New Molecular Thermometer for Temperature Measurements Using Infrared Light

A molecular thermometer has been developed by Chemists at Johannes Gutenberg University Mainz (JGU) in collaboration with Researchers from the German Federal Institute for Materials Research and Testing (BAM), Berlin. The gemstone ruby was the source of inspiration.

However, the new thermometer developed by the team led by Professor Katja Heinze at the JGU Institute of Inorganic Chemistry and Analytical Chemistry is a water-soluble molecule and not an insoluble solid. Just like a ruby, this molecule is made up of the element chromium which gives it its red color, which is the reason why it has also been named the molecular ruby. This molecular ruby is capable of being used for measuring temperature in several different environments because of its solubility: it can be introduced into micelles, nano-particles, solids and liquids. It thus has promising applications in the fields of medicine, biology and material sciences.

The molecular ruby in a solid (red) and dissolved (yellow) state can be used for contactless measurement of temperature. photo/(C): Sven Otto

The process of measuring the temperature with the molecular ruby is extremely straightforward. The appropriate site is irradiated with blue light, which is then absorbed by the molecular ruby that emits infrared radiation at two varied wavelengths. The emission of infrared at one of the two wavelengths becomes more intense based on the temperature. This is followed by determining the temperature on the basis of the subsequent ratio of intensity of the two wavelengths.

Anyone with a simple emission spectrometer can undertake this kind of measurement. The molecular ruby works at 100 degrees Celsius just as well as at minus 63 degrees Celsius, that is in a range relevant to everyday practice.

Sven Otto, a Doctoral candidate in Heinze's team

The principle of optical ratiometric temperature measurement is well known. However, it was earlier impossible to take measurements using just a single type of photoactive agent. To date, Scientists forever needed two dyes, i.e., one reference dye with emission that is independent of temperature and another that produced emission dependent on temperature.

Our molecular ruby, on the other hand, is simply made from inexpensive raw materials and no additional reference substances are required to measure temperature,It can be employed whenever we want to measure temperature without having to contact the object directly as with a conventional thermometer.

Professor Katja Heinze

The findings of this research have been published in a special edition of Chemistry, which has been designed to mark the 150th anniversary of the German Chemical Society (GDCh) and also features contributions from renowned German Researchers.

The German Research Foundation (DFG) within the framework of, inter alia, the Graduate School of Excellence Materials Science in Mainz (MAINZ) funded the research. Recently, the DFG approved a new priority program entitled "Light-controlled reactivity of metal complexes" that is coordinated by Professor Katja Heinze.

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