Graphene is an excellent material for applications in biosensing. The maturity of graphene devices has steadily increased over the years, having now reached a stage in which off-the-shelf graphene components are available on the market, placing biosensing within reach of startup businesses and research groups.

Graphene has several properties which make it favourable for use in biosensing. The 2D nature of the material in itself provides intrinsic advantages, because the entire material volume acts as a sensing surface. Furthermore, graphene provides excellent mechanical strength, biocompatibility, thermal and electrical conductivity, compactness, and potentially low cost.

Graphene field-effect transistors (GFETs) are the dominant technology for biosensing applications of this material. GFETs rely on well-established technology of charge carrier density changes in the presence of an analyte. Changes in charge carrier density in graphene, due to the presence of a species that is being detected, are registered as changes in voltage or current passing through the graphene transistor. Such a sensing principle can be applied for detection of gases, liquids, or solid materials such as biological material.

Image: Scheme of a graphene biosensor (reproduced from Materials Today 14, 308 (2011), creative commons).

GFET is a modification of the classic silicon field-effect transistor, ubiquitous in modern electronics. In traditional transistors, silicon acts as a thin conducting channel, the conductivity of which can be tuned with applied voltage. GFETs perform in a similar manner, except that the silicon is replaced with graphene, which yields a much thinner and hence more sensitive channel region. In sensing mode, channel conductivity is perturbed in the presence of an analyte. Due to the broad electrochemical potential and ability to be functionalized, GFETs present an attractive device for biomolecules to attach to, and because of graphene's ultimate thinness and extreme surface-to-volume ratio, electrical properties are sensitive to even the smallest concentration of attached molecules. Using GFET, biosensors with a detection limit of 10 pg/mL were produced for opioid molecules.

Figure: Sketch of GFET sensor (Reproduced from Chem. Sci., 2012, 3, 1764, with permission of The Royal Society of Chemistry).

Graphene biosensors thus satisfy the key demands on any sensing technology, such as specificity, reproducibility, stability, sensitivity, and linearity.

Figure: Graphenea GFET devices on a microchip.

Graphene oxide (GO) also has a strong potential for applications in biosensing. Scientists from the Fraunhofer institute in Berlin, for example, have modified their GO sensors to test for COVID-19 antibodies. Prior to that, the same researchers showed that a single drop of blood or saliva can be enough to accurately and reliably detect infection with other diseases within just 15 minutes. Disease detection is performed by a sensor that consists of a sheet of GO placed between two electrodes, functionalized with molecules that bind to a specific biomarker. Graphene oxide has a history of use in biosensing, including antibody detection, real-time breath detection, pesticide screening, DNA sensing, HS virus detection, and others.

Figure: Sensing applications of graphene oxide. From Arabian Journal of Chemistry 9, 238 (2016). Creative Commons license.

Graphenea has designed a range of GFET-based devices to make sensing easier for our customers. The GFET-S product range contains nearly a dozen different designs, aimed at different applications that customers may have. These products typically contain a microchip with a number of devices on it, ready for parallelized sensing action. The devices in the different products have different features and geometries, such as Hall bars, 2-probe GFET channels, encapsulated metal pads to avoid degradation when working with liquids, 3-probes, ultrathin backgates for individual control of each graphene device on chip, and different channel dimensions. This product range is aimed at researchers who wish to embark on graphene-based sensing and desire off-the-shelf working graphene devices that they can customize. For example, the GFET-S20 has been used by our customers to detect interleukin-6, a biomarker that is increasingly used as an indicator of inflammation, as an early warning sign for a range of diseases from asthma to cancer. The devices were also used as reliable, portable, fast detectors for COVID-19. Biosensors based on the GFET-S20 were shown to outcompete traditional ELISA and state of the art Simoa biosensors, having proven to be simple, fast, with an ultralow limit of detection (LOD).

Figure: GFET-S20, intended for use in liquid environments.

The use of GFET for biosensing has been made simpler by the introduction of additional products from the Graphenea Foundry. For instance, the MGFET product range is a step up from the GFET range, consisting of GFET devices on a microchip (die) that is attached to a chip carrier, with all contacts wirebonded. As such, a customer can just slip an MGFET into a socket on a measurement board and start working immediately.

If the customer so desires, they may obtain the Graphenea Card, which interfaces MGFET devices to the electrical equipment used for signal readout. The card contains 6 BNC connectors and a series of switches, allowing external access to each contact on the graphene device.

Figure: MGFET slotted into a Graphenea Card.

For a nearly turn-key solution for graphene-based biosensing, customers may turn to the Graphenea Cartridge S2X. The cartridge, like the Graphenea Card, interfaces GFET (S20) devices to readout electronics, but it also includes an inert casing with a reservoir where the customer can directly perform the biosensing.

Figure: Graphenea Cartridge.

With proven advantages over other commercially available solutions, a high sensing versatility, and ease of use when combined with Graphenea’s integration solution, GFET biosensors are satisfying the needs of many researchers and boosting the accessibility of biosensing research for everyone.