Graphene-based Materials in Health and Environment: New Paradigms
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Tian et al 33 reported that the PDT efficiency of nanographene can be further improved by a unique photothermal therapy PTT. The enhanced cell uptake was facilitated by high cell membrane permeability at a higher temperature. The synergistic photothermal and photodynamic effect further promoted cancer cell killing Figure 5. Figure 5 Schemes of the experimental design in photothermally enhanced photodynamic therapy.
Photothermally enhanced photodynamic therapy delivered by nano-graphene oxide. ACS Nano. Moreover, these nanoparticles showed high tumor accumulation when intravenously injected into the tumor-bearing mice. The in vivo results showed total ablation of tumor, indicating the pronounced synergistic effect of dual phototherapy Figure 6. Figure 6 In vivo cancer therapy in HeLa tumor-bearing mice. PDT only showed minimal effect on tumor growth, whereas PTT alone showed improved effect on tumor growth.
The dual therapy resulted in complete ablation of tumor tissue and no regrowth occurred within a span of 15 days. The mice with combined therapy showed no sign of tumor regrowth and the burned skin was also healed the arrow indicates the healed site. This unique approach can effectively improve mild PTT Figure 7. Figure 7 Irradiation-activated apoptosis.
Notes: A Schematic illustration of the sequential irradiation-activated high-performance apoptosis. The efficacy of combined treatment is compared with the additive efficacy of independent PDT and PTT treatments using t -tests with all P -values lower than 0. Reprinted from A multi-synergistic platform for sequential irradiation-activated high-performance apoptotic cancer therapy. Adv Funct Mater.
KGaA, Weinheim. As demonstrated by extensive previous experimental results, GO can be engineered to acquire highly integrated multiple functions in a single system. By conjugating with imaging probes, GO can be functionalized for biomedical diagnosis. The system generated cytotoxic singlet oxygen under nm laser irradiation for PDT.
Recently, Gollavelli and Ling 36 reported a single light-induced photothermal and photodynamic reagent with dual-modal imaging capability. The MFG serves as an excellent luminescence image reagent and T2-weighted magnetic resonance imaging contrast reagent owing to its fluorescence and superparamagnetic properties.
Graphene-based nanosystems have shown great potential for PDT of cancer. However, biosafety of the nanomaterials must be taken into consideration. The toxicity and behavior of graphene-based materials in biological systems have been extensively investigated. But functionalized nano-GO eg, by biocompatible surface coatings is shown to be much less harmful in both in vitro and in vivo experiments. Surface modification of graphene has been found to effectively decrease its in vivo toxicity. Toxicity of graphene also depends on the chemical structure, charge, size, number of layers, and defects.
Other factors include administration route, dose, time of exposure, as well as the cell types. Thus, more systematic investigations need to be carried out to fully understand the biological effects and to address safety concerns before implementation of clinical applications of any graphene-based materials. Graphene-based nanomaterials, mainly GO, have been extensively studied as an effective nanovehicle utilizing both organic PSs and inorganic nanoparticles such as TiO 2 and ZnO.
The unique physicochemical properties of graphene-based nanomaterials allow for efficient loading via both physical absorptions and chemical conjugations. Various strategies have been developed for GO-based PS delivery systems including targeted, target-activatable, and photothermally enhanced PDT.
Upon incorporation of PS into the GO nanovehicles, the stability, bioavailability, and photodynamic anticancer effects of PSs can be significantly improved, with distinctive therapeutic effects. However, there are critical issues to be addressed before clinical applications. In addition, these GO nanovehicles are generally in their pristine forms with highly dispersed particle sizes. More studies are required to find out the correlations between the physicochemical characteristics or structural modifications of graphenes and their biological impact.
Rational, well-designed graphenes that can satisfy clinical requirements comprise the current challenges in the development of versatile GO-based nanocarriers for medical diagnosis and therapy.
The physics, biophysics and technology of photodynamic therapy. Phys Med Biol. Photodynamic therapy of cancer: an update. CA Cancer J Clin. The present and future role of photodynamic therapy in cancer treatment. Lancet Oncol. How does photodynamic therapy work?
Photochem Photobiol. Photodynamic therapy. J Natl Cancer Inst. Current clinical and preclinical photosensitizers for use in photodynamic therapy. J Med Chem. Current states and future views in photodynamic therapy. Nanoparticles in photodynamic therapy: an emerging paradigm. Adv Drug Deliv Rev. Nanodrug applications in photodynamic therapy.
Photodiagnosis Photodyn Ther. Graphene and graphene oxide as new nanocarriers for drug delivery applications. Acta Biomater. Nano-graphene in biomedicine: theranostic applications. Chem Soc Rev. Application of graphene derivatives in cancer therapy: a review.
Interfaces for Neural Repair | Hospital Nacional de Paraplejicos
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Subscriber Login Email Address. Library Card. View: no detail some detail full detail. All rights reserved. Powered by: Safari Books Online. Large-area, continuous, transparent and highly conducting few-layered graphene films were produced by chemical vapor deposition and used as anodes for application in photovoltaic devices. A power conversion efficiency PCE up to 1. Organic light-emitting diodes OLEDs with graphene anodes have been demonstrated. The device was formed by solution-processed graphene on a quartz substrate. The electronic and optical performance of graphene-based devices are similar to devices made with indium tin oxide.
A carbon-based device called a light-emitting electrochemical cell LEC was demonstrated with chemically-derived graphene as the cathode and the conductive polymer Poly 3,4-ethylenedioxythiophene PEDOT as the anode. In a prototype graphene-based flexible display was demonstrated. The degree of curvature of the sheets above each cavity defines the color emitted. The device exploits the phenomena known as Newton's rings created by interference between light waves bouncing off the bottom of the cavity and the transparent material.
Increasing the distance between the silicon and the membrane increased the wavelength of the light. The approach is used in colored e-reader displays and smartwatches, such as the Qualcomm Toq. They use silicon materials instead of graphene. Graphene reduces power requirements.
In , researchers built experimental graphene frequency multipliers that take an incoming signal of a certain frequency and output a signal at a multiple of that frequency. Graphene strongly interacts with photons, with the potential for direct band-gap creation. This is promising for optoelectronic and nanophotonic devices. Light interaction arises due to the Van Hove singularity. Graphene displays different time scales in response to photon interaction, ranging from femtoseconds ultra-fast to picoseconds. Potential uses include transparent films, touch screens and light emitters or as a plasmonic device that confines light and alters wavelengths.
Due to extremely high electron mobility, graphene may be used for production of highly sensitive Hall effect sensors. These sensors are two times better than existing Si based sensors. Their size and edge crystallography govern their electrical, magnetic, optical, and chemical properties. Quantum confinement can be created by changing the width of graphene nanoribbons GNRs at selected points along the ribbon. A semiconducting polymer poly 3-hexylthiophene  placed on top of single-layer graphene vertically conducts electric charge better than on a thin layer of silicon. In a thin film or on silicon,  plate-like crystallites are oriented parallel to the graphene layer.
Uses include solar cells. Large-area graphene created by chemical vapor deposition CVD and layered on a SiO2 substrate, can preserve electron spin over an extended period and communicate it. Spintronics varies electron spin rather than current flow. The spin signal is preserved in graphene channels that are up to 16 micrometers long over a nanosecond. Spintronics is used in disk drives for data storage and in magnetic random-access memory. Electronic spin is generally short-lived and fragile, but the spin-based information in current devices needs to travel only a few nanometers.
However, in processors, the information must cross several tens of micrometers with aligned spins.
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Graphene is the only known candidate for such behavior. In Vorbeck Materials started shipping the Siren anti-theft packaging device , which uses their graphene-based Vor-Ink circuitry to replace the metal antenna and external wiring to an RFID chip. This was the world's first commercially available product based on graphene. When the Fermi level of graphene is tuned, its optical absorption can be changed. In , researchers reported the first graphene-based optical modulator. Operating at 1.
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A Mach-Zehnder modulator based on a hybrid graphene-silicon waveguide has been demonstrated recently, which can process signals nearly chirp-free. Its insertion loss is roughly A hyperlens is a real-time super-resolution lens that can transform evanescent waves into propagating waves and thus break the diffraction limit. In a hyperlens based on dielectric layered graphene and h- boron nitride h-BN can surpass metal designs. Based on its anisotropic properties, flat and cylindrical hyperlenses were numerically verified with layered graphene at THz and layered h-BN at THz, respectively.
The lens was created by spraying a sheet of graphene oxide solution, then molding the lens using a laser beam. It can resolve objects as small as nanometers, and see into the near infrared. It breaks the diffraction limit and achieve a focal length less than half the wavelength of light. Possible applications include thermal imaging for mobile phones, endoscopes , nanosatellites and photonic chips in supercomputers and superfast broadband distribution. Graphene reacts to the infrared spectrum at room temperature, albeit with sensitivity to times too low for practical applications.
However, two graphene layers separated by an insulator allowed an electric field produced by holes left by photo-freed electrons in one layer to affect a current running through the other layer. The process produces little heat, making it suitable for use in night-vision optics. The sandwich is thin enough to be integrated in handheld devices, eyeglass-mounted computers and even contact lenses. Graphene oxide membranes allow water vapor to pass through, but are impermeable to other liquids and gases. Graphene solar cells use graphene's unique combination of high electrical conductivity and optical transparency.
These films must be made thicker than one atomic layer to obtain useful sheet resistances. This added resistance can be offset by incorporating conductive filler materials, such as a silica matrix. Reduced conductivity can be offset by attaching large aromatic molecules such as pyrene sulfonic acid sodium salt PyS and the disodium salt of 3,4,9,perylenetetracarboxylic diimide bisbenzenesulfonic acid PDI. Using graphene as a photoactive material requires its bandgap to be 1. According to P.
Mukhopadhyay and R. Gupta organic photovoltaics could be "devices in which semiconducting graphene is used as the photoactive material and metallic graphene is used as the conductive electrodes". In , chemical vapor deposition produced graphene sheets by depositing a graphene film made from methane gas on a nickel plate.
A protective layer of thermoplastic is laid over the graphene layer and the nickel underneath is then dissolved in an acid bath. The final step is to attach the plastic-coated graphene to a flexible polymer sheet, which can then be incorporated into a PV cell. Silicon generates only one current-driving electron for each photon it absorbs, while graphene can produce multiple electrons.
In , researchers first reported creating a graphene-silicon heterojunction solar cell, where graphene served as a transparent electrode and introduced a built-in electric field near the interface between the graphene and n-type silicon to help collect charge carriers. Doping increased efficiency to 9. In , another team reported This lowers production costs and offers the potential using flexible plastics. In , researchers developed a prototype cell that used semitransparent perovskite with graphene electrodes. The design allowed light to be absorbed from both sides. Multilayering graphene via CVD created transparent electrodes reducing sheet resistance.
Performance was further improved by increasing contact between the top electrodes and the hole transport layer. They could even be used to extract hydrogen gas out of the atmosphere that could power electric generators with ambient air. The membranes are more effective at elevated temperatures and when covered with catalytic nanoparticles such as platinum. Graphene could solve a major problem for fuel cells: fuel crossover that reduces efficiency and durability. In methanol fuel cells, graphene used as a barrier layer in the membrane area, has reduced fuel cross over with negligible proton resistance, improving the performance.
In another project, protons easily pass through slightly imperfect graphene membranes on fused silica in water. Protons transferred reversibly from the aqueous phase through the graphene to the other side where they undergo acid—base chemistry with silica hydroxyl groups. Computer simulations indicated energy barriers of 0.
In a graphene coating on steam condensers quadrupled condensation efficiency, increasing overall plant efficiency by percent. Due to graphene's high surface-area-to-mass ratio , one potential application is in the conductive plates of supercapacitors. In February researchers announced a novel technique to produce graphene supercapacitors based on the DVD burner reduction approach. In a supercapacitor was announced that was claimed to achieve energy density comparable to current lithium-ion batteries.
Laser-induced graphene was produced on both sides of a polymer sheet. The sections were then stacked, separated by solid electrolytes, making multiple microsupercapacitors. The stacked configuration substantially increased the energy density of the result. In testing, the researchers charged and discharged the devices for thousands of cycles with almost no loss of capacitance. This makes them potentially suitable for rolling in a cylindrical configuration.
Also in another project announced a microsupercapacitor that is small enough to fit in wearable or implantable devices. Just one-fifth the thickness of a sheet of paper, it is capable of holding more than twice as much charge as a comparable thin-film lithium battery. The design employed laser-scribed graphene, or LSG with manganese dioxide. Their capacity is six times that of commercially available supercapacitors. In May a boric acid -infused, laser-induced graphene supercapacitor tripled its areal energy density and increased its volumetric energy density fold.
The new devices proved stable over 12, charge-discharge cycles, retaining 90 percent of their capacitance. In stress tests, they survived 8, bending cycles. Silicon-graphene anode lithium ion batteries were demonstrated in Stable Lithium ion cycling was demonstrated in bi- and few layer graphene films grown on nickel substrates ,  while single layer graphene films have been demonstrated as a protective layer against corrosion in battery components such as the battery case.
Researchers built a lithium-ion battery made of graphene and silicon , which was claimed to last over a week on one charge and took only 15 minutes to charge. In argon-ion based plasma processing was used to bombard graphene samples with argon ions. That knocked out some carbon atoms and increased the capacitance of the materials three-fold. Graphene does not oxidize in air or in biological fluids, making it an attractive material for use as a biosensor.
Of the various types of graphene sensors that can be made, biosensors were the first to be available for sale. In researchers proposed an in-plane pressure sensor consisting of graphene sandwiched between hexagonal boron nitride and a tunneling pressure sensor consisting of h-BN sandwiched by graphene. This structure is insensitive to the number of wrapping h-BN layers, simplifying process control.
Because h-BN and graphene are inert to high temperature, the device could support ultra-thin pressure sensors for application under extreme conditions.
In researchers demonstrated a biocompatible pressure sensor made from mixing graphene flakes with cross-linked polysilicone found in silly putty. Nanoelectromechanical systems NEMS can be designed and characterized by understanding the interaction and coupling between the mechanical, electrical, and the van der Waals energy domains. Quantum mechanical limit governed by Heisenberg uncertainty relation decides the ultimate precision of nanomechanical systems.
Quantum squeezing can improve the precision by reducing quantum fluctuations in one desired amplitude of the two quadrature amplitudes. Traditional NEMS hardly achieve quantum squeezing due to their thickness limits. A scheme to obtain squeezed quantum states through typical experimental graphene NEMS structures taking advantages of its atomic scale thickness has been proposed.
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Theoretically graphene makes an excellent sensor due to its 2D structure. The fact that its entire volume is exposed to its surrounding environment makes it very efficient to detect adsorbed molecules. However, similar to carbon nanotubes, graphene has no dangling bonds on its surface. Gaseous molecules cannot be readily adsorbed onto graphene surfaces, so intrinsically graphene is insensitive. The thin polymer layer acts like a concentrator that absorbs gaseous molecules.
The molecule absorption introduces a local change in electrical resistance of graphene sensors. While this effect occurs in other materials, graphene is superior due to its high electrical conductivity even when few carriers are present and low noise, which makes this change in resistance detectable.
Density functional theory simulations predict that depositing certain adatoms on graphene can render it piezoelectrically responsive to an electric field applied in the out-of-plane direction. This type of locally engineered piezoelectricity is similar in magnitude to that of bulk piezoelectric materials and makes graphene a candidate for control and sensing in nanoscale devices.
Promoted by the demand for wearable devices, graphene has been proved to be a promising material for potential applications in flexible and highly sensitive strain sensors. An environment-friendly and cost-effective method to fabricate large-area ultrathin graphene films is proposed for highly sensitive flexible strain sensor. Rubber bands infused with graphene "G-bands" can be used as inexpensive body sensors.
The bands remain pliable and can be used as a sensor to measure breathing, heart rate, or movement. Lightweight sensor suits for vulnerable patients could make it possible to remotely monitor subtle movement. Gauge factors of up to 35 were observed. Such sensors can function at vibration frequencies of at least Hz. In researchers announced a graphene-based magnetic sensor times more sensitive than an equivalent device based on silicon 7, volts per amp-tesla. The sensor substrate was hexagonal boron nitride. The sensors were based on the Hall effect , in which a magnetic field induces a Lorentz force on moving electric charge carriers, leading to deflection and a measurable Hall voltage.
In the worst case graphene roughly matched a best case silicon design. In the best case graphene required lower source current and power requirements. Graphene oxide is non-toxic and biodegradable. Its surface is covered with epoxy, hydroxyl, and carboxyl groups that interact with cations and anions. It is soluble in water and forms stable colloid suspensions in other liquids because it is amphiphilic able to mix with water or oil.