What is a sensor?
A sensor is a device that detects events that occur in the physical environment (like light, heat, motion, moisture, pressure, and more), and responds with an output, usually an electrical, mechanical or optical signal. The household mercury thermometer is a simple example of a sensor - it detects temperature and reacts with a measurable expansion of liquid. Sensors are everywhere - they can be found in everyday applications like touch-sensitive elevator buttons and lamp dimmer surfaces that respond to touch, but there are also many kinds of sensors that go unnoticed by most - like sensors that are used in medicine, robotics, aerospace and more.
Traditional kinds of sensors include temperature, pressure (thermistors, thermocouples, and more), moisture, flow (electromagnetic, positional displacement and more), movement and proximity (capacitive, photoelectric, ultrasonic and more), though innumerable other versions exist. sensors are divided into two groups: active and passive sensors. Active sensors (such as photoconductive cells or light detection sensors) require a power supply while passive ones (radiometers, film photography) do not.
Where can sensors be found?
Sensors are used in numerous applications, and can roughly be arranged in groups by forms of use:
- Accelerometers: Micro Electro Mechanical technology based sensors, used mainly in mobile devices, medicine for patient monitoring (like pacemakers) and vehicular systems.
- Biosensors: electrochemical technology based sensors, used for food and water testing, medical devices, fitness tracker and wristbands (that measure, for example, blood oxygen levels and heart rate) and military uses (biological warfare and more).
- Image sensors: CMOS (Complementary Metal-Oxide Semiconductor) based sensors, used in consumer electronics, biometrics, traffic and security surveillance and PC imaging.
- Motion Detectors: sensors which can be Infrared, Ultrasonic or Microwave/Radar technology. They are used in video games, security detection and light activation.
What is graphene?
Graphene is a two-dimensional material made of carbon atoms, often dubbed “miracle material” for its outstanding characteristics. It is 200 times stronger than steel at one atom thick, as well as the world’s most conductive material. It is so dense that the smallest atom of Helium cannot pass through it, but is also lightweight and transparent. Since its isolation in 2004, researchers and companies alike are fervently studying graphene, which is set to revolutionize various markets and produce improved processes, better performing components and new products.
Graphene and sensors
Graphene and sensors are a natural combination, as graphene’s large surface-to-volume ratio, unique optical properties, excellent electrical conductivity, high carrier mobility and density, high thermal conductivity and many other attributes can be greatly beneficial for sensor functions. The large surface area of graphene is able to enhance the surface loading of desired biomolecules, and excellent conductivity and small band gap can be beneficial for conducting electrons between biomolecules and the electrode surface.
Graphene is thought to become especially widespread in biosensors and diagnostics. The large surface area of graphene can enhance the surface loading of desired biomolecules, and excellent conductivity and small band gap can be beneficial for conducting electrons between biomolecules and the electrode surface. Biosensors can be used, among other things, for the detection of a range of analytes like glucose, glutamate, cholesterol, hemoglobin and more. Graphene also has significant potential for enabling the development of electrochemical biosensors, based on direct electron transfer between the enzyme and the electrode surface.
Graphene will enable sensors that are smaller and lighter - providing endless design possibilities. They will also be more sensitive and able to detect smaller changes in matter, work more quickly and eventually even be less expensive than traditional sensors. Some graphene-based sensor designs contain a Field Effect Transistor (FET) with a graphene channel. Upon detection of the targeted analyte’s binding, the current through the transistor changes, which sends a signal that can be analyzed to determine several variables.
Graphene-based nanoelectronic devices have also been researched for use in DNA sensors (for detecting nucleobases and nucleotides), Gas sensors (for detection of different gases), PH sensors, environmental contamination sensors, strain and pressure sensors, and more.
Commercial activities in the field of graphene sensors
In June 2015, A collaboration between Bosch, the Germany-based engineering giant, and scientists at the Max-Planck Institute for Solid State Research yielded a graphene-based magnetic sensor 100 times more sensitive than an equivalent device based on silicon.
In August 2014, the US based Graphene Frontier announced raising $1.6m to expand the development and manufacturing of their graphene functionalized GFET sensors. Their “six sensors” brand for highly sensitive chemical and biological sensors can be used to diagnose diseases with sensitivity and efficiency unparalleled by traditional sensors.
In September 2014, the German AMO developed a graphene-based photodetector in collaboration with Alcatel Lucent Bell Labs, which is said to be the world’s fastest photodetector.
In November 2013, Nokia’s Cambridge research center developed a humidity sensor based on graphene oxide which is incredibly fast, thin, transparent, flexible and has great response and recovery times. Nokia also filed for a patent in August 2012 for a graphene-based photodetector that is transparent, thin and should ultimately be cheaper than traditional photodetectors.
The latest graphene sensor news:
UK-based graphene technology company Paragraf has announced the close of its £12.8 million (over $16 million USD ) Series A round led by Parkwalk. The round also included investment from IQ Capital Partners, Amadeus Capital Partners and Cambridge Enterprise, the commercialization arm of the University of Cambridge, as well as several angel investors. The funding will aim to see Paragraf’s first graphene-based electronics products reach the market, transitioning the company into a commercial, revenue-generating entity.
Paragraf sets out to deliver IP-protected graphene technology using standard, mass production scale manufacturing approaches, enabling step-change performance enhancements to today’s electronic devices. The company’s first sensor products have reportedly demonstrated order of magnitude operational improvements over today’s incumbents. Achieving large-scale, graphene-based production technology may enable next generation electronics, including vastly increased computing speeds, significantly improved medical diagnostics and higher efficiency renewable energy generation as well as currently unachievable products such as instant charging batteries and very low power, flexible electronics.
Researchers at the U.S-based University of Rochester, along with colleagues at Delft University of Technology in the Netherlands, have designed a way to produce graphene materials using a novel technique: mixing oxidized graphite with bacteria. Their method is reportedly a more cost-efficient, time-saving, and environmentally friendly way of producing graphene materials versus those produced chemically, and could lead to the creation of innovative computer technologies and medical equipment.
"For real applications you need large amounts," says Anne S. Meyer, an associate professor of biology at the University of Rochester. "Producing these bulk amounts is challenging and typically results in graphene that is thicker and less pure. This is where our work came in". In order to produce larger quantities of graphene materials, Meyer and her colleagues started with a vial of graphite. They exfoliated the graphite-shedding the layers of material-to produce graphene oxide (GO), which they then mixed with the bacteria Shewanella. They let the beaker of bacteria and precursor materials sit overnight, during which time the bacteria reduced the GO to a graphene material.
Researchers from the Moscow Institute of Physics and Technology (MIPT) and Valiev Institute of Physics and Technology in Russia have demonstrated resonant absorption of terahertz radiation in commercially available graphene. The team declared this to be an important step toward designing efficient terahertz detectors, which would enable faster internet and a safe replacement for X-ray body scans.
THz radiation, also known as T-waves, is considered difficult to generate and detect. This gave rise to the notion of a “terahertz gap,” which roughly refers to the 0.1-10 THz frequency band in the electromagnetic spectrum. There are no efficient devices for generating and detecting radiation in this range. Nevertheless, T-waves are very important for humanity: They do not harm the body and so could replace X-rays in medical scans. Also, T-waves could make Wi-Fi much faster and open the door to astronomical research that is thus far untapped .
Researchers at Osaka University have invented a graphene-based biosensor to detect bacteria such as those that attack the stomach lining and that have been linked to stomach cancer. When the bacteria interact with the biosensor, chemical reactions are triggered which are detected by the graphene.
To enable detection of the chemical reaction products, the researchers used microfluidics to contain the bacteria in extremely tiny droplets close to the sensor surface.
Researchers at The University of Texas at Austin have developed a graphene-based wearable device that can be placed on the skin to measure a variety of body responses, from electrical to biomechanical signals.
The device is so lightweight and stretchable that it can be placed over the heart for extended periods with little or no discomfort. It also measures cardiac health in two ways, taking electrocardiograph and seismocardiograph readings simultaneously. The electrocardiogram (ECG) technique, a method that records the rates of electrical activity produced each time the heart beats. is rather well-known. Seismocardiography (SCG), a measurement technique using chest vibrations associated with heartbeats, is a bit less so. Powered remotely by a smartphone, the e-tattoo is the first ultrathin and stretchable technology to measure both ECG and SCG.