Standalone, Flexible, ambient Temperature, and sensitive ammonia vapor sensors via carbon nanotubes triggered localized coalescence of natural rubber

Ammonia vapor sensors are indispensable for a wide range of applications, from industrial monitoring to medical diagnosis. However, the development of flexible and standalone ammonia sensors has remained a significant challenge. This study presents a novel, low-cost, and facile approach for fabricating ammonia sensors that exhibit high sensitivity, flexibility, and standalone functionality, with immense potential for applications in the rapidly expanding field of flexible electronics. The sensors were fabricated using a new approach: localized coalescence of Natural Rubber Latex (NRL) onto carbon nanotubes (CNTs), which leads to exceptionally high carbon nanotube loading along with complete flexibility and mechanical integrity, surpassing the limitations of conventional methodologies. The localized coalescence (NRL@CNT) of the CNTs resulted in a mesh-like structure that significantly improved the stiffness and strength of the composite. Radiation cross-linking was employed to further stabilize the CNT network architecture, ensuring high conductivity even under deformation, while preserving the intrinsic properties of the NRL, as confirmed by dynamic mechanical analysis and positronium annihilation lifetime spectroscopy. Sensors fabricated on the spot by piercing two gold-plated steel pins in compression-molded thin films of gamma radiation processed NRL@CNT demonstrated broad-range sensitivity and high selectivity for ammonia vapors, exhibiting a linear response within the 8–500 µmol/L range with an impressive correlation coefficient of 0.99 and a low detection limit. This fabrication method is straightforward, scalable, and environmentally benign, offering a wide range of potential applications in fields such as healthcare, environmental monitoring, and flexible electronics.