Fig. 5: Surface functionalization of polydiacetylene (PDA)-based colorimetric sensors using chemical functional groups.

a Functionalization with amines and imidazolium groups for CO₂ detection, which react to form carbamate anions, triggering a blue-to-red color transition. Adapted with permission from ref. ¹²⁸. Copyright 2013 American Chemical Society. b Functionalization with ester for organophosphate pesticide detection, where hydrogen and covalent bonds facilitate a color shift. Adapted from ref. ¹³¹, copyright (American Chemical Society, 2025). c Functionalization with thymine-1-acetic acid (TAA) and orotic acid (OA) groups for Pb²⁺ detection through coordination interaction with carbonyl and nitrogen groups, leading to stable complex formation and a distinct color change. Adapted from ref. ¹³², copyright (Royal Society of Chemistry, 2025). d Functionalization with diaminotriazine (DAT) for the selective detection of thymine groups through the formation of specific hydrogen bonds between the carbonyl (C = O) and amino (N–H) groups of thymine. e Colorimetric response of PDA-DAT functionalization. Adapted with permission from ref. ¹³⁵, copyright (Elsevier B.V., 2023).