AgNPs/CQDs) were characterized by UV–vis and photoluminescence spectroscopy, Fourier transform-infrared spectroscopy, transmission electron microscopy, atomic force microcopy, X-ray diffraction, and field emission scanning electron microscopy. Then, the AgNPs/CQDs nanohybrid was casted on the glassy carbon electrode in order to prepare an amperometric hydrogen peroxide (H2O2) sensor. The electrochemical investigations show that the AgNPs/CQDs nanohybrid possesses an excellent performance toward the H2O2 reduction. In the optimum condition, the linear range of H2O2 determination was achieved from 0.2 to 27.0μM with high sensitivity (1.5μA/µM) and the limit of detection was obtained about 80nM (S/N=3). Finally, the prepared nanohybrid modified electrode was effectively applied to the H2O2 detection in the disinfected fetal bovine serum samples, and the recovery was obtained about 98%. The achieved results indicate that the AgNPs/CQDs nanohybrid with high reproducibility, repeatability, and stability has a favorable capability in electrochemical sensors improvement.

Carbon quantum dots: synthesis, characterization, and assessment of cytocompatibility

A simple method for the synthesis of water-soluble carbon quantum dots (CQDs) has been developed by chemical oxidation treatment of the flour. The as-synthesized CQDs were monodispersed sphere particles with the approximate diameter of 5-8nm, and exhibited strong fluorescence, excitation-dependent photoluminescence behavior and high photostability in a wide range of pH values. We investigated the cytotoxicity of as-prepared CQDs using rat mesangial cells (RMC). Compared with CdTe quantum dots, CQDs show no apparent cytotoxicity and much better biosafety property. The as-synthesized CQDs were also tested to label and image RMC in vitro and demonstrated to be highly promising biological fluorescent probes.

Synthesis of highly photoluminescent carbon dots via citric acid and Tris for iron(III) ions sensors and bioimaging

In this work, high quantum yield and strong photoluminescent carbon quantum dots (C-QDs) are successfully synthesized via a facile and green hydrothermal method using citric acid and Tris as precursors. The as-synthesized C-QDs with a quantum yield (QY) as high as 52% were characterized by UV, FT-IR, TEM, XPS and fluorescence spectroscope. TEM results show that C-QDs are mono-dispersed spherical particles and the diameter distribution of C-QDs is 2.8±1.1nm. The extraordinary photoluminescent properties and low cytotoxicity of C-QDs were obtained through optical property characterization and cytotoxicity assay. In addition, we found that the as-prepared C-QDs had a high affinity for Fe3+ ions and the response toward Fe3+ ions was highly linear (R2=0.997) over the concentration range from 2 to 50μM, which could provide an effective platform for portable detection of Fe3+ ions. Also, it is demonstrated that the photoluminescent C-QDs display hypotoxicity and are biocompatible for use as biosensors in living cells.