Portable Dual-Functional Ionic Liquid-Based Ratiometric Nano-optode for Detecting Spermine and Spermidine to Monitor Food Spoilage

The growing interest in detecting biogenic amines (BAs), particularly spermidine (SPD) and spermine (SPM), has created a strong need for highly effective analytical techniques. These volatile amines are abundant in protein-rich foods and serve as key indicators of food quality. Thus, chemical research prioritizes the development of straightforward, affordable, and portable colorimetric or fluorescence-based detection methods for these amines. To address these needs, we introduced nHIL, a cyan-light-emitting ionic-liquid-based nano-optode for ultrafast detection of BAs. In its pure form, HIL displays intense cyan fluorescence under 365 nm UV light, demonstrating its potential as a fluorescent security ink, and can detect BAs in a solvent-free condition. nHIL is highly specific and selective for SPD and SPM, with low LODs of 14.5 nM and 11.7 nM spectrophotometrically and 2.2 nM and 1.79 nM fluorometrically, respectively, making nHIL an effective dual-nature sensor and further enabling smartphone-based analysis for on-spot detection of BAs. Finally, we evaluated the proposed sensor’s performance on real food samples (mushrooms and meat), noting distinct changes in chromogenic and fluorogenic responses─specifically, a visible color shift and fluorescence quenching triggered by biogenic amine vapors released from the stored foods.