Functionalized Graphene Quantum Dots Research Articles

Synthesis, characterization and thermophysical properties of PAG-Amine functionalized graphene quantum dots based nanosuspension

This work presents the synthesis, characterization and evaluation of thermophysical properties of PAG (Polyalkylene glycol)-amine functionalized graphene quantum dots-based nanosuspension. The synthesis is carried out in two steps. In the first step graphene oxide is synthesized using Hummers method and in the next step synthesis of amine functionalized graphene quantum dots is done. The obtained quantum dots are further ultrasonicated in the Polyalkylene glycol resulting in varying concentrations of nanosuspension. For the characterization of graphene oxide Field Emission Scanning Electron Microscopy (FESEM) analysis is done, and for nanosuspension High-Resolution Transmission Electron Microscopy (HRTEM) and ultraviolet (UV)-spectrophotometer analysis is carried out. The thermophysical properties such as thermal conductivity and viscosity are examined using the Hamilton and Maxwell model which are further validated with experimental investigations.

Antibacterial property of dual-network hydrogel filled with amino functionalized graphene quantum dots

Bacterial infections seriously impair wound healing, so the development of wound dressings with high antimicrobial activity is of critical importance. In this study, amino functionalized graphene quantum dots (His-GQDs) were prepared via thermal pyrolysis of citric acid and histidine, and doped into a dual-network gelatin/sodium alginate (His-GQDs/G/SA) hydrogel to improve the antibacterial activity. The His-GQDs/G/SA hydrogel exhibited excellent antibacterial activity after 6 h of contact with bacteria. Simultaneously, the composite hydrogel could effectively alleviate the cytotoxicity of His-GQDs. The results of antimicrobial and biocompatibility tests demonstrate that the His-GQDs/G/SA dual-network hydrogel is a promising wound dressing to promote healing of infected wounds.

Unraveling the potential of graphene quantum dots against Mycobacterium tuberculosis infection.

The emergence of drug-resistant Mycobacterium tuberculosis (Mtb) strains has underscored the urgent need for novel therapeutic approaches. Carbon-based nanomaterials, such as graphene oxide (GO), have shown potential in anti-TB activities but suffer from significant toxicity issues. This study explores the anti-TB potential of differently functionalized graphene quantum dots (GQDs) - non-functionalized, L-GQDs, aminated (NH2-GQDs), and carboxylated (COOH-GQDs) - alone and in combination with standard TB drugs (isoniazid, amikacin, and linezolid). Their effects were assessed in both axenic cultures and in vitro infection models. GQDs alone did not demonstrate direct mycobactericidal effects nor trapping activity. However, the combination of NH2-GQDs with amikacin significantly reduced CFUs in in vitro models. NH2-GQDs and COOH-GQDs also enhanced the antimicrobial activity of amikacin in infected macrophages, although L-GQDs and COOH-GQDs alone showed no significant activity. The results suggest that specific types of GQDs, particularly NH2-GQDs, can enhance the efficacy of existing anti-TB drugs. These nanoparticles might serve as effective adjuvants in anti-TB therapy by boosting drug performance and reducing bacterial counts in host cells, highlighting their potential as part of advanced drug delivery systems in tuberculosis treatment. Further investigations are needed to better understand their mechanisms and optimize their use in clinical settings.

Novel palladium nanoparticles/4-aminophenol functionalized nitrogen-doped graphene quantum dots-based nanocomposite electrochemical sensor: Synthesis, characterization, capacitance, and dopamine sensing

In this study, an ultrasensitive electrochemical sensor based on palladium nanoparticles/4-aminophenol functional nitrogen-doped graphene quantum dots (PdNPs/4AP N-GQDs) composite was fabricated to detect dopamine (DA). The sensor was characterized by FTIR, UV–Vis, TEM, EDX, and XRD methods. The electrochemical analysis of the nanocomposite modified glassy carbon electrode (GCE) was conducted by cyclic voltammetry (CV). HOMO-LUMO energy levels and band gap energy was calculated from cyclic voltammograms, and the band gap energy was found to be small at 0.06 eV. The electrode reaction properties of dopamine on this developed ultrasensitive electrode were investigated by CV and differential pulse voltammetry (DPV), which showed that the electrode had electrocatalytic activity for dopamine sensing. Moreover, the developed electrode exhibited good sensitivity and improved performance, and the linear calibration curve for dopamine was calculated to have a LOD (limit of detection) of 21 pM in the range of 250 pM to 10 nM. Finally, the selectivity of the GQDs nanocomposite modified GCE towards dopamine was studied in the presence of several bioactive compounds with inhibitory effects. In addition, the specific capacitance of the nanocomposite material at 5 mV s−1 was found to be as high as 0.777F g−1. Furthermore, the dopamine selectivity of the sensor among some organic and inorganic interfering bioanalytes was investigated and the sensor was found to have excellent DA selectivity despite the bioanalytes.

Theoretical study on the utilization of N, O-functionalized graphene quantum dots in Li-S batteries

Lithium-sulfur (Li-S) batteries have high theoretical capacity and high energy density, and their practical application is difficult because of the “shuttle effect” induced by lithium polysulfides (LiPSs) and the difficulty of insoluble Li2S decomposition. Functionalized graphene quantum dots (GQDs) can anchor LiPSs and suppress the “shuttle effect” because of the various polar functional groups. This work investigates the effect of the size of GQDs and the N/O functional groups on the anchoring performance by first-principles calculations. In addition, the influence on the decomposition of Li2S, the diffusion of Li+, and the Gibbs free energy needed for the sulfur reduction reaction was also studied. The results show that the GQDs can effectively anchor LiPSs when the size is larger than 1.44 nm, and all the N/O-functionalized GQDs can also effectively anchor LiPSs. Among these N/O-functionalized GQDs, GQDs-COOH has the smallest Li+ diffusion energy barrier (0.52 eV) and low Li2S decomposition energy barrier (1.12 eV). It indicates that GQDs-COOH enables the rapid diffusion of Li+, ensures the smooth decomposition of Li2S, and catalyzes the effective conversion of LiPSs. Moreover, this work will promote the application of GQDs in Li-S batteries.

Functionalized graphene quantum dots with ZnO as a humidity sensor

Functionalized graphene quantum dots with ZnO as a humidity sensor

Spectrofluorimetric determination of vitamin D in the serum of autistic and healthy children using functionalized graphene quantum dots

Vitamin D is one of the most essential nutrients for brain development, and deficiencies during pregnancy and early childhood development might be associated with autism. Regular monitoring of serum 25-hydroxyvitamin D3 level could help in early diagnosis and therapy. Analytical measurement of serum 25-hydroxyvitamin D3 level using the traditional matrix-matched calibration technique yields inaccurate results due to absence of serum matrix free from 25-hydroxyvitamin D3. The aim of this work was to develop a validated spectrofluorimetric methodology based on the standard addition approach for quantifying 25-hydroxyvitamin D3 levels in real serum samples of autistic children. The spectrofluorimetric methodology utilizes functionalized graphene quantum dots as a fluorescent probe for selective quantification of 25-hydroxyvitamin D3 level, which is based on measuring the quenching properties of 25-hydroxyvitamin D3 on a fluorescent probe. The standard addition approach exhibits a minimal matrix interference since it identically utilizes the same matrix of each study sample for creating its own calibration curve. The method was validated using the guidelines outlined in ICH M10 draft for endogenous compounds quantification. The method was successfully applied for quantifying the serum 25-hydroxyvitamin D3 levels in autistic and healthy children, and autistic children had significantly lower serum 25-hydroxyvitamin D3 levels (with a mean ± SD of 23.80 ± 17.19) when compared to healthy children (with a mean ± SD of 50.13 ± 18.74, P < 0.001). These results suggested an association between vitamin D deficiency and autism.

Removal of Atrazine from contaminated water by functionalized graphene quantum dots

The limitation of clean water supplies and the increment of water pollution resources, like industrial processes, oil pollution, and herbicides, are urgent reasons for introducing new techniques for treating contaminated water. Atrazine is heavily used as a herbicide due to its high effectiveness and low price. However, its environmental persistence causes water contamination, and human exposure to Atrazine is linked to several health effects. This work presents a simulation study of the possibility of removing the Atrazine from water by functionally activated graphene quantum dots (GQDs), using density functional theory (DFT) at B3LYP/3-21G level. The activity of GQDs C46 with a total dipole moment of 0.9 is enhanced by the attachment of chemical groups; for instance, attaching CN and NO2 groups increases the total dipole moment to 8.744 and 9.123, respectively. The effect of the functionalized groups Carboxyl and cyanide was investigated, and confirmed that there was no structure deformation due to the functionalization process. Analysis of the obtained data shows the remarkable adsorption ability of GQDs activated by CN and NO2 groups toward the removal of atrazine herbicides due to positive adsorption energy 1.31, 128, and 1.3 eV obtained from pristine, carboxyl graphene, and cyanide graphene respectively. According to the calculated total charge on the complexes Atrazine and GQDs and Functionalized GQD, charge transfer mainly depends on the interaction pattern. The values of charges were − 0.02, 0.004, and − 0.004 for pristine, carboxyl, and cyanide graphene, respectively. Therefore, the observed results demonstrated the possibility of applying the chemically modified carbon quantum dots as a potential candidate for the treatment of contaminated water.

Fast proton transport enables the magnetic relaxation response of graphene quantum dots for monitoring the oxidative environment in vivo.

A magnetic relaxation switch (MRS) that targets small molecules such as H2O2 is difficult to realize because of the small size of the targets, which cannot gather enough MRS probes to form aggregates and generate a difference in magnetic relaxation times. Therefore, the development of small molecule-targeted MRS is strongly dependent on changes in the interfacial structure of the probe, which modulates the proton transport behavior near the probe. Herein, functionalized graphene quantum dots (GQDs) consisting of GQDs with disulfide bonds, polyethylene glycol (PEG), and paramagnetic Gd3+ were used as the MRS probe to sense H2O2. The structure of GQDs changed after reacting with H2O2. The PEG assembled a tube for transmitting changes in GQDs via proton transport and thus enabled the magnetic relaxation response of the probe towards H2O2. Pentaethylene glycol was experimentally and theoretically proven to have the strongest ability to transport protons. Such a probe can be applied in the differentiation of healthy and senescent cells/tissues using in vitro fluorescent imaging and in vivo magnetic resonance imaging. This work provides a reliable solution for building a proton transport route, which not only enables the response of the MRS probe towards the targets but also demonstrates the design of carbon nanostructures with proton transport behaviors.

Low-Temperature and Catalyst-Free Plasma Synthesis of Plastics-Derived Graphene Quantum Dots

The advanced industrial, social, and technological developments in modern society have rendered the production of around 300 million tons of plastic annually, yet only 50% or even less are being recycled. Moreover, the current recycling process is limited to the conversion of plastic wastes (PWs) into hydrocarbon fuels, which also requires the use of high temperatures and energies, long reaction time, and high-cost platinum-based catalysts. Therefore, there is an urgent need to develop a more sustainable and environmentally friendly method to recycle these PWs and possibly into functional materials for diverse applications.We introduce non-equilibrium and low-temperature microplasma technologies to convert PWs into graphene quantum dots (GQDs) at ambient conditions without any additional toxic chemicals, expensive catalysts, and sophisticated vacuum technologies. The reactive species generated by the plasma enables not only rapid deconstruction of PWs into small hydrocarbons moieties, but also simultaneous reconstruction of nanographene domain and nucleation into GQDs. GQDs are zero-dimensional carbon nanomaterials with unique quantum confinement and edge effects, which are hybridized by sp2 carbon in a honeycomb network. The quantum confinement and edge effects bestow GQDs with unique, tunable, and stable photoluminescence (PL) properties. Coupled with the biocompatibility, low toxicity, large surface area, and chemical inertness, GQDs can be employed in various applications, including imaging, sensing, optoelectronics, drug delivery, catalysis, and energy related applications. Nevertheless, the current syntheses of GQDs still need the use of high temperatures, strong acids or reducing agents, long reaction time, and tedious synthesis procedures.Here the utilization of microplasma enables the degradation and conversion of various plastics into functional GQDs with well-controlled structures in one-step at ambient conditions and catalyst-free manner, alleviating the current drawbacks in the GQDs synthesis. Among various PWs, polyethylene terephthalate-derived GQDs (PET-GQDs) exhibit enticing and bright white emission under 365 nm UV irradiation with a Commission Internationale de l’Eclairage 1931 of (0.29, 0.35). Moreover, the colloidal PET-GQDs can be exploited for heavy metal ions detection with a low limit of detection of 8.4 nM, while the composite film state is usable as sensitive temperature tag from 10 – 80 °C and LED panel. Our work provides an insight into the novel technologies for PWs recycling into functional nanomaterials in cost-effective, scalable, and environmentally friendly way.

Recent Progress on Functionalized Graphene Quantum Dots and Their Nanocomposites for Enhanced Gas Sensing Applications.

Gas-sensing technology has witnessed significant advancements that have been driven by the emergence of graphene quantum dots (GQDs) and their tailored nanocomposites. This comprehensive review surveys the recent progress made in the construction methods and applications of functionalized GQDs and GQD-based nanocomposites for gas sensing. The gas-sensing mechanisms, based on the Fermi-level control and charge carrier depletion layer theory, are briefly explained through the formation of heterojunctions and the adsorption/desorption principle. Furthermore, this review explores the enhancements achieved through the incorporation of GQDs into nanocomposites with diverse matrices, including polymers, metal oxides, and 2D materials. We also provide an overview of the key progress in various hazardous gas sensing applications using functionalized GQDs and GQD-based nanocomposites, focusing on key detection parameters such as sensitivity, selectivity, stability, response and recovery time, repeatability, and limit of detection (LOD). According to the most recent data, the normally reported values for the LOD of various toxic gases using GQD-based sensors are in the range of 1-10 ppm. Remarkably, some GQD-based sensors exhibit extremely low detection limits, such as N-GQDs/SnO2 (0.01 ppb for formaldehyde) and GQD@SnO2 (0.10 ppb for NO2). This review provides an up-to-date perspective on the evolving landscape of functionalized GQDs and their nanocomposites as pivotal components in the development of advanced gas sensors.

Functionalized Graphene Quantum Dots (GQDs) based Label-Free Optical Fluorescence Sensor for CD59 Antigen Detection and Cellular Bioimaging

Functionalized Graphene Quantum Dots (GQDs) based Label-Free Optical Fluorescence Sensor for CD59 Antigen Detection and Cellular Bioimaging

A coumarin-modified graphene quantum dot-based luminogen for the detection of cysteine in aqueous media.

A biocompatible fluorescence sensor for cysteine detection receives wide appreciation recently, because of its importance in the medical field. Functionalized graphene quantum dots (GQDs) are recently emerging biocompatible quantum dots, which are considered as suitable candidates for biomolecule detection. Motivated by this concept, here we have developed a versatile fluorescent probe based on 3-aminocoumarin (AMC) functionalized GQDs for the detection of cysteine (Cys). Modification on GQD with AMC resulted in a stable fluorescent probe with an enhancement in quantum yield of about 84% and 40 nm redshift in emission peak compared with bare GQD. The modified GQD is then used for the sensitive and selective detection of cysteine in aqueous media. The detection of Cys within the linear range of 50 nM to 1.5 μM was achieved with a detection limit (LOD) of 0.86 nM. Here, the AMC-GQD exhibit a turn-off fluorescence sensing behavior. The quenching mechanism was also explored. The sensing process follows dynamic quenching mechanism, which is attributed to the photoinduced charge transfer from AMC-GQD to Cys. The Stern-Volmer plot, energy-level alignment obtained from cyclic voltammetry measurements and density functional theory predictions give a valid proof for this. Furthermore, the sensor was applied efficiently to the determination of Cys in real water samples.

Self-assembly of MOFs-like materials by Zn2+ and histidine functionalized graphene quantum dots for the efficient removal of VOCs simulants

Volatile organic compounds (VOCs) in the field of printing and packaging, have caused great harm to the environment. Therefore, the removal of volatile organic compounds (VOCs) is a hot topic, and metal-organic frameworks (MOFs) and graphene quantum dots (GQDs) have been applied in this field. However, improving the removal efficiency of different VOCs by using the two kinds of materials is still a great challenge. Herein, ZIF-8 like materials of Zn-His-GQDs were prepared by assembling Zn2+ and histidine functionalized GQDs (His-GQDs) in this work. The morphologies, structure and adsorption performances of Zn-His-GQDs were investigated. These results showed that mesoporous Zn-His-GQDs with a specific surface area of 63.3 m2·g−1 had similar structure to ZIF-8. When the content of Zn-His-GQDs was 200 mg, the equilibrium adsorption capacity for toluene solution of 500 mg·L−1 and ethyl acetate solution of 1600 mg·L−1 was 350 mg·L−1 and 669.44 mg·L−1, respectively. Due to channel filling, cation-π interaction, π-π interaction, hydrogen bond and high surface energy, Zn-His-GQDs exhibited a relative high removal efficiency for high concentration of toluene and ethyl acetate. The removal rate of Zn-His-GQDs on toluene and ethyl acetate after five cycles remained 59.80 % and 36.75 %, respectively. Moreover, this kind of MOFs like materials maintained stable structure during the adsorption in different pH solutions. Therefore, as-prepared Zn-His-GQDs with excellent adsorption performances for typical VOCs simulants in this work have potential application in the treatment of VOCs in the field of printing and packaging.

Poly-L-lysine functionalized graphene quantum dots embedded zirconium metal–organic framework-based fluorescence switch on-off-on nanoprobe for highly sensitive and selective detection of taurine

Taurine is now widely used as a novel diagnostic biomarker for cardiovascular disease. Unfortunately, engaged techniques for the analysis of taurine are suffering from low sensitivity, poor selectivity, and a tedious process. In this work, the poly-L-lysine functionalized graphene quantum dots embedded UiO-66@NH2 metal–organic framework (PLL-fGQDs@UiO-66@NH2 MOF) based turn ‘On-Off-On’ fluorescent nanoprobe was designed for taurine sensing. Initially, synthesized PLL-fGQDs, UiO-66@NH2 MOF, and PLL-fGQDs@UiO-66@NH2 MOF nanoprobe were confirmed using UV–Vis spectroscopy, FT-IR analysis, particle size analysis, fluorescence study, PXRD, SEM-EDAX, HR-TEM, etc. Here, anticipated PLL-fGQDs incorporation into UiO-66@NH2 MOF nanoprobe portrayed a highly fluorescent nanoprobe for taurine sensing. The copper (Cu2+) ions addition in the fluorescent nanoprobe resulted in fluorescence dampness followed by taurine addition showed the recovery of quenched fluorescence. Principally, it might be because of the greater binding affinity of Cu2+ ions towards taurine-containing oxygen atoms of a sulfonic group and the nitrogen atom of an amine group. The linear concentration range, limit of detection (LOD), and limit of quantification (LOQ) of taurine were found to be 5 ng/mL to 360 ng/mL, 2.91 ng/mL, and 8.84 ng/mL, respectively. It also provides a high selectivity towards taurine in the occurrence of interfering agents whereas practical applicability was assured by spiked artificial serum samples analysis. In conclusion, the designed PLL-fGQDs@UiO-66@NH2 MOF nanoprobe offers high sensitivity, selectivity, good stability, repeatability, and practicability. In the future, it can be used as a new nanoprobe for taurine recognition with improved performance than the traditional methods.

Graphene Quantum Dots for Multifaceted Diagnostics

Due to their unique physical and electronic properties as well as high biocompatibility and water solubility, functionalized graphene quantum dots (GQDs) have found utilization in a variety of biomedical applications. GQDs can serve as carriers for drugs and genes while tracing their delivery pathways in vitro and in vivo with their visible and near-infrared fluorescence. In addition to therapeutic applications, our recent work explores diagnostic modalities of these novel nanomaterials. GQDs synthesized bottom-up form a single glucosamine precursor, or top-down from reduced graphene oxide can serve as nanoscale temperature sensors for biological processes. They exhibit linear and reversible visible/NIR fluorescence quenching by up to 19.3 % in suspension with temperature increase form 25 to 49 ⁰C. A more pronounced trend is observed in HeLa cells with over 40% quenching in that temperature range. Our findings suggest that such deterministic response can serve as non-invasive reversible/photostable mechanism for temperature sensing in microscopic subcellular biological environments. Another diagnostic modality of GQDs involves their capability for magnetic resonance imaging. When doped with Mn2+ ions during their bottom-up synthesis, GQDs exhibit substantial r₂/r₁ relaxation parameter ratios of 11.19, showing potential as dual-mode T1 or T2 contrast agents. Their Gd3+-doped counterparts possess r₂/r₁ ratios of 1.148 with high r1 of 9.546 mM-1s-1 compared to commercial contrast agents, suggesting their utilization as T1 contrast agents. Given that doping did not affect their biocompatibility or fluorescence properties, such doped GQDs can serve as multimodal MR and fluorescence imaging agents. Metal-doped GQDs possess the capability ultrasonic contrast imaging that can be utilized for higher precision and deeper tissue diagnostic applications. They demonstrate high-contrast properties in ultrasound brightness mode by a factor of 10 surpassing undoped GQD structures. The successful imaging enhancement was observed in tissue phantom and animal tissue, suggesting that GQDs can be tracked by ultrasound imaging and used as contrast agents for the improvement of the deterministic power of this widely available imaging approach. GQD intrinsic fluorescence can itself serve as a non-invasive diagnostic sensing tool, as it can be affected by the binding of different drugs, genes and biomolecules to the GQDs. This optical sensing mechanism is used in our work for identifying trace quantities of cancer-generated genes for early personalized cancer detection. The sensor is prepared from GQDs complexed with the bait DNA sequence complementary to the target pancreatic cancer miRNA. It effectively discriminates between complementary single-stranded DNA sequences and random control genes with the sensitivity in the nanomolar range. Cancer gene detection is further verified by identifying both, the stem and the loop portions of the pancreatic cancer-generated pre-miR-132. Given the success of these different diagnostic applications, GQDs can be considered a highly perspective theragnostic tool for a variety of disease targets.

Probing the tunable optical properties of highly luminescent functionalized graphene quantum dots as downconverters for superior detection of ultraviolet radiation

Detection and utilization of ultraviolet (UV) radiation are of paramount importance as commonly used Si photodetectors and photovoltaic cells suffer from poor UV response. Herein, we demonstrate the applications of graphene quantum dots (GQDs) as downconverters to sensitize Si photodiodes for extended and enhanced UV detection down to 300 nm and facilitating distinct visible response to UV wavelength-specific excitation. Stable blue (B-) and orange-red (R-) emitting nitrogen functionalized GQDs, synthesized by cost-effective solvothermal method, exhibit high photoluminescence (PL) quantum yield (57–62%), strong UV absorption, and large Stokes shift (130–250 nm). A scalable threefold improvement in UV response (330 nm) with a relative enhancement factor of 200% is recorded from a Si photodetector externally sensitized with visible-blind B-GQDs. The engineered combination of B- and R-GQDs in a tandem fashion exhibits distinct visible emission and facilitates bare-eye recognition of UV sub-bands. The present study provides a new pathway of UV detection with or without integrated devices by employing thin layers of solution-processed GQDs.

Edge Modification and Site-Selective Functionalization of Graphene Quantum Dots: A Versatile Technique for Designing Tunable Optoelectronic and Sensing Devices.

This work successfully traces the imprints of zigzag/armchair-edge modification and site-selective functionalization by different chemical species in dictating the structural, electronic, and optical properties of low-symmetry structural isomers of graphene quantum dots (GQDs). Our time-dependent density functional theory-based computations reveal that the electronic band gap reduction is greater for zigzag-edge functionalization than for armchair-edge modification by chlorine atoms. The computed optical absorption profile of functionalized GQDs exhibits an overall red shift with respect to their pristine counterpart, with the shift being more pronounced at higher energies. Markedly, the optical gap energy is regulated more substantially by zigzag-edge chlorine passivation while the armchair-edge chlorine functionalization is more effective in altering the position of the most intense (MI) absorption peak. The MI peak energy is exclusively decided by the significant perturbation in the electron-hole distribution produced by the structural warping of the planar carbon backbone realized by edge-functionalization while the interplay between frontier orbital hybridization and structural distortion governs the energies of the optical gap. In particular, the enhanced tunability range of the MI peak in comparison to the optical gap variation signals that the structural warping plays a more decisive role in modulating the MI peak characteristics. The energy of the optical gap and the MI peak along with the charge-transfer character of the excited states is critically dependent on the electron-withdrawing capability and the site of the functional group. This comprehensive study is extremely crucial for promoting the application of functionalized GQDs in designing highly efficient tunable optoelectronic devices.

Gold nanoparticles modified reduced graphene oxide nanosheets based dual-quencher for highly sensitive detection of carcinoembryonic antigen

In the current scenario, the dominance of cancer is becoming a disastrous threat to mankind. Therefore, an advanced analytical approach is desired as the need of the hour for early diagnosis to curb the menace of cancer. In this context, the present work reports the development of nano surface energy transfer (NSET) based fluorescent immunosensor for carcinoembryonic antigen (CEA) detection utilizing protein functionalized graphene quantum dots (anti-CEA/amine-GQDs) and a nanocomposite of nanostructured gold and reduced graphene oxide (AuNPs@rGO) as energy donor-acceptor pair, respectively. The obtained AuNPs@rGO nanocomposite has been characterized by different advanced analytical techniques. The functionality of the biosensor depends on quenching the fluorescence of anti-CEA/amine-GQDs donor species by AuNPs@rGO acceptor species, followed by the gradual recovery of GQDs' fluorescence after CEA addition. The efficient energy transfer kinetics have been envisaged by utilizing the AuNPs@rGO nanocomposite as a dual-quencher nanoprobe that revealed improved energy transfer and quenching efficiency (∼62 %, 88 %) compared to AuNPs (∼43 %, 81 %) as a single quencher. Further, the developed biosensing platform successfully detected CEA biomarker with notable biosensing parameters, including a wider linear detection range (0.001–500 ng mL−1), fast response time (24 min), and a significantly low detection limit (0.35 pg mL−1).

On using non-Kekulé triangular graphene quantum dots for scavenging hazardous sulfur hexafluoride components

The goal of present study is to explore how the size and functionalization of graphene quantum dots (GQDs) affect their sensing capabilities. Specifically, we investigated the adsorption of SO2, SOF2, SO2F2, and SF6 on GQDs that were functionalized with –CH3, –COCH3, and –NH2. We used density functional theory to analyse the electronic properties of these functionalized GQDs and found that the functionalization significantly altered their electronic properties. For example, the B3LYP H-L gap of pristine triangulene was 3.9eV, while the H-L gap of functionalized triangulene ranged from 2.8 eV to 3.6 eV (using the B3LYP functional). Our results indicate that –NH2 functionalized phenalenyl and triangulene provide strong interaction with SO2, with adsorption energies of −0.429 eV and −0.427 eV, respectively. These adsorption properties exhibit physisorption, leading to high gas sensitivity and superior recovery time. The findings of this study provide new insights into the potential use of GQDs for detecting the decomposed constituents of sulfur hexafluoride, which can be beneficial for assessing the operation status of SF6 insulated devices. Overall, our calculations suggest that functionalized GQDs can be employed in gas insulated systems for partial discharge detection.