A two-dimensional disposable full-history time-temperature indicator for cold chain logistics

Monitoring temperature change in the distribution process is one of the crucial points to guarantee the safety and efficacy of temperature-sensitive products such as drugs, vaccines, and foods. The traditional time-temperature indicators (TTIs) for this work are digital thermometers. However, due to their high cost, only a few digital sensors can be mounted in each refrigerator car. It is not possible to record the situation of each individual products. In addition, the time-temperature history curves measured by digital thermometer are easy to be tampered, limiting their application on indicating the validity of products. Although some low-cost and disposable chemical or physical TTIs have been reported, they always work based on only one parameter to indicate the experienced highest temperature, which cannot indicate how long does the products experience in different temperature. Here, multicolor plasmonic hydrogels allowing the in-situ formation of gold nanoparticles have been fabricated as the full-history time-temperature indicator (FHTTI). Different from traditional indicators, the two-dimensional FHTTI can separately indicate temperature and time with two non-interfering parameters: color and length, which guarantees the accuracy and completeness of reported time-temperature information. The FHTTI has achieved to monitor the time-temperature changes up to more than 30 days under complex variable-temperature conditions, showing great application potentials for the accurate full-history time-temperature indication of each single packaged product in cold chain logistics.