Graphene sensors: introduction and market status - Page 39

Researchers at the Technical University of Munich (TUM) have succeeded in linking graphene with a chemical group called porphyrins, which are well-known because of their notable functional properties (for instance, playing a central role in chlorophyll during photosynthesis). These new hybrid structures could be used in the field of molecular electronics, catalysis or even as sensors.

Many researchers focus on wet-chemical methods for attaching the molecules to the surface of the material. The TUM team, however, decided to take a different approach: The researchers were able to link porphyrin molecules to graphene in a controlled manner in an ultra-high vacuum using the catalytic properties of a silver surface on which the graphene layer rested. When heated, the porphyrin molecules lose hydrogen atoms at their periphery and can thus form new bonds with the graphene edges.

Researchers at North Carolina State University have developed a technique that enables the integration of graphene, graphene oxide (GO) and reduced graphene oxide (rGO) onto silicon substrates at room temperature by using nanosecond pulsed laser annealing. The advance may open the door to the possibility of creating new electronic devices, such as smart biomedical sensors.

In this new technique, the researchers start with a silicon substrate. They top that with a layer of single-crystal titanium nitride, using domain matching epitaxy to ensure the crystalline structure of the titanium nitride is aligned with the structure of the silicon. They then place a layer of copper-carbon alloy on top of the titanium nitride, again using domain matching epitaxy. Finally, the researchers melt the surface of the alloy with nanosecond laser pulses, which pulls carbon to the surface.

Researchers at the Korea Institute of Science and Technology (KIST) have developed a highly sensitive graphene-based biosensor capable of diagnosing diseases using a simple blood test.

The graphene-based biosensor can reportedly check the blood concentration of beta amyloid, which is known as a protein that causes dementia, utilizing a blood test for early age-related dementia (Alzheimer's disease) diagnosis. With the sensor, the research team confirmed the diagnostic capability for dementia through the blood samples of transgenic mice and normal mice models.

Department of Energy (DoE) funded researchers investigated the electronic properties of 2D hybrid organic-inorganic perovskite sheets, as an alternative to graphene and other materials. The researchers reported that such perovskites could rival graphene in PV applications, since the 2D crystals exhibited efficient photoluminescence, were easier to grow than graphene and it's possible to dope it to make the various varieties of ionic semiconductors needed to beat other 2D materials with tunable electronic/photonic properties.

Scientists created these new forms of hybrid organic-inorganic perovskites in atomically thin 2D sheets and first showed how they hold promise as semiconductor materials for photovoltaic applications. Next they showed how they could serve as an alternative to other 2D semiconductors that are widely studied as potential successors to silicon in future electronic devices.

Researchers at A*STAR have designed a low-cost, stable and ultrafast graphene oxide-based responsive humidity sensor that is said to be easy to manufacture, overcoming the challenge of producing a simple, fast and highly sensitive version. The ability to monitor and control humidity levels using accurate and reliable sensors is essential for efficient manufacturing and storage practices as well as everyday life.

Unlike most humidity sensors, which are electronic and require a power supply, GO-based colorimetric sensors respond to humidity levels by changing color that can be easily observed. For greater accuracy, the change in color can be quantitatively measured by analyzing the reflection spectra of the sensor. Because the GO sensor operates at the atomic level, it can rapidly respond to moisture changes.

An international team of researchers working at Penn State University have developed a highly sensitive chemical sensor using nitrogen-doped graphene as a substrate. This technique can detect trace amounts of molecules in a solution at very low concentrations.

A model showing the charge transfer (e-) mechanism of Rhodamine B molecules (top) interacting with N-doped graphene (bottom sheet) when excited with different laser lines, which leads to ultrasensitive molecular sensor with N doped graphene.

Raman spectroscopy was used for the development of this sensor, which is a common identification technique used to detect the unique internal vibrations of various molecules: when a laser light irradiates crystals or molecules, it scatters and shifts colors. That scattered light can be detected in the form of a Raman spectrum, which serves as somewhat of a unique fingerprint for every Raman-active irradiated system. Different colors in the visible spectrum will be associated to different energies.

The EU-funded GOSFEL project (Graphene on Silicon Free Electron Laser), demonstrated a new type of compact laser source, which exploits graphene to create a solid-state free electron laser. Compact and low-cost lasers could benefit many indusries, like communications, security, sensors and more.

Free Electron Lasers (FELs) offer an alternative to conventional lasers being potentially the most efficient, high powered and flexible generators of tunable coherent radiation from the ultra-violet to the infrared. However, currently FELs are prohibitively large and expensive. The GOSFEL project used graphene to create a compact, relatively inexpensive, solid-state version of such a laser.

Researchers in the Amber materials science research center at Trinity College Dublin, Ireland, have discovered a new behavior of graphene. They found that they can cause graphene to spontaneously assemble into ribbons and other shapes while lying on a surface. This could prove enough to make large graphene structures almost visible to the naked eye, and it operates in air at room temperature. The discovery was made almost accidentally while cutting graphene sheets, then realizing the techniques caused the graphene to spontaneously arrange itself.

In the short term, the researchers see their findings as potentially useful to pattern graphene sheets to simplify the production of electronic and other devices in larger volumes. However, they also think the self-assembly effect itself may be important as an active component of future sensors, actuators and machines.

Researchers from EPFL have reported the design of a tunable, graphene-based device that could significantly increase the speed and efficiency of wireless communication systems. Their system works at very high frequencies and is said to be delivering unprecedented results.

Current portable wireless systems usually come equipped with reconfigurable circuits that can adjust the antenna to transmit and receive data in the various frequency bands. Unfortunately, currently available technologies like MEMS and MOS that use silicon or metal do not work well at high frequencies - where data can travel much faster. For this end, the EPFL researchers have come up with a tunable graphene-based solution that enables circuits to operate at both low and high frequencies with unprecedented efficiency.

Researchers at the Georgia Institute of Technology have developed an electron beam technique to allow for the complete destruction of electronic data. The electron-beam writing technique that induces the deposition of carbon on a graphene surface, referred to as "focused electron beam induced deposition", is a type of direct-write additive lithographic technique. With the method, by altering the energy levels, exposure time, and location of the e-beam the rate of carbon deposition changes, leading to the re-write and direct-write events occurring.

This method allows for nanoscale engineering of future graphene-based devices for information. This means that not only can data be re-written, the original functionality of the device can be changed and energy storage devices, sensors and nanoelectronics could be re-configured.