A novel, sustainable, and multifunctional fluorescent polymer dot (FPDs) nanoemulgel was successfully synthesized from dialdehyde alginate (DAA) via a simple, eco-friendly microwave-assisted oxidation and carbonization route. The synthesized fluorescent polymer dot dialdehyde alginate (DAA-FPDs), characterized by TEM (particle sizes 15–88 nm) and DFT calculations, was engineered for comprehensive food safety monitoring. The resulting nanoemulgel exhibits remarkable pH-responsive dual functionality, crucial for intelligent packaging applications. It demonstrated distinct acid-induced emulgelation and solidification at pH 3, driven by the protonation of carboxyl groups protonation and a pronounced naked-eye color change from orange (pH 7) to dark brown/black (pH 12), validating its potential as a visual spoilage indicator. Furthermore, the DAA-FPDs function as a highly sensitive, intensity-based fluorescent biosensor for microbial detection. The sensor exhibited superior sensitivity toward Gram-negative E. coli with a LOD of 65.07 CFU/mL, compared to 155.48 CFU/mL for Gram-positive S. aureus. This differential sensing is governed by the distinct cell wall chemistries and the pH-dependent surface charge of the FPDs. In addition to sensing, the DAA-FPDs displayed potent broad-spectrum antimicrobial activity, yielding substantial Zones of Inhibition (ZOI) up to 46 mm against S. aureus. This study introduces a biodegradable, multi-functional nanoemulgel that combines structural, colorimetric, and fluorescent sensing with antimicrobial efficacy, presenting a comprehensive platform for enhancing food safety and minimizing waste.
Hebat-Allah S. Tohamy (Fri,) studied this question.