Scientists from Canada and Germany have created a paper sensor that is sensitive to the presence of air in carbon dioxide of less than six units of ppm. Under the action of carbon dioxide, which is obtained by interaction of CO2 and water, the organic fluorescent molecules on the sensor was protonirovanie. The fluorescence spectrum of this substance is shifted proportional to the concentration of carbon dioxide, what we can conclude about its content in the analyzed air. The results of a study published in ACS Applied Materials and Interfaces.
Continuous monitoring of the concentration of carbon dioxide in the air is often needed to ensure safe working conditions, is used in smart buildings, as well as important for some laboratory tests. It is often used sensors based on infrared absorption or with electrochemical sensors based on the resistance change material, or current in it. A cheaper and easier alternative can be paper sensors impregnated with a fluorescent substance.
One of such methods of detection based on the reaction of carbon dioxide with an amino group of a fluorescent dye are formed carbamates, which leads to damping or shift of the fluorescence spectrum. Also it is possible to estimate the concentration of carbon dioxide by its interaction with deproteinizirovanny amino groups of the fluorescent molecules. In addition, carbon dioxide can determine the amount of carbon dioxide which is formed upon contact of carbon dioxide and water. Interacting with sensitive to pH fluorescent dye carbonic acid changes its color or fluorescence intensity.
Hui Wang (Hui Wang) with colleagues from the University of Alberta put on paper the matrix is sensitive to changes of acidity of the fluorescent substance and tested the resulting gas sensor for carbon dioxide. Scientists lowered the paper into the alcohol solution of the chromophore bis-(4-pyridyl)-dineopentyl-p-phenylene-di vinylene (Np-P4VB), fluorescence spectrum which depends on the acidity of the medium, and allowed it to dry. The ability of the obtained sensor to determine the content of CO2 was checked, passing through it a mixture of carbon dioxide, nitrogen and water vapour, and measuring in real time the spectrum of its fluorescence using a miniature spectrometer. The authors have also tested the sensor for the analysis of more complex gas mixtures of atmospheric and exhaled air.