Graphene sensors: introduction and market status

Polaritons are coupled excitations of electromagnetic waves with either charged particles or vibrations in the atomic lattice of a given material. One of their most attractive properties is the capacity to confine light at the nanoscale, which is even more extreme in two-dimensional (2D) materials. 2D polaritons have been investigated by optical measurements using an external photodetector. However, their effective spectrally resolved electrical detection via far-field excitation remains unexplored. This hinders their exploitation in crucial applications such as sensing, hyperspectral imaging, and optical spectrometry, banking on their potential for integration with silicon technologies. 

Recently, researchers from Spain's ICFO, the University of Ioannina, Universidade do Minho, the International Iberian Nanotechnology Laboratory, Kansas State University, the National Institute for Materials Science (Tsukba, Japan), POLIMA (University of Southern Denmark) and URCI (Institute of Materials Science and Computing, have reported on the electrical spectroscopy of polaritonic nanoresonators based on a high-quality 2D-material heterostructure, which serves at the same time as the photodetector and the polaritonic platform. Subsequently, the team electrically detected these mid-infrared resonators by near-field coupling to a graphene pn-junction. The nanoresonators simultaneously exhibited extreme lateral confinement and high-quality factors. 

While graphene aerogels have advantageous properties like extremely low weight, high porosity and good electrical conductivity, engineers who tried to use them to develop pressure sensors have encountered some difficulties. 

Image credit: Nano Letters 2024

Specifically, many of these materials have an intrinsically stiff microstructure, which poses limits on their strain sensing capabilities. Researchers from Xi'an Jiaotong University, Northumbria University, UCLA, University of Alberta and other institutes recently introduced a new fabrication strategy for synthesizing aerogel metamaterials to overcome this limitation. This strategy fabricates a durable graphene oxide-based aerogel metamaterial that exhibits a remarkable sensitivity to human touch and motion.

Researchers from Korea, including ones from Seoul National University and Korea Research Institute of Standards and Science, have developed a room-temperature self-activated graphene gas sensor functionalized by nickel oxide (NiO) nanoparticles and demonstrated its application to wearable devices monitoring ammonia gas.

The team introduced NiO nanoparticles onto graphene micropatterns to create a highly selective and sensitive ammonia sensor that can operate effectively even in the demanding conditions of wearable electronics. This advancement represents a potential step forward in sensor technology, particularly for applications such as food quality monitoring and wearable devices that track air quality.

Researchers from the University of Cambridge, University College London, Imperial College London, Kumoh National Institute of Technology (KIT) and Beihang University have developed a wearable ‘smart’ choker for speech recognition, that has the potential to redefine the field of silent speech interface (SSI) thanks to embedded ultrasensitive textile strain sensor technology.

Where verbal communication is hindered, such as in locations with lots of background noise or where an individual has an existing speech impairment, SSI systems are a cutting-edge solution, enabling verbal communication without vocalization. As such, it is a type of electronic lip-reading using human-computer interaction. In their recent research, the scientists applied an overlying structured graphene layer to an integrated textile strain sensor for robust speech recognition performance, even in noisy environments.

Archer Materials has started experiments to detect and monitor chronic kidney disease on its Biochip graphene field effect transistor (“gFET”) sensors.

Archer, through one of its foundry partners, has reportedly verified a process that directly grows graphene surfaces to produce enhanced devices, rather than transferring the graphene to a device from a wafer, as previously done. The team has tested the devices by storing them in normal air conditions over a two-month period, finding no significant degradation in performance. 

Researchers from Tufts University recently developed a graphene-enhanced highly sensitive saliva-based cortisol sensor – eliminating the need for invasive blood tests.

The Point-of-Care (POC) electrochemical biosensor boasts a detection limit of 0.24 fg/mL, making it 100 times more sensitive than existing saliva tests. This innovation relies on the Gii-Sens “electrode” – a sensing strip produced by nanomaterial company, iGii – integrated into the sensor. 

In 2015, scientists at James Cook University in Queensland, Australia, and collaborators from institutions in Australia, Singapore, Japan, and the US developed a technique for growing graphene from tea tree extract. Now, scientists from James Cook University developed a process to synthesize graphene from tangerine peel oil, which they then used to recover silver from waste PV material. To demonstrate the quality of the recovered silver and the synthesized graphene, they made a dopamine sensor that reportedly outperformed reference devices.

The team synthesized “freestanding” graphene using non-toxic and renewable tangerine peel oil that can reportedly be used for the recovery of silver from end-of-life organic PV devices. The researchers said that their process result in high-quality graphene and demonstrated a remarkable ability to selectively recover silver from photovoltaic waste. One of the most surprising findings, according to the team, was how selective the graphene was in targeting silver.

Researchers from the Czech Republic's Palacký University’s CATRIN, the University of West Bohemia, and VSB-TUO have developed an innovative sensor capable of accurately measuring temperatures between 10 and 90 degrees Celsius. This novel sensor, based on a novel graphene derivative, stands out for its high precision, reliability, and resistance to humidity. Its applications range from industrial production and storage areas requiring remote temperature monitoring to integration into protective clothing.

“We developed the new material using fluorographene chemistry by removing fluorine atoms and attaching benzylamine to the available reactive sites. This proved to be a crucial step in creating the temperature sensor. This technology allowed us to significantly minimize the adverse effects of humidity, typically the most challenging issue for such devices,” explained Petr Jakubec from CATRIN, a co-author of the study published in the prestigious journal Advanced Electronic Materials.

Researchers at AMO GmbH, KTH Royal Institute of Technology, Senseair AB and the University of Bundeswehr have developed a waveguide-integrated incandescent thermal mid-infrared emitter using graphene as the active material. This innovative approach is said to significantly enhance the efficiency, compactness, and reliability of gas sensor systems, paving the way for widespread applications across various industries.

Many applications require robust, real-time air quality monitoring solutions, driving the demand for distributed, networked, and compact gas sensors. Traditional gas sensing methods, including catalytic beads and semiconducting metal oxide sensors, suffer from performance degradation, frequent calibration needs, and limited sensor lifetimes due to their reliance on chemical reactions. Absorption spectroscopy offers a promising alternative by utilizing the fundamental absorption lines of several gases in the mid infrared (mid-IR) region, including greenhouse gases. This method provides high specificity, minimal drift, and long-term stability without chemically altering the sensor. The ability to “fingerprint” gases through characteristic absorption wavelengths, such as carbon dioxide (CO₂) at 4.2 μm, makes it a promising technology for precise gas detection.

Scientists at the University of Bath, working in collaboration with Integrated Graphene, have created a new type of chemosensor (demonstrated for lactic acid sensing) which functions with electricity but without the need for reference electrodes or battery power. The new design potentially offers lower cost, better shelf-life, and ease of miniaturization compared to enzyme-based sensors. This could open up the possibility for an easy-to-use sensor to be used in remote locations, such as an athletics track, without the need for electricity-powered sensing equipment.

The sensor was able to detect lactic acid, a by-product generated by the body when it metabolizes carbohydrates or glucose for fuel, for example, during exercise. High levels of lactic acid are linked with higher risks of falling unconscious or into a coma and major organ failure.