Novel optical temperature and phase change sensor based on the response of hydroxypyrene to sucrose in water ice

Abstract

A novel optical temperature sensor based on the protonation states of 8- hydroxypyrene-1,3,6-trisulfonic acid trisodium, also known as pyranine, is developed and characterized. When water freezes and becomes ice, impurities create small pockets of liquid water, the sizes of which are dependent on temperature. Pyranine and sucrose are added to water as it freezes to create these pockets. Water of solvation molecules surrounding sucrose create a change in the ratio of protonated to deprotonated pyranine as a function of sucrose concentration within the liquid pockets. The protonated and deprotonated forms of pyranine emit light at 440 nm and 511 nm, respectively, which is captured with a photosensitive device. These phenomena are leveraged to create a temperature and phase change sensor within ice. The sensor is illuminated using 365 nm illumination and the fluorescence intensity ratio of the 44nm and 511nm emission peaks of pyranine is studied as a function of temperature and phase change in the range 258–293 K. By using this ratio, the temperature and phase changes within an ice block are measured in a temporally and spatially resolved manner. The temperature sensitivity within the ice phase is − 9.2 ± 0.1% K−1 which is better than conventionally used fluorescence-based temperature sensors. The pyranine and sucrose sensor is a promising candidate for an optical temperature sensor with high sensitivity within bulk ice.