Food-Activated Microneedle Sensor for Real-Time, Colorimetric Spoilage Monitoring of Pre-Packaged Food.

At a time of growing food insecurity, developing technologies to reduce food waste is critical. An inexpensive, colorimetric spoilage sensor for real-time food product assessment is reported. The sensor is composed of dehydrated gelatin microneedles that exhibit high mechanical integrity in their base state. However, once exposed to fluid-rich food environments, they rapidly transition to a hydrogel sensing state. Food-derived anthocyanins embedded within these microneedles enable pH-based spoilage monitoring. When applied to sealed fish products, these microneedles nondestructively penetrate through the packaging and are rehydrated by the underlying fish matrix. As the product ages, a defined color shift occurs, demonstrating strong correlation with quantitative spoilage markers. When applied to unsealed fish products for rapid testing, the large microneedle sensing interface enables accelerated colorimetric sensing. Finally, successful fresh vs spoiled categorization of smartphone-acquired images of the sensor using machine learning removes readout ambiguity, empowering consumers with independent real-time product monitoring.