N-doped C-dots Research Articles

A nanozyme based wearable device for colorimetric monitoring of UV radiation exposure in sunlight

In this study, nanozyme is used for monitoring the dose of ultraviolet (UV) in sunlight for the first time. We find that nitrogen-doped carbon dots (N-doped C-dots) can effectively catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) under different UV region including UVA, UVB, and UVC. In comparison, the N-doped C-dots fail to show the catalytic activity under visible light. The finding is applied for distinguishing UV light and visible light through the color change of TMB. More importantly, the photo-oxidation TMB catalyzed by N-doped C-dots can work well in a near neutral pH, which is beneficial for its application in wearable device due to the reducing of acid corrosion. Finally, a wearable bracelet is fabricated by integrating N-doped C-dots and TMB into hydrogels. The bracelet is used for monitoring the UV exposure in sunlight. The color change of TMB in the bracelet can be clearly observed by naked eyes or quantified by a smartphone. The bracelet is also used for distinguishing different weather condition such as sunny/cloudy or different place such as indoor/outdoor during a sunny day. This study provides the first example of nanozyme in wearable UV sensor and will stimulate the applications of nanozyme in wearable device.

Novel green synthesis of N-doped carbon dots from fruits of Opuntia ficus Indica as an effective catalyst for the photocatalytic degradation of methyl orange dye and antibacterial studies

• We have prepared Undoped and N-doped C-dots from Opuntia ficus Indica plant extract. • The synthesized Undoped and N-doped C-dots exhibit, the green fluorescence. • We found higher photocatalytic activity in N-doped C-dots than Undoped C-dots. • N-doped C-dots have utilized as photocatalytic for the degradation of Methyl orange dye. • Further we have study them anti-bacterial activity using gram negative and gram positive bacterias. A carbon dot is an attractive material for the photocatalytic degradation of organic pollutant. Moreover it’s extensively used as a material to control the growth of micro organisms. Herein we are reporting the synthesis of Undoped and N-doped carbon dots (N-CDs) derived from Opuntia Ficus Indica (O.F.Indica) fruits. Further we have well characterized by UV-Vis, FT-IR, XPS spectral, HR-TEM, Raman and XRD techniques. The synthesized Undoped and N-CDs are stable for 3 months. Finally we have found the N-CDs shows the higher photocatalytic activity then Undoped C-dots, due to presence of N-atom. We also have discussed the possible degradation mechanism of Methyl Orange (MO). Finally the N-CDs was utilized their antibacterial activities. We used Streptococcus Pyogenes, Staphylococcus Aureus , Klebsiella Pneumoniae, and Shigella Flexneri. Among them we found Streptococcus Pyogenes a bacterium was largely controlled the growth by our N-CDs.

Poly(Vinylamine) Derived N-Doped C-Dots with Antimicrobial and Antibiofilm Activities

Nitrogen-doped carbon dots (N-doped C-dots) was synthesized by using poly(vinyl amine) (PVAm) as a nitrogen source and citric acid (CA) as a carbon source via the hydrothermal method. Various weight ratios of CA and PVAm (CA:PVAm) were used to synthesize N-doped C-dots. The N-doped C-dots revealed emission at 440 nm with excitation at 360 nm and were found to increase the fluorescence intensity with an increase in the amount of PVAm. The blood compatibility studies revealed no significant hemolysis for N-doped C-dots that were prepared at different ratios of CA:PVAm for up to 500 μg/mL concentration with the hemolysis ratio of 1.96% and the minimum blood clotting index of 88.9%. N-doped C-dots were found to be more effective against Gram-positive bacteria than Gram-negative bacteria, with the highest potency on Bacillus subtilis (B. subtilis). The increase in the weight ratio of PVAm in feed during C-dots preparation from 1 to 3 leads to a decrease of the minimum bactericidal concentration (MBC) value from 6.25 to 0.75 mg/mL for B. subtilis. Antibiofilm ability of N-doped C-dots prepared by 1:3 ratio of CA:PVAm was found to reduce %biofilm inhibition and eradication- by more than half, at 0.78 mg/mL for E. coli and B. subtilis generated biofilms and almost destroyed at 25 mg/mL concentrations.

Synthesis and characterization of nitrogen-doped carbon dots as fluorescent nanoprobes with antimicrobial properties and skin permeability

Nitrogen doped carbon dots (N-doped C-dots) were prepared using polyethyleneimine (PEI) and citric acid (CA) as precursors via the hydrothermal method. Various weight ratios of PEI and CA, 1:0.5, 1:1, and 1:2, were used in the synthesis of N-doped C-dots. The N-doping of prepared C-dots was confirmed with an FT-IR peak that was observed at 1652 cm−1 assigned to N–H bending. The hydrodynamic diameters of prepared N-doped C-dots were 70.2 ± 6.9, 32.2 ± 4.7, and 11.5 ± 3.1 nm by DLS measurements, and surface charges values were 1.32 ± 0.8, 0.14 ± 0.2, and −1.57 ± 0.7 mV, for 1:0.5, 1:1, and 1:2 wt ratio based on PEI of CA, respectively. A high quantum yield 53 ± 4.8% according to quinine sulfate standard was determined for 1:1 C-dot prepared from 1:1 wt ratio of PEI:CA. The C-dots were found to inhibit growth of both Gram-negative and Gram-positive bacteria with no noted toxicity to mammalian cells in vitro. Skin permeation studies indicate that the particles permeate into and through the dermis within hours, indicating their potential use for topical administration.

One-step synthesis of positively charged bifunctional carbon dot/silver composite nanoparticles for killing and fluorescence imaging of Gram-negative bacteria

Positively charged C-dot/Ag composite nanoparticles were synthesized via the facile one-step hydrothermal reaction of L-arginine and silver nitrate. L-arginine was used not only as the carbon and nitrogen sources of N-doped C-dots but also as the reducing agent of silver ions. It was noteworthy that the resulting C-dots were negatively charged but the simultaneous reduction of silver ions made the resulting C-dot/Ag composite nanoparticles become positively charged. Furthermore, as compared to C-dots, the presence of Ag nanoparticles and the higher nitrogen content led to the redshift of excitation and emission intervals. Also, the enlarged excitation wavelength range in the visible light region made the resulting C-dot/Ag nanocomposite more useful in fluorescence imaging. In addition, the C-dot/Ag composite nanoparticles exhibited more excellent bacteria-killing capability than C-dots and were successfully used for the fluorescence imaging of E. coli because they could attach and release silver ions on the surface of E. coli. In conclusion, a facile one-step hydrothermal process has been successfully developed for the synthesis of C-dot/Ag composite nanoparticles, and the resulting C-dot/Ag composite nanoparticles are expected to have great potential in the killing and fluorescence imaging of Gram-negative bacteria.

Carbon nanodots chelated with metal ions as efficient electrocatalysts for enhancing performance of microbial fuel cell based on sulfate reducing bacteria

We report the electrocatalytic activity of a graphite electrode chemically coated with ultra-small nitrogen-doped carbon nanodots (N-doped C-dots), which formed an intermediate diazo-metal chelate phase. Its performance as cathode for enhanced current production was demonstrated in a dual-chamber microbial fuel cell (MFC) through synergistic cooperation with electroactive biofilm of sulfate-reducing bacteria (SRB) on the anode. For that purpose, the immobilized SRB biofilm on the anode facilitated direct transfer of electrons to the graphite surface by filaments network, known as nano-pili, which provided cell-to-cell link. A significantly improved acceleration of the electrons was measured on the cathode in the presence of chemically conjugated N-doped C-dots chelated with metal ions, because they acted as efficient electrocatalysts for oxygen reduction reaction (ORR) in a neutral phosphate buffer solution. As a result, the power density obtained from the occurred synergistic effect in MFC increased almost double higher than the initial value in the control experiment. The chemical resistance, exploitation life and the easy protocol for fabrication of the reported cathode coated with electrocatalytic nanolayer open up the possibility for new class cheap electrocatalytic electrodes with a wide practical applications in fuel cell engineering and technology.

One pot green synthesis of C-dots from groundnuts and its application as Cr(VI) sensor and in vitro bioimaging agent

The emergence of fluorescent carbon dots (C-dots) has received special attention due to their distinct characteristics which are advantageous for optical sensing and bioimaging applications. Cr(VI) is considered a hazardous environmental pollutant hence requires a simple and effective method for its detection and recovery. Herein, we have synthesized both C-dots and N-doped C-dots from ground nuts employing a cost-effective and green hydrothermal method. N-C-dots exhibits a remarkably enhanced quantum yield (17.6%) as compared to undoped C-dots (7.8%). In addition,the N-C-dots showed amazing selectivity towards Cr(VI) in the metal sensing application. Cr (VI) induced quenching of fluorescence was recovered using Humic acid as well as Glutathione thus exhibiting an off-on type sensing mechanism. The limit of detection (LOD) for Cr(VI) using N-C-dots was found to be 0.1 mg/L. C-dots possess comparatively low cytotoxicity than N-C-dots at higher concentration thereby making them an efficient candidate for bioimaging of MCF-7 cells.

Visible transparent white light emitting ink from a Ce3+ sensitized monodispersed Tb,Sm co-doped LaF3@C-dot nanocomposite.

Bright white light emission (CIE values 0.32 and 0.33) has been achieved by a single excitation source (254 nm) from a monodispersed nanocomposite composed of Ce3+, Tb3+ and Sm3+ doped LaF3 nanocrystals (NCs) and N-doped C-dots where Ce3+ acts as an excellent sensitizer. Controlled deposition of the C-dots onto the surface of the LaF3 NCs impedes conventional aggregation induced quenching (AIQ) of the C-dots in solid state. The transparent colloidal ink was coated onto an UV chip to fabricate a white light emitting diode (WLED) with a luminous efficacy of 8.72 lm W-1.

Insights on the solvatochromic effects in N-doped yellow-orange emissive carbon dots

We have demonstrated a rapid and facile synthetic method to prepare N-doped Cdots that has excitation independent-emission in yellow-orange region. The Cdots showed solvatochromic behavior in different solvents due to change in solvent polarity illustrating n → π* transition (edge band).

A dual-signal readout sensor for highly sensitive detection of iodide ions in urine based on catalase-like reaction of iodide ions and N-doped C-dots

In this work, a novel colorimetric and ratiometric fluorescence detection method for iodide ions (I−) was developed. In the presence of I−, the color of N-doped C-dots/H2O2/OPD system aqueous solution varied from colorless to yellow due to 2,3-diaminophenazine (OPDox) produced from I−-catalyzed H2O2-o-phenylenediamine (OPD) reaction. At the same time, the OPDox had an excellent fluorescence (FL) property. Under the excitation wavelength at 390nm, a novel FL emission ascribed to OPDox was clearly observed at 565nm. In addition, the FL at 565nm gradually increased, while the FL of emission peak at 450nm attributed to N-doped C-dots gradually decreased with the increasing concentration of I− due to the FL resonance energy transfer (FRET) between N-doped C-dots and OPDox. Therefore, a dual-signal optical sensor was developed for detection of I−. Under the optimized conditions, the linear response to I− was in the range of 0.09–50μM and the limit of detection was 0.06μM. Moreover, this proposed assay was successfully applied for the detection of I− in urine. These results indicate that the colorimetric and ratiometric fluorescence dual-readout assay method has great potential for applications in physiological and pathological diagnosis.

Green and economical synthesis of nitrogen-doped carbon dots from vegetables for sensing and imaging applications

A green, simple and low-cost approach was present to obtain N-doped C-dots using vegetables as the sole carbon source through facile one-pot hydrothermal treatment. The C-dots can serve as a suitable sensing platform for detection of Cu2+.

Solid-phase synthesis of highly fluorescent nitrogen-doped carbon dots for sensitive and selective probing ferric ions in living cells.

Carbon quantum dots (C-Dots) have drawn extensive attention in recent years due to their stable physicochemical and photochemical properties. However, the development of nitrogen-doped carbon quantum dots (N-doped C-Dots) is still on its early stage. In this paper, a facile and high-output solid-phase synthesis approach was proposed for the fabrication of N-doped, highly fluorescent carbon quantum dots. The obtained N-doped C-Dots exhibited a strong blue emission with an absolute quantum yield (QY) of up to 31%, owing to fluorescence enhancement effect of introduced N atoms into carbon dots. The strong coordination of oxygen-rich groups on N-doped C-Dots to Fe(3+) caused fluorescence quenching via nonradiative electron-transfer, leading to the quantitative detection of Fe(3+). The probe exhibited a wide linear response concentration range (0.01-500 μM) to Fe(3+) with a detection limit of 2.5 nM. Significantly, the N-doped C-Dots possess negligible cytotoxicity, excellent biocompatibility, and high photostability. All these features are favorable for label-free monitoring of Fe(3+) in complex biological samples. It was then successfully applied for the fluorescence imaging of intracellular Fe(3+). As an efficient chemosensor, the N-doped C-Dots hold great promise to broaden applications in biological systems.

Practical access to bandgap-like N-doped carbon dots with dual emission unzipped from PAN@PMMA core–shell nanoparticles

As emergent nanolights for bioimaging, catalysis, sensors, and photoelectronics, carbon dots (C-dots) have attracted much research attention. However, the practical and scalable preparation of C-dots has been less explored, even after various top-down and bottom-up approaches being reported recently. To this end, we discover a new approach to prepare C-dots by simply unzipping core–shell polymeric nanoparticles, prepared by a microemulsion polymerization. Uniformly distributed N-doped C-dots are prepared by the pyrolysis of PAN@PMMA core–shell nanoparticles at different temperatures, followed by dialysis. TEM analysis shows that many of the C-dots of 2–3 nm size are unzipped from each polymeric particle. All the purified C-dots show a bandgap-like photoluminescence (PL) behaviour, with dual emission and a stable PL between pH 5–12.