Dual Fluorescent Tetrastyrene Switches for Food Freshness and Environmental Monitoring

Fluorescent sensors are promising for efficient and pervasive healthcare and environmental monitoring. Such wide research interest has not yet delivered practical applications owing to a series of limitations of adopted fluorescent molecular probes. One of the key limitations is the versatility of such probes, typically not active on a wide pH spectrum or not sensitive to multiple stimuli. In this study, we demonstrate dual fluorescence response of a tetrastyrene (TPE) derivate, namely ((1E)-((4- (1,2, 2-triphenylvinyl-benzylidene)hydrazine)methyl)ferrocene (Fc-TPE), which shows responses to both acidic and alkaline environments. This phenomenon is possible due to hydrolysis of imine bonds under both acidic and alkaline conditions, which hinders competitive photoinduced electron transfer, thus enabling dual pH dependent fluorescent emission. At the same time, the sensitivity of the imine bonds to some cations can be exploited to trigger the same fluorescent switch for the detection of elements that present a health hazard for humans. As proof-of-principles of the multiresponsive capabilities, we report an Fc-TPE based hydrogel obtained by simple one-pot synthesis exhibiting a reversible fluorescent switching, allowing to monitor fish and meat freshness, as well as Cu²⁺ detection in solution. Our results can have a significant impact in delivering fluorescent molecular probes to smart optical sensors with relevant practical applications.