Aiming to develop universal, effective, and visually observable sensing nanomaterials for detecting concentrations of volatile organic compounds (VOCs), we fabricated a functionalized alumina aerogel sheet by embedding a chromatic conjugated polymer-polydiacetylene (PDA) in alumina aerogel pores, which underwent dramatic color changes upon exposure to different concentrations of VOCs. Taking the activated carbon as the example, we designed an air purification detection system by using the as-synthesized PDA-functionalized alumina aerogel sheets, which could give a definite indication from the changes of color. Overall, this study presents a simple and low-cost method to fabricate PDA-functionalized alumina aerogel sheet in which noncovalent interactions between the alumina aerogel sheet substrate and spin-coated PDA give rise to distinct chromatic properties after exposure to different concentrations of VOCs.