Researchers at Osaka University have invented a new biosensor using graphene, which is a material that consists of a one-atom-thick layer of carbon, to detect bacteria like 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 graphene. To enable detection of the chemical reaction products, the researchers used microfluidics to contain the bacteria in tiny droplets that are close to the surface of the sensor.
In order to get the bacteria to stick, the researchers covered the graphene with antibodies, which is a common way of anchoring bacteria to biosensor surfaces. Although antibodies are small, on the atomic scale and compared with the atom-thin layer of graphene, they are quite bulky and a bit large. While the bacteria interact with the antibodies on its surface block the signal. This signal blocking is known as Debye screening.
To overcome the blocking of the signal and screening limitation, the researchers instead decided to monitor the chemical reactions that are being performed by the bacteria in the presence of certain chemicals, which they added to the tiny water droplet. The chemicals produced in the reactions are far smaller than the antibodies and they can slip between them easily and reach the graphene surface. By analyzing the bacteria in the droplets that are generated through microfluidics, the bacteria and their reaction products can be kept close to the graphene surface and the concentration of the reaction products can even be monitored.
"Our biosensor enables highly sensitive and quantitative detection of bacteria that cause stomach ulcers and stomach cancer by limiting its reaction in a well-defined microvolume," study co-author Kazuhiko Matsumoto says.
The graphene sensing surface is able to feedback on electrical signals that depend on how much of the reaction product is present in the microdroplet and how quickly it's accumulating. These signals can be used to calculate the number of bacteria that are present in the droplet. The graphene is set-up in a field effect transistor or FET structure, the role is to increase the electrical detection signals from the graphene sensing surface.
"Our biosensor is essentially a mini-laboratory on a graphene FET. This sensor demonstrates how two-dimensional materials such as graphene are getting closer to being applied in practical medical and healthcare applications," first author Takao Ono says.
The results of this study can be used to make a new host of lab-on-a-graphene-FET biosensors to detect different bacteria. The detection of small concentrations of bacteria could be achieved in less than 30 minutes, this work represents the possibility of faster diagnoses for harmful bacteria in the future.
