Graphene Quantum Dot Nanocomposites Research Articles

Biomemristic Behavior for Water-Soluble Chitosan Blended with Graphene Quantum Dot Nanocomposite.

Bionanocomposite has promising biomemristic behaviors for data storage inspired by a natural biomaterial matrix. Carboxylated chitosan (CCS), a water-soluble derivative of chitosan avoiding the acidic salt removal, has better biodegradability and bioactivity, and is able to absorb graphene quantum dots (GQDs) employed as charge-trapping centers. In this investigation, biomemristic devices based on water-soluble CCS:GQDs nanocomposites were successfully achieved with the aid of the spin-casting method. The promotion of binary biomemristic behaviors for Ni/CCS:GQDs/indium-tin-oxide (ITO) was evaluated for distinct weight ratios of the chemical components. Fourier transform infrared spectroscopy, Raman spectroscopy (temperature dependence), thermogravimetric analyses and scanning electron microscopy were performed to assess the nature of the CCS:GQDs nanocomposites. The fitting curves on the experimental data further confirmed that the conduction mechanism might be attributed to charge trapping–detrapping in the CCS:GQDs nanocomposite film. Advances in water-soluble CCS-based electronic devices would open new avenues in the biocompatibility and integration of high-performance biointegrated electronics.

A titanium dioxide/nitrogen-doped graphene quantum dot nanocomposite to mitigate cytotoxicity: synthesis, characterisation, and cell viability evaluation.

Titanium dioxide nanoparticles (TiO2 NPs) have attracted tremendous interest owing to their unique physicochemical properties. However, the cytotoxic effect of TiO2 NPs remains an obstacle for their wide-scale applications, particularly in drug delivery systems and cancer therapies. In this study, the more biocompatible nitrogen-doped graphene quantum dots (N-GQDs) were successfully incorporated onto the surface of the TiO2 NPs resulting in a N-GQDs/TiO2 nanocomposites (NCs). The effects of the nanocomposite on the viability of the breast cancer cell line (MDA-MB-231) was evaluated. The N-GQDs and N-GQDs/TiO2 NCs were synthesised using a one- and two-pot hydrothermal method, respectively while the TiO2 NPs were fabricated using microwave-assisted synthesis in the aqueous phase. The synthesised compounds were characterised using Fourier transform infrared (FTIR) spectroscopy, high-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM) and UV-visible spectrophotometry. The cell viability of the MDA-MB-231 cell line was determined using a CellTiter 96® AQueous One Solution Cell Proliferation (MTS) assay. The obtained results indicated that a monodispersed solution of N-GQDs with particle size 4.40 ± 1.5 nm emitted intense blue luminescence in aqueous media. The HRTEM images clearly showed that the TiO2 particles (11.46 ± 2.8 nm) are square shaped. Meanwhile, TiO2 particles were located on the 2D graphene nanosheet surface in N-GQDs/TiO2 NCs (9.16 ± 2.4 nm). N-GQDs and N-GQDs/TiO2 NCs were not toxic to the breast cancer cells at 0.1 mg mL−1 and below. At higher concentrations (0.5 and 1 mg mL−1), the nanocomposite was significantly less cytotoxic compared to the pristine TiO2. In conclusion, this nanocomposite with reduced cytotoxicity warrants further exploration as a new TiO2-based nanomaterial for biomedical applications, especially as an anti-cancer strategy.

Functionalized rGO Interlayers Improve the Fill Factor and Current Density in PbS QDs-Based Solar Cells.

Graphene-quantum dot nanocomposites attract significant attention for novel optoelectronic devices, such as ultrafast photodetectors and third-generation solar cells. Combining the remarkable optical properties of quantum dots (QDs) with the exceptional electrical properties of graphene derivatives opens a vast perspective for further growth in solar cell efficiency. Here, we applied (3-mercaptopropyl) trimethoxysilane functionalized reduced graphene oxide (f-rGO) to improve the QDs-based solar cell active layer. The different strategies of f-rGO embedding are explored. When f-rGO interlayers are inserted between PbS QD layers, the solar cells demonstrate a higher current density and a better fill factor. A combined study of the morphological and electrical parameters of the solar cells shows that the improved efficiency is associated with better layer homogeneity, lower trap-state densities, higher charge carrier concentrations, and the blocking of the minor charge carriers.

Antimicrobial Activity of Zinc Oxide–Graphene Quantum Dot Nanocomposites: Enhanced Adsorption on Bacterial Cells by Cationic Capping Polymers

Development of low-cost, high-performance antibacterial reagents is of critical importance in the face of increasing occurrence of bacterial resistance against conventional antibiotics. In the pres...

Electrogenerated chemiluminescence on smartphone with graphene quantum dots nanocomposites for Escherichia Coli detection

Graphene quantum dots (GQDs) have recently exhibited great potential in electrogenerated chemiluminescence (ECL) due to their catalyst and amplification effect towards luminophores. Here, we prepared GQDs nanocomposites to amplify the ECL signals in tris(2,2′-bipyridyl)ruthenium(II)/tripropylamine (Ru(bpy)32+/TPA) assay. Universal serial bus interface on smartphone was used as the excitation source for ECL. The luminescence signals were then captured by the smartphone camera and processed by a smartphone-based image analysis application (APP). By immobilizing layer of sensitive Escherichia coli (E.coli) antibody on the electrode surface, our smartphone-based ECL system exhibited excellent linear response towards detection of E.coli in the concentration range of 10 cfu/mL to 107 cfu/mL. Due to the vast popularity and portability of smartphone, the scope of application in our system would be able to greatly satisfy the need for point-of-care testing. Thus, in this work, the quantum dots-amplified luminescence detection was integrated with portable analytical devices, offering low-cost and real-time electrochemical analysis.

Construction of crosslinked chitosan/nitrogen-doped graphene quantum dot nanocomposite for hydroxyapatite biomimetic mineralization

Crosslinked Chitosan/nitrogen doped-graphene quantum dot nanocomposites (CCS/NGQD NC) with 10 wt% of glutaraldehyd as crosslinker were fabricated under ultrasonic cavitation. Structure and physicochemical properties of the prepared nanocomposites (NC) were systematically characterized by a number of techniques. The swelling capacity of the crosslinked films in the simulated intestinal (pH 7.4) media was evaluated. However, rate of water ingress of specimens was nearly same, but, the CCS/NGQD NC 8 wt% showed the more water absorption ability than the CCS. Bioactivity of the CCS and CCS/NGQD NCs were evaluated by studying their ability to form of apatite on their surface after soaking in a simulated body fluid (SBF) for 30 days. In images of field emission scan electron microscopy, small island-like agglomerated apatite deposited on the sample surface. Also, the pH fluctuation displayed that the hydroxyapatite was formed on the surface of the samples after one month of immersion in SBF. The finding showed that the CCS/NGQD NCs immersed into SBF had a better apatite-forming bioactivity compared with the CCS, which may be due to the high surface area, adequate function groups and appropriate swelling of the NCs. Such improved behaviors of CCS/NGQD NCs may have potential use in the bone tissue engineering.

Highly-stable write-once-read-many-times switching behaviors of 1D\u20131R memristive devices based on graphene quantum dot nanocomposites

One diode and one resistor (1D–1R) memristive devices based on inorganic Schottky diodes and poly(methylsilsesquioxane) (PMSSQ):graphene quantum dot (GQD) hybrid nanocomposites were fabricated to achieve stable memory characteristics. Current-voltage (I-V) curves for the Al/PMSSQ:GQDs/Al/p-Si/Al devices at room temperature exhibited write-once, read-many-times memory (WORM) characteristics with an ON/OFF ratio of as large as 104 resulting from the formation of a 1D–1R structure. I-V characteristics of the WORM 1D–1R device demonstrated that the memory and the diode behaviors of the 1D–1R device functioned simultaneously. The retention time of the WORM 1D–1R devices could be maintained at a value larger than 104 s under ambient conditions. The operating mechanisms of the devices were analyzed on the basis of the I–V results and with the aid of the energy band diagram.

One-Step Synthesis of Size-Tunable Gold@Sulfur-Doped Graphene Quantum Dot Nanocomposites for Highly Selective and Sensitive Detection of Nanomolar 4-Nitrophenol in Aqueous Solutions with Complex Matrix

In this study, a simple one-step synthesis procedure for the fabrication of a gold nanoparticle (Au NP)@sulfur-doped graphene quantum dot (Au@S-GQD) with tunable size was developed for the sensitive and selective detection of 4-nitrophenol in water and wastewater with a complex matrix. The particle size of two to six layered S-GQD is in the range of 1–7 nm with a mean diameter of 4.0 ± 0.5 nm. The S-GQD serves as a reducing agent for both Au ions and 4-nitrophenol reduction to generate Au@S-GQD nanocomposites as well as to produce the absorption signal of 4-aminophenol at 307 nm. The particle size of Au@S-GQD is tunable by simply adjusting the Au precursor concentration, and the mean diameter increases from 5 to 25 nm when the Au precursor concentration increases from 50 to 200 μM. Moreover, the Au@S-GQD nanocomposite exhibits good UV–visible absorption properties, and the change of wavelength ratio between 307 and the SPR peak of Au at 530 nm (A307/A530) is used to detect nanomolar levels of 4-nitropheno...

Multifunctional chitosan-magnetic graphene quantum dot nanocomposites for the release of therapeutics from detachable and non-detachable biodegradable microneedle arrays.

Biodegradable chitosan-magnetic graphene quantum dot (MGQD) nanocomposites were prepared and investigated for the release of small and large molecular weight (MWt) therapeutics from detachable and non-detachable biodegradable microneedle arrays. The presence of MGQDs in chitosan increased the electrical conductivity and biodegradation rate of chitosan while maintaining its mechanical properties. The detachable microneedle arrays were created by including a water-soluble ring of poly(ethylene glycol) (PEG) at the base of the microneedle, which enabled the rapid detachment of the microneedle shaft from the base. The PEG ring did not impede the microneedle array performance, with mechanical properties and a drug release profile of low MWt lidocaine hydrochloride similar to microneedle arrays without the ring. Without the PEG ring, the chitosan-MGQD microneedles were electrically conductive and allowed for electrically stimulated release of large MWt therapeutics which was challenging without the stimulation. These results demonstrate that chitosan nanocomposites containing MGQDs with intrinsic photoluminescent and supermagnetic properties are promising materials for developing multifunctional microneedles for targeted and tracked transdermal drug delivery.

Incorporation of graphene quantum dots to enhance photocatalytic properties of anatase TiO2

Abstract

TiO2 nanoparticles and TiO2@graphene quantum dots nancomposites as effective visible/solar light photocatalysts

In this paper, the photocatalytic activity of TiO2 NPs was improved twice: the first by engineering its morphology to narrow the band gap and to increase the surface area and the second by incorporating the modified TiO2 NPs with graphene quantum dots (GQDs) to reduce electron-hole (e−h+) recombination rate. Three visible/solar light responsive photocatalysts including TiO2 nanoparticles (NPs) and two nanocomposites of TiO2 @ GQDs were prepared. The photocatalytic activity of the prepared photocatalysts, GQDs, and P25 against Rhodamine B (RhB) under visible light or sunlight radiation was investigated. The prepared TiO2 NPs possessed very small particle size of 7.62 nm, large surface area of 236 m2 g−1, and narrow band gap of 2.41 eV. TiO2 NPs could harvest the visible/solar light for degrading RhB. The photocatalytic activity of TiO2 @ GQDs nanocomposites prepared by hydrothermal and ultrasound methods under visible light radiation are much better than that of TiO2 NPs. Using PL spectra, it was found that GQDs in the nanocomposites can hinder (or delay) e−h+ recombination and hence improve the photocatlytic performance of TiO2 NPs. The photocatalytic degradation of RhB over TiO2 NPs and TiO2 @ GQDs nanocomposites prepared by hydrothermal and ultrasound methods under visible light radiation followed the pseudo-first-order kinetics with the rate coefficients of 0.126, 0.170, and 0.149 min−1, respectively.

Organic electronic synapses with pinched hystereses based on graphene quantum-dot nanocomposites

Organic electronic synapses (e-synapses) based on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/graphene quantum dot (GQD) nanocomposites are fabricated by using a solution method. Current–voltage (I–V) curves for the devices under dual positive bias voltage sweeps show that the conductance with a pinched hysteresis gradually increased with increasing applied voltage, and those for the devices under dual negative bias voltage sweeps gradually decreased with increasing applied voltage, indicative of the fingerprint of e-synapses. The current in the devices decreases with increasing concentration of GQDs in the active layer, and the devices fabricated utilizing the ratio of PEDOT:PSS to GQDs of 1:0.4 shows the best performance among the e-synapses. The carrier transport and operating mechanisms of the e-synapses are described on the basis of both the I–V results and the trapping and escape of electrons from the GQDs.

Synergistic antibacterial activity of PEGylated silver–graphene quantum dots nanocomposites

The emergence of antibiotic-resistant bacteria is a major threat to world-wide public health. Functionalized nanoparticles could offer novel strategies in this post-antibiotic era. In this study, we developed nanocomposites of silver nanoparticles decorated with graphene quantum dots (Ag-GQDs) using pulsed laser synthesis. The nanocomposites were PEGylated, which increases their biocompatibility and solubility in aqueous solutions. The HR-TEM micrographs of bare GQDs show that their size is in the range of 1.6–4nm, and the lattice spacing is 0.214nm, which corresponds to the (100) lattice fringes of graphene. The antibacterial activity of Ag-GQDs was evaluated and compared to that of bare GQDs and commercial silver nanoparticles (Ag-NPs) against both Gram-negative and Gram-positive bacteria, using Pseudomonas aeruginosa and Staphylococcus aureus as model bacteria, respectively. Concentration values of 25 and 50μg/mL are required for Ag-GQDs to inhibit the growth of S. aureus and P. aeruginosa bacteria, respectively. The fractional inhibitory concentration (FIC) index is below 0.5 indicating that there is a synergistic effect between Ag-NPs and GQDs. Kirby–Bauer tests showed that Ag-GQDs inhibit P. aeruginosa and S. aureus, in contrast to bare GQDs and Ag-NPs alone. Cell viability of normal mammalian cells treated with Ag-GQDs showed that cell viability is maintained at 100% for cells incubated with Ag-GQDs. The decoration of Ag-NPs with GQDs minimizes their cytotoxicity in mammalian cells and increases their biocompatibility. Ag-GQDs have potential applications in the fabrication of antibacterial coatings, self-sterile textiles, and personal care products.

Biodegradable and conductive chitosan–graphene quantum dot nanocomposite microneedles for delivery of both small and large molecular weight therapeutics

Chitosan–graphene quantum dot nanocomposites are used in microneedle arrays for transdermal delivery of small and large molecular weight drugs.