Extruded colour-based plastic film for the measurement of dissolved CO2

[Display omitted] •Preparation of a very CO2-sensitive thymol blue-LDPE film.•Used for both gaseous and dissolved CO2 measurements.•Long (>8months) storage lifetime under ambient conditions.•Very stable in water, salt water and acid.•Useful for environmental monitoring. Dissolved CO2 measurements are usually made using a Severinghaus electrode, which is bulky and can suffer from electrical interference. In contrast, optical sensors for gaseous CO2, whilst not suffering these problems, are mainly used for making gaseous (not dissolved) CO2 measurements, due to dye leaching and protonation, especially at high ionic strengths (>0.01M) and acidity (8months, with no loss of colour or function. Here, the performance of the TB plastic film is primarily assessed as a dissolved CO2 sensor in highly saline (3.5wt%) water. The TB film is blue in the absence of CO2 and yellow in its presence, exhibiting 50% transition in its colour at ca. 0.18% CO2. This new type of CO2 sensor has great potential in the monitoring of CO2 levels in the hydrosphere, as well as elsewhere, e.g. food packaging and possibly patient monitoring.