We have reported recently a series of UV-activated O2 indicator films [12–19] consisting of: a redox dye – methylene blue (MB), a sacrificial electron donor (SED) – glycerol, and nanoparticles of a UV-sensitive semiconducting photocatalyst (SC) – TiO2 , all encapsulated within a polymer – in the case of a water-based system, hydroxyethyl cellulose (HEC). We refer to such a macro powder TiO2 particle ink as a: powder TiO2 /MB/glycerol/HEC ink. These inks are printable on a large scale using a flexo printing process [20], which is commonly used for printing on flexible packaging materials. However, inkjet printing is now becoming increasing popular in the packaging industry. The most common applications of inkjet printing in the food packaging industry [20] are: datestamps, batch codes and any other variable information required on a package, with most food packages marked in some manner by inkjet printing.