A polydiacetylene-based colorimetric chemosensor for malondialdehyde detection: a food spoilage indicator†
A colorimetric chemosensor adopting polydiacetylene derivatives was rationally designed to detect malondialdehyde (MDA) as a potential food spoilage indicator. A newly developed diacetylene monomer containing an active methylene group effectively reacted with the aldehyde units of the MDA molecule via Knoevenagel-type condensation and resulted in a CC bond, judging from the results of FT-IR spectroscopy. When the monomer was incorporated into polydiacetylene liposomes, they exhibited a strong change in color from blue to red in the presence of MDA molecules, even though their sensitivity was partly affected by the feed ratio of the applied diacetylene monomers during liposome preparation. In addition, it was verified that the devised MDA chemosensor selectively responded to the divalent MDA, rather than the monovalent butanal. The detection limit of the optimized MDA chemosensor was about 250 μM in solution, but when a film-type MDA chemosensor was fabricated through the accumulation of the liposomes on top of a nylon membrane and then applied, the detection limit improved dramatically, reaching down to 10 μM at room temperature, even by judging the change in color with the naked eye. To confirm that the change of the resulting Hue angle can reflect the detection sensitivity of the MDA chemosensor under different experimental conditions, CIELAB analysis was conducted with the film-type MDA sensor. The results indicated that the Hue angle changed according to the MDA concentration, and the resulting slope can be quantitatively correlated with the sensitivity of the colorimetric detection system.