Precisive designing and drop-on-demand printing of spoilage-responsive colorimetric sensor array for intelligent food package

Package materials integrated with visible sensors straightforwardly indicating the freshness is shaping as a new generation package mode for food storage and logistic. In this study, a colorimetric sensor array (CSA) based on 12 pH-responsive indicators was precisely designed and prepared using drop-on-demand printing. The variation of CSA fingerprint dependent on the volatile organic compounds (VOCs) associated with meat spoilage can be easily documented with a smartphone, which was further quantified by evaluating the image pixel. It was demonstrated that the obtained CSA exhibits outstanding uniformity, stability (ΔE < 5), selectivity and reproducibility (<3.2 %). The detection limits for ammonia (NH 3 ), dimethylamine (DMA), and trimethylamine (TMA) were determined to be 0.11 ppm, 0.13 ppm, and 0.15 ppm, respectively. Besides, outstanding discernment capability toward the spoilage status in terms of meat type and storage time, was experimentally evidenced, by using chemometric tools including principal component analysis (PCA) and hierarchical cluster analysis (HCA). Then, the performance of the CSA was validated by benchmarking with official standard methods stipulated to evaluating meat freshness (pork and shrimp). A strong correlation ( R 2  = 0.991) was observed between the CSA fingerprints and the measurements of total volatile basic nitrogen (TVB-N), demonstrating that the CSA might be a powerful tool for online freshness monitoring.