On the sensing front, Raivo Jaaniso, Head of the Laboratory of Sensor Technologies at the University of Tartu (Estonia) leveraged the high sensitivity of single-atomic-layer graphene’s conductivity to defects and doping to create ultra-sensitive gas sensors through localized functionalization. “They are based on a small matrix of chemiresistive graphene sensors, functionalised with small amounts of metal oxides or precious metals”, Jaaniso explained, referring to a recently published paper in Applied Physics Letters, “Highly sensitive NO2 sensors by pulsed laser deposition on graphene”.
The paper describes how graphene can be functionalized to create adsorption centres of different types for target gases by so-called pulsed laser deposition (PLD), introducing locally and very precisely small amounts of materials onto pristine graphene. Using Ag and ZrO2 as the deposition material, the researchers were able to multiply the response to NO2 gas in air by 40 times in the case of PLD-modified graphene, in comparison with pristine graphene, reaching 7 to 8% at 40 ppb of NO2 and 20 to 30% at 1 ppm of the noxious gas. Many different gas sensors could be designed on a tiny sensor as the precise PLD tool can form a variety of defects or clusters on graphene from different atomic species with different “landing energies”, explains the paper, typically impacting under 1% of a monolayer’s through a single laser pulse.
They also found that signal recovery times and sensitivity at low concentrations could be further improved under UV light, extrapolating a level of detection as low as 1 ppb for NO2 (from a few to a few hundreds of ppbs). Jaaniso anticipates that with further research and investment, such sensors could be integrated into mobile phones to actively monitor toxic substances in the ambient air.