A Graphene Electrode Suitable For Sensing
As with other applications, graphene can be used to enhance existing properties and overcome limitations in various materials by transferring its unique properties into a hybrid/composite material. There are many ways in which graphene can detect molecules, making it an ideal choice as a material for use in sensors. Graphene’s intrinsic properties also makes it a good choice as a single-material sensor in many applications.
Sensors work by detecting a voltage change in the presence of an analyte. Because graphene has excellent conductive, thermal and adsorption properties as well as a large specific surface area. It provides many avenues for a molecule to be sensed. Graphene is very sensitive to a change in its surroundings, which is one of the key properties that all good sensors possess.
For sensor applications, the structure of graphene provides a unique surface for the adsorption of molecules. The defects present in a graphene sheet provide cavities that can improve the absorption efficiency of molecules to the surface, allowing them to be detected. Graphene can also act as a p-type semiconductor where they have hole-like charge carriers. For some applications, the depletion of holes from the valence band can lead to an increase in the resistance and therefore enhance sensitivity and response. The adsorption of molecules onto the surface can also trigger a change in the electrical conductivity of graphene. The surface adsorbates can either act as a donor or acceptor molecule, donating or removing electrons respectively. The voltage change with graphene, provides a measurable response which indicates that a molecule has been detected.
In hybrid materials, graphene tends to form π-π stacking interactions with the other components. These interactions can induce a charge-transfer mechanism across the de-localized electrons, resulting in enhanced sensitivity. In addition to adsorbing into the cavities on the graphene surface, molecules can also interact with the π-bonds. This can lead to a greater number of potential adsorption sites which increases the sensitivity of the material. A higher incorporation of graphene into a composite material has been found to produce a larger π-network.
Sensing is a large industry and has had a huge impact in across many industries. The ability to detect and distinguish at the molecular level has become increasingly important for the detection of contaminants in environmental processes; for a better understanding of how various electronics work; as well as how biomolecules interact. As advancements are made, the need to understand the underlying mechanisms becomes paramount to the development of sensing materials. Advanced sensors can answers these questions.
Graphene (as a single molecule or a composite) is currently used in various sensing environments nowadays as biosensors, optical sensors, temperature and humidity sensors, piezoelectric and piezoresistive sensors, capacitance sensors and gas sensors. This series of graphene sensor guides details many examples of how graphene films and composites are utilized in sensor applications.