Multi-Sensing Platform Based on 2D Monoelement Germanane

Covalently functionalized germanane is a novel type of fluorescent probe that can be employed in material science and analytical sensing. Here, a fluorometric sensing platform based on methyl-functionalized germanane (CH₃Ge) is developed for gas (humidity and ammonia) sensing, pH (1–9) sensing, and anti-counterfeiting. Luminescence (red–orange) is seen when a gas molecule intercalates into the interlayer space of CH₃Ge and the luminescence disappears upon deintercalation. This allows for direct detection of gas absorption via fluorometric measurements of the CH₃Ge. Structural and optical properties of CH₃Ge with intercalated gas molecules are investigated by density functional theory (DFT). To demonstrate real-time and on-the-spot testing, absorbed gas molecules are first precisely quantified by CH₃Ge using a smartphone camera with an installed color intensity processing application (APP). Further, CH₃Ge-paper-based sensor is integrated into real food packets (e.g., fish and milk) to monitor the shelf life of perishable foods. Finally, CH₃Ge-based rewritable paper is applied in water jet printing to illustrate the potential for secret communication with quick coloration and good reversibility by water evaporation.