Bioinspired Iontronic Gas Sensor for Selective CO₂ Sensing via Reversible Lysine Carbamylation

Carbon dioxide (CO₂) is ubiquitous in both natural and indoor atmospheres, playing a pivotal role in global climate regulation, air quality, and biological processes. However, their chemical inertness poses inherent challenges for developing compact, high-sensitivity detection platforms. In living organisms, CO₂ often modulates protein function through reversible carbamylation of lysine residues, illustrating a finely tuned molecular recognition mechanism. Inspired by this principle, we developed a bioinspired iontronic sensor by embedding lysine moieties into a cross-linked poly(ethylene glycol) diacrylate (PEGDA) hydrogel. Upon exposure to CO₂, the lysine ε-amino group forms transient carbamate adducts, inducing the electrostatic interaction, which disrupts Grotthuss-like conduction pathways and causes a distinct impedance increase. This lysine-based recognition enables high selectivity over interfering gases and operates reliably under ambient conditions. The resulting hydrogel sensor exhibits excellent linearity (R² > 0.995) from 0 to 2000 ppm of CO₂, with a theoretical detection limit of ∼76 ppm, suitable for indoor and ambient atmospheric CO₂ monitoring at low concentrations. Furthermore, it maintains stable performance over at least 28 days of repeated measurements and shows negligible cross-sensitivity toward common interfering gases (e.g., H₂S, CH₄, and formaldehyde). By harnessing lysine-CO₂ carbamylation within an ion-conducting matrix, our approach provides a versatile, low-power platform for precise CO₂ sensing in applications ranging from indoor environmental evaluation to plant-level respiratory monitoring.