Colorimetric Sensor Based on ZnO/Thiol-Functionalized Polydiacetylene Nanocomposites for Formaldehyde Detection in Food

Abstract Formaldehyde contamination in food products poses significant carcinogenic risks to human health. Herein, a highly sensitive colorimetric sensor based on zinc oxide (ZnO)/polydiacetylene (PDA)/thiol-functionalized PDA (PDA-SH) nanocomposites is developed for the detection of formaldehyde in both aqueous and gaseous phases. The incorporation of thiol-functionalized 10,12-pentacosadiynoic acid (PCDA) (PCDA-SH) and ZnO nanopellets enhances the interaction between PDA and formaldehyde, leading to a distinct blue-to-red color transition driven by conformational distortion of the PDA backbone. Structural and spectroscopic characterizations, including X-ray diffraction, Raman, FTIR, and differential scanning calorimetry analyses, reveal increased interlamellar spacing, backbone disorder, and disruption of π-conjugation upon formaldehyde exposure. The sensor exhibits a quantitative response over a wide concentration range (50−1000 ppm), with a limit of detection of 40 ppm and a linear correlation between colorimetric response and analyte concentration. Integration into a poly(dimethylsiloxane) (PDMS) matrix enables the fabrication of flexible and freestanding films for gas-phase detection. The ZnO/PDA/PDA-SH sensor demonstrates good stability, reproducibility, and selectivity toward formaldehyde, with minimal thermal interference below 60 °C. Furthermore, the proof-of-concept evaluation using squid samples, combined with image-based analysis, demonstrates the potential of the developed sensor for practical screening of elevated formaldehyde contamination in food samples. These results support the feasibility of the ZnO/PDA/PDA-SH composite as a simple colorimetric platform for practical formaldehyde detection.