Graphene sensors: introduction and market status - Page 52

Researchers from Korea's Sungkyunkwan University vertically integrated ZnO nanowires on graphene foams (3D graphene) and used this as electrodes for Parkinson's disease detection - to selectively detect uric acid (UA), dopamine (DA), and ascorbic acid (AA) by a differential pulse voltammetry (DPV) method.

The researchers explain that their electrode is optimized as it has a large surface area with mesoporous 3D graphene structures that facilitate ion diffusion easily. It also features high conductivity from the 3D graphene foam and high selectivity due to the active sites of the ZnO surface.

Students from Northwestern University managed to use pencils and regular paper to create functional sensor devices. They created two types of sensors - strain sensors and chemical vapor sensors.

Pencil and paper strain sensor

The students had a discussion about the conductive properties of graphene. They realized that when you draw a line on a piece of paper with a pencil, the pencil's graphite sheds numerous graphene sheets. They started exploring what these graphene sheets can be used for, and the first thing they tried is making a basic electrode.

Two months ago, Graphene Labs and Lomiko Metals launched a new company called Graphene 3D Labs that focuses on the development of high-performance graphene-enhanced materials for 3D Printing. Now we hear that Graphene 3D Lab filed a provisional patent application for the use of graphene-enhanced material, along with other materials, in 3D printing. This will enable the 3D printing of electronics devices - such as electronic circuits, sensors, or batteries.

The company's CEO, Daniel Stolyarov, says that they use Lomiko's high-quality graphene as the base material for producing graphene nanoplatelets, due to their cost and consistency in quality. The company says that adding graphene to polymers which are conventionally used in 3D printing improves the properties of the polymer in many different ways; it improves the polymers mechanical strength as well as its electrical and thermal conductivity.

Researchers from MIT and the University of California at Berkeley developed a new way to evenly functionalize graphene with oxygen at low (50-80 C) temperatures. The method is environmentally friendly (no harsh chemical treatment) and can be applied on a large scale.

The researchers use low-temperature annealing and this cause the oxygen atoms to form clusters. This leaves areas of pure-graphene between the oxygen clusters. This decreases the graphene's electrical resistance by four to five orders of magnitude (the oxygen clusters are insulating) which is good for applications such as sensing, electronics and catalysis.

Korean researchers developed a liquid-ion gated FET-type graphene-based aptasensor with highly sensitive and selective responses to various mercury ion concentrations. This sensor was shown to be a good detector of mercury in mussels.

Aptasensors are bio-sensors that use aptamers (artificial oligonucleotides: DNA or RNA) as a recognition element. The sensors developed in korea used a single-layer graphene sheet that was functionalized using an aptamer. This sensor is not just very sensitive and fast, but it's also flexible and highly stable mechanically.

Researchers from Nokia's Research Center in Cambridge developed a new humidity sensor based on graphene oxide. The researchers say that the new sensor is ultra fast (the fastest humidity sensor ever reported, in fact), thanks to the graphene 2D structure and its superpermeability to water molecules. The sensor Nokia developed is thin (15 nm), transparent and flexible.

The sensor's response and recovery time (the time to go from 10% to 90% of the high humidity value and vice versa) is less than 100 ms. The response rate is a function of the thickness of the GO, the thicker the film, the slower the sensor. Nokia has filed several patent applications regarding this work.

Researchers from Columbia University used graphene to produce the world's smallest FM radio transmitter using NEMS (nanoelectromechanical system, a scaled-down versions of MEMS which are used mostly for sensing of vibration or acceleration). This is not a practical FM radio design, but this technology may be used in wireless signal processing.

The researchers built a voltage controlled oscillator (VCO) that is used to create a FM signal. They used graphene to make a NEMS device with a frequency of about 100 Mhz (FM radio uses 87.7 to 108 Mhz). Low-frequency music signals from an iPhone were used to module the carrier signal, and these can be heard by using an ordinary FM receiver.

Researcher from Columbia University demonstrated that it is possible to electrically contact an atomically thin graphene (or any 2D material) only along its edge (rather than contacting it from the top). This new architecture enabled a new assembly technique that prevents interface contamination. This new assembly process resulted in the cleanest graphene ever made. They say that the new edge-contact geometry actually provides a more efficient contact without the need for complex processing.

This research work solved two graphene problems - contamination and contact. Having contacts just at the edges virtually eliminates external contamination. To achieve this breakthrough, the researchers fully encapsulated a single graphene sheet in a sandwich of thin insulating boron nitride crystals, employing a new technique in which crystal layers are stacked one-by-one.

Researchers at Purdue University are developing a new graphene "nanopetals" mass production process. Those nanopetals are graphene-based vertical nanostructures that look like tiny rose petals, and they have applications in sensors, heat-management, supercapacitors and batteries. This research is funded with a $1.5 million grant from the NSF.

The researchers hope to increase the production speed of nanopetal-coated surfaces to 10 square meters per hour, using a roll-to-roll process. This is a dramatic increase to current "laboratory-scale" production rate. The new process will use a vacuum-based plasma-enhanced chemical vapor deposition (PECVD).

Back in June 2013, Haydale (owned by ICL from May 2011) announced that it developed metal-free graphene-based inks. Haydale, established in 2003 with strong links with Swansea University, is developing and marketing carbon materials under the HDPlas brand. The company currently focuses on graphene, CNTs and zinc nanomaterials. Ray Gibbs, ICL's Commercial Directory was kind enough to update us on Haydale's new inks and more aspects of their business and technology.

Haydale developed their own Split-Plasma process to convert mined graphite ore into functionalised graphene flakes (nanoplatelets). This scalable and environmentally friendly method is claimed to be significantly quicker and substantially more cost efficient than other methods. Split-Plasma does not damage the materials and can be controlled to provide appropriate functionalisation levels that are not restricted to the chemical groups associated with other "wet" chemistry processing methods. One of its unique characteristics is that the process can (and has) been used to functionalise synthetically produced graphene materials.