From Wikipedia, the free encyclopedia

Potential graphene applications include lightweight, thin, flexible, yet durable display screens, electric circuits, and solar cells, as well as various medical, chemical and industrial processes enhanced or enabled by the use of new graphene materials.[1]

In 2008, graphene produced by exfoliation was one of the most expensive materials on Earth, with a sample the area of a cross section of a human hair costing more than $1,000 as of April 2008 (about $100,000,000/cm2).[2] Since then, exfoliation procedures have been scaled up, and now companies sell graphene in large quantities.[3] The price of epitaxial graphene on Silicon carbide is dominated by the substrate price, which was approximately $100/cm2 as of 2009.

Hong and his team in South Korea pioneered the synthesis of large-scale graphene films using chemical vapour deposition (CVD) on thin nickel layers, which triggered research on practical applications,[4] with wafer sizes up to 30 inches (760 mm) reported.[5]

In 2013, the European Union made a €1 billion grant to be used for research into potential graphene applications.[6]

In 2013 the Graphene Flagship consortium formed, including Chalmers University of Technology and seven other European universities and research centers, along with Nokia.[7]

Medicine

Tissue engineering

Graphene has been investigated for tissue engineering. It has been used as a reinforcing agent to improve the mechanical properties of biodegradable polymeric nanocomposites for engineering bone tissue applications.[8] Dispersion of low weight % of graphene (~0.02 wt.%) increased in compressive and flexural mechanical properties of polymeric nanocomposites.

Contrast agents/bioimaging

Functionalized and surfactant dispersed graphene solutions have been designed as blood pool MRI contrast agents.[9] Additionally, iodine and manganese incorporating graphene nanoparticles have served as multimodal MRI-CT contrast agents.[10] Graphene micro- and nano-particles have served as contrast agents for photoacoustic and thermoacoustic tomography.[11] Graphene has also been reported to be efficiently taken up cancerous cells thereby enabling the design of drug delivery agents for cancer therapy.[12] Graphene nanoparticles of various morphologies are non-toxic at low concentrations and do not alter stem cell differentiation suggesting that they may be safe to use for biomedical applications.[13]

Polymerase chain reaction

Graphene is reported to have enhanced PCR by increasing the yield of DNA product.[14] Experiments revealed that graphene's thermal conductivity could be the main factor behind this result. Graphene yields DNA product equivalent to positive control with up to 65% reduction in PCR cycles.[citation needed]

Devices

Graphene's modifiable chemistry, large surface area, atomic thickness and molecularly gatable structure make antibody-functionalized graphene sheets excellent candidates for mammalian and microbial detection and diagnosis devices.[15] Graphene is so thin water has near-perfect wetting transparency which is an important property particularly in developing bio-sensor applications.[16] This means that a sensors coated in graphene have as much contact with an aqueous system as an uncoated sensor, while it remains protected mechanically from its environment.

Energy of the electrons with wavenumber k in graphene, calculated in the Tight Binding-approximation. The unoccupied (occupied) states, colored in blue–red (yellow–green), touch each other without energy gap exactly at the above-mentioned six k-vectors.

Integration of graphene (thickness of 0.34 nm) layers as nanoelectrodes into a nanopore[17] can potentially solve a bottleneck for nanopore-based single-molecule DNA sequencing.

On November 20, 2013 the Bill & Melinda Gates Foundation awarded $100,000 'to develop new elastic composite materials for condoms containing nanomaterials like graphene'.[18]

In 2014, graphene-based, transparent (across infrared to ultraviolet frequencies), flexible, implantable medical sensor microarrays were announced that allow the viewing of brain tissue hidden by implants. Optical transparency was >90%. Applications demonstrated include optogenetic activation of focal cortical areas, in vivo imaging of cortical vasculature via fluorescence microscopy and 3D optical coherence tomography.[19][20]

Drug delivery[edit]

  • Researchers in Monash University discovered that the sheet of graphene oxide can be transformed into liquid crystal droplets spontaneously – like a polymer - simply by placing the material in a solution and manipulating the pH. The graphene droplets change their structure at the presence of an external magnetic field. This finding opens the door for potential use of carrying drug in the graphene droplets and drug release upon reaching the targeted tissue when the droplets change shape under the magnetic field. Another possible application is in disease detection if graphene is found to change shape at the presence of certain disease markers such as toxins.[21][22]
  • A graphene ‘flying carpet’ was demonstrated to deliver two anti-cancer drugs sequentially to the lung tumor cells (A549 cell) in a mouse model. Doxorubicin (DOX) is embedded onto the graphene sheet, while the molecules of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) are linked to the nanostructure via short peptide chains. Injected intravenously, the graphene strips with the drug playload preferentially concentrate to the cancer cells due to common blood vessel leakage around the tumor. Receptors on the cancer cell membrane bind TRAIL and cell surface enzymes clip the peptide thus release the drug onto the cell surface. Without the bulky TRAIL, the graphene strips with the embedded DOX are swallowed into the cells. The intracellular acidic environment promotes DOX’s release from graphene. TRAIL on the cell surface triggers the apoptosis while DOX attacks the nucleus. These two drugs work synergistically and were found to be more effective than either drug alone.[23][24]

Biomicrorobotics

Researchers demonstrated a nanoscale biomicrorobot (or cytobot) made by cladding a living endospore cell with graphene quantum dots. The device acted as a humidity sensor.[25]

Testing

In 2014 a graphene based blood glucose testing product was announced.[26][27]

Electronics

For integrated circuits, graphene has a high carrier mobility, as well as low noise, allowing it to be used as the channel in a field-effect transistor. Single sheets of graphene are hard to produce and even harder to make on an appropriate substrate.[28]

In 2008, the smallest transistor so far, one atom thick, 10 atoms wide was made of graphene.[29] IBM announced in December 2008 that they had fabricated and characterized graphene transistors operating at GHz frequencies.[30] In May 2009, an n-type transistor was announced meaning that both n and p-type graphene transistors had been created.[31][32] A functional graphene integrated circuit was demonstrated – a complementary inverter consisting of one p- and one n-type graphene transistor.[33] However, this inverter suffered from a very low voltage gain.

According to a January 2010 report,[34] graphene was epitaxially grown on SiC in a quantity and with quality suitable for mass production of integrated circuits. At high temperatures, the quantum Hall effect could be measured in these samples. IBM built 'processors' using 100 GHz transistors on 2-inch (51 mm) graphene sheets.[35]

In June 2011, IBM researchers announced that they had succeeded in creating the first graphene-based integrated circuit, a broadband radio mixer.[36] The circuit handled frequencies up to 10 GHz. Its performance was unaffected by temperatures up to 127 °C.

In June 2013 an 8 transistor 1.28 GHz ring oscillator circuit was described.[37]

Transistors

Graphene exhibits a pronounced response to perpendicular external electric fields, potentially forming field-effect transistors (FET). A 2004 paper documented FETs with an on-off ratio of ~30 at room temperature.[citation needed] A 2006 paper announced an all-graphene planar FET with side gates.[38] Their devices showed changes of 2% at cryogenic temperatures. The first top-gated FET (on–off ratio of <2 2007.="" class="reference" demonstrated="" id="cite_ref-39" in="" sup="" was="">[39]