Concentration Of Graphene Quantum Dots Research Articles

Carbon Nanostructured Immunosensing of Anti-SARS-CoV-2 S-Protein Antibodies.

The rampant spread and death rate of the recent coronavirus pandemic related to the SARS-CoV-2 respiratory virus have underscored the critical need for affordable, portable virus diagnostics, particularly in resource-limited settings. Moreover, efficient and timely monitoring of vaccine efficacy is needed to prevent future widespread infections. Electrochemical immunosensing poses an effective alternative to conventional molecular spectroscopic approaches, offering rapid, cost-effective, sensitive, and portable electroanalysis of disease biomarkers and antibodies; however, efforts to improve binding efficiency and sensitivity are still being investigated. Graphene quantum dots (GQDs) in particular have shown promise in improving device sensitivity. This study reports the development of a GQD-functionalized point-of-contamination device leveraging the selective interactions between SARS-CoV-2-specific Spike (S) Protein receptor binding domain (RBD) antigens and IgG anti-SARS-CoV-2-specific S-protein antibodies at screen-printed carbon electrode (SPCE) surfaces. The immunocomplexes formed at the GQD surfaces result in the interruption of the redox reactions that take place in the presence of a redox probe, decreasing the current response. Increased active surface area, conductivity, and binding via EDC/NHS chemistry were achieved due to the nanomaterial inclusion, with 5 nm, blue luminescent GQDs offering the best results. GQD concentration, EDC/NHS ratio, and RBD S-protein incubation time and concentration were optimized for the biosensor, and inter- and intra-screen-printed carbon electrode detection was investigated by calibration studies on multiple and single electrodes. The single electrode used for the entire calibration provided the best results. The label-free immunosensor was able to selectively detect anti-SARS-CoV-2 IgG antibodies between 0.5 and 100 ng/mL in the presence of IgM and other coronavirus antibodies with an excellent regression of 0.9599. A LOD of 2.028 ng/mL was found, offering comparable findings to the literature-reported values. The detection sensitivity of the sensor is further compared to non-specific IgM antibodies. The developed GQD immunosensor was compared to other low-oxygen content carbon nanomaterials, namely (i) carbon quantum dot (CQD), (ii) electrochemically reduced graphene oxide, and (iii) carbon black-functionalized devices. The findings suggest that improved electron transfer kinetics and increased active surface area of the CNs, along with surface oxygen content, aid in the detection of anti-SARS-CoV-2 IgG antibodies. The novel immunosensor suggests a possible application toward monitoring of IgG antibody production in SARS-CoV-2-vaccinated patients to study immune responses, vaccine efficacy, and lifetime to meet the demands for POC analysis in resource-limited settings.

Rapid Crystallization and Fluorescence of Poly(ethylene terephthalate) Using Graphene Quantum Dots as Nucleating Agents.

In this study, graphene quantum dots (GQDs) with a diameter of ~3 nm were successfully synthesized and incorporated into a poly(ethylene terephthalate) (PET) matrix to fabricate PET/GQDs nanocomposites. The impact of GQDs on the crystallization and thermal stability of the PET/GQDs nanocomposites was investigated. It was observed that the addition of only 0.5 wt% GQDs into the nanocomposites resulted in a significant increase in the crystallization temperature (peak temperature) of PET, from 194.3 °C to 206.0 °C during the cooling scan process. This suggested that an optimal concentration of GQDs could function as a nucleating agent and effectively enhance the crystallization temperature of PET. The isothermal crystallization method was employed to analyze the crystallization kinetics of the PET/GQDs nanocomposites, and the data showed that 0.5 wt% GQDs significantly accelerated the crystallization rate. Furthermore, the incorporation of GQDs into the PET matrix imparted photoluminescent properties to the resulting PET/GQDs nanocomposites. The PET crystals with GQDs as crystal nuclei and the crazes caused by defects played a vital role in isolating and suppressing the concentration quenching of GQDs. This effect facilitated the detection of defects in PET.

Chemically derived graphene quantum dots for high-strain sensing

Graphene quantum dots (GQDs) refer to graphene fragments with a lateral dimension typically less than 100 nm, which possess unique electrical and optical properties due to the quantum confinement effect. In this study, we demonstrate that chemically derived graphene quantum dots show great potential for making highly stretchable and cost-effective strain sensors via an electron tunneling mechanism. Stretchable strain sensors are critical devices for the field of flexible or wearable electronics which are expected to maintain function up to high strain values (> 30%). However, strain sensors based on conventional materials (i.e. metal or semiconductors) or metal nanoparticles (e.g. gold or silver nanoparticles) only work within a small range of strain (i.e. the former have a working range < 1% and the latter < 3%). In this study, by simply dropcasting solution-processed GQDs between the interdigitated electrodes on polydimethylsiloxane, we obtained devices that can function in the range from 0.06% to over 50% tensile strain with both the sensitivity and working range conveniently adjustable by the concentration of GQDs applied. This study provides a new concept for practical applications of GQDs, revealing the potential of this material for smart applications such as artificial skin, human-machine interfaces, and health monitoring.

Graphene quantum dots (GQDs) induce thigmotactic effect in zebrafish larvae via modulating key genes and metabolites related to synaptic plasticity

Graphene quantum dots (GQDs) recently gain much attention for its medicinal values in treating diseases such as neurodegeneration and inflammations. However, owing to the high permeability of GQDs across the blood-brain barrier, whether its retention in the central nervous system (CNS) perturbs neurobehaviors remains less reported. In the study, the locomotion of zebrafish larvae (Danio rerio) was fully evaluated when administrated by two GQDs in a concentration gradient, respectively as reduced-GQDs (R-GQDs): 150, 300, 600, 1200, and 2400 g/L, and graphene oxide QDs (GOQDs): 60, 120, 240, 480, and 960 g/L. After exposure, the larvae were kept for locomotion analysis within one week’s depuration. Substantial data showed that the basal locomotor activity of zebrafish larvae was not significantly changed by both two GQDs at low concentrations while weakened greatly with the increase of concentrations, and the total ATP levels of zebrafish larvae were also found to decrease significantly when exposed to the highest concentrations of GQDs. Next, the thigmotactic effect was observed to be remarkably induced in larvae by both two GQDs at any concentrations during exposure, and remained strong in larvae treated by high concentrations of R-GQDs after 7 days’ depuration. To be noted, we found that GQDs affected the synaptic plasticity via downregulating the mRNA levels of NMDA and AMPA receptor family members as well as the total glutamine levels in zebrafish larvae. Together, our study presented robust data underlying the locomotor abnormalities aroused by GQDs in zebrafish larvae and indicated the potential adverse effects of GQDs on synaptic plasticity.

Graphene quantum dot doped viscoelastic lyotropic liquid crystal nanocolloids for antibacterial applications.

Graphene quantum dots (GQDs) are prepared and characterized via X-ray diffraction (XRD), UV-Visible spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM) and photoluminescence (PL). GQDs are doped (5 mg and 10 mg) in the lyotropic liquid crystalline (LLC) lamellar and hexagonal phases to prepare GQD/LLC nanocolloids. Polarizing optical microscopy and X-ray diffraction measurement reveals that GQDs do not affect the lamellar and hexagonal LLC structures and may organize on their interface. Pure LLC phases and nanocolloids are studied for steady and dynamic rheological behavior. LLC phases and GQD/LLC nanocolloids possess shear thinning and frequency dependent liquid viscoelastic behavior. A complex moduli study of LLCs and GQD/LLC nanocolloids is carried out which indicates the gel to viscous transition in LLCs and GQD/LLC nanocolloids as a function of frequency. LLC phases and GQD/LLC nanocolloids are tested for antibacterial activity against Listeria ivanovii. The effect of surfactant concentration, LLC phase geometry and GQD concentration has been studied and discussed. A probable mechanism for the strong antimicrobial activity of LLCs and GQD/LLC nanocolloids is presented considering intermolecular interactions. The viscoelastic behavior and strong antibacterial activity (inhibition zone 49.2 mm) of LLCs and GQD/LLC nanocolloids make them valuable candidates for lubrication, cleaning, cosmetics and pharmaceutical applications.

Impact of Graphene Quantum Dots on Gas Foam Stability

This study presents a new application of coal-derived graphene quantum dots (GQD) in stabilizing surfactant-based foams. The methane foam generated by the surfactant itself is susceptible to rapid collapse due to various factors. When the GQDs are added to the surfactant in a mass ratio between 1:8 to 1:16, they self-assemble at the lamella and prevent liquid drainage and coalescence. The nanofluid composed of GQD and amphoteric surfactant reduced both the oil–brine and brine–gas interfacial tension to a greater extent compared to the surfactant alone. In addition, GQD helped alter the rock wettability to strongly water-wet conditions, as compared to weakly water-wet conditions with pure surfactant. The foam formed by the nanofluid was made up of smaller uniformly shaped bubbles with a thick lamella, whereas the foam formed by the surfactant had large polyhedral shaped bubbles with a thin lamella. The transmission electron microscope micrographs of the nanofluid emulsion with crude oil showed that the GQDs are highly interfacially active and tend to assemble on the surface of the oil droplets. Next, the foam stability and strength were investigated with pure surfactant and nanofluid in high salinity brine using water- and oil-wet sandpacks at reservoir conditions relevant to the Bakken formation. The dependence of foam half-life and steady-state apparent viscosity was studied as a function of surfactant and GQD concentration, gas fraction, flow rate, and brine salinity. It was observed that the addition of GQD increases both the foam half-life and steady-state apparent viscosity compared to pure surfactant. This work paved the way for the application of novel carbonaceous nanoparticles under challenging conditions where traditional nanoparticles cannot be used.

The aggregation of multiple miR-29a cancer biomarkers induced by graphene quantum dots: Molecular dynamics simulations

MicroRNAs (miRNAs) are small non-coding RNAs that play a role in regulating gene expression. MiRNAs are focused on as potential cancer biomarkers due to their involvement in the cancer development. New effective techniques for extracting miRNA from a biological matrix is important. Recently, graphene quantum dots (GQDs) have been used to detect DNA/RNA in many sensor platforms, but the application in miRNA extraction remains limited. To extract miRNAs, the miRNA adsorption and desorption on GQD are the key. Thus, in this work, the adsorption mechanism of excess miRNA on GQD in solution is revealed using Molecular dynamics simulations. The miRNA assemblies on one and two GQDs were studied to explore the possibility of using GQD for miRNA extraction. The folded miR-29a molecule, one of key cancer biomarkers, is used as an miRNA model. Three systems with one (6miR) and two GQDs (with parallel (6miR_2GP) and sandwich (6miR_2GS) organisations) in six-miR-29a solution were set. The data show excess miR-29a can reduce the miR-29a-GQD binding efficiency. The opening of intrabase pairing of GQD-absorbed miR-29a facilitates the interbase coupling resulting in the self-aggregation of miR-29a. The GQD organisation also affects the miR-29a adsorption ability. The additional GQDs result in the tighter miR-29a adsorption which can retard the miR-29a desorption. The proper GQD concentration is thus important to successfully collect all miR-29a and accommodate the easy miR-29a dissociation. Our results can be useful for a design of DNA probe and choosing decent nanosized GRA concentration for experimental setups.

Alone and combined toxicity of ZnO nanoparticles and graphene quantum dots on microalgae Gymnodinium.

Investigation of ZnO nanoparticles (nano-ZnO) and graphene quantum dots (GQDs) toxicology on dinoflagellate Gymnodinium helps to understand the effects of different surface characteristic nanoparticles on marine algae. The growth and biological responses of the algae exposed to 1, 10, 20mg L-1 nano-ZnO and GQDs in f/2 media were explored. Nano-ZnO showed slight effects on algal cells growth, while the growth inhibition rates of Gymnodinium increased as GQDs concentration increasing. Both nanoparticle treatments induced accumulation of reactive oxygen species and activated intracellular antioxidant defensive system, including SOD and ATPase, which were related to the two nanoparticles concentration. Under combined exposure of nano-ZnO and GQDs, the inhibitory effects decreased compared to the single GQDs and showed antagonistic effect. The addition of nano-ZnO could decrease the toxicity of GQDs due to aggregation and sedimentation interaction between nanoparticles. The morphologic change of the cells observed by SEM proved that nanoparticles adsorbed onto the cell surfaces and caused the cell shrinkage.

Green fabrication of graphene quantum dots from cotton with CaSiO3 nanostructure and enhanced photocatalytic performance for water treatment

Perovskite nanostructures have become one of the most alluring classes of materials because of their structure and properties, which have revolutionized many areas of electronics, optoelectronics, and photonics. In this research, CaSiO3 nanostructures have been prepared by hydrothermal synthesis as profitable and light-active materials for photocatalytic activities. The photocatalytic procedure is an eco-friendly method, which is recognized as an effective alternative for the degradation of multiple hazardous materials. In this regard, photocatalytic properties of oxide perovskite have been developed by effective incorporation of CaSiO3 nanostructures with graphene quantum dots (GQDs) under facile green low-cost hydrothermal conditions. The impact of two factors, including diverse varieties of surfactants and concentration of GQDs, was surveyed through XRD, FESEM images, and diffuse reflectance spectroscopy (DRS) on purity, structure, and photocatalytic performance. The results demonstrated that the CaSiO3/GQDs in high-level concentration showed higher visible-light photocatalytic activity. Besides, the kinetics of photocatalytic reactions was investigated, and the outcomes showed that higher photocatalytic performance possessed a higher reaction rate coefficient.

High-performance perovskite solar cells using the graphene quantum dot–modified SnO2/ZnO photoelectrode

Regardless of the excellent improvement in the assembling of perovskite solar cells (PSCs), the photon-harvesting performance of these devices is inadequate through the disproportionate recombination of generated charge carriers. The improvement of the charge carrier mobility can significantly reduce the recombination and help the perovskite devices reach the theoretical power conversion efficiency (PCE). The modification of charge selective contacts is one of the most effective approaches for reducing the carrier recombination. Herein, we introduce a facile and effective doping engineering approach based on graphene quantum dots (GQDs) for the modification of the SnO2/ZnO bilayer electron transport layer (ETL). A comparative study of perovskite films deposited on SnO2/ZnO layers with altered concentrations of GQDs was employed to significantly enhance the opto-electronic properties. The integration of GQDs into the ETL indicates a potential for improving the charge carrier transporting in PSCs. Overall, the PSC using the 4% GQD-modified ETL yields a PCE of 19.81% with a striking open-circuit voltage (VOC) of 1.17 V. Besides, 4% GQD-modified ETL-based devices enhance the long-term ambient and thermal stability.

Structure, morphology and modelling studies of polyvinylalcohol nanocomposites reinforced with nickel oxide nanoparticles and graphene quantum dots

Nickel oxide (NiO) nanoparticles (NPs) and graphene quantum dots (GQDs) reinforced polyvinyl alcohol (PVA) nanocomposite films were prepared using a solution casting technique. The physicochemical characteristics of PVA/NiO/GQDs (PNG) nanocomposite films were studied using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FESEM). The obtained PNG nanocomposite films showed good mechanical flexibility and improved tensile strength. The influence of nanofiller concentrations on PNG nanocomposite film. The obtained results demonstrate an increase in the activation energy (Ea) up to PNG3 upon increasing the GQDs concentration and thereafter, its decreases. The fundamental interactions of the constituents of PNG nanocomposite film were investigated using density functional theory (DFT). This study on electronic structure reveals that the PVA model indirectly interacts with GQDs through the NiO model. This configuration is favoured in terms of interaction energy (−78 kJ/mol) compared to the one in which PVA interacts directly with the GQDs model.

Resonant random laser emission from graphene quantum dots doped dye solution

In this letter, we report on the fabrication of dye doped graphene quantum dots (GQDs) random lasers with resonant feedback that are optically pumped with nanosecond pulses. GQDs, synthesized by the pyrolysis of citric acid, are used as the scattering elements in an ethylene glycol solution of rhodamine B dye. It is experimentally demonstrated that using GQDs instead of titania nanoparticles not only results in the multimode random lasing emission, but also increases the operating lifetime, significantly. We observe discrete lasing modes with subnanometer linewidths at the pump fluences above the threshold. Furthermore, the dependences of the random lasing emission characteristics on the pumping position and concentration of GQDs are investigated, experimentally.

Theoretical Evaluation of DNA Genotoxicity of Graphene Quantum Dots: A Combination of Density Functional Theory and Molecular Dynamics Simulations.

Owing to their unique morphology, ultrasmall lateral sizes, and exceptional properties, graphene quantum dots (GQDs) hold great potential in many applications, especially in the fields of electrochemical biosensors, bioimaging, drug delivery, gene delivery, etc. Their biosafety and potential genotoxicity to human and animal cells have been a growing concern in recent years. Especially, the potential DNA damage caused by GQDs is very crucial but still unclear. In this study, the effect of GQDs on DNA damage has been evaluated by a combination of molecular dynamics (MD) simulations and density functional theory. Our results demonstrate that the DNA damaging mechanism of GQDs depends on the size of GQDs. The small GQDs (seven benzene rings) tend to enter into the interior of DNA molecules and cause a DNA base mismatch. The relatively large GQDs (61 benzene rings) tend to adsorb onto the two ends of a DNA molecule and cause DNA unwinding. Due to the strong interaction between guanine (G) and GQDs, the effect of GQDs is much larger on G than on the other three bases (A, C, and T). In addition, the concentration of GQDs could also affect the results of DNA damaging.

High-flux nanofiltration membranes prepared with β-cyclodextrin and graphene quantum dots

In this study, high flux β-CD/GQDs nanofiltration (NF) membranes were prepared by interfacial polymerization with β-cyclodextrin (β-CD) as the aqueous monomer, graphene quantum dots (GQDs) as the additive and trimesoyl chloride (TMC) as the organic monomer. The addition of GQDs not only modulated the membrane surface properties, but also led to the formation of a loose selective layer due to the nonspecific hydrogen bonding interactions between GQDs and β-CD. The pure water flux of the β-CD/GQDs NF membranes increased from 122.2 to 474.7 L/m2h (at the pressure of 0.1 MPa) when the concentration of GQDs increased from 0 to 0.5 wt%, almost 3.9 times higher than that of the pristine β-CD membrane. The dye rejection of Eriochrome Black T and Congo Red essentially remained above 93.0%. The β-CD/GQDs NF membranes with superior filtration performance and excellent chlorine resistance hold great promise in dye wastewater treatment.

Polysulfone/graphene quantum dots composite anion exchange membrane for acid recovery by diffusion dialysis

The advancement in membrane-based separation technologies offers advantages over traditional ways. Recovery of acid from acidic waste stream is an important issue to be solved by greener route. Diffusion dialysis using anion exchange membranes (AEMs) is an energy-intensive and environment friendly process to be taken forward. Herein, we report the eco-friendly route for chloromethylation of polysulfone using chloromethyl ethyl ether (CMEE). Effect of chloromethyl ethyl ether concentration, reaction temperature, and reaction time are investigated to get maximum tethered chloromethyl group and high yield of product. Series of chloromethylated polysulfone membranes are prepared with different concentrations of graphene quantum dots (GQDs) followed by quaternization using trimethylamine. The prepared membranes are characterized by their water content, transport properties, and stabilities. Composite membranes show enhanced water uptake, ion exchange capacity, and mechanical stability compared to that of pristine membrane. Interestingly, to address the environmental impact of acids present in industrial waste, AEMs are employed for acid recovery from model waste at higher concentrations of acid and salt using diffusion dialysis. For prepared membranes, 35.5–47.5% acid recovery has been achieved in presence of metal ions. SCE-1.0 (1.0 wt % GQD/ QPSU) membrane shows the highest acid recovery (47.5%) among the membranes. Composite membranes suggest their potential utility in acidic effluent treatment via diffusion dialysis.

Hydrothermal synthesis of quantum dots dispersed on conjugated polymer as an efficient electrodes for highly stable hybrid supercapacitors

Hydrothermal synthesis of graphene quantum dots (GQDs) composited with conjugated polymer were investigated the high specific capacitance and cyclic stability of supercapacitor. The situ chemical polymerization method was employed to synthesize the polypyrrole - graphene quantum dots (PPY-GQDs) composite at different concentrations of GQDs. The size, morphology and structural phase of the PPY- GQDs composites was studied by using Transmission Electron Microscope (TEM), Field Emission Scanning Electron Microscope (FESEM), Atomic Force Microscope (AFM) and X-ray diffractometry (XRD) techniques respectively. The optical and electrochemical measurements were carried out by using Ultraviolet-Visible (UV--Vis) Absorption spectroscopy, Photoluminescence Spectroscopy (PL) and electrochemical work station. The cyclic voltammetry (CV) results show enhanced current density and area of CV loop with increasing scan rate and the concentration of GQDs. The Supercapacitor was fabricated by two electrodes owns a high energy density 67.8 Wh/kg and 93 Wh/kg at a power density of 1210 W/kg and 1430 W/kg for PGC1 and PGC3 composites. The highest specific capacitance values 467.32 and 647.54F/g are achieved by PGC1 and PGC3 composite compare to pure PPY. The PPY-GQDs composites achieved excellent cycle stability until the 2000 cycle. Thus, it demonstrates that GQDs is playing a unique and important role in improving the performance of a hybrid supercapacitor device.

Mechanisms behind excitation- and concentration-dependent multicolor photoluminescence in graphene quantum dots.

Despite numerous efforts, the mechanism behind multicolor photoluminescence (PL) in graphene quantum dots (GQDs) is still controversial. A deep insight into the origin of the multicolor emissions in GQDs is quite necessary for modulating their luminescence to facilitate the better use of this fluorescent material. Herein, GQDs with amino, carboxyl, and ammonium carboxylate groups were synthesized. The as-prepared GQDs exhibited intriguing excitation- and concentration-dependent multicolor PL characteristics. By regulating the excitation wavelength or concentration of GQDs, specific luminescence colors including blue, cyan, green, yellow, and even orange can be obtained. Systematic structural and optical studies indicated that the graphene basal plane and different functional groups dominantly exhibited nN 2P-σ*, π-π*, nO 2p-π* (-COOH), nO 2p-π* (-COO-) and nN 2p-π* electronic transitions, which appeared as multi-fluorescent centers that gave rise to the excitation-dependent multicolor PL. The occurrence of different types of electronic transitions and their color emissions were proved by pH-dependent PL measurements. In addition, systematic optical and morphology analyses revealed that GQDs could self-assemble into J-type aggregates with different morphologies and sizes as the concentration increased, and the observed concentration-dependent multicolor PL can be ascribed to aggregation-mediated energy level reconstruction in GQDs. Our findings further suggest that the competition among various fluorescent centers and self-aggregation processes dominated the luminescent properties of GQDs. This work will contribute to understand the origins of excitation- and concentration-dependent multicolor emissions in GQDs, which is also highly instructive for broadening the application fields of GQDs.

Graphene Quantum Dots in the Game of Directing Polymer Self-Assembly to Exotic Kagome Lattice and Janus Nanostructures.

Graphene quantum dots (GQDs) are the harbingers of a paradigm shift that revitalize self-assembly of the colloidal puzzle by adding shape and size to the material-design palette. Although self-assembly is ubiquitous in nature, the extent to which these molecular legos can be engineered reminds us that we are still apprenticing polymer carpenters. In this quest to unlock exotic nanostructures ascending from eventual anisotropy, we have utilized different concentrations of GQDs as a filler in free-radical-mediated aqueous copolymerization. Extensive polymer grafting over the geometrically confined landscape of GQDs (0.05%) bolsters crystallization instilling a loom which steers interaction of polymeric cilia into interlaced equilateral triangles with high sophistication. Such two-dimensional (2D) assemblies epitomizing the planar tiling of "Star of David" forming a molecular kagome lattice (KL) without metal templation evoke petrichor. Interestingly, a higher percentage (0.3%) of GQDs allow selective tuning of the interfacial property of copolymers breaking symmetry due to surface energy incongruity, producing exotic Janus nanomicelles (JNMs). Herein, with the help of a suite of characterizations, we delineate the mechanism behind the formation of the KL and JNMs which forms a depot of heightened drug accretion with targeted delivery of 5-fluorouracil in the colon as validated by gamma scintigraphy studies.

Unravelling the Aptamer-Analyte Interaction Dynamics through Fluorescence Quenching in Graphene Quantum Dots (GQDs) Based Homogeneous Assays.

Graphene quantum dots (GQDs) are used here as a biosensing platform for the recognition of the major food contaminant ochratoxin A (OTA), with a fluorescently labelled DNA aptamer (FAM OTA aptamer) functioning as the biorecognition element. The detection principle lies in the formation of noncovalent interactions between the FAM OTA aptamer and the GQD surface, and the consequent fluorescence quenching. The further change in the fluorescence signal, induced by the formation of the FAM OTA Aptamer/OTA conjugate during the detection step, could then be correlated to the presence and concentration of the target analyte. Upon tuning the concentration of GQDs, a switch in the biorecognition mechanism occurred. Specifically, while a lower GQD concentration (0.060 mg/mL) resulted in a restoration of the fluorescence intensity upon incubation with OTA, a higher GQD concentration (0.150 mg/mL) provided a further quenching of the final fluorescence intensity. Upon further calibration study, it was discovered that the latter mechanism provided a better option in terms of linearity of response, detection limit and selectivity.

Charge transport and electron recombination suppression in dye-sensitized solar cells using graphene quantum dots

Abstract In this study, TiO2 photoelectrodes were sensitized in different concentration of Graphene Quantum Dots (GQDs) solution to enhance photovoltaic performance and charge transport of DSSC. The performance of pristine TiO2 and TiO2-GQDs photoelectrodes were compared to investigate the effect of GQDs incorporation in DSSC. It was found GQDs increased light absorption of TiO2 photoelectrode at visible spectrum in the range of λ = 375 nm to λ = 600 nm, resulting highest current–density, Jsc and photon-to-current conversion efficiency, Ƞc. Solar cell sensitized in 7.5 mg/ml concentration of GQDs known as (PG 7.5) cell shown the highest reading by 15.49 mA cm−2 and 6.97%, which indicated an improvement by 28.07% and 70.83% for Jsc and Ƞ compare to pristine TiO2 DSSC at 12.10 mA cm−2 and 4.08%. Photoluminescence property own by GQDs may enhance photon emission to visible region when uv-ray excited on solar cell. Thus, generate more electron-hole pairs in the photoelectrode and enhance the photovoltaic parameters of DSSC. PG 7.5 cell also exhibited lowest series resistance (Rs) of 36.60 Ω, highest charge transfer resistance (Rct2) of 41.98 Ω and electron lifetime of 6.33 ms among other DSSC. These possibly due to suppression of recombination between TiO2/dye/electrolyte interfaces. Hence, resulting highest charge collection efficiency (CCE) of 53.42%. The EIS analysis confirmed the PV performance of the best cell of PG 7.5 since the same cell also generated the best photon-current conversion efficiency (PCE). This study revealed GQDs can enhanced photovoltaic parameter and charge collection efficiency of DSSC.