Aromatic short peptide-metal nanoassemblies in smart hydrogel sensors for real-time food freshness monitoring

INTRODUCTION: The accumulation of volatile biogenic amines (BAs) during food spoilage constitutes a global economic and public health burden. Conventional BA detection methods based on chromatography and electrochemistry are limited by expensive instrumentation and specialized procedures, making on-site monitoring difficult for supply chain personnel and consumers. The lack of portable, user-friendly sensing technologies for complex food matrices leaves a technological gap for real-time spoilage monitoring. OBJECTIVES: The aim of this study is to develop a hydrogel digital sensor (HDS) based on peptide self-assemblies (PSAs) for visual on-demand BA detection. Quantification of spoilage by smartphone analysis and validation of its efficacy in real-time freshness assessment of meat. METHODS: via noncovalent interactions to form blue-emitting PSA (B-PSA). Its fluorescence response to BA was investigated, revealing the mechanism of photo-induced electron transfer quenching. To enhance visualization, B-PSAs were co-encapsulated with red-emitting carbon dots in a stimuli-responsive hydrogel to generate white HDS. The semi-micro Kjeldahl method was applied as a control and validated by real-time monitoring using environmentally stored shrimp samples. RESULTS: B-PSAs exhibited bright blue fluorescence with quantum yield up to 63 % and selective quenching in the presence of BAs (detection limit: 0.784-3.752 ppm, response time < 60 s). HDS showed a clear white to red fluorescence color transition upon exposure to BAs, enabling quantitative analysis in RGB chromaticity space, with a response range that covered all freshness grades in the national standard. Real-time validation in meat samples confirmed strong correlation with the standard TVBN assay (Pearson coefficient: 0.97). CONCLUSION: This HDS combines a molecular level design with a user-friendly digital readout to provide a biocompatible, portable, low-cost and rapid spoilage detection platform. The system is expected to improve the efficiency of food supply chain management and provide consumers with a convenient freshness assessment tool.