Smart fluorescent bio-inks for DIW 3D printing: real-time food freshness sensors with dual-channel pH sensitivity

The development of smart indicator labels capable of visually monitoring food freshness through colorimetric changes is becoming increasingly vital for enhancing food safety and reducing waste. Despite this progress, most existing smart labels are tailored to specific food categories, limiting their versatility and broader application. To address this challenge, we have designed a multifunctional dual-channel fluorescent probe, SiO₂-FITC/Ru(phen)₃²⁺, by co-doping FITC and Ru(phen)₃²⁺ into silica nanoparticles. This innovative probe was seamlessly integrated into direct ink writing (DIW) 3D printing, enabling the fabrication of 4D smart labels with adjustable void fractions using bio-inks that leverage shear-thinning properties. These smart labels exhibit a linear and highly sensitive response to ammonia (NH₃) concentrations ranging from 50 to 15,000 ppm and carbon dioxide (CO₂) levels between 0 and 30% (v/v), with rapid detection times as short as 4 min. The integration of fast, intuitive, and precise detection mechanisms allows for non-destructive and real-time food freshness monitoring across diverse product categories, including vegetables, seafood, and meat products. In practical applications, the labels demonstrated exceptional accuracy in detecting spoilage indicators in shrimp, yellow croaker, pork, chicken breast, mushrooms, broccoli, fresh-cut cantaloupe, and spinach underscoring their adaptability and effectiveness. In conclusion, this work demonstrates the successful integration of nanotechnology with DIW 3D printing to produce versatile smart labels capable of accurately monitoring food freshness across various matrices. The scalability and adaptability of this approach offer significant potential for enhancing food safety and quality control in diverse sectors of the food industry.

Graphical Abstract