Graphene sensors: introduction and market status - Page 30

As part of a national research collaboration, Spanish researchers including the ICN2 have reached a milestone in graphene research, that potentially brings science a step closer to using graphene in filtration and sensing applications.

The researchers have successfully synthesized a graphene membrane with pores whose size, shape and density can be tuned with atomic precision at the nanoscale. Engineering pores at the nanoscale in graphene can change its fundamental properties. It becomes permeable or sieve-like, and this change alone, combined with graphene's intrinsic strength and small dimensions, points to its future use as the most resilient, energy-efficient and selective filter for extremely small substances including greenhouse gases, salts and biomolecules.

A research team from Japan has developed an integrated, high-speed and on-chip blackbody emitter based on graphene. The team reports that the device operated in NIR region including telecommunication wavelengths. A fast response time of ~ 100 ps, which is ~ 105 higher than the previous graphene emitters, has been experimentally demonstrated for single and few-layer graphene, the emission responses can be controlled by the graphene contact with the substrate depending on the number of graphene layers.

The team stated that graphene light emitters are greatly advantageous over conventional compound semiconductor emitters because they can be integrated on silicon chips due to simple fabrication processes of graphene emitters and direct coupling with silicon waveguide through an evanescent field. Because graphene can realize high-speed, small footprint and on-Si-chip light emitters, which are still challenges for compound semiconductors, the graphene-based light emitters can open new routes to highly integrated optoelectronics and silicon photonics.

Scientists from the Shanghai Institute of Ceramics in China have developed a 'smart' wallpaper based on highly flexible fire-resistant inorganic paper embedded with ultralong hydroxyapatite nanowires that serve as the substrate and graphene oxide as the thermosensitive sensor.

The authors explain: "After the paper-making process, hydroxyapatite nanowires and glass fibers are assembled into a well-defined multilayered structure spontaneously, which may be explained by the mechanical equilibrium between physical and chemical forces. The nacre-like multilayered structure is regarded as an effective strategy to balance the strength and toughness".

Researchers at Zhejiang University in China have designed a new type of aerogels, made of graphene and carbon nanotubes, that can be reversibly stretched to more than three times their original length, displaying elasticity similar to that of a rubber band. This stretchability, in addition to aerogels' existing properties like ultralow density, light weight, high porosity, and high conductivity, may lead to exciting new applications.

The scientists designed carbon aerogels consisting of both graphene and multi-walled carbon nanotubes assembled into four orders of hierarchical structures ranging from the nanometer to centimeter scale. To fabricate the material into aerogels, the researchers created an ink composed of graphene oxide and nanotubes, and then formed the aerogels via inkjet printing.

Graphite company Archer Exploration has redefined its existing relationship with the University of Adelaide, by shifting developmental focus away from industrial graphite applications to more consumer-focused graphene-based products.

The collaboration will aim to develop and implement graphene and carbon-based materials for use in complex biosensing which can target applications in human health. Research will explore graphene-based materials for complex biosensing to generate patents with commercial applications and will combine AXE's graphite and graphene materials with the research and development capability of the university.

A team of Chinese scientists from South China Normal University and Beihang University has used graphene to create an artificial gas detector that is as good as a dog's nose. Their work showed that the graphene-based nanoscrolls can mimic a dog's sensitive sniffer, which is lined with millions of tiny capillaries. Since the capillaries cover such a large surface area, they can detect smells at extremely low concentrations.

Drawing inspiration from the capillary structure, the researchers found a way to modify graphene with a polymer to make high-quality nanoscrolls. These nanoscrolls have a large surface area similarly to a dog's nose. They are stable at high temperatures, and are strong and durable.

Fraunhofer scientists have developed biosensors with graphene electrodes, produced cheaply and simply by roll-to-roll printing. A system prototype for mass production has already been established. This may change the current situation in which cell-based biosensors can be quite expensive to make, which often prevents them from being used. Cost factors for sensors that perform measurements electrically are the expensive electrode material and complex production.

Cell-based biosensors measure changes in cell cultures via electrical signals. This is done using electrodes which are mounted inside the Petri dish or the wells of a 'well plate'. If added viruses destroy a continuous cell layer on the electrodes, for example, the electrical resistance measured between the electrodes is reduced. In this way, the effect of vaccines or drugs (for example) can be tested: the more effective the active ingredient is, the smaller the number of cells that are destroyed by the viruses and the lower the measured resistance change will be. Also toxicity tests, such as on cosmetic products, can function according to the same principle and may replace animal experiments in the future. Another advantage is that if biosensors are linked to an evaluation unit, measurements can be continuous and automated.

The Graphene Pavilion at the GSMA Mobile World Congress has showcased two fascinating graphene-based photonics devices. The first is said to be the world's first all-graphene optical communication link operating at a data rate of 25 Gb/s per channel, and the second one, displayed at the Ericsson stand, is the first ultra-fast graphene-based photonic switch in an Ericsson testbed. These graphene-based photonic devices may become the building blocks of the next generation of mobile networks.

"5G will all be about optical communications, and the realization of the ultra-fast optical communication link with graphene is a real breakthrough. It is very exciting that it is already on display at the Ericsson stand," said ICREA Professor Frank Koppens from ICFO (The Institute of Photonic Sciences), Barcelona, the Scientific Chair of the Graphene Pavilion.

A team led by researchers from the Indian Institute of Technology (IIT) in Bombay, India, has developed a graphene-enhanced inexpensive, flexible pressure sensor that can be used for various health-care applications. The piezoresistive pressure sensor can reportedly monitor even small-scale movements caused by low-pressure variations.

The sensor can measure blood pulse rate in real time when placed on the wrist and neck. The sensor was also tested for its ability to monitor respiration; When placed on the throat, the sensor could detect changes in pressure when different words were pronounced. Interestingly, the fabricated sensor also showed good sensitivity in detecting large-scale motion monitoring, as in the case of bending and extension of finger joints.

Researchers from the University of British Columbia’s Okanagan campus have created a graphene-based wearable device capable of sensing and understanding complex human motion. This could lead to a practical way to monitor and interpret human motion, in what may become the next generation of health monitors.

The sensor called the GNF-Pad was made by infusing graphene nanoflakes into a rubber-like adhesive pad. According to the team, the sensor’s durability was tested by stretching it to see if it could maintain accuracy under strains of up to 350%. The device went through more than 10,000 cycles of stretching and relaxing while maintaining its electrical stability.