Graphene
Graphene is a wonder material having incredible properties first discovered at the University of Manchester in 2004. It is an ultra thin form of carbon with a lot of promise applications ranging from ultra fast transistors to DNA sequencing and flexible electronic screens. Graphene was discoed by Andre Geim and Konstantin Novoselov in 2010 for which they were awarded the Nobel Prize for Physics.
Small scale production
A simple technique of making graphene is the "Scotch tape" method of isolating graphene. This involves placing a sample of graphite onto sticky tape and then folding and peeling the tape several times to create progressively thinner layers of graphite eventually leading to a single layer of carbon.
Single-layer graphene can be identified using optical microscope by transferring the graphene to a silicon-based substrate and creating correct contrast to identify thin sheets of carbon. Graphene is the thinnest and strongest material with unusual electrical and optical properties. The electrons in graphene behave as if they are particles of light and do not get scattered.
Large scale production
Researchers at Rutgers University have successfully deposited thin films of chemically derived graphene oxide onto large wafers of silicon to 30 cm size which was previously done on few centimeters size.
Graphene oxide films are transparent and their electrical properties can be tuned from semi conducting to metallic by controlling their thickness. These and other interesting optoelectronic properties could be exploited by fabricating devices on various platforms.
The films produced are highly uniform over large areas and atomically thin. They are deposited by spin coating a concentrated aqueous solution of graphene oxide onto hydroxylated surfaces of Si/SiO2 while controlling the evaporation rate of the solvent used. The films can then be transferred onto any other substrate, or left freestanding. The film thickness can be controlled to vary from 1–2 layers to up to 30 layers, by simply changing the spin-coating speed, graphene oxide concentration or number of deposition cycles.
The films produced are electrically active and field-effect transistors can be made using the films. The material could be used in transparent electrodes for optoelectronic devices, such as solar cells and light-emitting diodes.
Cell growth on graphene oxide
Graphene oxide encourages the proliferation of bacteria and mammalian cells on its surface. Graphene oxide can be exploited in biomedicine and biotechnology to help develop materials and surfaces that could be used to culture human cells for tissue engineering or help produce increased amounts of biopharmaceuticals. If nutrients are included in the culture media on graphene oxide, the cells grow even faster and with higher density compared with cultures without it. In particular bacteria, they tend to form thick biofilms packed with bacteria and extra cellular polymeric substances.
Graphene oxide allows faster and more efficient growth of cells would indeed find many applications in the fields of biomedicine and biotechnology. Graphene oxide could be used to develop materials and surfaces that would be used to culture human cells for tissue engineering or to grow structures that could help heal wounds. This can be deployed in bioreactors to increase the production of biopharmaceuticals or to enhance the production of alternative fuels by organisms specially engineered for these purposes.
Graphene oxide paper
Graphene oxide has been created in to paper that is stiff and extremely strong but can be folded, wrinkled and slightly stretched. Researchers from Northwestern University in the US including Rodney Ruoff have discovered that large quantities of oxidized graphene can be weaved together into create a new type of paper that is stiffer and stronger than other thin materials.
Production
Graphite is oxidized to make graphite oxide leaving roughly half the carbon atoms with an attached oxygen atom, which is then mixed with water where these oxygen atoms repel water molecules, forcing the individual graphene oxide layers to disperse or "exfoliate". The researchers filter this exfoliated mixture through a membrane to collect the layers in such an arrangement to produce graphene oxide paper.
Structure
Normal graphite has a delicate structure, needing only a small lateral force to break apart its regularly-stacked layers, but the layers in graphene oxide paper interweave with one another and wrinkle on larger scales. This allows load to be distributed across the structure, making it stronger than graphite foil and "bucky paper", which is made from carbon nanotubes.
The interwoven structure also lets individual layers shift over each other, so that the collective layers become pliable. The paper can be chemically tuned by altering the amount of oxygen on the layers and by reducing the oxygen content it can be made in to a good conductor. The paper could be infused with polymers, ceramics or metals, to make composite materials that outperform their pure counterparts.
This wide array of properties could mean applications as diverse as membranes with controlled permeability to super capacitors for energy storage. This carbon-based material can be adapted for applications including molecular storage, ion conductors and super capacitors.
Antibacterial paper
Researchers at the Chinese Academy of Sciences have demonstrated that graphene could be used to make antibacterial paper to effectively stop the growth of E. Coli bacteria without being toxic to human cells.
The researchers have found that graphene derivatives, like graphene oxide and reduced graphene oxide, inhibit bacterial growth. Previous studies showed that graphene, and particularly graphene oxide is biocompatible and that biological cells can grow well on graphene substrates. While other nanoparticles, like silver, are well known antibacterial materials, they are often cytotoxic.
Production
The researchers made graphene paper by first synthesizing graphene oxide and reduced graphene oxide in water. This solution was then filtered through paper under vacuum. Freestanding graphene oxide and reduced graphene oxide sheets were then peeled off from the filter paper.
Antibacterial property
The cell membranes of E. Coli bacteria placed on the graphene sheets were severely destroyed. This occurs because graphene enters the endosome of the cell's cytoplasm, pushing it out of the cell. Almost 99% of the cells were destroyed after just two hours in contact with an 85 g/mL solution of graphene oxide at 37 °C. In contrast, the nanosheets were not toxic to mammalian cells under the same conditions.