Carbon Nanotubes Help Build Highly Accurate Sensors for Continuous Health Monitoring

Current sensors can measure various health indicators, such as blood glucose levels, in the body. However, there is a need to develop more accurate and sensitive sensor materials that can detect lower concentrations of certain substances. For instance, female hormones are present in the body at concentrations millions of times lower than glucose. To effectively study hormone fluctuations, highly sensitive sensors are required, and this necessitates a significant improvement in the accuracy of biosensors. In a new study, researchers have developed nanomaterials that could contribute to more accurate sensors for future healthcare applications. These advancements could lead to continuous health monitoring, enabled by carbon nanotubes.

Researchers at the University of Turku (Turku, Finland) have successfully created sensors using single-wall carbon nanotubes, which are well-suited for such applications. Single-wall carbon nanotubes are made from a single atomic layer of graphene. Until now, a major challenge in developing these materials has been that the nanotube manufacturing process yields a mix of conductive and semi-conductive nanotubes, which vary in chirality—the way the graphene sheet is rolled into the cylindrical shape of the nanotube. The electrical and chemical properties of nanotubes are highly dependent on their chirality. The research team developed methods to separate nanotubes with different chiralities, and in this study, they successfully distinguished between two nanotubes with similar chiralities while identifying their typical electrochemical properties.

Image: Carbon nanotubes with different chirality or “twist” have different optical properties (Photo courtesy of Mikael Nyberg/University of Turku)

By purifying and separating the carbon nanotubes, the researchers were able to test their differences as sensor materials. Although nanotubes are typically used in hybrid sensors when combined with other surfactants, the current study focused on sensors made entirely from nanotubes. Furthermore, the researchers gained precise control over the concentration of nanotubes, allowing them to compare the properties of different chiralities. One key finding was that one type of nanotube (6.5) was more efficient than the other (6.6) in adsorbing dopamine. Adsorption, which refers to the ability of a material to bind atoms or molecules to its surface, is especially crucial when the concentrations of the substances being measured are very low. The study's results are the first to demonstrate that the electrochemical response of the sensor is influenced by chirality. In future research, computational models could be employed to determine the optimal chirality for measuring each molecule.

“The result is significant because by being able to precisely control the properties of carbon nanotubes we can fine-tune the ability of the sensor material to detect changes in specific substances," said Doctoral Researcher Ju-Yeon Seo.

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