A novel dual-color fluorescent sensor with two pKas for on-site detection of pH in food.

[Display omitted] • The first pH fluorescent sensor with two pKa values. • This sensor enables monitoring of pH with the dual-color response. • The portable paper strips can be facilely fabricated based on the sensor. • The paper strips can be successfully employed for the real food analysis. Tracking pH fluctuations in food samples is important for ensuring food freshness. Fluorescent probes have been widely applied as promising tools for the on-site detection of pH changes; however, most of them can be applied only at either lower or higher pH ranges because their response structures commonly have a single acid dissociation constant (pKa). To address this problem, we designed a fluorescent sensor, called HMB, containing a methylpiperazine group with two pKa values, which exhibited a unique dual-color response to pH changes over a wide pH range. Furthermore, the HMB-based test strips are easily prepared and used as portable labels for the visual monitoring of food spoilage that results in microbial and anaerobic glycolytic pathways in real food (such as cheese and shrimp). To the best of our knowledge, this is the first fluorescent pH sensor with two pKa values, and we expect that this work will inspire more sensor designs for food quality control. [ABSTRACT FROM AUTHOR]