Bioinspired graphene-based metal oxide nanocomposites for photocatalytic and electrochemical performances: an updated review

Considering the rapidly increasing population, the development of new resources, skills, and devices that can provide safe potable water and clean energy remains one of the vital research topics for the scientific community. Owing to this, scientific community discovered such material for tackle this issue of environment benign, the new materials with graphene functionalized derivatives show significant advantages for application in multifunctional catalysis and energy storage systems. Herein, we highlight the recent methods reported for the preparation of graphene-based materials by focusing on the following aspects: (i) transformation of graphite/graphite oxide into graphene/graphene oxide via exfoliation and reduction; (ii) bioinspired fabrication or modification of graphene with various metal oxides and its applications in photocatalysis and storage systems. The kinetics of photocatalysis and the effects of different parameters (such as photocatalyst dose and charge-carrier scavengers) for the optimization of the degradation efficiency of organic dyes, phenol compounds, antibiotics, and pharmaceutical drugs are discussed. Further, we present a brief introduction on different graphene-based metal oxides and a systematic survey of the recently published research literature on electrode materials for lithium-ion batteries (LIBs), supercapacitors, and fuel cells. Subsequently, the power density, stability, pseudocapacitance charge/discharge process, capacity and electrochemical reaction mechanisms of intercalation, and conversion- and alloying-type anode materials are summarized in detail. Furthermore, we thoroughly distinguish the intrinsic differences among underpotential deposition, intercalation, and conventional pseudocapacitance of electrode materials. This review offers a meaningful reference for the construction and fabrication of graphene-based metal oxides as effective photocatalysts for photodegradation study and high-performance optimization of anode materials for LIBs, supercapacitors, and fuel cells.

One-Pot Solvothermal Synthetic Route of a Zinc Oxide Nanoparticle-Decorated Reduced Graphene Oxide Nanocomposite: An Advanced Material with a Novel Anticancer Theranostic Approach

This study focuses on a one-pot solvothermal synthetic route for the preparation of uniformly decorated zinc oxide nanoparticles on the surface of reduced graphene oxide (rGO/ZnO-NC) by using Andrographis paniculata leaf aqueous extract as an eco-friendly reducing agent. After characterizing the samples by different physical and chemical techniques, the anticancer activity of the synthesized rGO/ZnO-NC was examined on two human cancerous cell lines (HCT116 and A549) and one normal cell line (hMSCs). The MTT assays revealed that rGO/ZnO-NC exhibited dose-dependent cytotoxicity at a maximum concentration range of 10 ppm and the viability of the cells was drastically decreased to 95-96%. Measurement of reactive oxygen species (ROS) generation and Annexin V-FTIC staining assay revealed that rGO/ZnO-NC induced apoptosis in HCT116 and A549 cell lines. Thus, this study shows that the green-synthesized rGO/ZnO-NC has great potential in developing an efficacious novel therapeutic agent for cancers.

Efficient One-Pot Solvothermal Synthesis and Characterization of Zirconia Nanoparticle-Decorated Reduced Graphene Oxide Nanocomposites: Evaluation of Their Enhanced Anticancer Activity toward Human Cancer Cell Lines

This study mainly deals with an effective one-pot solvothermal synthetic pathway for the preparation of uniformly dispersed zirconium oxide nanoparticles on the flattened rough surface of reduced graphene oxide (ZrO₂/rGO NCs) using the aqueous leaf extract of Andrographis paniculata. After obtaining detailed information on the preparation and characterization, the anticancer activity of the synthesized ZrO₂/rGO nanocrystals (NCs) was evaluated on two human cancer cell lines (A549 and HCT116) along with one normal human cell line (hMSC). The 3-[4,5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide assays revealed that ZrO₂/rGO NCs exhibited a dose-dependent cytotoxicity pattern. The cell viability (%) drastically decreases up to 96-98% after exposure to an optimal concentration of 10 ppm nanocomposites. Analysis of both the reactive oxygen species generation and the Annexin V-FTIC staining assays reveal that ZrO₂/rGO NCs have the ability to induce apoptosis in A549 and HCT116 cell lines. Thus, the green synthesis of ZrO₂/rGO NCs shows potential in developing efficient therapeutic agents for cancer therapy.

Melatonin: Potential avenue for treating iron overload disorders

Iron overload as a highly risk factor, can be found in almost all human chronic and common diseases. Iron chelators are often used to treat iron overload; however, patient adherence to these chelators is poor due to obvious side effects and other disadvantages. Numerous studies have shown that melatonin has a high iron chelation ability and direct free radical scavenging activity, and can inhibit the lipid peroxidation process caused by iron overload. Therefore, melatonin may become potential complementary therapy for iron overload-related disorders due to its iron chelating and antioxidant activities. Here, the research progress of iron overload is reviewed and the therapeutic potential of melatonin in the treatment of iron overload is analyzed. In addition, studies related to the protective effects of melatonin on oxidative damage induced by iron overload are discussed. This review provides a foundation for preventing and treating iron homeostasis disorders with melatonin.

The Anticancer Efficacy of Thiourea-Mediated Reduced Graphene Oxide Nanosheets against Human Colon Cancer Cells (HT-29)

The current research focuses on the fabrication of water-soluble, reduced graphene oxide (rGO) employing thiourea (T) using a simple cost-effective method, and subsequently examining its anticancer characteristics. The cytotoxicity caused by graphene oxide (GO) and T-rGO is investigated in detail. Biological results reveal a concentration-dependent toxicity of GO and T-rGO in human colon cancer cells HT-29. A decrease in cell viability alongside DNA fragmentation is observed. Flow cytometry analysis confirms the cytotoxic effects. The novelty in this work is the use of raw graphite powder, and oxidants such as KMNO₄, NaNO₃, and 98 percent H₂SO₄ to produce graphene oxide by a modified Hummers method. This study demonstrates a simple and affordable procedure for utilising thiourea to fabricate a water-soluble reduced graphene oxide, which will be useful in a variety of biomedical applications.

Electrochemical sensor to detect terbutaline in biological samples by a green agent

In this research, reduced graphene oxide (RGO) which is a form of graphene oxide (GO) was formed through a reduction process using a "green agent" called Ascorbic acid (AA). RGO was then modified on the surface of the glassy carbon electrode (GCE) to generate RGO/GCE (an advanced electrode). The RGO/GCE was then used to detect Terbutaline (TB) in urine samples of volunteer athletes (n = 5) using well-known spectrophotometric analyses including X-ray diffraction analysis (XRD), Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible Spectroscopy (UV-Vis), and Raman and electrochemical methods using voltammetric analyses such as differential pulse anodic stripping voltammetry (DP-ASV) and cyclic voltammetry (CV). Comparing various analysis methods using RGO/GCE to detect TB in human urine samples, voltammetric analysis specifically DP-ASV demonstrated higher sensitivity and selectivity in detecting TB than spectrophotometric analyses. Thus, in this study, several factors that would affect the voltammetric signals such as pH and interferents were evaluated and the electroactive surface area was also calculated. Our findings indicated that the RGO/GCE showed excellent repeatability, reproducibility, and long-term stability suggesting that TB could be detected more effectively using RGO/GCE than bare GCE. The detection limit of 0.0052 μM achieved in this study indicated that RGO/GCE can effectively detect TB in human urine while demonstrating reasonable selectivity and sensitivity.

Graphene-based Nanomaterials in Fighting the Most Challenging Viruses and Immunogenic Disorders

Viral diseases have long been among the biggest challenges for healthcare systems around the world. The recent Coronavirus Disease 2019 (COVID-19) pandemic is an example of how complicated the situation can get if we are not prepared to combat a viral outbreak in time, which brings up the need for quick and affordable biosensing platforms and vast knowledge of potential antiviral effects and drug/gene delivery opportunities. The same challenges have also existed for nonviral immunogenic disorders. Nanomedicine is considered a novel candidate for effectively overcoming these worldwide challenges. Among the versatile nanomaterials commonly used in biomedical applications, graphene has recently earned much attention thanks to its special and inspiring physicochemical properties, such as its large surface area, efficient thermal/electrical properties, carbon-based chemical purity with controllable biocompatibility, easy functionalization, capability of single-molecule detection, anticancer characteristics, 3D template feature in tissue engineering, and, in particular, antibacterial/antiviral activities. In this Review, the most important and challenging viruses of our era, such as human immunodeficiency virus, Ebola, SARS-CoV-2, norovirus, and hepatitis virus, and immunogenic disorders, such as asthma, Alzheimer's disease, and Parkinson's disease, in which graphene-based nanomaterials can effectively take part in the prevention, detection, treatment, medication, and health effect issues, have been covered and discussed.

High flux and complete dyes removal from water by reduced graphene oxide laminate on Poly Vinylidene Fluoride/graphene oxide membranes

Dyes molecules are the most common pollutants of wastewater in the environment from the textile industry to numbers of technologies include dyeing, printing, and painting procedures. Among membrane-based separation approaches as established methods in the water treatment industry, polymers attracted massive attention in the production of membranes due to their low cost and high-performance filtration of pollutants. However, hydrophobicity and low speed of filtration along with limited decontamination performance against some of the dyes, demand new approaches and membranes to overcome drawbacks points. Herein, a new design introduced including a support layer made by Poly Vinylidene Fluoride (PVDF)/Graphene Oxide (PGO) composite membrane via immersion precipitation process and a thin layer (≤100 nm) of reduced graphene oxide (rGO) deposited (as an active layer) through a simple vacuum filtration method. It has been observed that the presence of the GO sheets in the PGO composite improved the hydrophilicity of the membrane, water flux (from ~90 L m^-2 h^-1 bar^-1 in pristine PVDF to ~1690 L m^-2 h^-1 bar^-1 in PGO), and anti-fouling property. By deposition of rGO laminate on PGO support, dyes separation as high as ~99% can be achieved for most of the cationic and anionic dyes due to electrostatic adsorption, π-π interactions and molecular sieving. This approach opens new insight on hybrid designs for graphene-polymers based membrane toward efficient and fast removal of pollutants from wastewater.

Graphene-Based Sensors for the Detection of Bioactive Compounds: A Review

Over the last years, different nanomaterials have been investigated to design highly selective and sensitive sensors, reaching nano/picomolar concentrations of biomolecules, which is crucial for medical sciences and the healthcare industry in order to assess physiological and metabolic parameters. The discovery of graphene (G) has unexpectedly impulsed research on developing cost-effective electrode materials owed to its unique physical and chemical properties, including high specific surface area, elevated carrier mobility, exceptional electrical and thermal conductivity, strong stiffness and strength combined with flexibility and optical transparency. G and its derivatives, including graphene oxide (GO) and reduced graphene oxide (rGO), are becoming an important class of nanomaterials in the area of optical and electrochemical sensors. The presence of oxygenated functional groups makes GO nanosheets amphiphilic, facilitating chemical functionalization. G-based nanomaterials can be easily combined with different types of inorganic nanoparticles, including metals and metal oxides, quantum dots, organic polymers, and biomolecules, to yield a wide range of nanocomposites with enhanced sensitivity for sensor applications. This review provides an overview of recent research on G-based nanocomposites for the detection of bioactive compounds, providing insights on the unique advantages offered by G and its derivatives. Their synthesis process, functionalization routes, and main properties are summarized, and the main challenges are also discussed. The antioxidants selected for this review are melatonin, gallic acid, tannic acid, resveratrol, oleuropein, hydroxytyrosol, tocopherol, ascorbic acid, and curcumin. They were chosen owed to their beneficial properties for human health, including antibiotic, antiviral, cardiovascular protector, anticancer, anti-inflammatory, cytoprotective, neuroprotective, antiageing, antidegenerative, and antiallergic capacity. The sensitivity and selectivity of G-based electrochemical and fluorescent sensors are also examined. Finally, the future outlook for the development of G-based sensors for this type of biocompounds is outlined.

Green and facile preparation of graphene/resveratrol/polyaniline composites for high-performance supercapacitors

A novel and environmentally-friendly resveratrol (RA) was used as an effective reagent for the preparation of reduced graphene oxide (rGO).

Reduced graphene oxide decorated with magnetite nanoparticles enhance biomethane enrichment

The addition of magnetite nanoparticles (MNPs), reduced graphene oxide (rGO), and reduced graphene oxide decorated with magnetite nanoparticles (rGO-MNPs) was evaluated during biomethane enrichment process. rGO-MNPs presented the highest beneficial impact on the hydrogenotrophic assays with an improvement of 47 % in CH₄ production. The improvement was linked to the increase of the electron shuttling capacity (ESC) by rGO-MNPs addition, which boosted the hydrogenotrophic activity of microorganisms, to the rGO and rGO-MNPs, which served as reservoirs of hydrogen, improving H⁠₂ transport from the gas to the liquid phase, and to the iron ions released, which acted as a dietary supply for microorganisms. Raman and XRD confirmed a greater disorder and lower crystallinity of rGO-MNPs after the hydrogenotrophic assays, with a lower effect at a nanoparticle concentration of 50 mg/L. Moreover, FTIR analysis indicated that rGO-MNPs were oxidized during the hydrogenotrophic tests. This study highlights the advantages of adding rGO-MNPs as a magnetic nanocomposite. Furthermore, rGO-MNPs can be easily recovered, minimizing their release to the environment.

Ultrasound-assisted Li+/Na+ co-intercalated exfoliation of graphite into few-layer graphene

In this work, we developed a novel approach for few-layer graphene by employing Li⁺/Na⁺ co-intercalated exfoliation assisted by ultrasound method. The experiments were conducted under the ultrasonic power of 300 W and the frequency of 40 kHz without the participation of any organic solvent. The effect of Li⁺/Na⁺ proportion on the exfoliation of graphite was intensively investigated. The structure and morphology of the as-exfoliated graphene nanosheets (UGN) was determined by a series of characterizations. The results showed that the thicknesses of the as-exfoliated graphene nanosheets were about 2.38-2.56 nm (about 7-8 layers) at the optimal Li⁺/Na⁺ ratio. The potential application of the as-exfoliated graphene nanosheets as additive in grease was evaluated by four-ball friction tester. The results demonstrated that the antifriction and antiwear performances of the grease with 0.06 wt% graphene were significantly improved by 21.35% and 30.32% relative to pure grease, respectively. The friction mechanism was proposed by detecting the worn surfaces.

Photoluminescence as a Complementary Tool for UV-VIS Spectroscopy to Highlight the Photodegradation of Drugs: A Case Study on Melatonin

In this work, a complementary ultraviolet-visible (UV-VIS) spectroscopy and photoluminescence (PL) study on melatonin (MEL) hydrolysis in the presence of alkaline aqueous solutions and the photodegradation of MEL is reported. The UV-VIS spectrum of MEL is characterized by an absorption band with a peak at 278 nm. This peak shifts to 272 nm simultaneously with an increase in the band absorbance at 329 nm in the presence of an NaOH solution. The isosbestic point localized at 308 nm indicates the generation of some chemical compounds in addition to MEL and NaOH. The MEL PL spectrum is characterized by a band at 365 nm. There is a gradual decrease in the MEL PL intensity as the alkaline solution concentration added at the drug solution is increased. In the case of the MEL samples interacting with an alkaline solution, a new photoluminescence excitation (PLE) band at 335 nm appears when the exposure time to UV light reaches 310 min. A down-shift in the MEL PLE band, from 321 to 311 nm, as a consequence of the presence of excipients, is also shown. These changes are explained in reference to the MEL hydrolytic products.

Agar-reduced graphene oxide selectively adsorbs organic dyes and strengthens double-network hydrogels

A straightforward and environmentally friendly method for synthesizing agar-reduced graphene oxide (ArGO) was devised. The topological features and emergent physical properties displayed by the novel carbon material were controlled by varying its water content. Dehydrated films of ArGO were found to be stable in water due to the π–π stacking interactions that formed between the aromatic components of its constituent sheets. In contrast, porous variants of ArGO afforded hydrogels that exhibited high swelling capacities. The intrinsic mechanical strength, elasticity and chemical stability of the hydrogels were further enhanced through adaption into double-network analogues. Such hydrogels, which were prepared using a facile and efficient one-pot methodology, exhibited a high fracture stress upon compression, and retained their shape in basic aqueous environments. These features can be expected to enable water purification and tissue engineering applications, among others.

Agar-reduced graphene oxide was conveniently synthesized from readily available precursors and found to selectively adsorb cationic organic dyes as well as to enhance the mechanical properties exhibited by various types of double-network hydrogels.

In Situ Study of Structure-Activity Relationship between Structure and Tribological Properties of Bulk Layered Materials by Four-Ball Friction Tester

Encouragingly, a lot of research studies have demonstrated that two-dimensional (2D) nanosheets applied as an additive in oils show preferable friction-reducing and wear resistance performance. However, the current issue was that an elusive way could be adopted to probe the structure-activity relationship between the structure and tribological properties of bulk layered materials due to the structural evolution during friction testing. In this study, we studied the structure-activity relationship between the structure and tribological properties of bulk layered materials (graphite, h-BN, WS₂, and MoS₂) by an in situ four-ball friction tester. The morphological and structural changes of the layered materials after in situ four-ball-milling were detected by a series of characterizations. This study revealed the friction-induced nanostructural evolution behaviors of bulk layered materials by a four-ball mode.

Bio-reduction of Graphene Oxide: Catalytic Applications of (Reduced) GO in Organic Synthesis

This work is based on various bio-reduction of graphene oxide into reduced graphene oxide and their applications in organic synthesis and group transformations. Graphene oxide, with abundant oxygencontaining functional groups on its basal plane, provides potential advantages, including excellent dispersibility in solvents and the good heterogeneous catalyst. This manuscript reviews various methods of synthesis of graphene and graphene oxide and a comparative study on their advantages and disadvantages, how to overcome disadvantages and covers extensive relevant literature review. In the last few years, investigation based on replacing the chemical reduction methods by some bio-compatible, chemical/impurity-free rGO including flash photo reductions, hydrothermal dehydration, solvothermal reduction, electrochemical approach, microwave-assisted reductions, light and radiation-induced reductions has been reported. Particularly, plant extracts have been applied significantly as an efficient reducing agent due to their huge bioavailability and low cost for bio-reduction of graphene oxide. These plant extracts mainly contain polyphenolic compounds, which readily get oxidized to the corresponding unreactive quinone form, which are the driving force for choosing them as bio-compatible catalyst. Currently, efforts are being made to develop biocompatible methods for the reduction of graphene oxide. The reduction abilities of such phytochemicals have been reported in the synthesis and stabilization of various nanoparticles viz. Ag, Au, Fe and Pd. Various part of plant extract has been applied for the green reduction of graphene oxide. Furthermore, the manuscript describes the catalytic applications of graphene oxide and reduced graphene oxide nanosheets as efficient carbo-catalysts for valuable organic transformations. Herein, important works dedicated to exploring graphene-based materials as carbocatalysts, including GO and rGO for organic synthesis including various functional group transformations, oxidation, reduction, coupling reaction and a wide number of multicomponent reactions have been highlighted. Finally, the aim of this study is to provide an outlook on future trends and perspectives for graphene-based materials in metal-free carbo-catalysis in green synthesis of various pharmaceutically important moieties.

Synthesis and Physicochemical Transformations of Size-Sorted Graphene Oxide during Simulated Digestion and Its Toxicological Assessment against an In Vitro Model of the Human Intestinal Epithelium

In the last decade, along with the increasing use of graphene oxide (GO) in various applications, there is also considerable interest in understanding its effects on human health. Only a few experimental approaches can simulate common routes of exposure, such as ingestion, due to the inherent complexity of the digestive tract. This study presents the synthesis of size-sorted GO of sub-micrometer- or micrometer-sized lateral dimensions, its physicochemical transformations across mouth, gastric, and small intestinal simulated digestions, and its toxicological assessment against a physiologically relevant, in vitro cellular model of the human intestinal epithelium. Results from real-time characterization of the simulated digestas of the gastrointestinal tract using multi-angle laser diffraction and field-emission scanning electron microscopy show that GO agglomerates in the gastric and small intestinal phase. Extensive morphological changes, such as folding, are also observed on GO following simulated digestion. Furthermore, X-ray photoelectron spectroscopy reveals that GO presents covalently bound N-containing groups on its surface. It is shown that the GO employed in this study undergoes reduction. Toxicological assessment of the GO small intestinal digesta over 24 h does not point to acute cytotoxicity, and examination of the intestinal epithelium under electron microscopy does not reveal histological alterations. Both sub-micrometer- and micrometer-sized GO variants elicit a 20% statistically significant increase in reactive oxygen species generation compared to the untreated control after a 6 h exposure.

Graphene Oxide Papers in Nanogenerators for Self-Powered Humidity Sensing by Finger Tapping

Triboelectric nanogenerators (TENGs) offer an emerging market of self-sufficient power sources, converting the mechanical energy of the environment to electricity. Recently reported high power densities for the TENGs provide new applications opportunities, such as self-powered sensors. Here in this research, a flexible graphene oxide (GO) paper was fabricated through a straightforward method and utilized as the electrode of TENGs. Outstanding power density as high as 1.3 W.m^-2, an open-circuit voltage up to 870 V, and a current density of 1.4 µA.cm^-2 has been extracted in vertical contact-separation mode. The all-flexible TENG has been employed as a self-powered humidity sensor to investigate the effect of raising humidity on the output voltage and current by applying mechanical agitation in two forms of using a tapping device and finger tapping. Due to the presence of superficial functional groups on the GO paper, water molecules are inclined to be adsorbed, resulting in a considerable reduction in both generated voltage (from 144 V to 14 V) and current (from 23 µA to 3.7 µA) within the range of relative humidity of 20% to 99%. These results provide a promising applicability of the first suggested sensitive self-powered GO TENG humidity sensor in portable/wearable electronics.

Antioxidant properties of ethenyl indole: DPPH assay and TDDFT studies

Ethenyl indole exhibits antioxidant activity in a substituent dependent manner. Ethenyls bearing strong electron withdrawing substituents show weak or no antioxidant activities, whereas ethenyls with electron donating substituents exhibit antioxidant properties comparable to vitamin E.

Graphene aerogel nanoparticles for in-situ loading/pH sensitive releasing anticancer drugs

Free polymer graphene aerogel nanoparticles (GA NPs) were synthesized by using reduction/aggregation of graphene oxide (GO) sheets in the presence of vitamin C (as a biocompatible reductant agent) at a low temperature (40 °C), followed by an effective sonication. Synthesis of GA NPs in doxorubicin hydrochloride (DOX)-containing solution results in the simultaneous synthesis and drug loading with higher performance (than that of the separately synthesized and loaded samples). To investigate the mechanism of loading and the capability of GA NPs in the loading of other drug structures, two groups of ionized (DOX, Amikacin sulfate and, d-glucosamine hydrochloride) and non-ionized (Paclitaxel (PTX)) drugs were examined. Furthermore, the relationship between the bipolar level of DOX solution (contributing to H-bonding of DOX and GO) and the amount of DOX loading was investigated. The DOX showed higher loading (>3 times) than PTX, as anticancer drugs. Since both DOX and PTX possess aromatic structures, the higher loading of DOX was assigned to its positive partial charge and ionized nature. Accordingly, other drugs (having positive partial charge and ionized nature, but no aromatic structure) such as Amikacin sulfate and d-glucosamine hydrochloride presented higher loading than PTX. These results indicated that although the π-π interactions induced by aromatic structures are important in drug loading, the electrostatic interaction of ionized drugs with GO (especially through H-bonding) is the dominant mechanism. DOX-loaded GANPs showed high pH-sensitive release (equivalent to the carrier weight) after 5 days, which can indicate benefits in tumor cell acidic microenvironments in-vivo.

Elucidating the Chemistry behind the Reduction of Graphene Oxide Using a Green Approach with Polydopamine

A new approach using X-ray photoelectron spectroscopy (XPS) was employed to give insight into the reduction of graphene oxide (GO) using a green approach with polydopamine (PDA). In this approach, the number of carbon atoms bonded to OH and to nitrogen in PDA is considered and compared to the total intensity of the signal resulting from OH groups in polydopamine-reduced graphene oxide (PDA-GO) to show the reduction. For this purpose, GO and PDA-GO with different times of reduction were prepared and characterized by Raman Spectroscopy and XPS. The PDA layer was removed to prepare reduced graphene oxide (RGO) and the effect of all chemical treatments on the thermal and electrical properties of the materials was studied. The results show that the complete reduction of the OH groups in GO occurred after 180 min of reaction. It was also concluded that Raman spectroscopy is not well suited to determine if the reduction and restoration of the sp2 structure occurred. Moreover, a significant change in the thermal stability was not observed with the chemical treatments. Finally, the electrical powder conductivity decreased after reduction with PDA, increasing again after its removal.

Biofabrication of Lysinibacillus sphaericus-reduced graphene oxide in three-dimensional polyacrylamide/carbon nanocomposite hydrogels for skin tissue engineering

The biological synthesis of reduced graphene oxide (rGO) from graphene oxide (GO) is an emerging phenomenon for developing biocompatible nanomaterials for its potential applications in nanomedicine. In this study, we demonstrated a simple, green, and non-toxic method for graphene synthesis using the live biomass of Lysinibacillus sphaericus as the reducing and stabilizing agent under ambient conditions. Ultraviolet-visible spectroscopic analysis confirmed the formation of graphene from GO suspension. X-ray diffraction studies showed the disappearance of the GO peak and the appearance of characteristic graphene broad peak at 2θ = 22.8°. Infrared analysis showed the decrease/disappearance of peaks corresponding to the oxygen-containing functionalities, and appearance of a peak at 1620 cm^-1 from unoxidized graphitic domains. Scanning electron microscopic images showed that L. sphaericus-reduced graphene oxide (L-rGO) contains aggregated graphene nanoflakes. Evaluation of the in vitro cytotoxicity of L-rGO nanosheets on human skin fibroblasts using the WST-1 assay did not show any significant effects after 24 h of exposure, which is indicative of biocompatibility. Polyacrylamide hydrogels with L-rGO were synthesized and used as scaffolds to support the growth and proliferation of skin fibroblasts. Cell viability assays and DAPI staining showed proliferation of fibroblasts and exhibited 83% of cell viability even after 28 days. Biofilm formation by Pseudomonas aeruginosa and Staphylococcus aureus was enhanced in nanocomposite hydrogels in the presence of 0.25 mg/mL GO and L-rGO in 48 h. Overall, this study showed that microbially-synthesized L-rGO can be used as a dopant in polymeric scaffolds for tissue engineering and highlighted their role in biofilm formation.

Emerging Trends in the Syntheses of Heterocycles Using Graphene-based Carbocatalysts: An Update

Graphene-based carbocatalysts owing to numerous amazing properties such as large specific surface area, high intrinsic mobility, excellent thermal and electrical conductivities, chemical stability, ease of functionalization, simple method of preparation, effortless recovery and recyclability have gained a superior position amongst the conventional homogeneous and heterogeneous catalysts. In this review, an endeavor has been made to highlight the syntheses of diverse heterocyclic compounds catalyzed by graphene-based catalysts. Further, the study also reveals that all the catalysts could be reused several times without significant loss in their catalytic activity. Additionally, most of the reactions catalyzed by graphene-based carbocatalysts were carried out at ambient temperature and under solvent-free conditions. Thus, the graphene-based catalysts do not merely act as efficient catalysts but also serve as sustainable, green catalysts. This review is divided into various sub-sections, each of which comprehensively describes the preparation of a particular heterocyclic scaffold catalyzed by graphene-derived carbocatalyst in addition to synthesis of graphene oxide and reduced graphene oxide, functionalization, and structural features governing their catalytic properties. Synthesis of heterocycles catalyzed by graphene-based carbocatalysts.

Multisulfonate hyperbranched polyglycerol functionalized graphene oxide as an efficient reusable catalyst for green synthesis of benzo[a]pyrano-[2,3-c]phenazines under solvent-free conditions

A novel acid catalyst was prepared based on growing hyperbranched polyglycerol (HPG) on the surface of graphene oxide. Then, the hydroxyl groups of HPG on graphene oxide were functionalized by sulfonate groups to form an acid catalyst. The catalyst displayed a good loading level of acidic groups on the surface because of coating graphene oxide with HPG. This new catalyst is demonstrated to be highly effective in the preparation of benzo[a]pyrano[2,3-c]phenazine dyes.

Comprehensive Application of Graphene: Emphasis on Biomedical Concerns

Graphene, sp² hybridized carbon framework of one atom thickness, is reputed as the strongest material to date. It has marked its impact in manifold applications including electronics, sensors, composites, and catalysis. Current state-of-the-art graphene research revolves around its biomedical applications. The two-dimensional (2D) planar structure of graphene provides a large surface area for loading drugs/biomolecules and the possibility of conjugating fluorescent dyes for bioimaging. The high near-infrared absorbance makes graphene ideal for photothermal therapy. Henceforth, graphene turns out to be a reliable multifunctional material for use in diagnosis and treatment. It exhibits antibacterial property by directly interacting with the cell membrane. Potential application of graphene as a scaffold for the attachment and proliferation of stem cells and neuronal cells is captivating in a tissue regeneration scenario. Fabrication of 2D graphene into a 3D structure is made possible with the help of 3D printing, a revolutionary technology having promising applications in tissue and organ engineering. However, apart from its advantageous application scope, use of graphene raises toxicity concerns. Several reports have confirmed the potential toxicity of graphene and its derivatives, and the inconsistency may be due to the lack of standardized consensus protocols. The present review focuses on the hidden facts of graphene and its biomedical application, with special emphasis on drug delivery, biosensing, bioimaging, antibacterial, tissue engineering, and 3D printing applications.

Lanthanide-doped upconversion nanoparticles complexed with nano-oxide graphene used for upconversion fluorescence imaging and photothermal therapy

In recent years, multifunctional nanoparticles have attracted much research interest in various biomedical applications such as biosensors, diagnosis, and drug delivery systems. In this study, we report an NIR imaging diagnosis and therapy nanoplatform which is developed by complexing upconversion nanoparticles (UCNP@OA) NaLuF4:Er3+,Yb3+ with nanographene oxide (NGO). The obtained nanocomposites UCNP@NGO showed excellent stability and low cell toxicity, which not only acted as upconversion luminescence (UCL) probes for tumor imaging, but also served as therapy agents by converting laser energy into thermal energy for photothermal therapy (PTT) with high photothermal conversion efficiency. This work highlights the potential of UCNP@NGO nanocomposites as an integrated theranostic nanoplatform for the UCL image combinatorial PTT of cancer, providing a promising candidate for clinical antitumor treatments.

Bioinspired gold nanoparticles decorated reduced graphene oxide nanocomposite using Syzygium cumini seed extract: Evaluation of its biological applications

The development of novel functionalized reduced graphene oxide nanocomposite materials keeping in mind environmental and health perspectives via green approaches is currently gaining enormous research interest in the field of nanoscience and nanotechnology. Herein, we report a bio-inspired green synthesis approach for gold nanoparticles decorated reduced graphene oxide nanocomposite in which Syzygium cumini seed extract (SCSE) is applied as natural reducing and stabilizing agent for the simultaneous reduction of chloroauric acid and graphene oxide (GO). The obtained nanocomposite was thoroughly investigated using UV-visible and FT-IR spectroscopy, XRD, SEM-EDX, TEM-SAED, Raman spectroscopy and XPS analysis. These characterization techniques clearly confirmed the successful synthesis of gold nanoparticles decorated reduced graphene oxide nanocomposite. In addition, this study evaluated the systematic and detailed analysis of AuNPs-rGO-NC and its efficacy towards cellular and antibacterial toxicological behavior. A detailed in-vitro cytotoxicity study was performed by analysing the percentage inhibition of cell viability, generation of reactive oxygen species (ROS) in cell lines using 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide (MTT) assay on human colorectal (HCT116) and lung (A549) cancer cell lines. Further, antibacterial toxicological evaluation was performed by analysing diameter of inhibition Zone (DIZ), activity index (AI), minimum bactericidal concentration (MBC), minimum inhibitory concentration (MIC), growth kinetics (GrK) and death kinetics (DeK) against Gram-negative bacterial strain Escherichia coli and Gram-positive bacterial strains Staphylococcus aureus and Bacillus subtilis. The cytotoxicity and antibacterial toxicological assays revealed that the synthesized nanocomposite showed significant anti-cancer activity towards A549 cell line and Gram-negative bacterial strain Escherichia coli compared to the rest.

Curcumin-loaded graphene oxide flakes as an effective antibacterial system against methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is responsible for serious hospital infections worldwide and represents a global public health problem. Curcumin, the major constituent of turmeric, is effective against MRSA but only at cytotoxic concentrations or in combination with antibiotics. The major issue in curcumin-based therapies is the poor solubility of this hydrophobic compound and the cytotoxicity at high doses. In this paper, we describe the efficacy of a composite nanoparticle made of curcumin (CU) and graphene oxide (GO), hereafter GOCU, in MRSA infection treatment. GO is a nanomaterial with a large surface area and high drug-loading capacity. GO has also antibacterial properties due mainly to a mechanical cutting of the bacterial membranes. For this physical mechanism of action, microorganisms are unlikely to develop resistance against this nanomaterial. In this work, we report the capacity of GO to support and stabilize curcumin molecules in a water environment and we demonstrate the efficacy of GOCU against MRSA at a concentration below 2 µg ml-1. Further, GOCU displays low toxicity on fibroblasts cells and avoids haemolysis of red blood cells. Our results indicate that GOCU is a promising nanomaterial against antibiotic-resistant MRSA.

The novel and efficient reduction of graphene oxide using Ocimum sanctum L. leaf extract as an alternative renewable bio-resource

The efficient, rapid, bio-inspired synthesis of reduced graphene oxide (rGO) nanosheets was explored using green leaf extract of Ocimum sanctum L. (Tulsi leaves). This mild biorenewable reducing agent containing eugenol, ascorbic acid, and polyols also acts as a stabilizer for the prepared rGO.

Bio-inspired unprecedented synthesis of reduced graphene oxide: a catalytic probe for electro-/chemical reduction of nitro groups in an aqueous medium

The first green reduction of graphene oxide (GO) using cashew leaf extract as a biorenewable catalyst containing water soluble tannins and gallic acid is reported herein. The synthesized rGO has been well characterized.

Fabrication of Nontoxic Reduced Graphene Oxide Protein Nanoframework as Sustained Antimicrobial Coating for Biomedical Application

Bacterial colonization on medical devices is a major concern in the healthcare industry. In the present study, we report synthesis of environmental sustainable reduced graphene oxide (rGO) on the large scale through biosynthetic route and its potential application for antibacterial coating on medical devices. HRTEM image depicts formation of graphene nanosheet, while DLS and ζ potential studies reveal that in aqueous medium the average hydrodynamic size and surface charge of rGO are 4410 ± 116 nm and -25.2 ± 3.2 mV, respectively. The Raman, FTIR, and XPS data suggest in situ conjugation of protein with rGO. The as-synthesized rGO protein nanoframework exhibits dose-dependent antibacterial activity and potential of killing of 94% of Escherichia coli when treated with 80 μg/mL of rGO for 4 h. The hemolytic and cytotoxicity studies demonstrate that rGO protein nanoframework is highly biocompatible at the same concentration showing significant antimicrobial properties. The rGO coated on the glass surface obtained through covalent bonding exhibits potent antibacterial activity. Antibacterial mechanism further demonstrates that rGO-protein nanoframework in dispersed state (rGO solution) exerts bactericidal effect through physical disruption accompanied by ROS-mediated biochemical responses. The rGO subsequently entering into the cytoplasm through the damaged membrane causes metabolic imbalance in the cells. In sharp contrast, physical damage of the cell membrane is the dominant antibacterial mechanism of rGO in the immobilized state (rGO coated glass). The obtained results help indepth understanding of the antibacterial mechanism of the biosynthesized rGO and a novel way to develop nontoxic antibacterial coating on medical devices to prevent bacterial infection.