Graphene sensors: introduction and market status - Page 54

Researchers from the University of Minnesota developed graphene-based quantum capacitance wireless vapor sensors. The sensor is made from a metal-oxide-graphene variable capacitor (varactor) coupled to an inductor, creating a resonant oscillator circuit. The resonant frequency is found to shift in proportion to water vapor concentration.

So basically in these sensors, a change in adsorbed water vapor concentration on the graphene surface translates into a shift in the resonant frequency of a resonant oscillator circuit. The sensors show fast response to abrupt changes in the humidity and further show a monotonic frequency shift with relative humidity that is reversible and stable, particularly after conditioning using repetitive humidity cycling.

Markets and Markets released a new graphene market report ("Graphene Electronics Market: 2013-2023") in which they forecast that the total graphene technology market will grow at an estimated 55.54% CAGR (Compound annual growth rate).

The total graphene market will reach $100 million in 2018 - and it will be used in a range of applications including RFID, smart packaging, supercapacitors, composites, ITO replacement, sensors, logic, memory and others. Overall the market will remain rather small according to this report. While graphene may revolutionaize a lot of industries and enable new products, the forecast is not promising for graphene producers and suppliers.

Attaching molecules to graphene is required for several applications (for example, attaching bio-molecules to enable bio-sensors), but graphene rejects these molecules. Now researchers from the Universities of Miami and California say that a slight pressure can help functionalize graphene.

It has been shown before that Graphene can participate in Diels-Alder reactions either as the diene or the dienophile, and it is well known that pressure accelerates this reaction. These researchers used polymer tips (80 nm wide), coated them with inks that are Diels-Alder reactants, and applied a gentle force to push the tips into a graphene sheet (the tips were mounted on an atomic force microscope). This created 20 µm by 40 µm patches of graphene decorated with patterns of dye dots.

Researchers from Nanyang Technological University developed a new camera sensor made from graphene that can detect a broad light spectrum - from visible to mid-infrared - at high sensitivity. The new sensor is 1,000 times more sensitive to light than current imaging sensors, yet it uses 10 times less energy as it operates at low voltages.

The researchers say that they used existing manufacturing practices (a CMOS process) which means that these new sensors can be commercialized rather easily. They now intent to find industry partners to develop this into a real product.

Graphene based sensors are made from an insulating layer coated with a graphene sheet. A worldwide research team led by the University of Illinois discovered that one can improve the sensitivity of graphene bases sensors by manipulating the chemical properties of the insulating layer used in those sensors.

It is known that a perfect graphene sheet is insensitive to other gas molecules, and it has to have "defects" to make it work. If the insulating layer is also perfect, the device is still not sensitive. But it turns out that a perfect graphene sheet on a insulating layer that has defects is also sensitive. This opens up a new "design space" for sensors - one can control the sensitivity by adding defects either to the graphene layer or the insulating layer.

Researchers from Kansas State University developed improved electron-tunneling based humidity, pressure or temperature sensing devices using graphene quantum dots. Those devices are more responsive in vacuum compared to most sensors. They will be able to detect trace amounts of water on Mars, for example.

To create the Quantum Dots, the researchers used nanoscale graphite cuttings to produce graphene nanoribbons. Chemically cleaving those ribbons into 100 nanometer sized pieces created the quantum dots.

Researchers from the Irish nanoscience institute CRANN developed a new graphene-based sensor technology that could become a new platform for low-energy, remotely powered sensors for all sorts of applications. One such application, specifically mentioned by the researchers is air quality control systems in automobiles. Other applications may include bacteria and parasite detection and diseases diagnosis.

The researchers developed what they refer to as Chemically Modulated Graphene Diodes (or GDS). These are made from a single layer of graphene on silicon. The graphene is exposed to liquids or gases and the diode can be made (by different doping) so that various absorbates will transfer charge.

Researchers from the Universities of Manchester and Nottingham developed a new ultra-fast bi-stable graphene transistor. They say that such transistors may enable new medical imaging and security devices.

A bi-stable transistor means that it can spontaneously switch between two electronic states. This new device is made from two layers of graphene separated by a boron nitride insulating layer. By applying a small voltage, you can tune the electron clouds in the graphene layers which induces the electrons so they move at high speed between the layers (by quantum tunneling over the thin insulating layer). This emits high-frequency electromagnetic waves (in the range between radar and infra-red).

Researchers from China's Xinyang Normal University developed a new titanium dioxide-modified graphene electrode that can detect the electrochemical signals of Orange II. This material, commonly used in OLEDs, wood stains and the textiles industry is sometimes illegally used to add red color to food, even though it is highly toxic.

The researchers say that their electrode detected nanomolar concentrations of Orange II in ketchup and chili product samples. Current Orange II detection techniques, such as chromatography-mass spectrometry and polarography, require complicated instrumentation and are time consuming and unsuitable for in situ analysis.

The UK's Engineering and Physical Sciences Research Council (EPSRC) awarded a £3.5 million ($5.3 million) to the University of Manchester, for graphene membranes research, with an aim to bring desalination plants, safer food packaging and enhanced disease detection closer to reality.

These highly selective graphene membranes are made from graphene platelets. The aim of the project is to produce working prototypes together with industrial partners. The university researchers already demonstrated that graphene oxide membranes are highly permeable to water, while being completely impermeable to gases and organic liquids when dry. Now they plan to combine graphene with a new type of polymers invented at Manchester (called Polymers of Intrinsic Microporosity, or PIMs) which hopefully enable membranes that are even better than pure graphene ones.