Mitigating ACQ and enhancing solubility: A dual strategy for real-time aquatic product freshness detection

Commercial fluorescent dyes for freshness detection are hindered by aggregation-caused quenching (ACQ) and poor solubility, compromising sensitivity to ammonia. Herein, we employ a dual strategy for designing fluorescein-based ionic liquid micelles to address these challenges: an electronic isolation approach to sensitize the commercial dye and a micelle preparation technique to enhance hydrophilicity. The electronic isolation strategy facilitated the design of an ionic liquid fluorescent probe, [P₆₆₆₁₄]₂[Fluo], derived from fluorescein, which effectively emitted fluorescence in highly aggregated states, thus mitigating ACQ. Additionally, the micelle preparation strategy improved the hydrophilicity of [P₆₆₆₁₄]₂[Fluo], enhancing its water solubility to 3.385 g/L and increasing the detection limit sensitivity for ammonia by more than threefold, achieving 3.8 ppb. This dual strategy was pivotal in overcoming the inherent limitations of conventional dyes, resulting in enhanced fluorescence and improved solubility for efficient ammonia detection. We then developed a dual-signal composite micelle probe combining [P₆₆₆₁₄]₂[Fluo] and Nile Red, which exhibited a wide detection range (0-35.0 ppm), ultralow detection limit (10 ppb), and high selectivity for biogenic amines. The practicality of this system was validated through the use of gel bead devices integrated with smartphone-based analysis for quantitative assessment of shrimp freshness, with results corroborated by traditional total volatile basic nitrogen (TVB-N) methods. This cost-effective, rapid-response, and nondestructive portable device presents a promising platform for real-time freshness detection of aquatic products.