Configuring Highly Sensitive Formaldehyde Colorimetric Sensors on Hierarchical Wood Substrates

Indoor formaldehyde (FA, HCHO) contamination is currently one of the most significant environmental concerns in daily life, making it vital to detect FA efficiently. Colorimetric FA detection is a fast, real-time method with results visible to the naked eye. However, most colorimetric FA sensors on the market have complex and expensive base materials. In this work, different sections were prepared as colorimetric sensor substrates according to the anisotropy of natural poplar trees. The response characteristics of FA on the different sections were compared, showing that the longitudinal section sensor senses theFA concentration 15 times lower than the concentration of FA that the cross-section sensor can sense. Additionally, the longitudinal channel wall in the wood hierarchical structure has a large concave surface area to facilitate the attachment of sensing materials and enhance FA detection. The fabricated longitudinal section sensor exhibits an ultralow FA detection limit of 50 ppb within 5 min, which is much lower than the WHO threshold level (80 ppb) and other colorimetric techniques. Moreover, the constructed sensor shows high FA selectivity on experimentation with typical indoor contaminants. This sensitive, highly selective, and fast-responding colorimetric strip is cost-effective for determining gaseous FA.