Fluorescence aqueous detection of CO2 via protonation of 2-phenyl-4-methylimidazole.

Carbon dioxide (CO2) concentration plays a critical role in human life and production, agricultural growth, and marine environments. However, compared to current CO2 detection methods, there remains a need to develop a simple, highly sensitive method that is applicable for both gaseous and aqueous-phase CO2 detection. Herein, we introduce a sensing film that is user-friendly, facile to fabricate, and fluorescently responsive to CO2. After extensive screening, we selected a 2-phenyl-4-methylimidazole (PMZ)@polymethyl methacrylate (PMMA) film that is suitable for aqueous-phase detection and exhibits high-sensitivity fluorescence response to CO2. In aqueous media, CO₂ induces a blue shift in the PMZ@PMMA sensing film's fluorescence emission. The sensing film is based on the dissolution of CO2 in water to form carbonic acid, followed by the protonation of the fluorescent material in the film by the protons from carbonic acid, resulting in the formation of a protonated product (PMZH+). The response time of this sensing film is approximately 5 min, and its detection linear range is 1.8%-6.0%, which makes it well-suited for monitoring CO2 concentrations in brewing process control, agricultural production and storage, life-science incubation, and early-stage safety alarms. The preparation of this sensing film is relatively simple, and the film is easy to store. It provides a theoretical basis and practical platform for CO2 sensing.