N-type hydroxylated reduced graphene oxide for DMMP molecular olfactory sensing

The exceptional specificity of biological olfactory sensing has motivated efforts to tackle the persistent challenge of low selectivity in chemiresistive-type gas sensors. In this paper, we draw inspiration from biological recognition mechanisms for organophosphonates and develop n-type hydroxylated reduced graphene oxide (HRGO) as a molecular olfactory sensor for the sarin surrogate, methyl dimethylphosphonate (DMMP). HRGO is synthesized through a controlled selective reduction of graphene oxide, converting most of the oxygen-containing groups into hydroxyl groups. The corresponding sensor demonstrates ultrahigh selectivity for DMMP at room temperature, with a fast response time of approximately 5   seconds and a detection limit as low as 5 ppm. Furthermore, we grafted calix[6]arene onto HRGO via van der Waals forces, significantly enhancing the Schottky contact between HRGO and the Au electrode, which in turn improved the sensor's stability. Additionally, the introduction of the hydrophobic aromatic rings in calix[6]arene boosted the sensor's humidity resistance of low-concentration detection resolution. A possible bionic sensing mechanism was then proposed, in which DMMP was first adsorbed by the electron-rich conjugated benzene rings of n-type HRGO, followed by phosphonylation at the hydroxyl sites. This work offers valuable insights into the field of molecular olfactory sensing as well as artificial olfaction.