Polyelectrolyte-Based Colorimetric and Electrochemical RFID Sensor for Ammonia Gas Monitoring for Smart Packaging Applications

Ensuring food safety is a critical priority in the food industry, where spoilage and contamination cause economic losses and health risks. Among freshness indicators, ammonia (NH₃) detection serves as a precise marker of spoilage, as it is a volatile byproduct of protein degradation caused by microbial activity. In this study, we developed an eco-friendly, colorimetric, and electrochemical RFID-based ammonia gas sensor with a self-powered barcode for food quality monitoring. This system enables qualitative monitoring via visual changes and quantitative assessment through impedance variations. Our approach focuses on a polyelectrolyte system leveraging protonated chitosan interactions with Ca²⁺, inducing cross-linking with anthocyanin structures, catalyzing copigmentation, and enabling rapid ammonia detection. This interaction enhanced copigmentation and sensitivity, resulting in a visible color shift from purple to blue within 60 min of NH₃ exposure, while the control sensor exhibited no color change even after 24 h. The eco-friendly electrode was produced via laser-induced graphene following parameter optimization, achieving a sheet resistance of 43 Ω/sq on the bio-based substrate. Conductivity was further enhanced by anthocyanin incorporation due to its aromatic structure, facilitating graphene-like electrode formation. Raman spectroscopy confirmed an intense and symmetric 2D peak at 2700 cm⁻¹, exceeding the G peak intensity, while SEM images revealed a well-defined LIG structure on the substrate. The sensor exhibited excellent visual detection capabilities, with an untrained observer perceiving the color change (ΔE > 5) within 60 min of ammonia exposure. Impedance measurements detected NH₃ in 5 min, achieving an LOD of 835 mg/m³ in 15 min and a sensitivity of 0.00117 Ω/mg/m³. Utilizing the triboelectric effect, we developed a self-powered barcode generating an open-circuit voltage of up to 25 V with a simple finger slide, supporting integration into smart food packaging. Additionally, an RFID antenna, designed as a proof-of-concept, exhibited resonance shifts and return loss variations due to polymer matrix impedance changes after 30 min of NH₃ exposure, confirming its viability for real-time, non-invasive food spoilage detection. This work demonstrates the feasibility of polyelectrolyte-based ammonia sensors for food safety applications, leveraging controlled ion interactions to enhance detection sensitivity. The combination of self-powered sensing, RFID communication, and sustainable materials, highlight its potential for next-generation smart packaging technologies.