Comparison of Ammonia Sensors Between Protonated Cytosine and Protonated Pyridine-containing Polydiacetylenes

Abstract

Selective and sensitive sensors for ammonia detection are essential in monitoring and human health risk assessment due to its inherent toxicity. Significantly, the emergence of user-friendly and rapid on-site detection sensors has garnered considerable importance. Polydiacetylene (PDA) constitutes an intriguing class of stimuli-responsive chromogenic materials that have undergone extensive exploration in various sensing applications. Herein, a simple paper-based naked-eye detectable colorimetric sensor using cytosine-linked PDA and pyridine-linked PDA was developed. Two sensing platforms were developed through the protonation of the cytosine ring, resulting in CyPDA-H (hemi-protonated), CyPDA-H+ (fully protonated). Additionally, another sensing platform was developed through protonation of the pyridine ring, resulting in 4PyPDA-H+. CyPDA-H, CyPDA-H+, and 4PyPDA-H+ exhibit a vivid naked-eye visible blue-to-red color transition upon exposure to ammonia, with respective detection limits of 77, 117, and 24 ppm. This color change is achieved through the deprotonation mechanism. The self-assembly behavior, topochemical polymerization, morphology, and comparative sensing potential of sensors toward ammonia were systematically investigated through spectroscopy and microscopy analysis. These sensor systems offer significant advantages in terms of simplicity, on-site detection, portability, and visualization.