Nitrogen Co-doped Graphene Quantum Dots Research Articles

Highly Sensitive and Selective Fluorescence and Smartphone-Based Sensor for Detection of Rutin Using Boron Nitrogen Co-doped Graphene Quantum Dots.

This research explores the fluorescence properties and photostability of boron nitrogen co-doped graphene quantum dots (BN-GQDs), evaluating their effectiveness as sensors for rutin (RU). BN-GQDs are biocompatible and exhibit notable absorbance and fluorescence characteristics, making them suitable for sensing applications. The study utilized various analytical techniques to investigate the chemical composition, structure, morphology, optical attributes, elemental composition, and particle size of BN-GQDs. Techniques included X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The average particle size of the BN-GQDs was determined to be approximately 3.5 ± 0.3nm. A clear correlation between the emission intensity ratio and RU concentration was identified across the range of 0.42 to 4.1μM, featuring an impressively low detection limit (LOD) of 1.23nM. The application of BN-GQDs as fluorescent probes has facilitated the development of a highly sensitive and selective RU detection method based on Förster resonance energy transfer (FRET) principles. This technique leverages emission at 465nm. Density Functional Theory (DFT) analyses confirm that FRET is the primary mechanism behind fluorescence quenching, as indicated by the energy levels of the lowest unoccupied molecular orbitals (LUMOs) of BN-GQDs and RU. The method's effectiveness has been validated by measuring RU concentrations in human serum samples, showing a recovery range between 97.8% and 103.31%. Additionally, a smartphone-based detection method utilizing BN-GQDs has been successfully implemented, achieving a detection limit (LOD) of 49nM.

Designed fluorescence "on-off-on" probe based on cobalt, zinc, and nitrogen co-doped graphene quantum dots: A case of quinalphos sensing.

In this study, we developed a new fluorescence "on-off-on" sensor utilizing water-soluble cobalt/zinc-nitrogen co-doped graphene quantum dots (Co/Zn-N-GQDs) to recognize quinalphos pesticide in vegetable and fruit samples. Primarily, the synthesis method employed a one-pot hydrothermal approach, using betel leaves as a natural precursor and cobalt ("Co"), zinc ("Zn"), and urea ("N") as dopant sources. The Co/Zn-N-GQDs probes underwent comprehensive analytical characterization. The Co/Zn-N-GQDs were synthesized with a remarkable luminescence yield of 31.49%, exhibiting excitation at 320 nm and emission peak at 393 nm. Interestingly, the luminescence of Co/Zn-N-GQDs was selectively "Turned Off" by Cu2+ via a static quenching setup. Remarkably, quenched fluorescence was surprisingly reactivated upon adding quinalphos to the quench setup, indicating a direct correlation between luminescence reactivation and quinalphos concentration. Briefly, this phenomenon is ascribed to the functional groups in quinalphos, such as quinoxalinyl and phosphorothioate, which chelate with Cu2+ ions, disrupting the nonfluorescent Cu2+-Co/Zn-N-GQDs complex. The design sensor demonstrated a limit of detection (LOD) of 0.11 μM and a broad linear span of 0.5 to 200 μM. In conclusion, Cu2+-Co/Zn-N-GQDs sensor showed immediate applicability, stability, and reproducibility, making it highly effective for quinalphos sensing in various samples.

Facile and rapid method to synthesis sulfur and nitrogen co-doped graphene quantum dots as an electrode material with excellent specific capacitance for supercapacitors application

The current invention pertains to the expeditious simple synthesis of electrode materials that improve the storage capacity of supercapacitors (SCs). Sulfur and nitrogen co-doped graphene quantum dots (SN-GQDs) are synthesized using a microwave-assisted hydrothermal (MAH) process at low pressure and with a short reaction time. The utilization of SN-GQDs in conjunction with Polyaniline (PANI) has the potential to enhance the supercapacitor's energy and power density, owing to their notable specific capacitance. Implementing SN-GQDs material as an SCs electrode, exhibiting an outstanding specific capacitance of 1040 F/g at an applied current density of 0.5 A g−1. Furthermore, a composite of SN-GQDs/PANI is synthesized and the electrochemical performance is compared with the as-synthesized PANI. The symmetrical SCs are fabricated using SN-GQDs/PANI composite, and PANI. At a current density of 0.5 A g−1 SN-GQDs/PANI composite-based SC displays a superior energy density of 44.25 Wh/kg at a power density of 1.227 kW/kg. This is high in comparison to PANI-based SC which shows an energy density of 18.71 Wh/kg at 0.8 kW/kg power density at the same current density. The SC created using SN-GQDs/PANI composite exhibits superior properties and is a promising material for SC applications.

Experimental and theoretical studies on the photoelectrocatalytic property of titanium dioxide nanoarrays improved by S,N co-doped graphene quantum dots

In this paper, sulfur and nitrogen co-doped graphene quantum dots (S,N-GQDs) were compounded with titanium dioxide (TiO2) nanorods by chemical surface modification. S,N-GQDs in diameter of 5 nm are uniformly distributed on the surface of TiO2 nanorod arrays. The presence of CS bonds in S,N-GQDs not only broaden the absorption of visible light by GQDs, but also enhanced the visible light absorption of S,N-GQDs/TiO2 composites. The photocurrent densities of S,N-GQDs/TiO2 were 3.66 times that of unmodified TiO2. The calculation results of density functional theory (DFT) showed that the band gap of S,N-GQDs is significantly reduced compared to GQDs, indicating that electrons are more likely to transit to higher energy levels and form more activation sites. Moreover, compared with TiO2, the DFT calculation results of band gap, density of states and charge density difference of S,N-GQDs/TiO2 showed that S,N-GQDs/TiO2 had a wide wavelength of visible light absorption and better electron-hole separation ability, resulting in the superior photoelectrocatalytic property. This research provides favorable analytical value for the development of photocatalysts based on heterostructures.

Synthesis of Bone Meal-derived 4-Carboxyphenylboronic Acid Functionalized Sulfur and Nitrogen Co-doped Graphene Quantum Dots Nanoprobe for Sialic Acid Sensing

Detection of sialic acid using advanced sensors in milk-based products is essential in the food industry. Therefore, the present work reports the sulfur and nitrogen-doped graphene quantum dots from bone meal functionalized with boronic acid (Boro-S/N-dGQDs) nanoprobe for sialic acid sensing applications. Briefly, S/N-dGQDs were functionalized with 4-carboxyphenylboronic acid to improve performance of fluorescent sensors toward the detection of sialic acid. Here, boronic acid surface decoration on S/N-dGQD was confirmed by several spectral characterizations. The addition of different quantities of sialic acid results in a directly proportionate correlation to fluorescence quenching. It gives a broad linear range of 50 ng/mL to 1000 ng/mL and a limit of detection of 6.04 ng/mL. Also, it displayed remarkable selectivity, likely due to interaction of sialic acid-containing 1,2-diol with hydroxyl group of Boro-S/N-dGQDs nanoprobe. Designed sensor demonstrated good stability and reproducibility. Real-time analysis of sialic acid in different milk-based products confirmed practicability of Boro-S/N-dGQDs.

Review on Hyaluronic Acid Functionalized Sulfur and Nitrogen Co-Doped Graphene Quantum Dots Nano Conjugates for Targeting of Specific Type of Cancer.

Many people lose their lives to cancer each year. The prevalence of illnesses, metabolic disorders, high-risk infections, and other conditions has been greatly slowed down by expanding scientific research. Chemotherapy and radiation are still the initial lines of treatment for cancer patients, along with surgical removal of tumors. Modifications have been made in chemotherapy since medicines frequently have substantial systemic toxicity and poor pharmacokinetics and still do not reach the tumor site at effective concentrations. Chemotherapy may now be administered more safely and effectively thanks to nanotechnology. Nanotechnology-based graphene quantum dots (GQDs) are very applicable in breast cancer detection, as a drug delivery system, and in the treatment of breast cancer because of their physical and chemical properties, lower toxicity, small size, fluorescence, and effective drug delivery. This paper analyzes the GQDs as cutting-edge platforms for biotechnology and nanomedicine also its application in drug delivery in cancer. It shows that GQDs can be effectively conjugated with hyaluronic acid (HA) to achieve efficient and target-specific delivery.

N/S-GQDs/KMnO4 hybrid as a colorimetric and fluorescent dual-signal readout probe for sensitive and selective detection of ascorbic acid

A nitrogen and sulfur co-doped graphene quantum dots (N/S-GQDs) and permanganate was employed to prepare a N/S-GQDs/KMnO4 dual-signal readout colorimetric and fluorescent probe for sensitive detection of ascorbic acid (AA). In the detection system, the addition of KMnO4 quenched significantly the fluorescence (FL) of N/S-GQDs, meanwhile, the transparent aqueous dispersion of N/S-GQDs changed into yellow–brown with new absorption peak (maximum absorption at 338 nm). Interestingly, introduction of AA into the N/S-GQDs/KMnO4 system could recover the quenched fluorescence and result in a decrease in the absorbance (at 338 nm) of the test solution in a concentration dependent manner, and hence demonstrated the potential practical use of the sensing system for AA detection. Based on various spectroscopic studies, it has been concluded that the static as well as inner filter effect was the main quenching mechanisms in the detection system. The dual-response sensor showed linear response in the concentration range between 0.01 and 30 µM with the limit of detection (LOD) of 8.3 nM and 100 nM, respectively, for the fluorescent and colorimetric detections. In addition, the proposed detection system has been successfully applied to the detection of AA in vitamin C tablets. Moreover, the proposed detection strategy is convenient and fast, prevents complex and tedious probe preparation procedure, and capable of visual detection of AA.

Highly sensitive fluorescent probe for mesotrione based on nitrogen and sulfur co-doped graphene quantum dots

Highly sensitive fluorescent probe for mesotrione based on nitrogen and sulfur co-doped graphene quantum dots

One pot synthesis of cobalt and nitrogen co-doped graphene quantum dots based fluorescence ‘On-Off-On’ probe for dimethoate sensing: A proof of concept

Dimethoate, which is widely used in agriculture, has harmful effects on organs. To address this issue, advanced sensors are crucial for detecting it in real samples. Notably, graphene quantum dots (GQDs)-centered fluorescent sensors offer numerous advantages such as high sensitivity, selectivity, and good stability. Therefore, in this work, we designed a new cobalt/nitrogen co-doped GQD (Co/N-GQD) fluorescence switch “On-Off-On” sensor to achieve selective dimethoate detection. In brief, the synthesis of Co/N-GQDs, achieved through the hydrothermal method, involves Pithecellobium dulce fruit peel as a green precursor, along with cobalt (Co) and urea as dopant sources. Extensive spectral characterizations, including FTIR, UV–Vis spectroscopy, zeta potential analysis, particle size analysis, HR-TEM, Raman, PXRD, and fluorescence studies, were conducted to validate the fabrication of Co/N-GQDs. The resulting nanosized Co/N-GQDs exhibited an enhanced quantum yield of 49.78 %. In terms of sensing, the fluorescence intensity of Co/N-GQDs is selectively quenched (“Turned Off”) by Cu2+ through a dynamic quenching mechanism. When dimethoate is included in the quenching system, a proportional correlation is observed between dimethoate concentration and fluorescence reactivation. This phenomenon is attributed to the potential of dimethoate, which contains amide and phosphorodithioate functionalities, to displace Cu2+ from the electrostatic complex through chelation. Remarkably, the sensor achieves a limit detection limit (LOD) of 64.08 ng/mL, offering a broad linear range spanning from 10 to 800 ng/mL. In addition, it exhibited real-time applicability, good stability, and reproducibility. In conclusion, the design of Cu2+–Co/N-GQDs can be used as a proof of concept for dimethoate sensing within various sample contexts.

A smartphone-integrated nanosensor based on N, P co-doped graphene quantum dots for fluorescence detection of acid red 18 in food

Exploring graphene quantum dots (GQDs) that can be done to contaminant residue detection has been widely concerned. Herein, we develop nitrogen and phosphorus co-doped graphene quantum dots (N, P-GQDs) with a strong green emission (quantum yield: 0.582) by using the resorcinol and phosphonitrilic chloride trimer as precursors via the one-step hydrothermal method. The synthesized N, P-GQDs exhibit excellent photostability and excitation-independent characteristic. Meaningfully, N, P-GQDs exhibit good fluorescence response to acid red 18 (AR18) and possess a good linear relationship over the range of 0–50 μM (the detection limit: 27 nM). Meanwhile, the fluorescence resonance energy transfer is considered as the possible sensing mechanism. Furthermore, a smartphone-assisted sensing platform is designed for the detection of AR18, which can realize on-site quantitative analysis and exhibit excellent on-site detection capability (the detection limit: 43 nM). Therefore, the present strategy has a prospective value for the application in the on-site monitoring of AR18.

Portable and Flexible High Performance All-solid-state Planar Micro-supercapacitors Based on Nitrogen and Oxygen Co-doped Graphene Quantum Dots

The rapid development of intelligent technology puts forward higher requirements for portable and flexible energy storage devices. In this paper, nitrogen and oxygen co-doped graphene quantum dots were used as electrode material of flexible planar micro-supercapacitors (PMSCs) and the electrode/gap width was 6 μm/2 μm. Electrochemical performance of the flexible devices was investigated at different bending angles with scan rates of 0.01 V/s to 10000 V/s. When bending 75°, the area capacitance and the energy density were 2.61 μF cm−2 and 0.36 nWh cm−2 at the scan rate of 0.01 V/s, and the power density was 173.66 μW cm−2 at the scan rate of 10000 V/s. When bending 0°, the area capacitance and energy density were the same as that when bending 75°, and the power density was 198.36 μw cm−2. The output current of the two flexible devices was 200 μA when bending 75° and 250 μA when bending 0°. The capacitance retention was 87.5% when bending 75° and 90.4% when bending 0° at the scan rate of 500 V/s after 10000 cycles. The results indicated that the bending has little effect on the electrochemical performance of the flexible PMSCs.

Outstanding Electrochemical Performance of Planar On-chip Micro-supercapacitors Based on Nitrogen and Oxygen Co-doped Graphene Quantum Dots at High Scan Rates

In recent years, researchers continue optimizing and innovating in the selection of supercapacitor electrode materials and fabrication processes. In this paper, the fabrication process and electrochemical performance of an all-solid-state planar on-chip micro-supercapacitors (POMSs) with nitrogen and oxygen co-doped graphene quantum dots as electrode material will be demonstrated. Graphene quantum dots (GQDs) electrode films were prepared by a modified liquid-air interface self-assembly method, and patterned by photolithography. The resulting POMSs achieved an area capacitance of 25.53 μFcm−2, and its areal energy density and areal power density are 3.55nWh cm−2 and 8.79 μW cm−2 correspondingly. It is worth noting that the POMSs have excellent rate capability and can maintain outstanding performance at ultrahigh scan rate of 10000 V s−1. The POMSs have a short time constant which is 3.16 μs, and the capacitance characteristics can be maintained over 99.1% in 10000 cycles of charge and discharge at a scan rate of 5000 V s−1 in the cyclic stability test.

N, F-doped graphene quantum dots effectively inhibit the fibrillization of amyloid-beta peptide (1–42)

Developing novel inhibitors for the fibrillization of amyloid peptides and understanding the relevant assembly processes are essential for biomedical and biomaterial sciences. Herein, we have synthesized and characterized the nitrogen and fluorine co-doped graphene quantum dots (N, F-GQDs), and investigated their inhibition of the fibrillization of Amyloid-beta peptide (1–42) (Aβ42) by monitoring the assembly morphologies in the Aβ42/N, F-GQDs systems. Our results indicate that the N, F-GQDs functionalized with multiple surface groups effectively inhibits the fibrillization of amyloid Aβ42. The strong adsorption of Aβ42 on N, F-GQDs significantly reduces the generation of β-sheet structures and the cytotoxicity of Aβ42/N, F-GQDs aggregates. Accordingly, a morphological evolution from the long fibrils of Aβ42 to the spherical particles and unique closed-loop structures of Aβ42/N, F-GQDs have been captured. A possible interpretation for the observed phenomena in the presence of N, F-GQDs has been proposed by combining the different inhibition effects of other GQDs on the fibrillization of Aβ42 and the results from various control experiments. Moreover, the inhibition activity of N, F-GQDs demonstrates good adaptability to resist the fluctuation of pH value and the interference of divalent metal ions, facilitating their practical applications in the future.

Microwave synthesis of boron- and nitrogen-codoped graphene quantum dots and their detection to pesticides and metal ions

Through developing a highly efficient solid-phase microwave-assisted (SPMA) synthesis technique, we were able to synthesize graphene quantum dots (GQDs) that were doped with nitrogen and boron atoms. The as-synthesized GQDs were employed as sensing probes for detecting pesticides and iron ions within aqueous solutions. The SPMA approach is very versatile for in-situ doping of multiple atoms within the graphitic structure of GQDs. The maximal B/C and N/C atomic ratios within the GQD structures were reached as high as 28.6 and 86.4 at.%, respectively. For the B-/N-codoped GQDs, the N dopants comprises of pyrrolic/pyridinic N and graphitic N, whereas the B doping mainly involves two bonding types (i.e., B4C and BCO2) inserted into or decorated on the GQD skeleton structure. Based on the analysis of the Stern-Volmer plots, the B-/N-codoped GQDs can be employed as probing nanomaterials toward Fe2+ and paraquat detection thanks to their incredible sensitivity throughout the photoluminescent quenching. The PL quenching mechanism of GQDs is usually governed by the GQD‒(paraquat)x intermediates formation and the resulting π–π stacking that can easily quench and aggregate. The findings of this work pave the pathway to engineering the chemical compositions as well as the crystalline structures of GQDs, used for energy and other sensing devices.

Phthalocyanines and graphene quantum dots nano-systems as dual anti-cancer sensitizers for photo-sonodynamic combinatorial therapy

This work reports on the preparation of cationic thiazole phthalocyanines (Pcs) conjugates to nitrogen doped (NGQDs) and nitrogen co-doped (NSGQDs) graphene quantum dots (GQDs). The photo-sonodynamic combinatorial therapy (PSDT) activities of the conjugates were determined in vitro using cancer cells lines. The conjugates demonstrated the generation of reactive oxygen species (ROS) under the treatment technique. The singlet oxygen and hydroxyl radicals were generated by the Pc-GQDs upon exposure to light ad low frequency ultrasound in PSDT. Additionally, cancer eradication was observed in vitro for the PSDT treatment using the Pc-GQDs conjugates. The ROS generation and cell eradication studies showed that the NGQDs conjugates performed better compared to the NSGQDs conjugates. The PSDT treatments were compared to the photodynamic therapy (PDT) and sonodynamic therapy (SDT) monotreatments. For the combination therapies, both the ROS generation and the cancer eradication efficiencies were increased compared to the PDT and SDT monotreatments. • Zn phthalocyanines are conjugated to N and NS doped graphene quantum dots (GQDs). • The conjugates are used photo-sonodynamic therapy against cancer cells. • N doped GQDs conjugates performed better than NS doped GQDs conjugates.

Distinctive sensing nanotool for free and nanoencapsulated quercetin discrimination based on S,N co-doped graphene dots

A selective and sensitive fluorescent nanoprobe (sulfur and nitrogen co-doped graphene quantum dots, S,N-GQDs) was designed for both detection and discrimination between free and quercetin-loaded nanoemulsion in food samples of diverse nature. Quercetin nanoemulsions (Q-NEs) were synthesized by a phase inversion temperature (PIT) procedure, while S,N-GQDs were synthesized using a bottom-up methodology by means of simple hydrothermal treatment of citric acid and cysteamine. Both synthetized nanomaterials (analyte and fluorescent probe), were carefully characterized through advanced spectroscopic and high-resolution microscopic techniques. It was observed that fluorescence intensity of S,N-GQDs could be markedly and distinctively quenched by the addition of both quercetin forms through inner filter effect (IFE) mechanisms, exhibiting static quenching events for free quercetin and Q-NEs but with a characteristic 13 nm red-shift spectra in presence of Q-NEs. Linear dynamic ranges between 0.05 and 10 mg L−1 and 0.025–70 mg L−1, with detection limits of 17 and 8 μg L−1 were revealed for free and nanoquercetin, respectively. After nanostructural and physic-chemical optimization, the discrimination strategy was metrologically validated and applied to nutraceutical supplements containing nanoencapsulated quercetin and on diverse free quercetin products such as onion peels and dietary supplements. Accuracy and reliability were proved by means of a statistical comparison with the results obtained by a μHPLC-DAD method (paired Student's t-test at 95% confidence level). The method provides the exciting prospect of analyzing new designed nanoencapsulated bioactives without altering their native nanostructure, as well as being able to accomplish the challenge to distinguish between both forms of quercetin.

Planar on-chip interdigital microelectrodes based on nitrogen and oxygen co-doped graphene quantum dots for microsupercapacitors

The electrochemical performances of microsupercapacitors depend on the electrode materials. And graphene quantum dots are a very ideal electrode materials. In particular, nitrogen or oxygen doping is beneficial to enhance the Faraday reaction kinetics and improve the interfacial wettability of the carbon electrode and electrolyte solution. In this paper, nitrogen and oxygen co-doped graphene quantum dots were used as electrode materials and the electrode film was prepared by a modified liquid-air interface self-assembly method. The microsupercapacitors had high electrochemical characteristics including the area capacitance which was 98 μF cm−2, the energy density which was 0.014 μWh cm−2, the power density which was 51.07 μW cm−2 and the excellent time constant which was 0.12 ms. Meanwhile, the capacitance retention rate was 97.3% after 10,000 cycles.

Nitrogen and sulfur co-doped graphene quantum dot-modified electrode for monitoring of multivitamins in energy drinks

A glassy carbon electrode was modified with nitrogen and sulfur co-doped graphene quantum dots immobilized in chitosan for the monitoring of multivitamins. The graphene quantum dots were synthesized using a simple citric acid/l-cysteine pyrolysis procedure. The co-doping with nitrogen and sulfur in the graphene matrix was confirmed by spectroscopic techniques. Electron microscopy results showed that the synthesized quantum dots had a diameter of 3.4 ± 1.4 nm. Electrochemical techniques showed excellent current responses to vitamin oxidation provided by the modified electrode compared to the bare electrode. The parameters of square wave voltammetry were optimized in order to obtain the best current responses and to study the electrochemical oxidation of vitamins. The calibration plots for vitamins B2, B6 and B12 were constructed in 0.1 mol L−1 sodium acetate buffer (pH 5.0) with limits of detection of 0.30, 30.1 and 0.32 nmol L−1, respectively. Lastly, the modified electrode was effectively implemented in the quantification of vitamins in classic and fruit-based energy drink samples.

Photolithographic fabrication and electrochemical characterization of planar on-chip micro-supercapacitors based on nitrogen and oxygen co-doped graphene quantum dots with superior capacitance retention rates

Compared with graphene, nitrogen and oxygen co-doped graphene quantum dots can make up for the limitation of graphene active sites. Here, we demonstrated the fabrication of planar on-chip micro-supercapacitors based on nitrogen and oxygen co-doped graphene quantum dots. The interdigital micro-electrodes were prepared on the surface of the electrode thin film by the photolithographic technique. Notably, the electrochemical performance of the micro-supercapacitors had significantly increased. The area capacitance was 18.74 μF cm−2. Furthermore, this work offered the areal energy density of 2.60 nWh cm−2 and the areal power density of 116.43 μW cm−2. After 10,000 cycles at 5000 Vs−1, the capacitance retention rate of 99.23% was obtained. Meantime, the corresponding time constant was 10.03 μs.

Construction of NaYF4: Yb, Ho/B, N-GQDs nanocomposites for double anti-counterfeiting fluorescence ink

Fluorescent nanomaterials with multiple anti-counterfeiting play a vital role in economic and social fields in our daily lives. In this work, a hybridized composite of boron and nitrogen co-doped graphene quantum dots (B, N-GQDs) and lanthanide-doped up-conversion NaYF4 was prepare for a double anti-counterfeiting application. The composite was obtained by one-pot hydrothermal method and it was commixed with glycerol in a ratio of 4 : 1 to prepare a fluorescence ink, which exhibited independent blue and green fluorescence emissions under ultraviolet light and near-infrared laser excitation. Therefore, it had a considerable application in confidential communications, logo designing and file encryptions.